Time to Task Failure Differs With Load Compliance For Right-handed, But Not For Left-handed Individuals

Abstract

Preferential use of elbow flexor muscles associated with hand dominance can lead to variations in neuromuscular activation strategies in right-handed individuals (Williams et al. 2003). Few studies have investigated the adaptations that occur in individuals with a left-hand preference. PURPOSE: The purpose of the study was to determine the influence of hand dominance (dominant vs. non-dominant) and handedness (right or left handed) on the time to failure for fatiguing contractions that required force or position control with the elbow flexor muscles. METHODS: Nine right- (RH) and six left-handed (LH) individuals (23.9 ± 4.2 yrs, 6 women) completed two fatiguing contractions with their dominant (D) and non-dominant (ND) arms until failure. The tasks involved either exerting a constant force (force control) equal to 20% of their maximal voluntary contraction (MVC) force or maintaining an elbow angle of 1.57 rad (position control) while supporting an equivalent mass. EMG activity was recorded with an intramuscular electrode for the brachialis and surface electrodes for the short and long heads of biceps brachii, brachioradialis, and triceps brachii. RESULTS: Averaged across D and ND arms, time to failure for RH subjects was longer for the force (303 ± 113 s) than the position task (219 ± 76 s, p = 0.001), whereas LH subjects had similar times to failure for the force (370 ± 137 s) and position tasks (310 ± 134 s, p = 0.15). MVC force declined similarly across task, dominance, and handedness (p = 0.07). In RH subjects, initial average EMG (aEMG) activity was similar for force (16.6 ± 5.19 %MVC) and position tasks (16.97 ± 4.81 %MVC, p = 0.08). LH subjects displayed greater initial aEMG activity during the force (25.5 ± 8.1 %MVC) compared to the position task (20.8 ± 5 %MVC, p < 0.001). Elbow flexor EMG rates of increase were similar across task, dominance, and handedness (force: 1.0 ± 0.001, position: 1.0 ± 0.002, p = 0.87). In RH subjects, coactivation ratio was greater in the ND arm (ND: 0.3 ± 0.25, D: 0.14 ± 0.08, p < 0.001). LH subjects had similar coactivation ratios across arms (D: 0.32 ± 0.26, ND: 0.26 ± 0.15, p = 0.12). CONCLUSION: These findings suggest that RH and LH individuals use different neuromuscular activation strategies to perform fatiguing contractions that require force or position control with their D and ND arms. NIH award NS 43275.