Chasing Symmetry: Inter-limb Imbalances & Performance in Youth Tennis

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Original study

Madruga-Parera, Marc^1,2; Bishop, Chris³; Fort-Vanmeerhaeghe, Azahara⁴; Beltran-Valls, Maria R.^2,5; Skok, Oliver G.⁶; Romero-Rodríguez, Daniel¹ Interlimb Asymmetries in Youth Tennis Players: Relationships With Performance, Journal of Strength and Conditioning Research: October 2020 – Volume 34 – Issue 10 – p 2815-2823 doi: 10.1519/JSC.0000000000003152
Click here for abstract

Background & Objective

Tennis, by nature, is a multidirectional sport that requires individuals to perform numerous unilateral movements. For example, 70% of movements that occur on a tennis court occur from a lateral position (see HERE). Therefore, a difference in function or performance between limbs (i.e. interlimb asymmetries) can have significant effects on an individual’s ability to perform optimally.

The objective of this study was to investigate the asymmetries present in young tennis players during a fitness testing battery.

What They Did

Twenty-two elite youth tennis players (16.3 yr) were tested  over two days that were separated by a 72h rest period, with each players’ training load decreased by 50% during the testing period to support testing performance. Day 1 consisted of three unilateral jump tests (countermovement jump (CMJ), broad jump, and lateral jump) and a 180-degree turn change of direction (CoD) test. On the second day, players performed a CoD task (shuffle and crossover step) that was resisted by an isointertial device (Byomedic System SCP).

All subjects performed three practice trials for all tests and a specific warm-up prior to testing, which consisted of 5-min of light jogging, dynamic stretches, and lower-body strength exercises (lunges, inchworms, and bodyweight squats).

What They Found

The greatest levels of asymmetry were found on the single-leg CMJ (15.8%) and the smallest on the CoD tests (1.83%). With these scores considered, negative correlations were found between CoD asymmetries and the single-leg CMJ on the dominant and non-dominant side. This suggests that when used together, CoD and jump tests do not accurately describe the asymmetry profile of an individual.

Differences between limbs for all tests was reported, with the dominant limb (eighteen athletes had right side dominance) being the stronger side in all tests.

The CoD tests revealed a lower degree of asymmetry compared to the jump tests. This suggests that CoD tests may not be as sensitive as jump tests at revealing imbalances. Factors, such as linear speed, have previously been found to mask poor unilateral performance in CoD tasks (see HERE). Secondly, no relationship was found between the results of the 180-degree CoD test and CoD isointertial test.

Practical Takeaways

The aim of any good long-term athletic development programme is to eliminate an over-reliance on a single strategy (e.g. taking off from only the right foot from a 90-degree cut when cutting from the left leg could be more advantageous to return a shot). Practically, ensuring that coaches tally up repetitions from the right- and left-hand side of the body allows coaches to document how many CoD movements are performed on both limbs during a session. This ensures that we are doing our bit to prevent overuse injuries during closed tasks.

According to Bishop and colleagues (see HERE), a defining factor in effective CoD performance is the range of motion at the ankle. They suggest that a greater range of motion provides enhanced stability and balance ability, which allows athletes to “bank in and out” of a movement faster. In the attached video, a host of exercises such as single-leg RDL’s, squats, box step-ups, and skater hops with reaches can be seen. These movements create a fantastic foundation for young athletes, but further, will support athletes in developing ankle range of motion in a dynamic manner. Using 2 sets x 10 reps of these exercises in a warm-up will make a huge difference over acute periods (4-6 weeks) and should help tennis performance.

Inter-limb asymmetries will, for the most part, exist due to the natural preference of an athlete to move a certain way. High imbalances between limbs can be a strong predictor of injury but is not necessarily a reason to act immediately. For example, in the podcast below, Chris Bishop discusses that when measuring asymmetries, coaches must ensure that this is done often (every 2-4 weeks) so that the imbalance is not purely a data anomaly. Consistency, bilateral (e.g. front/back squat), and unilateral (e.g. pistol squats, reverse lunges) training are the recommendation for reducing imbalances.

Reviewer’s Comments

“This study provides practitioners with a guide to test lower-limb asymmetries. Monitoring of inter-limb asymmetry is important, as athletes who show higher levels of asymmetry (>15%) between-limb difference are at a greater risk of lower- limb injury. Furthermore, although limb dominance is relatively normal, reductions in jump height and CoD performance have also been previously reported (see HERE) when a large imbalance is present. This will be detrimental to tennis performance, so ensuring that these are monitored is important.

A limitation of this study though, is that the participants’ stage of maturation was not considered. In the attached article, Madruga-Parera and colleagues reported that higher levels of asymmetry were present circa-peak height velocity than those who were pre-/post-peak height velocity. The authors attribute this to a temporary loss in motor control, commonly known as “adolescent awkwardness”, which occurs during PHV and results in compromised physical outputs. Future studies must consider this in a youth cohort to ensure data validity. Finally, both CoD tests were poor at revealing asymmetries. Jump testing may be a more time-effective and reliable test to measure inter-limb asymmetries.”

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