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Callie G. Dickinson, Makayla D. Holyfield, Nicholas T. Bachelor, Kristin M. Mendez, Kevin K. McCully. University of Georgia, Athens, GA.

BACKGROUND: Muscle mitochondria play an essential role supplying energy, especially during strenuous exercise. Near infrared spectroscopy (NIRS) has been developed as a method of noninvasively assessing muscle mitochondrial capacity as a rate of recovery of muscle metabolism after exercise. The purpose of this study was to adapt the NIRS measurements to allow for rapid and repeated assessments of mitochondrial capacity, and to measure the time course of changes in mitochondrial capacity after strenuous, fatigue-inducing exercise. METHODS: Healthy male and female, college-aged participants were tested (n=9, age=20.7±1.5 yrs, BMI=24.5±3.6 Kg/M2). Subjects performed one minute of rapid (~2 Hz) plantar flexion exercise on a custom pneumatic ergometer. Muscle mitochondrial capacity was measured before and immediately after the exercise. A NIRS was device was placed on the left medial gastrocnemius muscle. The mitochondrial capacity test used 30-second electrical stimulation to activate the muscle (except right after plantar flexion exercise) followed by six, five-second cuff occlusions repeated four times. The four trials were collected at 49, 154, 259, and 365 seconds post-exercise, each resulting in a separate mitochondrial capacity rate constant. RESULTS: Muscle acceleration decreased to 50.9±16.9% of starting values indicating muscle fatigue resulting from the strenuous exercise. Mitochondrial capacity was reduced at the first time point from 2.25±0.45 to 1.0±0.4 (p<0.01). The fourth time point had significant recovery from the first post-exercise time point (2.1±0.6, p<0.01) and was not significantly different from the initial pre-exercise values (p=0.479). CONCLUSIONS: The 54% reduction in mitochondrial capacity supports the hypothesis that a minute of strenuous exercise transiently impairs mitochondrial capacity that recovers in six minutes in young, healthy individuals. The NIRS method has the potential to follow time course changes in muscle mitochondrial capacity. Further studies of the transient effects of exercise on muscle mitochondrial capacity in healthy as well as diseased populations is warranted.

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