5 must-read research reviews on performance by Science for Sport

SPECIAL EDITION 5 must-read research reviews on performance

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Page Number

Section

Link to Abstract Review Title

Study Details

Practical Takeaways from study

Related links to learn more about the topic

Reviewers comments on the study

Strength & Conditioning

[Abstract]

Optimal methods for maximising strength gains in athletes OBJECTIVE A high level of muscular strength is desirable for most athletes, as it not only helps protect against injury, but also enhances sporting performance. Therefore, understanding the training considerations to improve strength (e.g. methods, loading strategies, set configurations) and the underlying physiological factors that affect muscular strength is crucial for strength coaches. WHAT THEY DID The authors searched for studies and reviews on this topic published in the PubMed and Medline databases, as well as Google Scholar, up until July, 2017. They primarily focused on maximal dynamic strength rather than isometric or reactive strength. They included search terms such as ‘periodization’, ‘muscular strength’, ‘hypertrophy’, ‘bodyweight training’, ‘machine resistance training’, ‘weightlifting’, ‘plyometric training’, ‘eccentric training’, ‘unilateral resistance training’, ‘variable resistance training’, ‘training to failure’, ‘training status’, and ‘rest interval’. WHAT THEY FOUND There were a number of important findings from the review:  Strength development is underpinned by a combination of morphological (e.g. muscle CSA) and neural (e.g. motor unit recruitment) factors.  Block periodisation may produce the greatest improvements in strength, as well as rate of force development (RFD) and power.  Bilateral training, eccentric training, accentuated eccentric loading, and variable-resistance training may be the best ways to maximise strength gains.  Bodyweight exercise, isolation exercises, plyometrics, unilateral exercise, and kettlebell training are inferior methods to improve strength, but are still relevant as they can be used to improve RFD and power, and to challenge motor demands.  Training to failure is not necessary to maximise strength gains.  Multiple sets may increase strength gains more so than single sets.  While cluster sets may benefit hypertrophy and power adaptations, they may not benefit strength improvements to such a degree; however, more research is needed on this topic.  Inter-set rest intervals ranging from 2-5 min may provide the greatest strength-power benefits.

Practical Takeaways There are a number of important takeaways related to the findings of this review. Firstly, while multiple sets was found to be superior to single sets for strength development, the number of sets prescribed should be based on their training status and the doseresponse relationship for muscular strength development. For example, a beginner may only need 1-2 sets per exercise to maximise the strength response (so doing 3-4 sets may only increase fatigue for no further gain), whereas a more advanced athlete may need 4-5 sets to maximise strength gains. Furthermore, while 2-5 min rest was found to be optimal for strength gains in this review, ideal rest interval length is likely to vary athlete to athlete depending on the athlete’s training age, fibre type, and genetics; so auto-regulation is perhaps best practice in this scenario. Finally, this review suggests that weaker athletes should focus on developing a strength foundation before power-type exercises and training methods (plyometrics and potentiation complexes) are emphasised. It suggests that stronger athletes, however, begin to emphasise power-type exercises and training strategies while maintaining/improving their strength levels in order to maximise physical performance.

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Tim’s Comments “With over 250 references, it’s great to see a comprehensive and well-written review on this massive topic. Most importantly, it’s fantastic how the authors have presented the findings in a way that is so practically applicable for strength coaches. In line with the prior review too, it is clear from this review that no single exclusive training method can achieve the range of adaptations required for both strength and power. Combining heavy and light loads (moved quickly) may produce the desired strength adaptations while also developing RFD and power characteristics that are critical to sport performance. Finally, I am looking forward to seeing more research on accentuated eccentric loading and cluster sets in the future – two very promising methods for enhancing strength gains.”

Strength & Conditioning

[Abstract]

Linear and multidirectional speed: Can we use PAP to improve them? OBJECTIVE Post-activation potentiation (PAP) is a phenomenon in which muscular performance is enhanced after prior contraction. It has been shown to increase subsequent rate of force development in the muscle. While many studies have assessed the effect of PAP on linear speed, there is a need to synthesise all of this data in order to come up with practical recommendations for the strength and conditioning coach. There is also limited knowledge of the effect of PAP on change of direction (COD) speed. Therefore, this study reviewed the current literature on the PAP response for both linear and COD speed. WHAT THEY DID The authors completed a narrative literature review on the effect of PAP on linear and COD speed, with a focus on the practical applications of these results. They also conducted a brief meta-analysis of the available literature regarding PAP and linear speed. Where appropriate, percentage changes and magnitude-based inferences (as shown by effect sizes) were documented. Effect sizes were calculated for those data whose mean SD (standard deviation) values were presented numerically within the manuscript. WHAT THEY FOUND PAP and linear speed This review suggests that linear speed can be potentiated by a strength-based conditioning activity (CA) such as a back squat (using loads of 60-90%), or a plyometric-based CA such as alternate leg bounding. It is important to note that studies have shown a large degree of individual variation in how much linear speed can be potentiated. There is also large variance in the methodology used in these studies (different exercises, reps/intensities, time-periods between CA and performance). PAP and COD speed There is far less research on the effect of PAP on COD speed (only 2 studies to date), however, preliminary investigations seem promising. Ultimately, more research is needed before definitive conclusions and practical applications can be more accurately provided.

Practical Takeaways One of the biggest takeaways for strength and conditioning coaches from this literature review is that there is a huge variance in responses between individuals using PAP. Therefore, prescribing blanket PAP methods for all athletes will not optimise results across the board. It is crucial for the strength coach to measure individual responses to different protocols and see how the athlete responds. The strength coach should experiment with different rest times between the CA and speed/COD task, different exercises (e.g. bilateral, unilateral, knee-dominant, hip-dominant, etc), and different intensities (60-95% 1RM). It is only after experimenting with this that the strength coach will know what works best for each individual. Furthermore, while it appears that the optimal rest period (on average) between the CA and subsequent performance is around 6-7 minutes, in a practical setting, time constraints will likely not allow for you to wait this long between activities. One way to at least ensure a couple of minutes between the CA and subsequent task is to place a low-level “filler” exercise between the two. For example: heavy back squat > hip mobility drill for 2 min > depth jump. While this likely won’t maximise the PAP effect, it will at least allow for better results than moving straight from one to the other, when acute fatigue may impair performance. Finally, PAP work doesn’t have to be confined to the gym. On field, doing alternate leg bounds as part of your warm-up before maximal sprinting may help enhance subsequent sprint performance. For example, the strength and conditioning coach might get the athletes warm, then do some bounds followed by dynamic stretches (to allow for time between CA and sprinting), and then proceed to maximal sprints.

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Tim’s Comments “While PAP is certainly a fascinating topic, it is important to remember that things like PAP are the 1-2%’s, or the so-called “icing on the cake” in a programme. Do NOT base your strength programming around maximising PAP. Base your programming around getting athletes stronger, more robust/resilient, and more powerful. Furthermore, research has shown that stronger/more advanced athletes are the ones who see the best results from PAP anyway. Because of this, I personally would not recommend worrying about PAP unless you are working with more advanced athletes who can at least squat 1.5 x bodyweight. Before that point there are more important things to focus on. On a different note, it is interesting to see the lack of studies on the effect of PAP on COD speed. It would be great to see research on whether a heavy lateral sled drag or lateral bound could be used to potentiate COD performance in the near future!”

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Youth Development

[Abstract]

Loaded vs. unloaded plyometric training on speed and power OBJECTIVE The purpose of this study was to compare the effects of either a loaded or unloaded plyometric sessions on speed and power in elite young soccer players (age 15.9 ± 1.2 Years). WHAT THEY DID All athletes were assessed (pre & post) on their sprinting speed over 5-, 10-, and 20-m, mean propulsive power (MPP) relative to player’s body mass in the jump squat and squat and counter movement jumps. The athletes were pair-matched in two training groups; 1) loaded (8% of bodyweight) vertical and horizontal jumps and 2) unloaded vertical and horizontal plyometrics. The duration of this study was 6 weeks, with 12 plyometric sessions occurring during the soccer preseason period. WHAT THEY FOUND Both groups (unloaded and loaded) experienced improvements in their jumping ability after a 6 -week training programme at a 90% confidence level. However, both plyometric sessions failed to produce worthwhile changes in maximal speed and power performances. This suggests that both a loaded and unloaded plyometric session improved jumping qualities, but not power or speed.

Practical Takeaways In previous editions of the Performance Digest, it has been suggested that youth athletes may be able to tolerate loaded Plyometrics under specific context. This study has somewhat answered our questions, by providing us with an analysis of unloaded vs. loaded jumps. Whilst this study has no conclusive benefits to adopting loaded-jump variations in practice, it neither refutes the addition of them. In other words, loaded jumps were ‘safe’ for the sample in this study, which will hopefully lead onto more investigations in this area. In light of this study, the reader may look to incorporate loaded variations in their programmes. Some examples include augmented loading, which can be achieved with either a dumbbell or a medicine ball to a drop landing. Check out the video attached for an interesting variation of a jump that loads the landing phase and incorporates upper body control. It is important to remember that these variations should only really occur when landing mechanics are sound. This study has supported this by using a sample of 15+ years, indicative of emotional maturity, post-peak height velocity (on average) and technical competence.

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Tom’s Comments “This study mentions that the ‘failure’ of this programme to create worthwhile adaptations to both power and speed were possibly related to an interference effect of concurrent training methods. For example, this study had little control over the volume or intensity of these players external training (pitch-based, gym-based, other leisure activities). The authors of this study were honest and used high-levels of academic rigour to ensure reliability. I think if more studies employed the same standards of data analysis, many would come to a similar conclusion with regards to an interference effect. I am surprised that improvements in jump performance did not correlate to either mean propulsive power or sprint speed. One of the mechanisms responsible in both sprinting and jumping is the stretch shortening cycle (SSC), where a powerful concentric contraction follows an elongated muscle tendon unit caused by an eccentric (lengthening) contraction. However, this may have again been dampened by additional training activity.”

Strength & Conditioning

[Abstract]

Are change of direction speed and reactive agility actually related? OBJECTIVE Agility can be defined as “a rapid whole-body movement with change of velocity or direction in response to a stimulus.” Agility can be defined as an “open” skill due to its reactive nature or perceptual component. Meanwhile, change of direction speed (CODS) is considered a "closed" skill. The decision-making process is essential to agility and several authors have reported that agility is a defining performance criterion in several sports. The aim of this study was to determine if there were differences in agility performance when testing CODS and then an agility-based task using identical scenarios. Secondly, the study aimed to identify the relationship between CODS and agility with straight-line sprinting, reactive lower-limb power, and anthropometric characteristics. WHAT THEY DID 45 male and 31 female team-sport athletes participated. The agility testing protocol employed the use of FitLights, where LED lights can be programmed for specific or random activation and be deactivated by direct contact or proximity. Lights were placed in 4 different arrangements: frontal (FR), universal (UN), semi-circular (SC), and lateral (LA) - I’ve linked a picture of each configuration in the infographic link below. The testing protocol for the CODS condition provided participants with advanced knowledge on the sequential order of the lights. In the agility condition, the light activation was unknown and non-sequential. Two trials were performed for each configuration. Each configuration was done in a separate session so testing was performed over 4 sessions. Speed and power testing involved a 15m sprint and a flying 15m sprint using timing lights. Lower-limb power was assessed by a 10m timed single-leg jump test where the subject jumped using their dominant leg as fast as possible for 10m. WHAT THEY FOUND The differences between CODS and agility testing protocols were statistically significant in most of the tests. The greatest difference was in the UN configuration, with 22% for men and 31% for women, followed by the SC configuration, with 16% for men and 10% for women. The smallest differences were in the LA configuration at approximately 10% in both groups. UN and FR configurations had weak correlations between CODS and agility performance in both men and women. However, LA configuration showed the strongest correlations with r = 0.66 for women and 0.52 for men. A significant positive correlation was also observed for CODS and agility in the SC configuration in women with r = 0.53. Among men, significant negative correlations were observed between LA-agility and body height (r = -0.43) and LA-CODS and body weight (r = -0.42). Among women, body height generally had a negative effect on agility testing, where significant negative correlations were observed with FR-agility (r = 0.42), UN-agility (r = -0.64), and SC-agility (r = -0.64). Many of the tests correlated with 15m and flying 15m sprints, with strongest correlations between flying 15m and the SC-CODS and agility protocols (r = 0.58 and 0.64, respectively). Performance in the 10m single-leg jump test showed significant moderate to strong correlations with the SC and LA configurations. The rest of the correlations for the performance tests with agility were generally weak to moderate correlations.

Practical Takeaways CODS and agility performance were found to be significantly different among men in all 4 configurations. Women showed smaller differences in CODS and agility during all 4 configurations. Interestingly, the UN configuration produced the greatest difference between CODS and agility in both men and women. This could be due to the complex demands of the test, requiring considerable visual scanning and attention. Hence, peripheral perception and other cognitive components are critical for performance in this test. It seems the more complex the movement structure, the greater difference seen between CODS and agility. Body height seemed to negatively affect agility in both men and women, which is expected due to the higher center of mass putting the subject at a decreased biomechanical advantage for changes of direction. Sprint performance and reactive power testing generally showed weak to moderate correlations with most agility tests, suggesting that agility testing is not just dependent on physical potential or anthropometric factors, but also on cognitive and sensory factors. I’ve linked an article I wrote below (see article #1) that covers the perceptual components of agility and its importance to agility performance. In this article, you can see how that can be put into practical use, which I will also discuss in my comments to the right.

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James’s Comments “It is clear from this and previous research that CODS and agility are 2 independent qualities. However, to really distinguish between athlete’s ability to produce “a rapid whole -body movement with change of velocity or direction in response to a stimulus,” the stimulus must be specific to the sport. It has been shown that higher skilled athletes only perform better in agility tests when reacting to a sport-specific stimulus compared to lower skill athletes (e.g. elite vs semiprofessional). This asks many questions of practitioners and the use of cones, reactive lights, and other reaction methods. For example, are we improving agility using reactive stimuli that aren’t sport-specific? It is also important to note that in team sports, you have offensive and defensive agility and both scenarios require a different skillset to recognise various situations. There are many ways to be able to train both qualities in the same drill. Some very simple examples of this are 1v1, 2v1, 3v2, 3v3, drills etc. Creating variation in these drills is simple and can be as easy as changing the athlete’s entry position into the drill. Small-sided games can also be used with an agility focus. Here are some guidelines to have a game emphasise agility: 1)

Reducing the number of players (3-a-side vs. 5-aside).

Greater density of the game (more players in a given space), meaning they’ll be a greater number of agility manoeuvers.

Reducing the number of passes allowed before scoring increases agility demand.

Having the sport coach provide encouragement during the game can help athletes that lack engagement get more involved.

If you are interested in the big hitters in this area, you can search for Dr. Warren Young and Dr. Sophia Nimphius who have published many of the papers in this area.”

Strength & Conditioning

[Abstract]

Don’t just sprint in a straight line: why curved running is important OBJECTIVE

WHAT THEY DID

WHAT THEY FOUND

When training and testing sprint ability, the focus is typically on linear (straight-line) speed. However, due to the open nature of team-sports, sprinting is often completed in a curvilinear (nonstraight line) manner. As such, the aim of this study was to assess the characteristics of sprinting such as sprint angle and evaluate any positional differences in sprint angle and number of sprints in elite youth soccer players.

Data was collected by Catapult GPS of thirteen elite youth male soccer players who compete in the U18 Premier League during six official matches. Raw data was plotted and given coordinates when running velocity exceeded 24 km.h-1. This process involved:

A number of key findings were reported within this study:



Determining a line between the first and last point of the sprint (chord line).



various positions for sprint angle with fullbacks performing smaller angled sprints compared to all other positions.

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A second line was plotted using the first three data points to calculate the initial trajectory.



Once both lines were plotted (like a V shape), the angle between them was then calculated to give the angle of the curvilinear sprint.



The average number of sprints, sprint angle, number of sprints between 0-5°, 5-10°, 1015°, and 15°+ were calculated for different positions.

Practical Takeaways Irrespective of the playing position, it appears that the average sprint angle (curve of the sprint from initial trajectory to end point) for soccer players during a match is around 5°. One of the main differences with curvilinear running/sprinting compared to linear sprinting is that the body leans inwards (as opposed to remaining more upright). Thus, players are influenced by centrifugal force and consequently need to produce a mediolateral ground-reaction force in order to counteract the centrifugal force and stay balanced whilst running. As running velocity increases, having the strength and technique to overcome these forces may be an important determinant in curvilinear sprint performance. The vast majority of sprint training and testing in soccer is linear, therefore, testing curvilinear sprinting alongside traditional linear sprints may help inform practitioners about players who need to further develop this skill. While the average sprint angle is around 5°, curvilinear sprints may be required to be performed up to a 30° angle. This has important implications for training, rehabilitation, or designing “worst-case scenario” drills. For example, an athlete returning from a hamstring injury may start to introduce small angle (5-10°) accelerations alongside linear speed progressions. As the athlete progresses to maximal velocity, introducing a “worst-case scenario” sprint may involve a more aggressive 30° curved sprint to prepare them for matchplay.

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Substantial differences existed between the

Those playing as a centre-forward performed larger angled sprints compared to all other positions. Centre -forwards performed a greater number of sprints between 10-15° and 15°+ compared to all other positions.

⇒ Fullbacks, wide-midfielders, and centreforwards performed more sprints compared to centre-backs and centre-midfielders.



There were no differences between sprint distances for all positions.

James’ Comments “While linear speed is of upmost importance, not just for performance but also for hamstring health, curvilinear sprinting cannot be forgotten. Perhaps testing could be performed similar to a “change of direction (COD) deficit” (see Performance Digest Issue #28 for more on this topic), where time or velocity can be measured for a 20 m linear sprint and 20 m curved sprint during 1-3 different angles. Ranking the athletes based on the deficit between the linear sprint and curved sprints, then splitting them by the median score may help identify which athletes need a greater emphasis on curvilinear sprinting. Furthermore, the skill of curvilinear running/sprinting should be trained alongside linear sprint or agility training. This may involve curved running around cones, as well as large agility games . These larger spaces may allow for higher speed agility manoeuvres, which is likely to encourage a “swerve” or curved run to evade defenders.”

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