Muscle Mitochondrial Capacity Is Impaired Immediately Following Maximal Exercise.

Mitochondria are essential in supplying energy to skeletal muscle. Near-infrared spectroscopy (NIRS) was developed to noninvasively assess mitochondrial capacity (mV̇O2max) as a rate constant of metabolic recovery after exercise. Purpose: This study measured the time course mV̇O2max following both maximal and submaximal exercise. Methods: Healthy male and female participants were tested (n = 12 maximal and n = 8 submaximal exercise). A NIRS device was placed on the left medial gastrocnemius. Participants performed either 1 min of maximal, rapid (~2 Hz), or submaximal (~0.37 Hz) plantar flexion exercise on a custom pneumatic ergometer. mV̇O2max was measured before and immediately after exercise. mV̇O2max measurements consisted of four incomplete recovery curves of muscle metabolism taken after 30 s of electrical muscle stimulation except in the first post-exercise to be consistent with the use of pre-exercise trial. The four recovery curves were collected 50-, 156-, 260-, and 366-s postexercise, each producing an mV̇O2max rate constant. Results: After maximal exercise, muscle acceleration decreased to 52 ± 18% (P = 0.001) of prevalues. mV̇O2max was reduced from the pre-exercise mean at the first post-trial (2.16 ± 0.44 to 1.21 ± 0.52 min−1, P < 0.001). The fourth trial showed recovery from the first (2.2 ± 0.46 min−1 vs 1.21 ± 0.52 min−1, P < 0.001) and was not significantly different from pre-exercise values (2.2 ± 0.46 vs 2.16 ± 0.44 min−1, P = 0.41). No change in acceleration or mV̇O2max was seen after submaximal exercise (P > 0.05). Conclusions: The 56.7% reduction in mV̇O2max supports the hypothesis that in young, healthy individuals, a minute of maximal exercise transiently impairs mV̇O2max, which then recovers within 6 min. The NIRS method shows promise in tracking time course changes in mV̇O2max and warrants further investigation of the transient effects of exercise on mV̇O2max. [ABSTRACT FROM AUTHOR]