Muscle Fatigue and Activation Pattern of Upper Back and Shoulder Girdle Muscles in Archers

Abstract

Control strategy of movement, especially in multiple joint, may alter as one of muscles fatigue. In archery, consistent and repeated movement is performed during whole practice session or in competition game. Therefore, an archer may easily change activation pattern if one of the major contributive muscles is fatigue. It has been wildly using median frequency (MF) of EMG signal as a examine way to muscle fatigue. PURPOSE: To investigate the strategy and fatigue state of upper back and shoulder girdle muscles during a whole practice session in elite and sub-elite archers. METHODS: Two archers with one won a gold medal of personal archery game in 2005 World University Games were recruited in this study. They performed on practice session with 144 arrows and rules simulated to formal competition with the duration was 2–3 hours approximately. Electromyographic (EMG) signals were recorded from upper trapezius (TRA), Infra-spinatus (INFRA), posterior teltoid (TEL), Rhomboid (RHOM), Latissimus dorsi (LAT) muscles on pull side of the body. Maximal voluntary isometric contraction (MVIC) before practice session was used to normalize EMG signal. Normalized root mean square (RMS) EMG and median frequency (MF) were calculated within one second by releasing an arrow which denned by accelerometers attached on wrist. The first and the last 3 sets with 18 trials (n=1 8) individually (6 trials per set) were compared. T-test for repeated measures was used. RESULTS: Significant decrease in MF in INFRA muscle (79±5 Hz vs. 59±6 Hz, p < 0.05) was demonstrated on sub-elite archer during the session. In elite one, it revealed slightly shift in MF but not significant in INFRAmuscle. Besides, TEL, TRA, INTRA, RHOM and LAT muscles activities detected from sub-elite archer were significantly increased (21.0±4.6% vs. 25.8±5.0%; 33.1±4.1% vs. 34.5±5.7%; 26.3±5.0%vs. 36.1±5.0%; 21.6±3.0%vs. 27.7±4.6%; 17.5±2.4% VS.19.2±3.0% respectively, p < 0.05), but only INFRA muscle activity was increased significantly in elite one (17.6±2.2% vs. 19.6±2.7%, p < 0.05). CONCLUSION: Muscle fatigue did occur in sub-elite archer's INFRA muscle but not in elite one during a practice session. Muscle activation pattern would alter following one of the mainly muscle fatigue. The scientific information may offer the coach as a reference resource to avoid overtraining due to muscle fatigue.