Dynamics not magnitude of exercise hyperemia correlate with aerobic muscle metabolic performance

Background: Working muscles recruit blood flow to support their elevated demand for aerobic ATP synthesis, a phenomenon known as exercise hyperemia. In vivo optical recordings of blood flow dynamics in arm muscle of healthy individuals revealed substantial inter-individual differences in peak blood flow index in response to the surrogate exercise intervention of cuff inflation and deflation. We hypothesize that the magnitude of the hyperemic response is closely related to and influences muscle metabolic performance. To explore this, we investigated in a cohort of healthy individuals performing bouts of dynamic exercise if such variations in peak hyperemic blood flow affected homeostasis of energy and pH balance in working muscle and post-exercise metabolic recovery kinetics. Methods: Hereto, we performed interleaved quantitative in vivo 1 H magnetic resonance blood oxygenation level-dependent (BOLD) imaging (MRI) and 31 P MR spectroscopy ( 31 P MRS) recordings from the upper arm musculature prior to, during and after a five minute bout of arm-cycling against a 15 W workload, respectively. From these datasets we derived three MRI parameters (BOLD MAX (%), time-to-peak (TTP; s) and initial slope of BOLD signal change (BOLD IS; %) informing on magnitude and timing of the hyperemic response to exercise, respectively, and three MRS parameters (change in phosphocreatine level (ΔPCr; %) and pH drop during exercise, and time to 95% recovery of PCr (95RT) post-exercise) informing on aerobic metabolic performance of the working muscle. Results: Each subject recruited all available motor units of the upper-arm musculature to complete the arm-cycling task evidenced by >80% depletion of intramuscular PCr stores. We found a threefold range of variation in both BOLD MAX and TTP, and a fivefold range in BOLD IS among individuals within the tested cohort. Correlation analysis next revealed that the absolute value of BOLD IS, not BOLD MAX, best predicted aerobic muscle metabolic performance. Conclusion: These results suggest that individual vascular responsiveness to dilatory versus constrictive agents rather than magnitude of exercise hyperemia per se govern aerobic metabolic performance of healthy working upper-arm muscle. This work was supported in part by grants from the Dutch Research Council, domain Applied and Engineering Sciences (MTH, AJN, GJS) and the Spieren voor Spieren Foundation (JAJ). 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.