Heat Stress And Load Carriage Do Not Alter The Association Between Cardiopulmonary Strain And Exertion In Females

Strong positive correlations exist among heart rate (HR), oxygen uptake (VO2), and ratings of perceived exertion (RPE) during ambulation in temperate conditions without load carriage. Whether these associations change during ambulation under hot environmental conditions with and without load carriage remains unclear, especially among females. PURPOSE: To evaluate the correlations among HR, VO2, and RPE under temperate (TEMP; 22 °C, 20% relative humidity [RH]) and hot (HOT; 40 °C, 20% RH) conditions during unloaded and loaded (33% body mass [BM]) walking. METHODS: Fifteen females (25 ± 5 y, ht = 160.9 ± 8.6 cm, BM = 63.6 ± 12.8 kg, VO2max = 38.7 ± 3.5 mL.kg-1.min-1) walked four min at each speed (0.63, 0.98, 1.34, and 1.70 m.s-1; 0% incline) in each environmental condition with and without load carriage. The final two minutes of expired gas collection were averaged for each speed while HR and RPE (Borg 0-10 scale) were collected at the end of each speed. The percent HR reserve (%HRR) and VO2 reserve (%VO2R) were calculated using measured resting and maximal HR and VO2. Pearsons r was used to assess bivariate correlations among continuous data while Spearman’s rho (rs) was used to determine bivariate correlations for ordinal data (i.e., RPE). RESULTS: In TEMP, %HRR and %VO2R were strongly correlated (unloaded: r = 0.82, p < 0.01; loaded: r = 0.91, p < 0.01) while moderate correlations were observed for %VO2R and RPE (unloaded: rs = 0.53, p < 0.01; loaded: rs = 0.59, p < 0.01) and %HRR and RPE (unloaded: rs = 0.53, p = 0.01; loaded: rho = 0.56, p < 0.01). In HOT, %HRR and %VO2R were strongly correlated (unloaded: r = 0.81, p < 0.01; loaded: r = 0.85, p < 0.01) while moderate correlations were observed for %VO2R and RPE (unloaded: rs = 0.55, p < 0.01; loaded: rs = 0.69, p < 0.01) and %HRR and RPE (unloaded: rs = 0.48, p = 0.01; loaded: rs = 0.57, p < 0.01). CONCLUSION: Increased ambient temperature and external load do not appreciably alter the bivariate associations among cardiopulmonary and RPE measures in females during walking. The views expressed in this abstract are those of the authors and do not reflect the official policy of the U.S. Government, Department of Energy, Department of the Army, or Department of Defense. Funding provided through the Medical Technology Enterprise Consortium (#W81XWH-22-9-0014).