title: Age and gender effects on the proximal propagation of an impulsive force along the adult human upper extremity.
abstract: We tested the null hypotheses that neither age, gender nor muscle pre-cocontraction state affect the latencies of changes in upper extremity kinematics or elbow muscle activity following an impulsive force to the hand. Thirty-eight healthy young and older adult volunteers lay prone on an apparatus with shoulders flexed 75° and arms slightly flexed. The non-dominant hand was subjected to three trials of impulsive loading with arm muscles precontracted to 25, 50, or 75% of maximum pre-cocontraction levels. Limb kinematic data and upper extremity electromyographic (EMG) activity were acquired. The results showed that pre-cocontraction muscle level (p < 0.001) and gender (p < 0.05 for wrist and shoulder) affected joint displacement onset times and age affected EMG onset times (p < 0.05). The peak applied force (F1) occurred a mean (± SD) 27 (± 2) ms after impact. The latencies for the wrist, elbow, and shoulder displacements were 21 ± 3, 29 ± 5, and 34 ± 7 ms, respectively. Because the latencies for elbow flexion and lateral triceps EMG were 23 ± 5 and 84 ± 8 ms, respectively, muscle pre-activation rather than stretch reflexes prevent arm buckling under impulsive end loads.
authors: Biomechanics Research Laboratory (BRL), Department of Mechanical Engineering, University of Michigan, 3212 G. G. Brown, 2350 Hayward St., Ann Arbor, MI, 48109-2125, USA, yunjulee@umich.edu.
authors: Yunju
authors: Y
authors: Lee
authors: James A
authors: JA
authors: Ashton-Miller
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D005260:Female; D018737:Hand Strength; D006801:Humans; D008297:Male; D012727:Sex Characteristics; D034941:Upper Extremity
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