Eliminating asymmetry: plyometrics vs. combined training

Physical training is a key component of optimizing performance in sport. Following the widespread acknowledgement that strength training is an essential element of optimizing performance, the implementation of plyometric training has become commonplace in the preparation of athletes of all types. However, when implementing plyometrics, specificity is important. As seen in a previous issue of Sports Performance Bulletin (see this article), unilateral and bilateral strength training have different effects on testing outcomes. Unilateral strength training leads to better outcomes during unilateral tests and bilateral training leads to better performance during bilateral performance. It is reasonable therefore to suspect that this is true of plyometric training as well.

Reducing asymmetry

In most sports, athletes using one leg at a time in an alternate fashion. However, a lack of performance (eg strength) in one leg can’t be fully compensated for by increased performance with the other leg. As such, reducing performance asymmetries in the limbs is a key consideration for improving overall performance. This is especially true with asymmetries that show up when jump tests are carried out because these tests are specific to the activities (eg running, sprinting etc) that athletes engage in most. While there is some research investigating the reduction of limb asymmetries revealed during jump tests, it’s not immediately clear which types of training are most effective for reducing these asymmetries. If we can find a training method that is especially effective at reducing these asymmetries, we are better placed to improve performance.

New research

To try and answer this question, a group of Chinese researchers have carried out a meta-analysis study (a study that pools all the previous data on a topic to come up with more robust conclusions) to provide clarity as to whether plyometric training is an effective way of positively influencing limb asymmetry⁽¹⁾. Furthermore, they wanted to understand which types of plyometrics might have the most favorable impact.

The authors included eight different studies in their meta-analysis, and these studies had a total of 157 participants in total. Limb asymmetry was a defined as ‘differences in jumping performance between the limbs’. As the numerical description of asymmetry can be expressed in different ways, and researchers across these eight different studies had often chosen to describe asymmetry differently, the authors took a standardized approach to doing so. This ensured that comparisons between studies were fair and accurate.