Biomechanics by Janus de Lange

MODULE: BIOMECHANICS Sports biomechanics is the science that deals with an athlete’s movement whilst also considering the internal and external forces that are in effect whilst performing any desired movement Sport biomechanics studies the effects of forces on sport performance. Using laws and principles grounded in physics that apply to human movement, athletes and coaches can make sound decisions to develop efficient sport techniques. When coaches understand how forces work in sports and how athletes can leverage these forces, they have a clear advantage over those who lack these tools. Coaches with a command of both mental training tools and sports training principles can make amazing things happen on the field. Biomechanics and kinesiology, areas of study about human movement, can help coaches: • Analyze sport movements, • Select the best training exercises, • Reduce or prevent injuries, • Design or choose the sport equipment that best matches athletes’ personal needs. • Maximize economy and efficiency of movements.

Biomechanical Analysis of Movement Biomechanics Kinetics Cause of movement Forces

Kinematics Effects of forces on system

Moments

Linear

Angular

Kinematics is the branch of biomechanics about the study of movement with reference to the amount of time taken to carry out the activity. • Distance and displacement

• Speed and velocity

Distance (length of the path a body follows) and displacement (length of a straight line joining the start and finish points) are quantities used to describe a body’s motion. e.g. in a 400m race on a 400m track the distance is 400 metres but their displacement will be zero metres (start and finish at the same point).

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Speed and Velocity = distance travelled ÷ time taken

Speed and velocity describe the rate at which a body moves from one location to another. Average speed of a body is obtained by dividing the distance by the time taken and average velocity is obtained by dividing the displacement by the time taken e.g. a swimmer in a 50m race in a 25m length pool who completes the race in 71 seconds - distance is 50m and displacement is 0m (swimmer is back where they started) so speed is 50/71= 0.70m/s and velocity is 0/71=0 m/s

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Linear kinetics Kinetics is concerned with what causes a body to move. Momentum, inertia, mass, weight and force. • Momentum: mass x velocity • Inertia: the reluctance of a body to change whatever it is doing • Mass: the quantity of matter of which a body is composed of - not affected by gravity - measured in kilograms (kg) • Weight: force due to gravity -9.81m/s² • Force: a pushing or pulling action that causes a change of state (rest/motion) of a body - is proportional to mass x acceleration is measured in Newtons (N) where 1N is the force that will produce an acceleration of 1 m/s² in a body of 1kg mass The classification of external or internal forces depends on the definition of the ‘system’. In biomechanics, the body is seen as the ‘system’ so any force exerted by one part of the system on another part of the ‘system’ is known as an internal force all other forces are external.

Angular kinetics

Power is defined as the rate at which energy is used or created from other forms • Power = energy used ÷ time taken • Power = (force x distance) ÷ time taken • Power = force x velocity

Kinetic energy is the mechanical energy possessed by a moving object. Kinetic Energy = ½ x mass x velocity² (joules)

Kinetic energy and power

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Translation and couple A force that acts through the centre of a body result in movement (translation). A force whose line of action which does not pass through the body’s centre of gravity is called an eccentric force and results in movement and rotation. Example - if you push through the centre of an object it will move forward in the direction of the force. if you push to one side of the object (eccentric force) it will move forward and rotate.

A couple is an arrangement of two equal and opposite forces that cause a body to rotate.

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Types of Motion It is important to distinguish between two types of motion: • Linear (or Translational) Motion Movement in particular direction (and would include the resultant of more than one linear force acting on an object). Example: a sprinter accelerating down the track. • Rotational Motion Movement about an axis. The force does not act through the centre of mass, but rather is “off centre,” and this results in rotation. Example: ice skater’s spin. Examples of Rotation Principles: Ice Skating The ice-skater begins to spin with arms spread apart then suddenly brings them closer to the body. The end result of tightening up is that the skater’s spin (angular velocity) increases, seemingly miraculously. Examples of Rotation Principles: Gymnastics Following a series of rapid somersaults in a tight position, the gymnast does a forward flip with the body positioned more or less straight. By opening up, the gymnast increases the moment of inertia, thereby resulting in a decrease in angular velocity. Examples of Rotation Principles: Diving After leaving the high diving board, the diver curls tightly and then opens up just before entering the water. By opening up before entry, the diver increases the moment of inertia, thereby slowing down the angular velocity.

Principles of biomechanical analysis Seven principles that can be grouped into four broad categories: • Stability • Maximum effort • Linear motion • Angular motion

STABILITY • Principle 1: The lower the centre of mass, the larger the base of support, the closer the centre of mass to the base of support, and the greater the mass, the more stability increases. Four subcomponents Example: Sumo wrestling

MAXIMUM EFFORT • Principle 2: The production of maximum force requires the use of all possible joint movements that contribute to the task’s objective. Examples: golf, bench press

MAXIMUM VELOCITY • Principle 3 : The production of maximum velocity requires the use of joints in order from largest to smallest. Examples: hockey slapshot , hitting a golf ball slapshot

LINEAR MOTION • Principle 4: The greater the applied impulse, the greater the increase in velocity. Example: slam dunking a basketball slam

LINEAR MOTION

ANGULAR MOTION

• Principle 5 : Movement usually occurs in the direction opposite that of the applied force. Examples: high jumper, cyclists, runners

ANGULAR MOMENTUM

• Principle 6: Angular motion is produced by the application of a force acting at some distance from an axis, that is, by torque. • Principle is also known as the principle of the production of angular motion Example: baseball pitchers

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• Principle 7: Angular momentum is constant when an athlete or object is free in the air. • This principle is also known as the principle of conservation of angular momentum, and its key component is the fact that, once an athlete is airborne, he or she will travel with constant angular momentum. Example: Diver

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Biomechanics is the study that uses principles of physics to show how forces interact with a human body. This includes muscle actions, anatomical locations, anatomical terminology, description of joint movement, planes of motion, force couples, leverage forces, the force-velocity relationship.

MUSCLE ACTIONS CONCENTRIC Muscle exerts force, shortens and overcomes resistance (positive contraction). A concentric muscle contraction is a type of muscle activation that increases tension on a muscle as it shortens. Concentric contractions are the most common types of muscle activation athletes perform in a gym when lifting weights. Exercises that cause concentric contractions Common exercises that cause concentric contractions include the lifting phase of a bicep curl, a squat or a pull up. Running up hill or climbing stairs also causes the quadriceps to contract concentrically. Concentric contractions are common to many sports in which you need to generate a lot of power or explosive force. Also known as: Muscle shortening ECCENTRIC Muscle exerts force, lengthens and is overcome with resistance. An eccentric muscle contraction is a type of muscle activation that increases tension on a muscle as it lengthens. Eccentric contractions typically occur when a muscle opposes a stronger force, which causes the muscle to lengthen as it contracts. Exercises that cause eccentric contractions Common exercises that cause an eccentric contraction include going down stairs, running downhill, lowering weights and the downward motion of squats, push ups or pull ups. Eccentric contractions are common to many sports in which you need controlled or resisted types of movements. Eccentric contractions are associated with the onset of delayed muscle soreness. Eccentric muscle contractions also appear to be associated with greater muscle strengthening than when using concentric contractions ISOMETRIC Muscle exerts force, but does not lengthen, i.e. the tension developed by the muscle is equal to the load against which it is acting. For optimal muscle function, muscles need to develop moving and holding strength. Isometric action is mainly a function of tonic stabilisers. Muscle action that produces movement occurs in phasic mobilises. Isometric exercise is a type of muscle workout in which you perform isometric muscle contraction. An isometric muscle contraction occurs when your muscle exerts force without changing its length. In other words, when you do an isometric muscle contraction, your joint doesn’t move. Unlike concentric (when the muscle shortens as it works) and eccentric (when the muscle lengthens when it works) types of contractions, isometric muscle contraction neither lengthens nor shortens the muscle fibres. Pros and cons of isometric muscle contraction There are pros and cons to doing isometric exercise. On the one hand, it is convenient. Isometric exercise requires no special equipment and very little time. But because the muscle fibres don’t move during an isometric contraction, you won’t get strong all the way throughout the muscle’s range of motion. Strength gains are limited to specific spots related to the position you’re in when you do the exercise. Perhaps most important is that for people with high blood pressure (hypertension), isometric exercise is not a good idea. Isometric exercise has a tendency to increase your blood pressure. Isometric muscle contraction may be useful when you’re immobilized and/or healing, and you need to reduce your level of activity. If moving a part of your body would damage your joint in some way, your physical therapist or doctor may start you with isometrics. Isometrics are also used to help people who have been very inactive to get their muscle groups firing again.

Examples: It’s possible to strengthen the muscles at the back of your neck with isometric exercise. Start with your head and neck in vertical alignment with your trunk. Interlace your fingers and place your clasped hands behind your head. They should be placed at the bottom of your skull where it starts to curve down. With your hands, pull your head forward, but resist that force by pulling back with your head. NOTE: If you have neck pain or an injury, be sure to talk to your health care provider before doing this isometric exercise.

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MUSCLE - MUSCLE SPINDLE JOINTS - SENSORS IN THE CAPSULE TENDONS - GOLGI TENDON ORGAN

The central nervous system (CNS) constantly processes sensory information processed by movement. The information comes from special sensors:

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ANATOMICAL LOCATIONS Movements are explained and described in relation to a standard anatomical position in which the body is standing upright, feet parallel, arms hanging to the side and palms facing forward.

A. Midsagittal plane: Movements of flexion and extension take place in the sagittal plane. B. Coronal plane: Movements of abduction and adduction (lateral flexion) take place in the coronal plane. C. Transverse plane: Movements of medial and lateral rotation take place in the transverse plane.

ANATOMICAL TERMINOLOGY

SAGITAL PLANE

Any plane parallel to the medial plane. Movements can be seen from the side

Facing forward or located at the front

POSTERIOR

Behind or towards the back

PROXIMAL

Towards the centre of the body

DISTAL

Away from the centre of the body

SUPERIOR OF CEPHALIC

Above or towards the head

INFERIOR OR CAUDAL

Below or towards the feet

PRONE

Lying face down on chest

TRANSVERSE PLANE

Divides the body into superior and inferior (upper and lower) parts. Movements can be seen from the top or bottom

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Towards the midline of the body

MEDIAL PLANE

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ORIENTATION AND ANATOMICAL PLANES

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DESCRIPTION OF JOINT MOVEMENT

EXTENTION

Movements in a sagital plane that take part of the body backwards from the anatomical position, e.g. extension of the neck.

HYPEREXTENTION

Extension beyond the normal range of movements, e.g. Lumbar spine extension.

ABDUCTION

Moving the body away from the medial plane, e.g. abduction of hip or side splits on the reformer.

ADDUCTION

Bringing the body part back towards or beyond the midline, e.g. hip adduction or crossover press on electric chair.

LATERAL FLEXION

Movements of the trunk or neck in the frontal plane away from the medial plane, e.g. the mermaid.

LATERAL ROTATION

A movement in a transverse plane which takes a body part outwards, e.g. lateral rotation of the hips (original PILATES stance).

MEDIAL ROTATION

A movement in the transverse plane which takes a body part inwards, e.g. medial rotation of the shoulder.

SUPINATION

Refers to the forearm when the palms face forward. It can also refer to the arch of the foot turning outwards.

PRONATION

Refers to the forearm when the palms of the hand face downwards/backwards. It can also refer to the arch of the foot being flush with the ground (flat footed).

EVERSION

Turning the sole of the foot outwards.

INVERSION

Turning the sole of the foot inwards.

DORSI FLEXION

Bringing the toes upwards towards the chin.

PLANTERFLEXION

Pointing of the toes.

ANKLE SPINATION

A combination of inversion, planter flexion and forefoot adduction.

CIRCUMDUCTION

A sequential movement describing a cone.

ROTATION

Circular motion of the body.

RETRACTION

Backwards movement of the mandible or scapula.

PROTRACTION

Movement of the scapula.

ELEVATION

Raising a body part.

DEPRESSION

Lowering of a body part.

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Decreasing the angle between 2 (two) bones in the sagital plane, e.g. flexion of the hip.

FLEXION

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Body Movements: Lateral View

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Muscular force Muscular force can be described as a force that results in an acceleration or deceleration of a second object. They are characterised by magnitude (how much) and direction (which way they are moving). Length-tension relationship Length-tension relationship can be described as the length at which the muscle can produce the greatest force. There is an optimal muscle length at which actin and myosin filaments in the sarcomere have the greatest degree of overlap. This results in the muscle to producing maximum force out of the muscle at length. However, if the muscle lengths are altered as a result of misaligned joints or poor posture they will not be able to produce sufficient force to allow for optimal movement. Force-velocity curve The force-velocity curve can be described as the ability of muscles to produce force with increased velocity. As the muscle contracts concentrically, the ability to produce force decreases. The opposite theory is applied to eccentric muscle action, as the velocity of the muscle increases, the ability of the force increases. Force-coupled relationships The forced-couple relationship can be described as the muscle groups moving together to produce movement around a joint. Muscles in a forced couple produce force and pull on the bone/bones that they are connected to. This is because each muscle has different attachment sites that pulls at different angles and as a result creates different forces on that joint. All muscle movement produced must involve all muscle actions and functions to ensure correct joint movement. So, all muscles working together for the production of correct movement are described as to be working in a forced-coupled-relationship. Muscular leverage The amount of force that the kinetic muscle can produce is not solely dependent on motor recruitment or muscle size, but also on the leverage of the muscles and the bones. The joints of the body are our levers which are moved and manipulated by force of the muscles. The movement around the joint axes are described as rotory motion. The turning effect around a joint referred to as torque. The neuromuscular system is responsible for manipulating force. The amount of leverage the kinetic chain will depend on the leverage of the muscles in relation to the resistance. The difference between the distance that the weight is from the centre of the joint and the muscle attachment and the direction the muscle pulls will determine the muscles efficiency that will be able to manipulate the movement. The muscle attachment sites or the line of pull of the muscles generates cannot be altered. The simplest way to alter the amount of force that a joint generates is to move the resistance. I.e. the closer the weight is to the joint the less force (torque) it creates and, the farther the weight is from the joint, the more force it creates.

RANGE OF MOTION EXERCISES Range of motion refers to the distance and direction a joint can move to its full potential. Each specific joint has a normal range of motion that is expressed in degrees after being measured with a goniometer (i.e., an instrument that measures angles from axis of the joint). Limited range of motion refers to a joint that has a reduction in its ability to move. The reduced motion may be a mechanical problem with the specific joint or it may be caused by diseases such as osteoarthritis, rheumatoid arthritis, or other types of arthritis. Pain, swelling, and stiffness associated with arthritis can limit the range of motion of a particular joint and impair function and the ability to perform usual daily activities.

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Normal Values (in degrees): • Hip flexion (bending) 0-125 • Hip extension (straightening) 115-0 • Hip hyperextension (straightening beyond normal range) 0-15 • Hip abduction (move away from central axis of body) 0-45 • Hip adduction (move towards central axis of body) 45-0 • Hip lateral rotation (rotation away from center of body) 0-45 • Hip medial rotation (rotation towards center of body) 0-45

Range-of-Motion Exercises Physical therapy can help to improve joint function by focusing on range-of-motion exercises. The goal of these exercises is to gently increase range of motion while decreasing pain, swelling, and stiffness. There are three types of range-of-motion exercises: • Active range-of-motion - patient exercises without any assistance • Active assistive range-of-motion - patient requires some help from therapist to do the exercises • Passive range-of-motion - therapist or equipment moves patient through range of motion (no effort from patient) Normal Range of Motion for Each Joint It’s important to know the normal range of motion for each joint. After physical examination, if it is determined that you have limited or abnormal range of motion in one or more joints, you can put together a treatment plan with your doctor. You can be reassessed for range of motion to determine if the treatment is effective. Patients who have joint surgery must also go through extensive rehabilitation to get back to normal range of motion in the affected joint.

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• Elbow supination (rotation outward) 0-90 • Wrist flexion 0-90 • Wrist extension 0-70 • Wrist abduction 0-25 • Wrist adduction 0-65 • Metacarpophalangeal (MCP) joints abduction 0-25 • MCP adduction 20-0 • MCP flexion 0-90 • MCP extension 0-30 • Interphalangeal proximal (PIP) joints of fingers flexion 0-120 • PIP extension 120-0 • Interphalangeal distal (DIP) joint of fingers flexion 0-80 • DIP extension 80-0 • Metacarpophalangeal joint of thumb abduction 0-50 • MCP of thumb adduction 40-0 • MCP of thumb flexion 0-70 • MCP of thumb extension 60-0 • Interphalangeal joint of thumb flexion 0-90 • Interphalangeal joint of thumb extension 90-0

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• Knee flexion 0-130 • Knee extension 120-0 • Ankle plantar flexion (movement downward) 0-50 • Ankle dorsiflexion (movement upward) 0-20 • Foot inversion (turned inward) 0-35 • Foot eversion (turned outward) 0-25 • Metatarsophalangeal joints flexion 0-30 • Metatarsophalangeal joints extension 0-80 • Interphalangeal joints of toe flexion 0-50 • Interphalangeal joints of toe extension 50-0 • Shoulder flexion 0-90 • Shoulder extension 0-50 • Shoulder abduction 0-90 • Shoulder adduction 90-0 • Shoulder lateral rotation 0-90 • Shoulder medial rotation 0-90 • Elbow flexion 0-160 • Elbow extension 145-0 • Elbow pronation (rotation inward) 0-90

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Examples of prime mover exercises

LEG EXTENTION

LEG CURL

Quadriceps Vastus lateralis, Rectus femoris, Vastus medialis

Hamstrings Biceps femoris, Semitendinosus, Semimembranosus

Knee Joint

PUSH UP

LAT PULL DOWN

Deltoids Supraspinatus, Infraspinatus, Subscapularis Minor

Biceps Brachialis, Biceps Brachii, Brachioradialis

Triceps Triceps Brachii

Shoulder & Elbow Joint

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Elbow Joint

Back muscles Trapezius, Rhomboids, Latissimus Dorsi

Pectorals Pectoralis Major, Pectoralis Minor

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SEATED DUMBELL SHOULDER PRESS

LEG PRESS

Deltoids Supraspinatus, Infraspinatus, Subscapularis Minor

Quadriceps Vastus lateralis, Rectus femoris, Vastus medialis

Triceps Triceps Brachii

Hamstrings Biceps femoris, Semitendinosus, Semimembranosus

Shoulder & Elbow Joint

Hip & Knee Joint

STANDING TRICEPS PUSH DOWN

Knee Joint

Elbow Joint

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Triceps Triceps Brachii

Calves Gastrocnemuis, Soleus

STANDING CALF RAISE

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Biceps Brachialis, Biceps Brachii, Brachioradialis

ABDOMINAL CRUNCH Abdominals Rectus abdomanis, Transversus abdominus, External oblique, Internal oblique

Elbow Joint

Spine

STANDING BICEPS DUMBBELL CURL

BIOMECHANICAL ANALYSIS OF MOVEMENT The below are examples biomechanical analysis of the following movements.

Sprinting

Throwing

The leg action in running is one that takes place in a sagital plant about a transverse axis. The actions are concerned with three joints the hip, knee and ankle. During the time the foot is in contact with the floor, the drive of the leg is achieved through contractions of muscles causing movement at all three joints. At the hip, a ball and socket joint is formed by the femur and pelvic girdle, there is a powerful extension and hyperextenion, brought about by the action of the muscles of the hamstrings group (biceps femoris, semitendinosis and semimembranosis) and the gluteal muscles (gluteus maximus and minimus). At the knee, a hinge joint formed from the tibia and femur, there is extension, mainly as a result of the action of the quadriceps group of muscles (rectus femoris, vastus medialis, vastus lateralis and vastus intermedialis). At the ankle, a hinge joint formed by the tibia and calcaneus, there is plantar flexion, brought about principally by the action of the gastrocnemius. During the recovery Phase; at the hip, the hip flexors, which in this movement include the iliopsoas, cause flexion. At the knee, the hamstring group produces flexion.

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In over arm throwing, there are two phases, the preparatory phase, and the throwing phase, both involving actions at the shoulder, and the elbow, Taking the arm back in preparation involves extension at the elbow. The elbow is a hinge joint formed by the humerus and ulna. Extension is produced by the actions of the triceps brachii muscle. At the ball and socket joint formed between the humerus and the scapula, there is horizontal hyperextension of the shoulder caused by the action of the posterior deltoid, assisted by the latissimus dorsi. The throwing phase involves flexion of the elbow due to the action of the biceps brachii and horizontal flexion at the shoulder, caused by the action of the pectoralis major and the anterior deltoids.

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Racket strokes

The preparatory phase is similar to that of throwing. Taking the arm back in preparation involves supination of the forearm and extension at the elbow. The forearm involves a pivot joint formed between the radius and ulna. The elbow is a hinge joint formed by the humerus and ulna. Supination is produced by the action of the supinator muscle. Extension is produced by the actions of the triceps brachii muscle. At the ball and socket joint formed between the humerus and the scapula, there is horizontal hyperextension of the shoulder caused by the action of the posterior deltoid muscle, assisted by the latissimus dorsi. These actions are mainly occurring in the transverse plant around a longitudinal axis. The striking phase is based on movements that occur at the wrist, elbow, shoulder and trunk. At the wrist there is rotation (pronation) caused by the action of the pronator teres. At the elbow there is primarily extension, caused by the action of the triceps brachii. At the shoulder there is horizontal flexion, caused by the pectoralis major and the anterior deltoid. In the trunk there is rotation, caused mainly by the external oblique muscles.

Squat

In the squat, normal actions are complicated by the effects of gravity. Gravity demands that muscles work by both shortening during contraction; a concentric contraction, and by lengthening during contraction; an eccentric contraction. In simple terms, those muscle actions that move the body upwards against gravity involve concentric contractions of the prime mover, whilst those involved in descent are eccentric contractions of the same prime movers. Thus in the upward phase of a squat, there is extension at the hip brought about by a concentric contraction of the gluteals (gluteus maximus and minimus), and the hamstrings (biceps femoris, semitendinosis and semimembranosus). At the same time, there is extension at the knee due to concentric contraction of the quadriceps group (rectus femoris, vastus medialis, vastus lateralis and vastus intermediais). The ankle goes through plantar flexion, due to a concentric contraction of the gastrocnemius. In the downward phase, the same muscles groups work, but this time eccentrically to control descent against gravity. Thus there is an eccentric contraction of the gluteals to allow hip flexion, an eccentric contraction of the quadriceps to permit knee flexion, and an eccentric contraction of the gastrocnemius to allow dorsiflexion at the ankle.

Press up

The press up also involves control of descent against gravity and hence eccentric and concentric contractions of the prime movers. The main two joints involved in the movement are the elbow and the shoulder. The action at elbow is flexion during the downward movement, and extension in the upward movement. The main agonist is the triceps brachii working eccentrically during flexion and concentrically during extension. These movements take place in a sagittal plane around a transverse axis.

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The action at the shoulder - emphasised in a wide-arm push up - is that of horizontal adduction in the downward movement and horizontal abduction in the upward movement. The main agonist is the pectorails major, working eccentrically during horizontal abduction, and concentrically during horizontal abduction. These movements take place in the transverse plane around a longitudinal axis.

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Example of how to conduct an anatomical analysis of movement: Muscles and joints involved in a push-up Pushups are a body-weight exercise that works the chest, shoulder, triceps and abdominal muscles. Pushups can enhance any fitness program, whether your goals are to build muscular strength or endurance. There are many variations on this classic exercise, with or without additional equipment, that are used to either change the difficulty or challenge the muscles in a different way. The basic mechanics require a series of movement at multiple joints to raise and lower the body. Setup A standard pushup begins in plank position: face down on a mat, supporting yourself on your toes and with your hands out slightly wider than your shoulders. You should maintain a straight line through your shoulders, hips and back, making sure you do not dip or arch. Steadying yourself in this position requires isometric muscle action from the deltoid group in your shoulders and abdominals throughout the exercise. Isometric muscle action occurs when no movement is associated with a contraction. Descending Phase The pushup motion begins with an inhale as you bend your elbows to lower your body toward the floor. Bending your elbow is known as elbow flexion. In prone position, you are working with gravity as the elbow flexes in order to control yourself on the way down. This motion requires an eccentric contraction from the triceps. Once your elbows are flexed at 90 degrees, you begin to horizontally adduct the shoulder blades, squeezing them together, to finish the move. Ascending Phase From the “down” position, concentric muscle action is required to lift yourself back up against gravity. Your pectoralis major is the main mover in this phase of a pushup as you abduct your shoulder blades. Elbow extension is caused by the triceps to push you back to starting position. A 2005 study from the “Journal of Strength and Conditioning Research” found that the pec major and triceps were responsible for lifting 40 percent of the body’s total weight in a normal pushup. Variations According to a 1990 study in the journal “Biomedical Sciences Instrumentation,” the distance between your hands, the positioning of your hands relative to your shoulders, your relation to gravity, the positioning of your feet and your speed all affect the load on all muscles involved in a pushup, including the main movers and the static supporters. For example, modifying a pushup by performing it on your knees reduces the amount of weight being lowered and lifted, which reduces the total load on the muscles. What muscles do the pushup work? The muscles of your upper torso. The muscles of your upper torso include the following: • Pectoral muscles (pectoralis major and pectoralis minor) • Deltoid muscles (the muscles in the shoulder) • Muscles of the upper arm (biceps and triceps muscles) • Muscles of the upper back (latissimus dorsi, rhomboids and trapezius). Each of these muscle groups are responsible for either flexion, extension, pushing or pulling.

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The following muscle groups are trained when doing push ups: • Pectoral muscles • Triceps (back of the arm) • Biceps (front of the arm) • Front and rear heads of the deltoids • Rhomboids and trapezius • Latissimus dorsi

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Muscle Structures and Mechanics Diagram of head and neck muscle

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Structure of a skeletal muscle

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Muscle Fibre TYPES Skeletal muscle is made up of bundles of individual muscle fibers called myocytes. Each myocyte contains many myofibrils, which are strands of proteins (actin and myosin) that can grab on to each other and pull. This shortens the muscle and causes muscle contraction. It is generally accepted that muscle fiber types can be broken down into two main types: slow twitch (Type I) muscle fibers and fast twitch (Type II) muscle fibers. Fast twitch fibers can be further categorized into Type IIa and Type IIb fibers. These distinctions seem to influence how muscles respond to training and physical activity, and each fiber type is unique in its ability to contract in a certain way. Human muscles contain a genetically determined mixture of both slow and fast fiber types. On average, we have about 50 percent slow twitch and 50 percent fast twitch fibers in most of the muscles used for movement. Slow Twitch (Type I) The slow muscles are more efficient at using oxygen to generate more fuel (known as ATP) for continuous, extended muscle contractions over a long time. They fire more slowly than fast twitch fibers and can go for a long time before they fatigue. Therefore, slow twitch fibers are great at helping athletes run marathons and bicycle for hours. Fast Twitch (Type II) Because fast twitch fibers use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength or speed than slow muscles. However, they fatigue more quickly. Fast twitch fibers generally produce the same amount of force per contraction as slow muscles, but they get their name because they are able to fire more rapidly. Having more fast twitch fibers can be an asset to a sprinter since she needs to quickly generate a lot of force. Type IIA Fibers These fast twitch muscle fibers are also known as intermediate fast-twitch fibers. They can use both aerobic and anaerobic metabolism almost equally to create energy. In this way, they are a combination of Type I and Type II muscle fibers. Type IIB Fibers These fast twitch fibers use anaerobic metabolism to create energy and are the “classic” fast twitch muscle fibers that excel at producing quick, powerful bursts of speed. This muscle fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types, but it also has a much faster rate of fatigue and can’t last as long before it needs rest.

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Fiber Type and Performance Our muscle fiber type may influence what sports we are naturally good at or whether we are fast or strong. Olympic athletes tend to fall into sports that match their genetic makeup. Olympic sprinters have been shown to possess about 80 percent fast twitch fibers, while those who excel in marathons tend to have 80 percent slow twitch fibers.

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Muscle roles: What is an agonist, antagonist, stabilizer, fixator or neutralizer muscle Muscles must work together to produce different bodily movements and a particular muscle’s role may change depending on the movement. Synergy and Synergists The most important aspect to understand about how muscles function to produce a joint movement is synergy. Synergy means that two or more things work together to produce a result that is greater than any of those things could do alone, so that the whole result is greater than the sum of the individual effects of the agents involved. Even the simplest joint movement requires muscles working together in this synergistic or cooperative fashion. When a group of muscles work together to optimally perform a given motor task this is known as a muscle synergy Muscles that are directly involved in producing a certain joint movement are called agonists and muscles that are indirectly involved, by some other role, are called synergists. However, even if a muscle adds directly to a joint’s movement by adding it’s own torque, it can still correctly be called a “synergist”. Just as other muscles, such as stabilizers, neutralizers, and fixators, that help the movement by opposing unwanted movement or by helping to stabilize the joint are synergists. So, the word synergists is not a very useful word, in itself, when describing muscular roles since it is much too inclusive and the way it is used is contradictory to it’s definition because it excludes muscles that could rightly be called synergists by their “synergistic” role in a joint movement. This happens when all the muscles involved in a movement besides the prime movers are termed synergists, as if the prime movers themselves are not synergists. These muscles, which contribute to a movement indirectly could more clearly be called supporters a muscle that indirectly assists in producing a joint movement is the agonist’s synergist Agonist (Prime Mover) An agonist is a muscle that is capable of increasing torque in the direction of a limb’s movement, and thus produce a concentric action. In other words, the muscle can produce a force that accelerates a limb around it’s joint, in a certain direction. This does NOT mean that this direction is the only one the muscle can produce force in but only that it is capable of this and thus is directly involved in producing a certain movement, making it a prime mover. To keep it simple, then, an agonist is a muscle that causes rotational movement at a joint by producing torque. A movement can always have more than one agonist although a certain agonist may be capable of producing more torque than its partner. They are also sometimes called protagonists.

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The brachialis, for instance, is another elbow flexor, located inferior to the biceps on the upper arm. Unlike the biceps, which inserts onto the radius, which is able to rotate, the brachialis inserts onto the ulna which cannot rotate. This, it can be said that the brachialis is the only pure flexor of the elbow joint whereas the larger biceps can also supinate the forearm.

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When most people think of elbow flexion they think of the more superficial biceps brachii. But the brachialis is the only pure elbow flexor. The biceps brachii is an agonist for elbow flexion. It is assisted by the brachialis and the brachioradialis. These are the agonists of elbow flexion, all of which are capable of flexing the elbow joint to some extent. Agonist’s synergists roles: stabilizer, fixator and neutralizer Some muscles involved in a joint action do not directly contribute a torque force to the movmement but assist the movement in indirect ways. These roles that are commonly referred to as synergist muscles. These roles are many but some of the basic terms used to describe these muscles are stabilizer, neutralizer and fixator. However, the term stabilizer, for our purposes, means the same thing as fixator. The term stabilizer needs further clarification before we move on to the fixator. Stabilizers and stabilization There is more than one way to categorize the functional role of muscles. It depends on perspective. When may look at the muscles in terms of their function is specific movements or we may look at them in terms of the entire body as a system, complete with many subsystems. The latter view is not what we are concerned with in this explanation but the when viewed this way muscles are classified according to their function rather than their role in a particular movement. The word stabilizer or stabilization has a much broader and complex definition. This view sees the body as a system of motor (or mobilizer) and stabilizer muscles. This concept was first proposed by Rood and furthered by the work of Janda and Sahrmann as well as by Comerford and Mottram who proposed the concept of local and global stabilizers and global mobilizers. Although, the concept of a stabilizing muscle can still be viewed in terms of a single movement in this system, certain muscles are considered to have the primary function of stabilizers in the body, being, by virtue of their position, shape, angle or structure, more suited to work as a stabilizer than as a mobilizer. For instance, this view teaches us that the abdominal group of muscles, once primarily thought of as a muscle we perform situps with, is much more important as a major stabilizer of the spine. This lesson may lead us to train those muscles in a way that supports their function, thus making us stronger and more injury free.

Fixator muscle

The type of stabilizer we discuss here, however, are fixators, which are active during one movement and at one joint. There are certain muscles that act primarily as stabilizes because of their angle of pull. An example of such muscles is a group of muscles known as the rotator cuff muscles of the shoulder girdle. This group comprises the supraspinatus, infraspinatus, teres minor and subscapularis. These muscles are mainly known as muscle of rotation for their contribution to external and internal rotation of the shoulder but they are actually much better suited for the primary role of stabilization and they are very important in stabilizing the humeral head in the glenoid fossa.

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A fixator is a stabilizer that acts to eliminate the unwanted movement of an agonist’s, or prime mover’s, origin. Many muscles are attached to more than one bone. When this happens the muscles are said to be multiarticulate or multijoint muscles. When these muscles contract they tend to move both bones to which they are attached. This would, of course, make everyday movements quite impossible.

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For instance, consider elbow flexion by the biceps brachii. When you do a curl, the biceps acts to flex the elbow. However, the biceps is attached at two places, proximally and distally. Its distal attachment, the insertion, is to the radius. It’s the radius bone we want to move when we curl a dumbbell. One of its proximal attachments, though, the origin, is to the scapula. The scapula is one heck of a mobile bone. In fact, it has no real bony attachments of its own. When the biceps contracts it will tend to draw the radius and the scapula together. The movement of the scapula must be prevented. This is accomplished by fixators. Specifically, the trapezius and rhomboids work isometrically to keep the scapula from moving on the torso. Neutralizer muscle Neutralizers, like fixators, act to prevent unwanted movement. But instead of acting to prevent the unwanted movement of a body part they act to pull against and cancel out an unwanted line of pull from the agonist or prime mover. Many muscles can produce a pulling force in more than one direction so that an undesired joint action may occur simultaneously with the desired on. Neutralizers prevent this. For example, the biceps brachii can do more than flex the elbow. It can also supinate the forearm (twist the forearm so that the palm faces up). In order for bicips action to flex the elbow with the forearm also being supinated another muscle must cancel out the supination torque that the biceps also produces. The pronator teres, being the principal forearm pronator, is responsible for this. Test the action of the pronator teres for yourself. You can easily palpate the pronator teres by flexing your elbow and making a fist as if you are holding a hammer (this is a “neutral” forearm position). The pronator teres will start to contract. You can feel it with your opposite fingers inside the middle of your forearm. Now, relax your forearm and bring your hand up toward the ceiling. You will feel the pronator teres relax and lengthen. At first it was contracting to provide a pronating force against the biceps supinating force while the elbow is flexed. When you supinated your forearm, it relaxed to allow this action to take place. On the other hand, if forearm supination were desired without elbow flexion, the triceps would act isometrically to resist the flexion, making it a neutralizer. Antagonist An antagonist is a muscle that is capable of opposing the movement of a joint by producing torque that is opposite to a certain joint action. This is usually a muscle that is located on the opposite side of the joint from the agonist. The triceps, an extensor of the elbow joint, is the antagonist for elbow flexion, and it would also be correct to say that the tricep is an antagonist to the biceps, and vice versa. In order for an agonist to shorten as it contracts the antagonist must relax and passively lengthen. This occurs through reciprocal inhibition, which is necessary for the designated joint movement to occur unimpeded. Reciprocal inhibition is a neural inhibition of the motor units of the antagonist muscle. When the agonist muscle contracts, this causes the antagonist muscle to stretch. Normally, this stretching would be followed by a stretch reflex which would make the muscle being stretched contract against the change in length. If this were allowed to happen unchecked then it would result in very jerky or oscillatory movement since the stretch reflex in the antagonists would elicit a new stretch reflex in the agonist, so on and so forth. The inhibition of the alpha-motoneurons in the antagonist are brought about by **Ia-inhibitory interneurons of the spinal cord, which are excited by IA afferents in the agonist muscle. However, antagonists are not always inactive or passive during agonist movements. Antagonists also produce eccentric actions in order to stabilize a limp or decelerate a movement at the end of a motion. For instance, during running the hip extensors are antagonists to the hip flexors, which act to bring the femur forward during the running stride. So, the hip extensor muscles must relax to some degree to allow this forward motion of the thigh to take place. However, the extensors must also act to arrest this forward motion at the top of the stride. So the antagonists both relax to allow the motion to happen and then contract to put the brakes on it. This makes for a very fine balance of activity between agonist and antagonist pairings. Agonist antagonist coactivation or co-contraction When both the agonist and antagonist simultaneously contract this is called coactivation. It can be advantageous for coactivation to occur for several reasons. For instance, when movements require a sudden change in direction, when heavy loads are carried, and to make a joint stiffer and more difficult to destabilize.

Spurt and shunt muscles

The purported reason that co-contraction may occur during changes in direction is that modulating the level of activity in one set of muscles is more economical than alternately turning them on and off. For heavy loads, increased joint stiffness is desirably for lifting heavier loads and co-contraction of the core muscles of the torso routinely occurs during these activities. For fine motor activities of the fingers, as well, complex co-contraction activity is needed. It should be noted that the word co-contraction is only used to describe the simultaneous activity of agonist/antagonist parings and should not be used to describe the simultaneous action of various agonist muscle groups.

Muscles can also be described as being spurt or shunt muscles. These roles are largely unknown in the strength training world but are described in the orthopedic and physical therapy fields. Again, we will consider the elbow joint.

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When a muscle acts on a bone it actually produces a force that, if one were to do a vector analysis, could be resolved into two component forces. These components are an angular component and a transarticular component. The angular component is actually the perpendicular or vertical component of the muscle’s force. We normally call this the rotary component. If allowed to act alone this force would cause the bone to rotate around the joint. The rotary component is also known as a swing component.

The transarticular component is a parallel or horizontal component. It acts along the shaft of the bone and may produce a force that pulls the bone away from the joint or toward it, depending on the angle of the joint. This component, therefore, is also known

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as either a stabilizing component or a destabilizing component. When the component is stabilizing it is also known as a shunt component and shunt muscles are muscles that tend pull the bones of a joint together. The Brachioradialis Muscle can act as a shunt muscle due to itâ&#x20AC;&#x2122;s position.

During elbow flexion, the angular component, the one that makes the radius move around the elbow joint, is the swing component. The brachioradialis is an example of a shunt muscle, which is able to provide a compressive force. A certain muscle may exert a stronger spurt or shunt force. If the spurt force is stronger it is called a spurt muscle. If the shunt force is stronger it is called a shunt muscle. Which happens depends on the location of the muscle and whether the distal or proximal attachment is free to move. Generally, the distance of the origin and insertion of a muscle to the joint axis of rotation determines whether a muscle acts as a spurt or shunt muscle. When the distance of the insertion is greater than the distance of the origin, the muscle is considered a shunt muscle. when the origin is farther from the joint axis than insertion, the muscle is a spurt muscle. This is important because a shunt muscle may protect a joint from powerful distracting or compressive forces during certain movements. A shunt muscle could be considered a stabilizer muscle as it help to stabilize a joint during movement. You should be able to visualize, using the image of the brachioradialis above, how the insertion distance allows such a muscle to exert a shunt or stabilizing force on the bone and joint regardless of the joint angle. Imagine a dumbbell curl with the elbow flexed to greater than 90 degrees. The brachioradialis, like most of the elbow flexors, will pull the bone toward the elbow joint at this angle. However, imagine what would happen if the insertion were much closer to the elbow rather than all the way down at the end of the radius at the wrist.

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As the angle of elbow flexion passes 90 degrees this same parallel pull is no longer pulling the bone toward the joint but is pulling the bone away from the joint, resulting in a translational or dislocating force. But since the insertion is so distant, at the wrist, the angle of elbow flexion does not affect the direction of the parallel component and it remains a shunt component, making the brachiradialis a shunt muscle, always able to exert a stabilizing force.

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Movement Analysis Detailed analysis of movement is a complex activity requiring sophisticated equipment. However, basic analysis of movement can be done visually and should involve the following: • A description of the actual movements which occur at the joints involved • The plane(s) in which the movement occurs • The muscles producing the movement • The function of the muscles involved (agonists, antagonists, synergists & fixators) • The type of contraction (isotonic -concentric or eccentric, isometric) • The range of the muscle action (inner, middle, outer) Analysis of sprinting The leg action in running is one that takes place in a sagittal plane about a transverse axis and involves the hip, knee and ankle joints. The bones of the hip involved are the femur and pelvic girdle which form a ball and socket joint.The bones of the knee involved are the femur and tibia which form a hinge joint. The bones of the ankle involved are the tibia and calcaneus which form a modified joint. Each of these joints produces two actions, one when the leg is in contact with the ground (driving phase) and one when the leg is not in contact with the ground (recovery phase).

Driving Phase Joints involved

Action

Agonist Muscle

Hip

Extension and hyperextension

Gluteal muscles (gluteus maximus and gluteus minimus) and Hamstrings (biceps femoris, semimembranosus, semitendinosus)

Knee

Extension

Quadriceps group of muscles (rectus femoris, vastus medialis, vastus lateralis and vastus intermedialis)

Ankle

Plantar flexion

Gastrocnemius

Joints involved

Action

Agonist Muscle

Hip

Flexion

Iliopsoas

Knee

Flexion

Hamstrings (biceps femoris, semimembranosus, semitendinosus)

Ankle

Dorsi flexion

Tibialis anterior

Recovery phase

Analysis of throwing The leg action in running is one that takes place in a sagittal plane about a transverse axis and involves the hip, knee and ankle joints. The bones of the hip involved are the femur and pelvic girdle which form a ball and socket joint.The bones of the knee involved are the femur and tibia which form a hinge joint. The bones of the ankle involved are the tibia and calcaneus which form a modified joint. Each of these joints produces two actions, one when the leg is in contact with the ground (driving phase) and one when the leg is not in contact with the ground (recovery phase).

US Agonist Muscle

Preparatory phase Action

Horizontal hyperextension

Posterior deltoids and latissimus dorsi

Elbow

Humerus and ulna

Extension

Triceps brachii

Throwing phase

Agonist Muscle

Articulating bones

Action

Humerus and scapula

Horizontal flexion

Anterior deltoids and Pectoralis major

Elbow

Humerus and ulna

Flexion

Biceps brachii

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Joints involved Shoulder

Articulating bones Humerus and scapula

Joints involved Shoulder

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Analysis of racket strokes There are two phases to striking a ball with a racket, the preparatory phase and the striking phase. Most actions are rotational in the transverse plane and longitudinal axis and the three joints concerned are the wrist, elbow and the shoulder The elbow is a hinge joint formed by the humerus and ulna. The shoulder is a ball and socket joint formed between the humerus and the scapula The wrist forms a condyloid joint between the ulna and carpal bones.

Preparatory phase Joints involved

Articulating bones

Action

Agonist Muscle

Wrist

Ulna and carpal Radius and ulna

Supination

Supinator

Elbow

Humerus and ulna

Extension

Triceps brachii

Shoulder

Humerus and scapula

Horizontal hyperextension

Posterior deltoid and latissimus dorsi

Striking Phase Joints involved

Articulating bones

Action

Agonist Muscle

Wrist

Ulna and carpal Radius and ulna

Pronation

Pronator teres

Elbow

Humerus and ulna

Flexion

Biceps brachii

Shoulder

Humerus and scapula

Horizontal flexion

Pectoralis major and Anterior deltoid

Rotation

External obliques

Trunk Analysis of jumping

The action in jumping is one that takes place in a sagittal plane about a transverse axis and involves the hip, knee and ankle joints. The bones of the hip involved are the femur and pelvic girdle which form a ball and socket joint. The bones of the knee involved are the femur and tibia which form a hinge joint. The bones of the ankle involved are the tibia and calcaneus which form a modified joint.

Preparatory phase Joints involved

Action

Agonist Muscle

Hip

Extension and hyperextension

Gluteal muscles (gluteus maximus and gluteus minimus) and Hamstrings (biceps femoris, semimembranosus, semitendinosus)

Knee

Extension

Quadriceps group of muscles (rectus femoris, vastus medialis, vastus lateralis and vastus intermedialis)

Ankle

Plantar flexion

Gastrocnemius

Analysis of kicking The action in kicking is one that takes place in a sagittal plane about a transverse axis and involves the hip, knee and ankle joints. The bones of the hip involved are the femur and pelvic girdle which form a ball and socket joint. The bones of the knee involved are the femur and tibia which form a hinge joint. The bones of the ankle involved are the tibia and calcaneus which form a modified joint. Kicking comprises of two phases, the preparatory phase and the kicking phase.

Preparatory phase

Agonist Muscle

Gluteal muscles (gluteus maximus and gluteus minimus)

Knee

Flexion

Hamstrings (biceps femoris, semimembranosus, semitendinosus)

Ankle

Plantar flexion

Gastrocnemius

Joints involved

Action

Agonist Muscle

Hip

Flexion

Knee

Extension

Ankle

Plantar flexion

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KICKING phase

Action Extension and hyperextension

Joints involved Hip

Gastrocnemius

Quadriceps group of muscles (rectus femoris, vastus medialis, vastus lateralis and vastus intermedialis)

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MUSCLE ACTION Isotonic Contractions Isotonic contractions are those which cause the muscle to change length as it contracts and causes movement of a body part. There are two types of Isotonic contraction: 1. Concentric Concentric contractions are those which cause the muscle to shorten as it contracts. An example is bending the elbow from straight to fully flexed, causing a concentric contraction of the Biceps Brachii muscle. Concentric contractions are the most common type of muscle contraction and occur frequently in daily and sporting activities. 2. Eccentric Eccentric contractions are the opposite of concentric and occur when the muscle lengthens as it contracts. This is less common and usually involves the control or deceleration of a movement being initiated by the eccentric muscles agonist. For example, when kicking a football, the Quadriceps muscle contracts concentrically to straighten the knee and the Hamstrings contract eccentrically to decelerate the motion of the lower limb. This type on contraction puts a lot of strain through the muscle and is commonly involved in muscle injuries

Isometric Contractions Isometric contractions occur when there is no change in the length of the contracting muscle. This occurs when carrying an object in front of you as the weight of the object is pulling your arms down but your muscles are contracting to hold the object at the same level. Another example is when you grip something, such as a tennis racket. There is no movement in the joints of the hand, but the muscles are contracting to provide a force sufficient enough to keep a steady hold on the racket.

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The amount of force a muscle is able to produce during an isometric contraction depends on the length of the muscle at the point of contraction. Each muscle has an optimum length at which the maximum isometric force can be produced.

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Length - Tension Relationship

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Three Types Of Levers In The Body What levers does your body use? Muscles and bones act together to form levers. A lever is a rigid rod (usually a length of bone) that turns about a pivot (usually a joint). Levers can be used so that a small force can move a much bigger force. This is called mechanical advantage.

There are four parts to a lever - lever arm, pivot, effort and load.

In our bodies: • bones act as lever arms • joints act as pivots • muscles provide the effort forces to move loads • load forces are often the weights of the body parts that are moved or forces needed to lift, push or pull things outside our bodies.

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Levers can also be used to magnify movement, for example, when kicking a ball, small contractions of leg muscles produce a much larger movement at the end of the leg. Levers are able to give us a strength advantage or a movement advantage but not both together.

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Types of levers CLASS 1 LEVER - nod your head The pivot is the place where your skull meets the top of your spine. Your skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward. For this lever, the pivot lies between the effort and load. A see saw in a playground is another example of a Class 1 lever where the effort balances the load. Nature of Science Scientists make models to demonstrate their explanations. Often models are constructed to demonstrate how things work. This model uses a physics idea of levers to provide an explanation for muscle/bone movement. The physics explanation of levers supports this model. Pivot diagram of a class 1 lever: skull and neck

Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For a Class 1 lever the pivot lies between the effort and the load. A see saw in a playground is an example of a Class 1 lever where the effort balances the load. The place where your skull meets the top of your spine is a Class 1 lever. Your skull is the lever arm and the neck muscles at the back of the skull provide the force (effort) to lift your head up against the weight of the head (load). When the neck muscles relax, your head nods forward.

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CLASS 2 LEVER - stand on tip toes The pivot is at your toe joints and your foot acts as a lever arm. Your calf muscles and Achilles tendon provide the effort when the calf muscle contracts. The load is your body weight and is lifted by the effort (muscle contraction). The load is between the pivot and the effort (like a wheelbarrow). The effort force needed is less than the load force, so there is a mechanical advantage. This muscular movement at the back of your legs allows you to move your whole body a small distance.

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Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For the Class 2 lever the load is between the pivot and the effort (like a wheelbarrow). The effort force needed is less than the load force, so there is a mechanical advantage. Standing on tip toes is a Class 2 lever. The pivot is at your toe joints and your foot acts as a lever arm. Your calf muscles and achilles tendon provide the effort when the calf muscle contracts. The load is your body weight and is lifted by the effort (muscle contraction). CLASS 3 LEVER â&#x20AC;&#x201C; Bend your arm The pivot is at the elbow and the forearm acts as the lever arm. The biceps muscle provides the effort (force) and bends the forearm against the weight of the forearm and any weight that the hand might be holding. The load is further away from the pivot than the effort. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement â&#x20AC;&#x201C; a small contraction of the biceps produces a large movement of the forearm. This type of lever system also gives us the advantage of a much greater speed of movement.

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Many muscle and bone combinations in our bodies are of the Class 3 lever type

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Different classes of levers are identified by the way the joint and muscles attached to the bone are arranged. For a Class 3 lever the load is further away from the pivot than the effort. There is no mechanical advantage because the effort is greater than the load. However this disadvantage is compensated with a larger movement. This type of lever system also gives us the advantage of a much greater speed of movement. A bent arm is a Class 3 lever. The pivot is at the elbow and the forearm acts as the lever arm. The biceps muscle provides the effort (force) and bends the forearm against the weight of the forearm and any weight that the hand might be holding. What is torque? In the examples above, the effort and load forces have acted in opposite rotation directions to each other. If a load tries to turn the lever clockwise, the effort tries to turn the lever anticlockwise. Forces acting on a lever also have different effects depending how far they are away from the pivot. For example when pushing a door open it is easier to make the door move if you push at the door handle rather than near to the hinge (pivot). Pushing on the door produces a turning effect, which causes rotation. This turning effect is called torque (or leverage). The formula for calculating the amount of torque is:

torque = force x perpendicular distance to the pivot The force is measured in newtons and the distance to the pivot is measured in metres or centimetres, so the unit for torque will be either newton metres (Nm) or newton centimetres (Ncm).

You can increase the amount of torque by increasing the size of the force or increasing the distance that the force acts from the pivot. Thatâ&#x20AC;&#x2122;s why the door handle is far away from the hinge.

The load and weight of the lower leg produce a clockwise torque about the knee. The lower leg will rotate in a clockwise direction. If the hamstring muscle at the back of the upper leg contracts with a strong force, it produces an anticlockwise torque that holds the leg up.

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Forces from our muscles produce torques about our joints in clockwise and anti-clockwise directions. If the torques are equal and opposite, the lever will not rotate. If they are unequal, the lever will rotate in the direction of the greater torque. In this diagram, the load and weight of the lower leg produce a clockwise torque about the knee. The lower leg will rotate in a clockwise direction

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In this diagram, lifting the weight like the person on the left produces a greater torque about the lower spine (pivot) - the lifting force is at a greater perpendicular distance to the pivot. The back muscles must exert a huge force to provide a torque that balances the torque from the weight being lifted.

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It is important to lift a heavy weight close to your body to reduce the torque produced around your lower spine

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Stabilisers and Mobilisers Muscles

Muscles can be divided into two types: mobilisers and stabilisers.

Mobilisers

Mobilisers are found close to the body’s surface and tend to cross two joints and are typically made up of fast twitch fibres that produce power but lack endurance. They assist rapid or ballistic movement and produce high force.

Stabilisers

Stabilisers are situated deeper, invariably only cross one joint, and are made up of slow twitch fibres for endurance and postural control.

Imbalance

Both groups of muscles work in a complementary fashion to stabilise and move, over time the mobilisers can inhibit the action of the stabilisers and begin to move and attempt to stabilise on their own. This inhibition of the stabilisers and preferential recruitment of the mobilisers is central to the development of “imbalance” and is what we want to prevent.

Balance and strength

Assessment of an athlete’s muscle balance and strength should be conducted on a regular basis.

Muscle balance and strength

A speed strength imbalance between two opposing muscle groups may be a limiting factor in the development of speed. Muscle balance testing to compare the strength of opposing muscle groups is important to prevent injury and guarantee maximum speed of muscle contraction and relaxation. Muscle imbalance can slow you down and result in injury

Strength checks Leg press/body weight ratio Your leg strength/body weight ratio indicates how easily you can get and keep your body moving at high speeds. This ratio is important to speed improvements in short distances. A good ratio is 2.5 times your “body weight”. If it is less than 2.5 then you should consider modifying the program to develop leg strength. Leg strength test The squat is considered the most functional leg strength test in predicting sprinting and jumping ability. Good 1RM (one rep max) scores are: • Male athletes 2 × “Body Weight” • Female athletes 1.5 × “Body Weight” Hamstring/Quadriceps strength For each leg record the 1RM for the leg curl and leg extension exercises. Divide your leg curl score by the leg curl extension to find the ratio for each leg. For each leg, the curl score should be at least 80% of your extension score. If the score is less than 80% then you need to devote more training attention to the hamstrings. To reduce the chance of injury the ratio should be at least 75%. Bench Press This is a test for upper body strength. The need for maximum upper body strength varies between sports and so it does not always need to be tested for. Good 1RM scores are: • Male athletes 1.25 × “Body Weight” • Female athletes 0.8 × “Body Weight”

Balance checks

For each of the following exercise the right and left limb 1RM scores should not differ by more than 10%. • Hamstrings (leg extension) • Quadriceps (leg curl) • Arm Curl • One arm military press • Single leg press

Plantar flexion/dorsi flexion

Ankle

Inversion/eversion

Leg

Extension/flexion

Hip

Extension/flexion

Shoulder

Flexion/extension

Elbow

Flexion/extension

Lumbar

Flexion/extension

3:1 1:1

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Ankle

OC Ratio 3:2 1:1

2:3 1:1 1:1

Movement

Joint

The following table (Dintiman 1998) is reported values for joint agonist-antagonist muscle ratios at slow isokinetic speeds:

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