Effects of hand positions on neuromuscular control strategies in closed-kinetic-chain push-ups

Background: The push-up is a widely utilized closed kinetic chain exercise for upper body strength training, characterized by its versatility in hand positions. To elucidate the mechanisms underlying push-ups performed with varying hand positions, numerous studies have investigated differences in individual joint and muscle variables between these variations and standard push-ups. However, the underlying multi-joint neuromuscular control strategies remain unclear. This study aims to identify different neuromuscular control strategies by comparing muscle synergies across four push-up variations with standard push-ups. Methods: Thirteen male fitness enthusiasts participated in this study, performing five push-ups each with various hand positions: standard push-up (SP), wide grip push-up (WGP), narrow grip push-up (NGP), internally rotated push-up (IRP) and externally rotated push-up (ERP). Electromyographic (EMG) activity of ten major muscles in the dominant right upper limb was recorded. Muscle synergies were extracted using non-negative matrix factorization. Results: All push-up variations can be decomposed into two muscle synergies. More differences were seen in Synergy 1 compared to SP: WGP had higher posterior deltoid (p = 0.001, d = −1.571), NGP had higher triceps brachii (p < 0.001, d = −1.816) and upper trapezius (p < 0.001, d = −1.843), and ERP had lower flexor carpi ulnaris (p = 0.005, d = 1.437) and extensor carpi radialis (p = 0.011, d = 1.346) but higher biceps brachii (p = 0.002, d = −0.858) muscle weights. Synergy 2 showed higher similarity across variations. Conclusions: Hand position variations do not alter the number of muscle synergies but modify their patterns. More differences occur in the centrifugal to nadir phase (Synergy 1). Therefore, a greater focus of attention on the centrifugal phase may be more effective in achieving the training effect of each type of push-up.