TM-9-3

Other Instruments Used to Measure Isotonic Strength In addition to the use of free weights or machines, maximal isotonic strength can be measured using dynamometers. A dynamometer is a device capable of measuring force. Hand-grip and back-lift dynamometers have been used to evaluate grip strength and back strength, respectively, for many years. Dynamometers operate in the following way. When force is applied to the dynamometer, a steel spring is compressed and moves a pointer along a scale. By calibrating the dynamometer with known weights, one can determine how much force is required to move the pointer a specified distance on the scale.

The advantages of the isotonic dynamometer as a measure of strength testing include low cost of equipment and the fact that force is dynamically applied which may simulate sport specific movements.

Grip Dynamometer Objective: To measure the strength of your hand grip.

Age level: Age 16 through college level.

Reliability: Test-retest reliability coefficients of .91 to .96 have been reported.

Validity: Face validity is generally accepted for this test.

Equipment: Grip dynamometer.

Directions: The grip dynamometer is used to measure the grip strength of the hand. It has an adjustable handle to fit the size of the hand and a maximum needle indicator for ease of scoring. The scoring dial is marked off in kilograms, from 0 to 100.

Other Considerations: At one time it was believed that grip dynamometer scores correlated with total body strength. However, a prolific amount of research conducted over the past two decades clearly indicates that this is not the case and in fact scores on the grip dynamometer seem to correlate highly with‌well‌grip strength. What do you know?

Back and Leg Dynamometer

Objective: To measure the strength of the lower and upper back.

Age level: Age 16 through college level.

Reliability: Reliability has been reported for tests with this instrument, ranging from .86 into the .90s.

Validity: Face validity is generally accepted for this test.

Equipment: Back dynamometer and a chain and bar attachment.

Directions: This instrument consists of a scale that measures from 0 to 2500 lb in 10 pound increments attached to a strong platform, with a chain and bar attachment for individual adjustments according to height.

As previously mentioned, dynamometers operate in the following way. When force is applied to the dynamometer, a steel spring is compressed and moves a pointer along a scale. By calibrating the dynamometer with known weights, one can determine how much force is required to move the pointer a specified distance on the scale.

Other Considerations: The advantages of isotonic strength testing include low cost of equipment and the fact that force is dynamically applied, which may simulate sport-specific movements.

The disadvantages of dynamometer isotonic testing using a 1-RM technique include the possibility of subject injury and the fact that it does not provide information concerning the force application over the full range of motion. This point will be discussed again in the next chapter. The main drawback of this instrument is the expense involved for a limited number of exercises.

Isokinetic Assessment of Strength Over the past several years many commercial computer assisted devices to assess dynamic muscular force have been developed. The most common type of computerized strength measurement device on the market is an isokinetic dynamometer, which provides variable resistance. The term isokinetic means moving at a constant rate of speed. A variable resistance isokinetic dynamometer is an electronic-mechanical instrument that maintains a constant speed of movement while varying the resistance during a particular movement. The resistance offered by the instrument is an accommodating resistance, which is designed to match the force generated by the muscle. A force transducer inside the instrument constantly monitors the muscular force generated at a constant speed and relays this information to a computer, which calculates the average force generated over each time period and joint angle during the movement.

This type of strength assessment provides a great deal more information than that supplied by a 1-RM test. The 1-RM test provides only the final outcome, which is the maximum amount of weight lifted during this particular movement. That is, a 1-RM test does not provide information about the differences

in force generation over the full range of movement. Therefore, a computer assisted isokinetic instrument appears to offer advantages over the more traditional 1-RM test.

Practically the same advantages that were mentioned for isotonics are inherent to isokinetics.

However, as previously stated, unlike isotonics, isokinetics have the advantage of putting the muscle under maximum tension at every point in the range of motion. Since isokinetic exercises are always performed with the use of machines, isokinetics can be somewhat safer than isotonics. Some machines are extremely expensive and they require trained administrators to give the test, making the instrument cost prohibitive for most school settings.

Variable-Resistance Measurement of Strength Several commercial companies market weight machines that vary the resistance (weight) during dynamic muscular contractions. The measurement of strength using a variable resistance device is similar in principle to isotonic tests using 1-RM or three to six repetitions, with the exception that the variable resistance machine creates a variable resistance over the range of movement. This variable resistance is typically achieved via a "cam," which in theory is designed to vary the resistance according to physiological and mechanical factors that determine force generation by muscles over the normal range of movement.

Advantages of these devices include the fact that most sport movement patterns are performed using variable forces, and the design of these machines makes adjustment of weight easy, and therefore little time is required for measurement. A disadvantage of these machines is the high cost; this is compounded by the fact that several individual machines are often required to measure strength in different muscle groups.

Isometric Strength Tests The objective of isometric strength testing is to measure strength at specific angles without the movement of resistance or the joint involved. Remember that strength is specific to the angle of push or pull, consequently, isometric strength scores and isotonic strength scores have not been found to correlate with each other very highly. In some cases they seem to be independent components of strength. Isometric strength is measured with instruments, which calculate the force you can exert statically by the muscle being evaluated. In an isometric contraction the muscle does not shorten (isometric means “constant length�) even though the person is exerting maximal force. Isometric strength varies with the angle of the joint and does not provide a measure of strength throughout the normal range of motion of a joint.

There are several instruments that are used to measure isometric strength. Some of the more popular devices are as follows.

Tensiometer Objective: to measure the strength of various muscle groups at specific angles.

Age level: age 16 through college level.

Reliability: Test-retest reliability coefficients of .93 to .98 have been reported.

Validity: Face validity is generally accepted for this test.

Equipment: The equipment required for various tests with the tensiometer includes a strap with D ring, a pair of cables with adjusters, a goniometer to establish correct joint angles, and a specially constructed table for various exercise positions.

Directions: The tensiometer is an instrument that indicates the pounds of pressure exerted.

The large tensiometer measures up to 300 pounds a smaller tensiometer is used when measurements are expected below 30 pounds, owing to the inaccuracy of the lower end of the 300 pounds instrument. The smaller tensiometer measures accurately from 0 to 100 pounds.

The reliability of the tensiometer is quite high; objectivity coefficients for practically all tests were in the .90s.

You most likely have seen a tensiometer used at an airport. For instance, have you ever seen a jeep taxi a plane into a parking area? The nose of the plane will have a cable attached to it that leads to the back end of the jeep. While the jeep is taxing the plane to the parking area, a grounds crewman will periodically attach a tensiometer onto the cable in order to measure the cable tension. He is testing to make sure the tension on the cable is not great enough to snap the cable. When you test for strength of an individual you use basically the same procedure. The tester attaches a cable to an immoveable object like an exercise table and then has the subject pull on the end of the cable with a strap. As the subject applies force over the cable, the cable tightens and the tensiometer pointer is deflected to indicate the amount of force applies during the movement.

The fact that the tensiometer is lightweight and portable makes it an attractive device for making strength measurements in the field. The cable tensiometer has been used in physical therapy to evaluate training progress to injured limbs. It has been argued that since the cable tensiometer can be applied to measure static strength at many different joint angles, this technique might be more effective in evaluating strength gains during therapeutic training than conventional weight lifting tests (McArdle and Katch 1996; Katch 1996). The measurement of isometric strength is typically performed at several joint angles. Isometric testing at each joint angle usually consists of two or three trials of maximal contractions (contraction durations of approximately five seconds); the best of these trials is considered to be the measure of strength.

Advantages of isometric testing using computerized equipment include the fact that these tests are generally simple and safe to administer. Disadvantages include the high cost of some commercial devices and the fact that many sport activities involve dynamic movements. Further, because of strength differences over the full range of joint movement, isometric measurements must be made at numerous joint angles; this increases the amount of time required to perform a test.

Summary First of all, you may have noticed that none of the tests reported in this chapter were designed for children under the age of twelve. Although many physical education instructors and sports coaches test younger children for strength, this is a mistake of significant magnitude. Children under twelve years of age should not engage in heavy resistance exercise or strength testing because the long bones are not

completely ossified prior to this age. Heavy resistance exercise by children this young may cause premature ossification of the long bones and thus stunt normal growth. Let me explain in young children there is a growth place in the long bones called the epiphysis plate. In normal children, these growth places do not ossify until they reach approximately 18 years of age. As you probably have already guessed the growth places enable the long bones to grow in proportion to the child's growth patterns. However, when heavy resistance exercises are used by adolescents they cause the premature closure or ossification of the epiphyseal plates. When this occurs the child's growth will be stunted.

Medical research has also revealed that curvature of the long bones can occur from engaging in heavy resistance exercise at a young age. Of course, this is not to say that young children should avoid physical activities, it is maximum stress exercise that can be dangerous for young children, not physical exercise in general.

As you know by now the one repetition maximum (1-RM) method of evaluating muscular strength involves the performance of a single, maximal lift. This refers to the maximal amount of weight that can be lifted during one complete dynamic repetition of a particular movement (e.g., bench press). As mentioned this can be very dangerous especially if the subjects are not highly skilled. Because of safety concerns, some physical educators, physical therapists and exercise scientists have recommended that an isotonic test consisting of three or five repetitions be substituted for the 1-RM test. The rationale is that the incidence of injury may be less with a weight that can be lifted a maximum of three (3-RM) or five (5-RM) times compared to the heavier weight that can be lifted during a 1-RM contraction. This concept seems plausible but at the present time there is no research which indicates that a 3-RM or a 5-RM is measuring the same component of strength that a 1-RM is measuring. That is a research study you could very well do for you post doctorial work. Remember, I already gave you a doctor’s degree in chapter one. The general rule is that any time you do more than 5 repetitions with a weight you are sacrificing strength for muscular endurance, and any time you do less than 10 repetitions you are sacrificing muscular endurance for strength.

This brings up another important point. Tests such as the Isotonic Strength Test devised by Johnson in which push-ups, pull-ups, dips, and sit-ups are performed for the maximum number of repetitions you can complete are not valid instruments for measuring strength. First of all most of these measure are neither absolute nor relative. For example, who do you think is going to do more pull-ups a person who weighs 300 pounds or a person who weighs 140 pounds‌most likely the latter person is going to do more? The person who weighs 300 pounds might have greater absolute and relative strength in that particular exercise, (He might have much stronger latisamus muscles) but because he has to pull-up his own weight his strength in that particular exercise may not be apparent. The same is true of dips, sit-ups, push-ups etc. In fact, with these movements most individuals can perform significantly more repetitions than five repetitions; consequently, in that case, strength is obviously not the factor being evaluated. This type of invalid testing is what drives students crazy and what gives physical education a bad reputation. Don’t contribute to the mess we already have in the field. Do what is right even if it takes you a few hours more. WORD!