Velocity dependence of eccentric strength in young and old men: the need for speed!

卷:40

Power, Geoffrey A. ; Makrakos, Demetri P. ; Stevens, Daniel E. ; Rice, Charles L. ; Vandervoort, Anthony A.

关键词: aging;    muscle;    lengthening;    residual force enhancement;    stiffness;    weakness;    elderly;    EMG;   

DOI  :  10.1139/apnm-2014-0543

学科分类：食品科学和技术

【 摘 要 】

Older adults better maintain eccentric strength relative to isometric strength, as indicated by a higher ratio of eccentric: isometric torque as compared with younger adults. The effect of increasing angular velocities (>200 degrees/s) on the age-related maintenance of eccentric strength has not been tested and thus it is unknown whether the eccentric: isometric ratio is velocity dependent in old age. The purpose of this study was to investigate eccentric strength of the ankle dorsiflexors over a large range of lengthening angular velocities in young and older men. Isometric neuromuscular properties were assessed on a HUMAC NORM dynamometer. Nine young (similar to 24 years) and 9 older (similar to 76 years) healthy men performed maximal voluntary eccentric contractions at angular velocities of 15-360 degrees/s. Despite near full voluntary activation (>95%), the older men were similar to 30% weaker than the young men for isometric strength (P < 0.05). Across all lengthening velocities, older men had a greater eccentric: isometric ratio than young men (P < 0.05). Additionally, there was a velocity dependence of strength in both young and older men: eccentric strength increased as velocity increased up to 120 degrees/s (P < 0.05) and plateaued thereafter. In young and older men, eccentric strength at 15 degrees/s was similar to 20% and similar to 40% greater than isometric strength (P < 0.05), while at 360 degrees/s eccentric strength was similar to 50% and similar to 90% greater, respectively (P < 0.05). These findings indicate that with increasing angular velocity, both young and older men have considerable increases in the eccentric: isometric ratio of torque production.