Strength Asymmetries In The Upper Limbs Of Right- And Left-handed Individuals

Abstract

Motor skill tasks involving the upper body often show performance asymmetries favouring the dominant hand, and right-handers often show greater asymmetries than left-handers. However, very little is known about strength asymmetries in right- and left-handed people. PURPOSE: To determine the amount of strength asymmetry between the dominant (DOM) and non-dominant (NONDOM) upper limbs for various strength tasks in right- and left-handers. METHODS: Fifteen right-handers (RH) and fourteen left-handers (LH) completed seven maximal strength tasks (via a Norm or handgrip dynamometer), each for the DOM and NONDOM upper limb. Five tasks involved elbow flexion (EF) contractions: 1) Isometric (1.57 rad); 2) concentric fast (3.14 rad s-1); 3) concentric slow (0.52 rad s-1); 4) eccentric fast (3.14 rad s-1); and 5) eccentric slow (0.52 rad s-1); and two tasks involved isometric contractions of the wrist/hand: 1) ulnar deviation (UD) and 2) handgrip (HG). For each task, percent strength asymmetry scores were computed using the following formula: [(DOM strength score - NONDOM strength score) / stronger limb score] × 100. Positive scores indicate a DOM advantage. Activity of the agonist and antagonist muscles during maximal contractions was recorded via electromyography. DOM and NONDOM elbow flexor and medial forearm muscle thickness was measured via ultrasound. RESULTS: RH showed a significant DOM advantage for UD (+11.7 [SD 12.9] %; p<0.01) and HG (+8.1 [SD 8.1] %; p<0.01), whereas LH showed no significant strength asymmetry for hand tasks. No significant strength asymmetries were observed for EF tasks for either group. For both RH and LH, agonist and antagonist muscle activation was not significantly different between DOM and NONDOM for any task. There were no significant differences in muscle size between limbs. CONCLUSIONS: Right-handers exhibit greater strength asymmetry than left-handers for isometric hand strength tasks, but not for elbow flexor strength tasks. Since there was no significant difference in muscle size or peripheral muscle activation patterns, the neural basis of the dominant hand strength advantage in right-handers may be supraspinal. The lack of strength asymmetry in the upper limbs of left-handers might be due to more equal use of the limbs in tasks of daily living.