Worker heat stress prevention and work metabolism estimation: comparing two assessment methods of the heart rate...

The heart rate thermal component ( $$ ) can increase with body heat accumulation and lead to work metabolism (WM) overestimation. We used two methods (VOGT and KAMP) to assess $$ of 35 forest workers throughout their work shifts, then compared $$ at work and at rest using limits of agreement (LoA). Next, for a subsample of 20 forest workers, we produced corrected WM estimates from $$ and compared them to measured WM. Although both methods produced significantly different $$ time-related profiles, they yielded comparable average thermal cardiac reactivity (VOGT: 24.8 bpm °C^-1; KAMP: 24.5 bpm °C^-1), average $$ (LoA: 0.7 ± 11.2 bpm) and average WM estimates (LoA: 0.2 ± 3.4 ml O₂ kg^-1min^-1 for VOGT, and 0.0 ± 5.4 ml O₂ kg^-1min^-1 for KAMP). Both methods are suitable to assess heat stress through $$ and improve WM estimation. Practitioner summary: We compared two methods for assessing the heart rate thermal component ( $$ ), which is needed to produce a corrected HR profile for estimating work metabolism (WM). Both methods yielded similar $$ estimates that allowed accurate estimations of heat stress and WM at the group level, but they were imprecise at the individual level. Abbreviations: AIC: akaike information criterion; bpm: beats per minute; CI: confidence intervals; CV: coefficient of variation in %; CV drift: cardiovascular drift; ΔHR_T: the heart rate thermal component in bpm; ΔHR_T: the heart rate thermal component in bpm; ΔΔHR_T: variation in the heart rate thermal component in bpm; ΔT_C: variation in core body temperature in °C; HR: heart rate in bpm; HRmax: maximal heart rate in bpm; Icl: cloting insulation in clo; KAMP: Kampmann et al. (2001) method to determe ΔHR_T; LoA: Limits of Agreement; PMV-PPD: the Predicted Mean Vote and Predicted Percentage Dissatisfied; PHS: Predicted Heat Strain model; RCM: random coefficients model; SD: standard deviation; TC: core body temperature in °C; TCR: thermal cardiac reactivity in bpm °C^-1; τ_ΔHRT: rate of change in the heart rate thermal component in bpm min^-1; τ_TC: rate of change in core body temperature in °C min^-1; t_α,n-1: Student's t statistic with level of confidence alpha and n^-1 degrees of freedom; TWL: Thermal Work Limit model; $$ : oxygen consumption in ml O₂ kg^-1 min^-1; $$ max: maximal oxygen consumption in ml O₂ kg^-1 min^-1; VOGT: Vogt et al. (1973) method to determine ΔHR_T; WBGT: Wet-Bulb Globe Temperature in °C; WM: work metabolism.