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1 Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL, USA; Geriatric Research, Education, and Clinical Center, Muscle Research Laboratory, Birmingham VA Medical Center, Birmingham, AL, USA
2 Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL, USA
3 Geriatric Research, Education, and Clinical Center, Muscle Research Laboratory, Birmingham VA Medical Center, Birmingham, AL, USA; Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL, USA
* To whom correspondence should be addressed. E-mail: mbamman{at}physiology.uab.edu.
The purposes of this study were to examine age and gender differences in knee extensor strength, power, and fatigue using open and closed chain testing procedures. We tested the hypothesis that specific strength (strength / unit muscle mass) would not differ by age, while age differences in specific power and fatigue would remain consequent to blunted maximal contractile velocity. Skeletal muscle performance was examined in 28 young (26.9±0.7 yrs) and 24 older (63.6±0.8 yrs) males and females. Assessments included: one-repetition maximum strength for knee extension, leg press, and squat; concentric knee extensor peak power, velocity, and fatigability; and sit-to-stand power, fatigability, and relative neural activation (EMG activity during sit-to-stand normalized to EMG activity during isometric maximum voluntary contraction). Thigh lean mass (TLM, kg) was assessed by dual energy x-ray absorptiometry. Specific strength (N/kg TLM) and specific power (Watts/kg TLM) were estimated by dividing absolute values by TLM. Age differences in specific strength were observed for knee extension only (Young, 41.2±1.0 N/kg TLM; Older, 32.4±1.0 N/kg TLM, P<0.05). Adjusting for TLM did not negate age differences in knee extension specific power (25-41% lower in older, P<0.05) across loads tested. Older adults experienced fatigue across 10 repetitions of knee extension as peak velocity fell 24%(P<0.05). Deficits in concentric power persist after adjusting for TLM as maximum contractile velocity falls markedly with aging. Older adults are less capable of sustaining maximum concentric velocity during repetitive contractions. These findings suggest that velocity impairments are a possible contributor to mobility loss and falls risk among older adults. Interventions for improving contractile velocity should be pursued.
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