Effects of 5 weeks of bench press training on muscle synergies: a randomized controlled study

The ability to perform forceful muscle contractions has important implications in sports performance and in activities of daily living. However, there is a lack of knowledge on adaptations in inter-muscular coordination following strength training. The purpose of the present study was therefore to assess muscle synergies before and after five weeks of bench press training. Thirty untrained male subjects were randomly allocated to a training group (TRA) or a control group (CON). Following the pretest, TRA completed five weeks of bench press training, before completing a posttest, while subjects in CON continued their normal life. During test sessions, surface electromyography (EMG) was recorded from 13 different muscles. Muscle synergies were extracted from EMG data using nonnegative matrix factorization. To evaluate differences between pretest and posttest, we performed a cross-correlation analysis and a cross-validation analysis, in which the synergy components extracted in the pretest session were recomputed, using the fixed synergy components from the posttest session. Two muscle synergies accounted for >90% of the total variance, and reflected the concentric and eccentric phase, respectively. TRA significantly increased 3RM in bench press with 19.0% [25;75 percentile, 10.3%;21.7%] (p<0.001), while no change occurred in CON. No significant differences were observed in synergy components between groups. However, decreases in correlation-values for intra-group comparisons in TRA may suggest that the synergy components changed, while this was not the case in CON. Strength and conditioning professionals may consider monitoring changes in muscle synergies in training and rehabilitation programs as a way to benchmark changes in inter-muscular coordination.