A comparison of bilateral muscular imbalance ratio calculations using functional tests

Bilateral muscular imbalance can increase the risk of injury and negatively impact sporting performance. Bilateral muscular imbalances are typically calculated as ((side 1-side 2)/reference value) x 100, to provide a percentage value of the difference between limbs. Using different numerator (right-left or strong-weak) or reference values (left, right, strong, weak, average of the two) could mask or inflate the true difference value. The present study aimed to compare the bilateral muscular imbalance ratio calculations, using the absolute difference between limbs as the numerator and the five different options as reference values. Twenty three males (21.6±1.9 years, 1.80±0.06 m, 80.5±13.8 kg) and eleven females (20.8± 1.5 years, 1.62±0.03 m, 68.0±6.5 kg) performed the one-legged 6m timed test and the onelegged triple hop distance test. The five possible combinations were compared with a 2 (gender) x 2 (functional test) x 5 (calculation method) ANOVA for each test. Significant differences (P<0.05) were found between gender when the right leg was used as the reference value (males:6.1%, females:9.1%), and within calculation methods for males (range:5.9%-6.5%) and females (range:8.4%-9.4%), with low effect sizes (range: 0.07-0.26). The present findings demonstrate that using a different reference value for calculating bilateral muscular imbalances does not result in a practically significant difference. These findings can be used to inform a more standardised calculation method which will afford conditioning coaches a more correct evaluation and monitoring of training and rehabilitation programmes.