Nondominant arm advantages in load compensation during rapid elbow joint movements

Abstract

This study was designed to examine interlimb asymmetries in responding to unpredictable changes in inertial loads, which have implications for our understanding of the neural mechanisms underlying handedness. Subjects made repetitive single joint speed constrained 20 degrees elbow flexion movements, while the arm was supported on a horizontal, frictionless, air-jet system. On random trials, a 2-kg mass was attached to the arm splint prior to the "go" signal. Subjects were not given explicit information about the mass prior to movement nor were they able to view their limb or the mass. Accordingly, muscle activity, recorded prior to peak tangential finger acceleration, was the same for loaded and baseline trials. After this point, substantial changes in muscle activity occurred. In both limbs, the load compensation response was associated with a reduction in extensor muscle activity, resulting in a prolonged flexion phase of motion. For the nondominant arm, this resulted in effective load compensation, such that no differences in final position accuracy occurred between loaded and baseline trials. However, the dominant arm response also included a considerable increase in flexor muscle activity. This substantially prolonged the flexor acceleration phase of motion, relative to that of the nondominant arm. As a result, the dominant arm overcompensated the effects of the load, producing a large and systematic overshoot of final position. These results indicate more effective load compensation responses for the nondominant arm; supporting a specialized role of the nondominant arm/hemisphere system in sensory feedback mediated error correction mechanisms. The results also suggest that specialization of the dominant arm system for controlling limb and task dynamics is specifically related to feedforward control mechanisms.

FIG. 1.

Experimental setup.

FIG. 2.

Four representative profiles from the nondominant (left column) and dominant (right column) arm groups. The insets depict sample trials that contributed to the averaged profiles. Data were synchronized to peak tangential finger acceleration and averaged across all 5 loaded trials and the 5 baseline trials that directly preceded each loaded trial. A: averaged elbow displacement. B: averaged elbow velocity. Data normalized to the average amplitude of the baseline trials. Loaded trials (– – –); baseline trials (——).

FIG. 3.

Kinematic comparisons for dominant and nondominant arm groups across subjects and conditions. A: total elbow displacement. B: difference between conditions: total elbow displacement. C: peak elbow velocity. D: difference between conditions: peak elbow velocity. E: time 0 crossing—elbow velocity. F: difference between conditions: time 0 crossing—elbow velocity. **Results from statistical analysis are significant.

FIG. 4.

Two representative profiles of EMG recordings for biceps brachii, brachioradialis, long head of the triceps brachii, and anconeus. A: averaged nondominant arm muscle activity. B: averaged dominant arm muscle activity. Gray pattern: baseline trials; cross-hatched pattern: loaded trials.

FIG. 5.

EMG impulse comparisons for dominant (white) and nondominant (gray) arm groups. A: biceps brachii. B: brachioradialis. C: long head of the triceps brachii. D: anconeus. No pattern: baseline trials; cross-hatched pattern: loaded trials. **Results from statistical analysis are significant.