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Muscle Physiology Lab |
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University of Massachusetts-Amherst |
30 Eastman Lane, 22 Totman Bldg Amherst, MA 01003 |
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| Phone: 413-545-5305 | ||||||
| Lab Director: Jane Kent-Braun, Ph.D. | ||||||
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Recently Completed Studies
Intramyocellular Oxygenation During Ischemic Muscle Contractions In Vivo
Authors: Michael A. Tevald, P.T., Ph.D., Ian R. Lanza, Ph.D., Douglas E. Befroy, D.Phil, Jane A. Kent-Braun, Ph.D.
Journal: Journal of Applied Physiology
There is some evidence that the fall in intramyocellular oxygen content during ischemic contractions is less than during ischemia alone. We used proton magnetic resonance spectroscopy to determine whether peak deoxy-myoglobin (dMb) obtained during ischemic ankle dorsiflexion contractions attained the maximal dMb level observed during a separate trial consisting of contractions performed after 10 min of ischemia alone. In 5 healthy young men, the rate of myoglobin desaturation was rapid at the onset of ischemic contractions and then slowed as contractions continued, attaining only 85±3.1% (mean±SE) of max dMb at the end of contractions (p=0.04). Myoglobin desaturation continued at a very low rate during ischemic "recovery" and attained maximal (96±5.7% of max, p=0.59) within 10 min. Notably, contractions performed after 10 min of ischemia did not affect dMb (p=0.77), suggesting that full desaturation had already been achieved. The blunting of desaturation during ischemic contractions is likely a result of slowed mitochondrial oxygen consumption due to limited oxygen availability.
Age-related resistance to skeletal muscle fatigue in preserved during ischemia
Authors: Linda Chung, Damien Callahan, and Jane Kent-Braun
Journal: Journal of Applied Physiology
During voluntary contractions, the skeletal muscle of healthy older adults often fatigues less than young adults, a result that has been explained by relatively greater reliance on muscle oxidative metabolism in the elderly. Purpose: To investigate whether this age-related fatigue resistance was eliminated when oxidative metabolism was minimized via ischemia induced by cuff (220 mmHg) around the thigh. Hypotheses: 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 re-establish the fatigue resistance of the old. Methods: 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. Results: 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. Conclusion: 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.
For more completed studies, see our publications page