Excess Body Weight Affects Viscoelastic Properties of Triceps Surae in Older Women

Abstract

Aging, inactivity, and excess body weight may negatively affect the passive work absorbing capacity of human skeletal muscle. The objective of this study was to examine the influence of excess body weight on the viscoelastic properties of the triceps surae in older women. Twenty-five women, 65-80 yr, were separated into normal weight (NW, BMI 蠄 24.9 kg m-2, n = 11) and overweight groups (OW, BMI 蠅 25.0 kg m-2, n = 14). Resistive torque of the triceps surae was recorded on an isokinetic dynamometer by passively moving the ankle from a plantarflexed to dorsiflexed position. Stiffness was calculated as the slope of the passive torque vs. position curve from 1.57 – 1.48 rad (90 – 85 deg) of dorsiflexion, and work absorption was calculated as the area under the curve. Maximal voluntary isometric strength of the triceps surae was recorded, then participants walked at maximal speed on an instrumented treadmill while muscle activation was recorded by electromyography (EMG). Stiffness was higher in NW (40.0 ± 15.7 Nm rad-1) than in OW (26.4 ± 12.7 Nm rad-1, p = 0.032), as was stiffness per kg (0.70 ± 0.28 vs. 0.37 ± 0.16 Nm rad-1 kg-1, p = 0.002). Work absorption was not statistically different between NW (0.48 ± 0.29 Nm rad) and OW (0.36 ± 0.16 Nm rad, p = 0.31) nor when expressed per kg (0.0083 ± 0.0052 vs. 0.0050 ± 0.0023 Nm rad kg-1, p = 0.078). Stiffness per kg was correlated to strength (r = 0.66, p < 0.001), peak vertical ground reaction force during walking (r = 0.72, p < 0.001), and EMG (r = -0.40, p = 0.046) with similar relationships for work absorption. OW older women have low stiffness of triceps surae, which may impair ability to absorb and return work during stretch-shortening cycles. Low stiffness in OW may limit propulsive forces during walking and necessitate greater muscle activation for active force generation. Supported by NIH L30TR000588-02