Changes in Muscle Activity Imbalance of the Lower Limbs Following 3 Weeks of Supplementary Body-Weight Unilateral Training

This study examined the effects of a short-term supplementary body-weight training program on changes in the muscle activity imbalance of the lower limbs during high-speed running in soccer players. Fifteen professional male soccer players took part in the study (age: 25 ± 5 years, body mass: 79.2 ± 10.8 kg, stature: 177 ± 10 cm, training experience: 12 ± 5 years). The evaluations of lower limb muscle activity imbalance via surface electromyography (sEMG) were performed twice (pre- and post-intervention), at a three-week interval. The sEMG was measured bilaterally from the area of quadriceps (Q), hamstrings (H), and gluteal muscles (G) during high-speed running at 18 km/h using sEMG shorts. Between measurements, the athletes performed the supplementary body-weight program of the lower limbs 4 times a week for 3 weeks. The training included six body-weight exercises performed unilaterally. The load progression included an additional set of each exercise in successive weeks of the experiment. The two-way repeated-measures ANOVA indicated a statistically significant main interaction for time × muscle (p = 0.006; F = 6.948; η2 = 0.332). The post-hoc analysis for the interaction effect of time × muscle showed a statistically significant decrease in muscle imbalance for the post-intervention compared to the pre-intervention for the H (p < 0.001; ES = 1.32), G (p = 0.002; ES = 0.92), and T (p < 0.001; ES = 1.54), but not for Q (p = 0.56; ES = 0.14). Moreover, there was a statistically significant greater imbalance between the H, G, and T muscles versus Q (p = 0.043, ES = 1.15; p = 0.006, ES = 1.57; p = 0.001, ES = 1.69, respectively) for the values recorded pre-intervention. Changes in muscle activity after 3 weeks of sports-specific movement patterns were statistically significant. For the gluteal (G) and hamstring (H), the imbalance between the limbs decreased significantly (p = 0.01). The imbalance in the quadriceps muscles (Q), with respect to each limb, did not decrease significantly (p = 0.82) following the training intervention. Conclusions: The results of this study indicate that in-season soccer training supplemented with a body-weight training program successfully decreases gluteal and hamstring imbalance between limbs after 3 weeks of training.