Author(s): MENDONÇA, P., DUTRA, Y.M., ZAGATTO, A.M., Institution: UNESP, Country: BRAZIL, Abstract-ID: 2627

INTRODUCTION:
The temporal association between prefrontal cortex (PFC) oxygenation and perceptual responses (Fatigue, Rating of Perceived Exertion [RPE], and Pain) remains insufficiently explored, especially under heat stress, when cardiovascular strain may exacerbate cerebral deoxygenation and perceptual strain (1). This study aimed to investigate the impact of heat stress on PFC oxygenation and perceptual responses during cycling, as well as the associations between these measures.
METHODS:
On separate occasions, 12 healthy participants (2 fem; V̇O₂max: 43±6 mL·kg⁻¹·min⁻¹) performed three constant work-rate cycling trials at heavy domain in thermoneutral (CONT; 20±2°C; 55±7% RH) and hot (HEAT; 38±2°C; 43±9% RH) environments. One trial was performed to task failure in each environment (i.e., CONT and HEAT), and a third trial was conducted under thermoneutral condition until the time of task failure (TTF) recorded in the hot environment to obtain a matched duration comparison (ISO). Tissue saturation index (TSI) of PFC were continuously assessed by near-infrared spectroscopy (NIRS), and perceptual responses were recorded every 4min using Fatigue (1-10), RPE (6-20), and Pain (1-10) scales. For TSI and perceptual outcomes, data was initially analyzed for every 20% exercise duration, and the area under the curve (AUC) was estimated. Paired t test was performed to compare TTF, TSI and perceptual responses between conditions. Spearman correlations were performed to assess correlations between the AUC of the outcomes across conditions. Statistical significance was set at p<0.05.
RESULTS:
TTF was lower (p<0.001) in HEAT (31±14min) than CONT (60±24min). Higher values of TSI, Fatigue, RPE, and Pain were observed in CONT compared to HEAT (all p≤0.040). When comparing HEAT with ISO, the TSI did not alter significantly (p=0.826), only Fatigue presented significant difference (p=0.006), being higher in the HEAT. In both CONT and HEAT, correlations (p<0.001) were observed for the TSI with Fatigue (r=0.79 and 0.92, respectively), RPE (r=0.79 and 0.96, respectively), and Pain (r=0.73 and 0.69, respectively). For the ISO, correlations were observed for TSI (p≤0.02) with Fatigue (r=0.65), RPE (r=0.90), and Pain (r=0.79).
CONCLUSION:
Heat stress reduced TTF in cycling (CONT>HEAT). Exposure to a hot environment alone (HEAT vs ISO) increased the perception of Fatigue during cycling, without changing TSI, RPE, or Pain. Notably, prefrontal cortex TSI during heavy-domain cycling appeared to preserve the functional oxygen supply-demand balance and to parallel exercise-induced perceptual responses, regardless of exercise duration or environmental condition.
(1) Périard JD, et al., (2013).