Removing the thermal component from heart rate provides an accurate V˙O2 estimation in forest work

Heart rate (HR) was monitored continuously in 41 forest workers performing brushcutting or tree planting work. 10-min seated rest periods were imposed during the workday to estimate the HR thermal component (ΔHRT) per Vogt et al. (1970, 1973). V˙O2 was measured using a portable gas analyzer during a morning submaximal step-test conducted at the work site, during a work bout over the course of the day (range: 9-74 min), and during an ensuing 10-min rest pause taken at the worksite. The V˙O2 estimated, from measured HR and from corrected HR (thermal component removed), were compared to V˙O2 measured during work and rest. Varied levels of HR thermal component (ΔHRTavg range: 0-38 bpm) originating from a wide range of ambient thermal conditions, thermal clothing insulation worn, and physical load exerted during work were observed. Using raw HR significantly overestimated measured work V˙O2 by 30% on average (range: 1%-64%). 74% of V˙O2 prediction error variance was explained by the HR thermal component. V˙O2 estimated from corrected HR, was not statistically different from measured V˙O2. Work V˙O2 can be estimated accurately in the presence of thermal stress using Vogt et al.'s method, which can be implemented easily by the practitioner with inexpensive instruments.