Inter-limb Functional Asymmetry and the Development of Pain in Collegiate Volleyball Players: A Preliminary Study

Purpose Functional asymmetry is a potential risk factor for musculoskeletal pain in athletes, but how it affects volleyball players has not been widely investigated. We therefore aimed to explore the association between inter-limb asymmetry in performance-based tests and the development of lower extremity pain in collegiate volleyball players over a competitive season. Methods In this preliminary study, 26 male collegiate volleyball players (mean age = 20.6 ± 1.0 years) underwent preseason testing, including the star excursion balance test (anterior direction), side hop test, and single-leg hop for distance. Pain status was tracked on a biweekly basis using an online survey with an 11-point numerical rating scale. Based on reporting frequency, some athletes were classified into the pain group (pain reported on ≥ 80% of surveys) or into the no-pain group (pain reported on 0%). Inter-limb asymmetry was calculated as |1 − (left/right)| for each performance test. Results There was significantly greater asymmetry in the star excursion balance test in the pain group (n = 9; 0.29 ± 0.25) than in the no-pain group (n = 10; 0.04 ± 0.03, p  = 0.040). Overall trends towards higher asymmetry were seen in the pain group, but no significant differences between the groups were observed in the side hop test asymmetry index (pain group: 0.13 ± 0.12, no-pain group: 0.06 ± 0.04, p  = 0.203) or single-leg hop asymmetry index (pain group: 0.16 ± 0.17, no-pain group: 0.04 ± 0.05, p  = 0.117). Conclusion Greater inter-limb asymmetry in dynamic balance was associated with frequent pain in a group of volleyball athletes. Our preliminary findings suggest that functional asymmetry screening, especially in dynamic balance, might be useful for early detection of athletes who may be at risk of developing non-traumatic pain. Trial Registration UMIN000054720