The effect of acute heat exposure on the determination of exercise thresholds from ramp and step incremental exercise

Abstract

The aim of this study was to examine how respiratory (RT) and lactate thresholds (LT) are affected by acute heat exposure in the two most commonly used incremental exercise test protocols (RAMP and STEP) for functional evaluation of aerobic fitness, exercise prescription and monitoring training intensities. Eleven physically active male participants performed four incremental exercise tests, two RAMP (30 W•min -1 ) and two STEP (40 W•3 min -1 ), both in 18°C (TEMP) and 36°C (HOT) with 40 % relative humidity to determine 2 RT and 16 LT, respectively. Distinction was made within LT, taking into account the individual lactate kinetics (LTIND) and fixed value lactate concentrations (LTFIX). A decrease in mean power output (PO) was observed in HOT at LT ( -6.2 ± 1.9 %), more specific LTIND (-5.4 ± 1.4 %) and LTFIX (-7.5 ± 2.4 %), compared to TEMP, however not at RT (-1.0 ± 2.7 %). The individual PO difference in HOT compared to TEMP over all threshold methods ranged from -53 W to +26 W. Mean heart rate (HR) did not differ in LT, while it was increased at RT in HOT (+10 ± 8 bpm). This study showed that exercise thresholds were affected when ambient air temperature was increased. However, a considerable degree of variability in the sensitivity of the different threshold concepts to acute heat exposure was found and a large individual variation was noticed. Test design and procedures should be taken into account when interpreting exercise test outcomes.

Effect of acute heat exposure on the determination of critical power and W′ in women and men

“…In our study, a 6.5 ± 3.3% decrease in PO at CP was found in HOT compared with TEMP, which was similar in women and men. This is consistent with the majority of the studies that showed a reduction in the absolute PO corresponding to the maximal metabolic steady state with acute heat exposure (Bourgois et al, 2023; de Barros et al, 2011; Lorenzo et al, 2011; Maunder et al, 2021). It has been noticed that the extent of the reduction, induced by heat, varies between studies, i.e.…”

“…PO corresponding to the maximal metabolic steady state with acute heat exposure (Bourgois et al, 2023;de Barros et al, 2011;Lorenzo et al, 2011;Maunder et al, 2021). It has been noticed that the extent of the reduction, induced by heat, varies between studies, i.e.…”

“…Previous studies demonstrated a reduction in absolute power output (PO) at the exercise threshold demarcating the heavy‐to‐severe boundary, i.e. conceptually similar to CP (Keir et al, 2015), in hot environmental conditions (Bourgois et al, 2023; de Barros et al, 2011; Lorenzo et al, 2011; Maunder et al, 2021), mostly using blood lactate‐related determination methodologies. However, the use of blood lactate for determining the heavy‐severe boundary is questioned (Jones et al, 2019).…”