Follower arm muscle activity during the driver swing and its association with stroking performance in male golfers of different skill levels.

Objective: This study aims to investigate the activation patterns of the follower-arm muscles during the driver swing in male golfers of different skill levels and to examine their associations with stroking performance parameters, with the goal of elucidating the functional role of the follower arm in the golf swing. Methods: Sixteen right-handed golfers (8 National Level 1 and 8 National Level 2 athletes) participated, and multiple valid swing trials were collected from each participant with each individual swing treated as a measurement unit. Surface electromyography (sEMG) signals were collected from the follower-side triceps brachii, biceps brachii, pronator teres, flexor carpi ulnaris, and extensor carpi radialis brevis. The swing cycle was divided into five phases (P1-P5). Inter-group comparisons of normalized EMG were performed using Statistical Parametric Mapping (SPM). The root mean square (RMS) amplitude of each muscle per phase was compared between groups using t-tests. Spearman correlation analysis was employed to explore the relationships between muscle RMS and stroking performance. Results: No significant inter-group differences were found in stroking performance parameters or swing phase durations (p > 0.05). SPM analysis revealed that Level 1 athletes exhibited lower triceps brachii activation during the 80%-87% swing cycle (p = 0.022), higher pronator teres activation during 70%-72% (p = 0.032), higher flexor carpi ulnaris activation during 78%-86% (p = 0.017), and lower extensor carpi radialis brevis activation during 56%-64% (p = 0.019) compared to Level 2 athletes. The RMS comparisons at the uncorrected α = 0.05 level showed that Level 1 athletes had lower biceps brachii activation in P2 (p = 0.028), higher flexor carpi ulnaris activation in P4 (p = 0.011), and lower triceps brachii activation in P4 (p = 0.044) than Level 2 athletes. Exploratory correlation analyses revealed nominal associations (uncorrected p < 0.05) between flexor carpi ulnaris activation during P2 and carry distance (ρ = 0.528), biceps brachii activation during P2, P3 and backspin (ρ = 0.574, 0.575), and pronator teres activation during P3 and angle of attack (ρ = 0.592). Conclusion: The activation of the flexor carpi ulnaris, pronator teres, and other follower arm muscles exhibited temporal specificity and showed nominal associations with stroking outcomes. Skill-level differences were observed in both the SPM and RMS of muscle activation, with the most pronounced distinctions occurring in phase specific patterns during the downswing and follow through. The mechanical mechanisms underlying these activation patterns and their functional relevance to the stroking performance remain uncertain, warranting further investigation with synchronized kinematic and kinetic measurements.