The relationship between mitochondrial function and forearm critical impulse in healthy young adults

Exercise physiologists have long investigated the contributions of convective oxygen delivery (e.g. blood flow) versus oxygen utilization (e.g. mitochondrial function) in determining a healthy individual’s aerobic capacity. Current evidence indicates differences in oxygen delivery explains a substantial amount of interindividual variability in critical power/impulse during small muscle mass exercise. However, whether mitochondrial function contributes to this variability is unknown. Purpose: To investigate whether mitochondrial function contributes to interindividual variation in forearm critical impulse. Methods: 12 healthy males (mean age 22 ± 3 years) completed two visits (1 familiarization/practice, 1 experimental). During the experimental visit, subjects rested, quietly, in a supine position with arms supported at heart level, for 10 minutes. After which, they completed a mitochondrial function test consisting of 15 maximal forearm contractions with their non-dominant arm (0.5 seconds contract, 0.5 seconds relax, for 15 seconds). Within 5 seconds of completion of the contractions, a pneumatic cuff, wrapped around the exercising upper arm, was inflated/deflated 18 times at specific intervals (5s/5s 6 times, 7s/10s 4 times, 10s/15s 4 times, 10s/20s 4 times); cuff inflation pressure was set to 230mmHg. Upon completion of the cuff occlusion series, subjects rested quietly for 15 minutes. Following this rest period, subjects completed critical force/impulse maximal hand grip exercise test where participants completed 200 maximal voluntary effort contractions (1s contraction, 2s relaxation, for 10 minutes). Forearm skeletal muscle oxygenation (via near-infrared spectroscopy) and handgrip contraction force (via electronic force transducer) were recorded continuously. Mitochondrial function was evaluated as the tau of an exponential decay function generated by plotting the slope of deoxy-hemoglobin during each of the cuff inflations against time. Contraction impulse was calculated as the integral of contraction force trace and critical impulse was calculated as the average contraction impulse across the final 30 contractions of the maximal exercise test. Results: Participants displayed a range of Critical impulse (94.99-222.71 N·s) and a mitochondrial function range of tau (38.76-76.92 s). Linear regression analysis revealed that mitochondrial function does not explain variation in critical impulse (r=0.048, r 2 =0.002, p=0.88). Conclusion: These findings suggest that differences in individual critical impulse are not explained by differences in mitochondrial function. Confirming previous research that found interindividual differences in oxygen delivery accounts for the majority of differences in critical impulse between young health individuals. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.