James E. Brown, Riley Melton, Jakob D. Lauver, Timothy Rotarius, Justin P. Guilkey. Coastal Carolina University, Conway, SC.

BACKGROUND: Muscle oxidative capacity (MOC) is the maximal rate at which the muscle can utilize oxygen to meet the energy demand of exercise. Measurements of MOC from muscle biopsies have shown that MOC is an important aspect of endurance performance and increases with endurance training, even in highly trained athletes. Recently, near-infrared spectroscopy (NIRS) measurement of muscle oxygen uptake (mVO2) during brief arterial occlusions has shown to be a valid, reliable indicator of MOC. Endurance training throughout a collegiate cross-country season can lead to adaptations that increase MOC and performance. However, it is unclear if NIRS-derived MOC measurements are sensitive enough to detect changes in response to endurance training in highly fit athletes. This study will assess changes in MOC, via NIRS, in highly-fit collegiate runners across a cross-country season. METHODS: Collegiate cross-country runners will be tested pre- and post-season. Maximal oxygen uptake will be measured from an individualized treadmill test to characterize changes in fitness. MOC will be determined from a series of 20 short (5-10 sec) arterial occlusions interspersed with short recoveries. Rapid inflation cuffs placed on the distal portion of the thigh will be inflated to 300 mmHg during occlusions and released during recovery. Deoxyhemoglobin (HHb), collected at 10 Hz, will be measured at the gastrocnemius using NIRS. To calibrate the signal to individuals, a 5-min arterial occlusion will be performed to determine maximal deoxygenation (highest HHb) and the hyperemic response after cuff release will determine minimum HHB (maximal oxygenation). All data will be normalized to the minimum and maximum deoxygenation. HHb will be corrected for changes in blood volume using methods described by Ryan et al (2012). The slope of change in HHb during the first 3-5 seconds of each occlusion will be the mVO2. Each mVO2 will be plotted and a mono-exponential decay curve will be fitted to determine the time constant; time constant is indicative of MOC. A paired sample t-test will compare MOC from pre- to post-season. Alpha level will be set to 0.05 a priori. ANTICIPATED RESULTS: Changes in mitochondrial enzyme activity in response to endurance training have shown improvements in MOC in highly trained athletes. Therefore, it is expected that MOC, as measured by NIRS, will increase from pre- to post-season in cross-country runners.

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