Age-associated Changes In Normalised Torque Of The Knee-extensors During Maximal Effort Contractions In Women

Abstract

Ageing is associated with a significant reduction in peak torque, however, current research demonstrates that the age-associated reduction in peak torque is substantially less marked for eccentric compared with isometric and concentric contractions. These findings suggest that ageing may be associated with a change in the ability to generated peak eccentric torque per unit-area of lean muscle mass compared with isometric and concentric contractions. PURPOSE To examine the effect of ageing on normalised torque of the knee-extensor muscles during isometric, concentric and eccentric contractions in women. METHODS Sixteen young women (YW; 23.4±3.7years) and 18 older women (OW; 68.5±8.7 years) volunteered to participate in the present study. Lean muscle volume of the right knee extensor muscle group was determined by summing a series of MRI axial images. Peak torque of right knee extensors was determined under isometric conditions at an angle of 60° (0° being full extension) and under concentric and eccentric conditions at ±60°/s. Normalised torque for each muscle action was subsequently determined as: [peak torque (Nm)/lean muscle volume (cm3)] × 1000. Age comparisons were performed using unpaired t-tests with significance set at p <0.05. RESULTS Lean muscle volume was significantly higher for the YW with 1567cm3 compared with 1235cm3 for OW (p <0.05). For Y Wpeak torque for the isometric, concentric and eccentric contractions were 169±18Nm, 156±16Nm and 174±21Nm, respectively. Peak torque for the isometric, concentric and eccentric contractions were 128±16Nm, 122±14Nm and 152±16Nm, respectively. Peak torque was significantly greater for the young women for all muscle actions (p <0.05). Normalised torque during the isometric and concentric contractions was not significantly different between age groups with values of 108±13kNm.m-3 and 100±12kNm.m-3 for YW, respectively, and 104±12kNm.m-3 and 98±11kNm.m-3 for OW, respectively. However, normalised eccentric torque was significantly higher for OW compared with YW with values of 123±13kNm.m-3 and 111±1 1kNm.m-respectively, (p <0.05). CONCLUSIONS Ageing in women is associated with an increase in the ability to generate peak eccentric torque per unit of lean muscle mass while isometric and concentric efforts are relatively unaffected. The mechanisms responsible for this finding are yet to be fully determined; however, adjustments in musculotendinous stiffness and passive resistive torque and the reduced rate of cross-bridge detachment associated with the slowing of muscle contraction may be involved. Such findings may have implications for normal ambulation in older adults.