Strength Training with Same Ranges of Motion at Different Muscle Lengths does not Change Muscle Activation among Synergist Muscles

Objective. Strength training adaptations involve the synergistic activation of different muscles during training and rehabilitation. The aim of this study was to verify changes in electromyographic activity and the synergism of Vastus Medialis and Vastus Latera­lis after 12 weeks of knee extension training. Methods. Eighteen untrained young women were divided into 2 groups, performing training with matched duration of muscle actions, volume, frequency, rest between sets, and intensity. Both protocols used the same range of motion of 35°, but in differ­ent positions: initial range of motion between 100°-65° and final between 65°-30° of knee flexion, resulting in different muscle lengths. We analyzed the electromyographic signal amplitude, activation ratio between muscles, and cross-correlation. Results. The results demonstrated that in both groups the VM and VL decreased their EMG activity (p = 0.001 and p = 0.017, respectively). There was an increase in the mean value of the VM/VL activation ratio from 0.97 to 1.092 (p = 0.001) in both protocols and decreased cross-correlation value when comparing pre- and post-train­ing (p = 0.001). However, there were no significant differences between the two posi­tions for any of the analyzed parameters. Conclusions. The restricted degrees of freedom in the exercise, the matching of train­ing load components, as well as its submaximal magnitude, and the adoption of the same range of motion for both protocols seemed to have prevailed in these results, overshadowing the differences in quadriceps muscle lengths between the protocols.