TY - JOUR
T1 - Age-related enhancement of fatigue resistance is evident in men during both isometric and dynamic tasks
AU - Lanza, Ian R.
AU - Russ, David W.
AU - Kent-Braun, Jane A.
PY - 2004/9
Y1 - 2004/9
N2 - It has been suggested that the effects of old age on the ability to resist fatigue may be task dependent. To test one aspect of this hypothesis, we compared the neuromuscular responses of nine young (26 ± 4 yr, mean ± SD) and nine older (72 ± 4 yr) healthy, relatively sedentary men to intermittent isometric (3 min, 5 s contract/5 s rest) and dynamic (90 at 90°/s) maximum voluntary contractions (MVC) of the ankle dorsiflexor muscles. To assess the mechanisms of fatigue (defined as the ratio of postexercise MVC to preexercise MVC), we also measured isometric central activation ratios (CAR), tetanic torque, contractile properties, and compound muscle action potentials before and immediately after exercise. Because dynamic contractions are more neurally complex and metabolically demanding than isometric contractions, we expected an age-related fatigue resistance observed during isometric exercise to be absent during dynamic exercise. In contrast, older men (O) fatigued less than young (Y) during both isometric (O = 0.77 ± 0.07, Y = 0.66 ± 0.02, mean ± SE; P < 0.01) and dynamic (O = 0.45 ± 0.07, Y = 0.27 ± 0.02; P = 0.04) contractions (ratio of postexercise to preexercise MVC), with no evidence of peripheral activation failure in either group. We observed no obvious limitations in central activation in either group, as assessed using isometric CAR methods, after both isometric and dynamic contractions. Preexercise half-time of tetanic torque relaxation, which was longer in O compared with Y, was linearly associated with fatigue resistance during both protocols (r = 0.62 and 0.66, P ≤ 0.004, n = 18). These results suggest that relative fatigue resistance is enhanced in older adults during both isometric and isokinetic contractions and that age-related changes in fatigue may be due largely to differences within the muscle itself.
AB - It has been suggested that the effects of old age on the ability to resist fatigue may be task dependent. To test one aspect of this hypothesis, we compared the neuromuscular responses of nine young (26 ± 4 yr, mean ± SD) and nine older (72 ± 4 yr) healthy, relatively sedentary men to intermittent isometric (3 min, 5 s contract/5 s rest) and dynamic (90 at 90°/s) maximum voluntary contractions (MVC) of the ankle dorsiflexor muscles. To assess the mechanisms of fatigue (defined as the ratio of postexercise MVC to preexercise MVC), we also measured isometric central activation ratios (CAR), tetanic torque, contractile properties, and compound muscle action potentials before and immediately after exercise. Because dynamic contractions are more neurally complex and metabolically demanding than isometric contractions, we expected an age-related fatigue resistance observed during isometric exercise to be absent during dynamic exercise. In contrast, older men (O) fatigued less than young (Y) during both isometric (O = 0.77 ± 0.07, Y = 0.66 ± 0.02, mean ± SE; P < 0.01) and dynamic (O = 0.45 ± 0.07, Y = 0.27 ± 0.02; P = 0.04) contractions (ratio of postexercise to preexercise MVC), with no evidence of peripheral activation failure in either group. We observed no obvious limitations in central activation in either group, as assessed using isometric CAR methods, after both isometric and dynamic contractions. Preexercise half-time of tetanic torque relaxation, which was longer in O compared with Y, was linearly associated with fatigue resistance during both protocols (r = 0.62 and 0.66, P ≤ 0.004, n = 18). These results suggest that relative fatigue resistance is enhanced in older adults during both isometric and isokinetic contractions and that age-related changes in fatigue may be due largely to differences within the muscle itself.
KW - Ankle dorsiflexors
KW - Central activation
KW - Compound muscle action potential
KW - Contractile properties
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U2 - 10.1152/japplphysiol.01351.2003
DO - 10.1152/japplphysiol.01351.2003
M3 - Article
C2 - 15145914
AN - SCOPUS:4344676828
SN - 8750-7587
VL - 97
SP - 967
EP - 975
JO - Journal of applied physiology
JF - Journal of applied physiology
IS - 3
ER -