CORRELATION BETWEEN NON-INVASIVE MITOCHONDRIAL CAPACITY ASSESSMENT AND OXYGEN UPTAKE KINETICS FOLLOWING MODERATE INTENSITY EXERCISE

Alexis Coleman, Justin P. Guilkey, Timothy R. Rotarius. Coastal Carolina University, Conway, SC. BACKGROUND: Mitochondrial capacity (mVO2) is important for our understanding of exercise capacity as it plays a vital role in aerobic metabolism. Pulmonary oxygen uptake (pVO2) kinetics have been shown to closely match mVO2. Non-invasive measures of mVO2 using near-infrared spectroscopy (NIRS) have become increasingly popular as it has been found to be a reliable measure of mVO2. The purpose of the present investigation was to assess the relationship between mVO2 and pVO2 on- and off-kinetics following moderate intensity exercise. METHODS: Seven healthy males (24 ± 5 yrs.) performed 2 bouts of moderate intensity (80% of lactate threshold) cycling exercise for 6 minutes followed by a 5-min cooldown at 20W. mVO2 assessment was performed prior to and following each exercise bout. pVO2 was continuously recorded breath-by-breath. Phase II kinetics (on-kinetics) were analyzed using either a 1- or 2-component exponential model after interpolating to 1 s and ensemble averaging each trial. mVO2 was determined from 20 short (5-10 s) arterial occlusions. Deoxyhemoglobin (HHb) was measured at the vastus lateralis and the slope of change in HHb during the first 3-5 seconds of each occlusion was plotted over time as mVO2. pVO2 off-kinetics and mVO2 were analyzed using a mono-exponential decay model. Matched pairs t-tests were used to compare pVO2 on- and off-kinetics and pre- and post-mVO2. Pearson correlation coefficients were computed to assess relationships between pVO2 on- and off-kinetics and pre- and post-mVO2 recovery constants. Significance was established if p \u3c 0.05. RESULTS: pVO2 on- and off-transient kinetics were similar (ON: 44.0 ± 11.0 s; OFF: 34.4 ± 9.5 s). mVO2 recovery kinetics were similar before and after exercise (PRE: 30.4 ± 6.1 s; POST: 28.9 ± 11.5 s). pVO2 off-kinetics were not correlated with mVO2 recovery prior to exercise (r = 0.447), but was strongly correlated with post-exercise mVO2 (r = 0.700). pVO2 on-kinetics were not correlated with mVO2 prior to (r = -0.596) or after (r = -0.293) exercise. CONCLUSION: Non-invasive assessment of mVO2 is not affected by a bout of moderate intensity exercise. mVO2 was not different pre- and post-exercise. pVO2 off-kinetics are positively and strongly correlated to mVO2 post-exercise but not correlated with pre-exercise mVO2. There is no correlation between mVO2 and pVO2 on-kinetics before or after moderate exercise

PHYSIOLOGICAL EFFECTS OF INTERVALS DURATION DURING AEROBIC EXERCISE WITH BLOOD FLOW RESTRICTION

Grayson Sossamon, Timothy R. Rotarius, Jakob D. Lauver, Justin P. Guilkey. Coastal Carolina University, Conway, SC. BACKGROUND: Aerobic exercise with blood flow restriction (BFR) has been shown to elicit positive physiological adaptions. A mechanism of adaptation with BFR is increased local metabolic stress, however, BFR can also increase cardiac work. Metabolic stress and cardiac work could be affected by the work interval duration during BFR but the acute physiological effects of interval duration with BFR are unexplored. This study will examine the effect of work interval duration on the local metabolic stress and cardiac work during low-intensity aerobic exercise with BFR. METHODS: Healthy males (18-25 yrs) will complete a graded exercise test to determine WR for experimental conditions. On separate days, participants will complete three experimental interval (INT) exercise protocols with intermittent BFR, in a random order. All protocols will consist of a 4-min warm-up ([20 W] WU), work INTs (35% peak power), and 1-min recovery INTs (20 W) between work INTs. The work INTs in the three protocols will be: 1) six 2-min INTs (2-min INT), 2) twelve 1-min INTs (1-min INT), and 3) three 4-min INTs (4-min INT). During work INTs, BFR cuffs will rapidly inflate to 60% of limb occlusion pressure (LOP) and deflate during recovery INTs. LOP will be the pressure at which the posterior tibial artery pulse ceases by Doppler auscultation. In each protocol, the duration of work INTs and BFR will be 12 mins. Gas exchange, heart rate (HR), and tissue oxygen saturation (StO2) of the vastus lateralis, via near-infrared spectroscopy, will be collected throughout exercise. To quantify local metabolic stress, StO2 will be averaged over the last 30 sec of the WU and expressed as change from WU. Blood pressure (BP) will be taken manually and rate pressure product (RPP) will be calculated to assess cardiac work. Due to the different protocol durations, data will be compared at 0% (end of WU), 33%, 67%, and 100% of each protocol duration. Differences between protocols will be determined by a 2-way (trial x time) repeated measures ANOVA. Significance will be established if p ≤0.05. ANTICIPATED RESULTS: It is hypothesized StO2 will have a greater decrease from WU and RPP will be greater, suggesting greater local metabolic stress and cardiac work in 4-min INT compared to 1-min INT and 2-min INT. If the hypothesis is confirmed, training with longer intervals could elicit greater local adaptations, but cardiac work will be increased during training

CHANGES IN NEAR-INFRARED SPECTROSCOPY ASSESSED MUSCLE OXIDATIVE CAPACITY IN COLLEGIATE CROSS-COUNTRY ATHLETES

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