Exercise Attenuates Age‐Associated Reductions in Muscle Strength and Cardiorespiratory Fitness in Mice

Abstract

Aging is associated with losses in muscle strength and cardiovascular fitness that may be offset with regular exercise. While exercise adaptations may diminish with age, robust adaptations still occur. We tested the hypothesis that aging reduces muscle function and cardiorespiratory endurance, however voluntary (running wheel, RW) or prescribed (treadmill (TM) training) exercise will attenuate these aging‐associated decreases in strength and fitness. In vivo plantarflexor maximal force and fatigue (% of max force after 10 contractions) were measured in young (4 mo. old) and aged (24 mo. old) sedentary (SED) mice and following 2 wks of RW (24h wheel access) or TM training (45 min/day, 5 day/wk). Cardiorespiratory adaptations were assessed with pre‐ and post‐maximal treadmill tests. Maximal muscle force was lower in aged than young SED mice (1.1±0.04 vs. 1.6±0.07 g/kg BW, respectively, p<0.05). In young groups, neither RW nor TM increased force over SED. In aged groups, RW and TM were associated with respective 22 and 26% higher maximal forces than aged SED mice (p<0.05), but still were lower than young groups. Plantarflexor fatigue resistance was higher in aged than young SED mice (50±3 vs. 35±3% of max, respectively, p<0.05) with no age differences in RW and TM groups. In treadmill pre‐tests, young groups ran longer than aged groups (9:23±0:52 vs. 5:09± 0:51, respectively p<0.05). Increases in treadmill time after training occurred only in young and aged TM with respective 25:34±8:24 and 16:42±2:39 increases from pre to post test (p<0.05). These findings suggest voluntary and prescribed exercise attenuate some age‐associated reductions in muscle force, but prescribed exercise is most effective in improving cardiorespiratory fitness in young and older mice.