(52) LINKS BETWEEN PHYSIOLOGICAL AND PERCEPTUAL STRAIN IN UNCOMPENSABLE HEAT STRESS DURING MODERATE-INTENSITY CYCLING

Introduction: In athletics, industry and the military, it is often not feasible for performance staff to monitor everyone during heat stress. An underexplored area of potential efficiency may be to survey perceptual data in attempts to quantify individual heat strain. Purpose: The purpose of this study was to 1) identify the effectiveness of the perceptual strain index (PeSI) in predicting physiological strain index (PhSI), heart rate (HR), rectal temperature (T_re), and skin temperature (T_sk) in hot-dry (HD) and warm-humid (WH) conditions with matched wet-bulb global temperature (WBGT) during 60-min moderate-intensity cycling; and 2) explore potential use of perceptual responses for the evaluation of physiological strain during uncompensable heat stress. Methods: Ten healthy, physically active, non-heat-acclimatized males (29 ± 7y, 179 ± 11cm, 77.4 ± 9.3kg, 1.96 ± 0.18 m2 body surface area, 51.9 ± 5.3mL/kg/min Vo₂peak) performed two randomized, crossover, matched exercise trials (60-min cycling ~55% V̇o₂peak) in HD (39.2°C, 30% RH) and WH (34.2, 55% RH) conditions. HR, T_re, T_sk, rating of perceived exertion (RPE), and thermal sensation were measured at multiple time points during trials. PhSI and PeSI were calculated using previously validated equations (1, 2). Mixed-effects repeated measures analyses employing subject-specific maximum pseudo-likelihood (MSPL) estimation were conducted to explore how PeSI predicts physiological outcomes (PhSI, HR, T_re, and T_sk). This was done across five time points (baseline to 1 hour at 15-min intervals) during trials. Statistical significance was set as p ≤ .05. Results: PeSI predicted PhSI (β = 1.33, p < .001), HR (β = 27.528, p < .001), T_re (β = .103, p =.013), and T_sk (β = .274, p =.001) in both HD and WH conditions. There were no differences in PhSI (p = .92), HR (p = .916), and T_re (p = .765) between trials, regardless of time. T_sk was significantly greater in HD compared to WH conditions (p = .002), regardless of time. Conclusions: Our data suggests perceptual parameters (PeSI) appropriately predicted physiological measures (PhSI, HR, T_re, and T_sk) during moderate-intensity exercise in uncompensable conditions. Projection models were confirmed in hot environments with varying humidity, but matched WBGT. Practical Applications: In hot field settings (e.g., athletics, firefighting and military operations), when a direct, accurate measurement of physiology is unavailable or limited, PeSI is a reliable alternative for monitoring physiological responses (PhSI, HR, T_re, and T_sk) at varying levels of humidity with matched WBGT. Utilizing PeSI could optimize monitoring and managing individual work or exercise in heat stress when direct measurement tools are unavailable. Acknowledgements: This research was funded by a Graduate Professional Student Congress Research Grant at the University of Arkansas.

References:
1. Tikuisis P, Mclellan T, Selkirk G. Perceptual versus physiological heat strain during exercise-heat stress, Med Sci Sports Exerc 34: 1454-146, 2002.
2. Moran DS, Shitzer A, Pandolf KB. A physiological strain index to evaluate heat stress, Am J Physiol Regul Integr Comp Physiol 275: R129-R134, 1998.