Influence of sleep deprivation on the relation and agreement between indices of objective and subjective strain in young and older males during simulated occupational heat stress-a randomized trial.

Occupational heat stress and sleep deprivation can impair workers' physiological function. As industries use perceptual responses to assess heat strain, we examined how sleep deprivation affects the relation and agreement between perceptual and physiological strain after normal sleep and 24 h sleep deprivation. Twenty male participants (10 young (23 (3) years), 10 older (61 (4) years)) underwent three 30 min exercise bouts (150, 200, and 250 W/m2) in hot-dry conditions (40 °C, ~13% relative humidity) after normal sleep or 24 h sleep deprivation. Physiological strain index (PSI) and adaptive PSI (aPSI) were calculated using core and skin temperatures and heart rate. Perceptual strain index (PeSI) and modified PeSI (mPeSI) were calculated from rating of perceived exertion and thermal sensation or comfort, respectively. Linear mixed-effects models were used to compare physiological and perceptual measures between conditions. Agreement between measures was evaluated using Bland-Altman analysis. Data are reported in arbitrary units (AU) on a 0-10 scale. PeSI increased with PSI (P < 0.001), and was not influenced by sleep deprivation (P = 0.526). mPeSI increased with PSI (P < 0.001), and was not influenced by sleep deprivation (P = 0.968). Similarly, PeSI and mPeSI increased with aPSI (P < 0.001), and were not influenced by sleep deprivation (P > 0.063). Mean biases between markers of perceptual and physiological strain ranged from 0.6 to 1.2 AU, while the limits of agreement (LoA) between indices ranged from -5.1 to 7.2 AU. Sleep deprivation did not appreciably modify the group-level relation between markers of perceptual and physiological strain; however, the LoA, which consistently spanned ~50% or more of the 10 unit scale, highlights the variability in perceived and actual strain.