Relationship Between Offensive Performance and Symmetry of Muscle Function, and Injury Factors in Elite Volleyball Players

In volleyball, successful offensive performance is influenced not only by physical muscle function but also by injury status. The purpose of this study was to analyze the relationship between muscle function—including strength, balance, and symmetry—and injury history in relation to offensive performance (OP) and ultimately sought to find factors required to improve OP. The final analysis included 60 players in attacking positions (36 in the symmetry group and 24 in the asymmetry group). Muscle strength was assessed using isokinetic testing for shoulder and knee extension. Balance was evaluated using the Upper Quarter Y-Balance Test (UQ-YBT) and the Lower Quarter Y-Balance Test (LQ-YBT). The asymmetry index (AI, ≥10%) was calculated by comparing the dominant and non-dominant sides. The results showed that the asymmetry group had a higher injury rate and lower offensive performance (OP) than the symmetry group (p < 0.05). In multiple regression analysis, no significant predictors were found on the non-dominant side, whereas significant variables were identified only on the dominant side. The key variables influencing OP were shoulder and knee extension strength, UQ-YBT scores, and the AI of knee extension. A 13.8% improvement in shoulder extension strength on the dominant side increased the likelihood of enhanced offensive performance (OP) by 2.54 times. A 10.5% improvement in the asymmetry index (AI) of knee extension was associated with a 1.52-fold increase in OP (p < 0.05). Shoulder and knee flexion did not significantly affect OP in any of the tests (p > 0.05). In conclusion, offensive performance in volleyball is associated with the greater shoulder and knee extension strength of the dominant side, as well as positive changes in UQ-YBT scores and the AI of knee extension.