Age-related resistance to skeletal muscle fatigue is preserved during ischemia.
During voluntary contractions, the skeletal muscle of healthy older adults often fatigues less than that of young adults, a result that has been explained by relatively greater reliance on muscle oxidative metabolism in the elderly. Our aim was to investigate whether this age-related fatigue resistance was eliminated when oxidative metabolism was minimized via ischemia induced by cuff (220 mmHg). We hypothesized that 1) older men (n = 12) would fatigue less than young men (n = 12) during free-flow (FF) contractions; 2) both groups would fatigue similarly during ischemia; and 3) reperfusion would reestablish the fatigue resistance of the old. Subjects performed 6 min of intermittent, maximal voluntary isometric contractions of the ankle dorsiflexors under FF and ischemia-reperfusion (IR) conditions. Ischemia was maintained for the first 3 min of contractions, followed by rapid cuff deflation and reperfusion for 3 additional minutes of contractions. Central activation, peripheral activation, and muscle contractile properties were measured at 3 and 6 min of contractions. Older men fatigued less than young men during FF (P </= 0.02), ischemia (P < 0.001), and reperfusion (P < 0.001). During FF, activation and contractile properties changed similarly across age groups. At the end of ischemia, central (P = 0.02) and peripheral (P </= 0.03) activation declined more in the young, with no effect of age on the changes in contractile properties. Thus age-related fatigue resistance was evident during FF and IR, indicating that differences in blood flow and oxidative metabolism do not explain the fatigue resistance of old age.
Chung
Linda H
LH
Dept. of Kinesiology, Univ. of Massachusetts, 108 Totman Bldg., 30 Eastman Lane, Amherst, MA 01003, USA. janekb@kin.umass.edu
Callahan
Damien M
DM
Kent-Braun
Jane A
JA
D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000378:metabolism; D004558:Electric Stimulation; D006801:Humans; D007511:Ischemia / Q000378:metabolism / Q000503:physiopathology*; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000378:metabolism / Q000503:physiopathology*; D018384:Oxidative Stress; D012039:Regional Blood Flow; D015424:Reperfusion; D013997:Time Factors