Abstract
Purpose
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.
Methods
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).
Results
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).
Conclusion
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.
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Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
Abbreviations
- BLa- :
-
Blood lactate
- CI95% :
-
95% Confidence interval
- GET:
-
Gas exchange threshold
- HOT:
-
Hot environmental conditions
- HR:
-
Heart rate
- LT:
-
Lactate threshold
- LTFIX :
-
Fixed blood lactate concentration threshold
- LTIND :
-
Individual lactate threshold
- PO:
-
Power output
- RAMP:
-
Ramp incremental exercise
- RCP:
-
Respiratory compensation point
- RH:
-
Relative humidity
- RT:
-
Respiratory threshold
- STEP:
-
Step incremental exercise
- SV:
-
Stroke volume
- TEMP:
-
Temperate environmental conditions
- \(\dot{\text{V}}\text{O}_2\) :
-
Oxygen uptake
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Acknowledgements
The authors would like to thank the subjects for their commitment to the study. This study was funded by the Special Research Fund of the Ghent University (Ghent, Belgium).
Funding
This research was funded by the Special Research Fund of the Ghent University (Ghent, Belgium) in the context of a doctoral fellowship (n° BOF.DOC.2019.0033.01).
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GB, JGB, PM and JB conceived and designed research. GB, AC and KC conducted the experiments and analysed the data. GB, AC and JB wrote the manuscript. All authors revised and approved the manuscript.
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Bourgois, G., Colosio, A.L., Caen, K. et al. The effect of acute heat exposure on the determination of exercise thresholds from ramp and step incremental exercise. Eur J Appl Physiol 123, 847–856 (2023). https://doi.org/10.1007/s00421-022-05106-y
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DOI: https://doi.org/10.1007/s00421-022-05106-y