Cerebral oxygenation and skeletal muscle responses to time trial, maximal oxygen uptake and time to exhaustion...

This study investigated cerebral and neuromuscular responses to three exercise models: time trial (TT), maximal oxygen uptake ( ${\dot{V}}_{O_2\max }$ ) and time to exhaustion (TTE). Fourteen participants completed the tests in the following order: ${\dot{V}}_{O_2\max }$ , TT and TTE. To compare responses across different intensities, TT and ${\dot{V}}_{O_2\max }$ trials were matched for total work (kJ), and the average TT power output was used to set intensity for TTE. Throughout exercise, near-infrared spectroscopy from the prefrontal cortex and electromyography from the vastus lateralis and rectus femoris were recorded. Ratings of perceived exertion and the feeling scale were collected post-exercise. Total work was similar across trials. Tissue oxygenation index (TOI) was significantly lower during TT (P = 0.0308) and TTE (P = 0.0400) than ${\dot{V}}_{O_2\max }$ . Deoxyhaemoglobin increased more during TTE (P < 0.0001), and oxyhaemoglobin was higher during TTE from 60% to 100% of test completion (P = 0.0040-0.0001). Participants rated ${\dot{V}}_{O_2\max }$ as more pleasant (6.7 ± 2.9) than TT (5.9 ± 3.0, P = 0.0412) and TTE (4.9 ± 2.3; P = 0.0124). Despite equivalent work, each exercise model elicited distinct neurophysiological profiles and distinct temporal patterns of prefrontal oxygenation and muscle activation. TT and TTE showed earlier reductions in TOI than ${\dot{V}}_{O_2\max }$ , but end-exercise brain oxygenation was similarly reduced across paradigms, while ${\dot{V}}_{O_2\max }$ was perceived as more pleasant. These findings suggest that exercise modality alters the trajectory, rather than the endpoint, of prefrontal oxygenation/perfusion responses.