Author(s): BOSSI, A.H., HOPKER, J., Institution: EDINBURGH NAPIER UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2141

INTRODUCTION:
The relationship between cycling power output and time to exhaustion (TTE) displays a curvilinear form that can be linearised by employing the logarithm of TTE. This relationship persists even for exhaustive intermittent exercise, wherein high- and low-intensity intervals of fixed power and duration are alternated. While training status, body dimensions, and sex influence the power outputs someone can generate, seemingly comparable cyclists can still manifest considerable inter-individual variability in TTEs. This study explored which factors might contribute to longer TTEs during high-intensity interval training (HIIT).
METHODS:
The dataset of Bossi et al. (2023) was reutilised. Sixteen male and two female competitive cyclists (age: 38 ± 11 years, maximal oxygen uptake (V̇O2max): 54 ± 9 ml·kg-1·min-1) performed an incremental test, two 3-min all-out tests, and two 20-min time trials to establish physiological and performance benchmarks after a familiarisation (visits 1 and 2). Then, in randomised order, participants performed four HIIT sessions to exhaustion at power outputs associated with different intensity prescription methods (visits 3 to 6). HIIT sessions consisted of 4-min work intervals interspersed with 2-min active recoveries. The natural logarithm of TTE in seconds was modelled using linear mixed models, with participant as a random effect, and HIIT power output, age, height, body mass, the maximal scores in the incremental test (V̇O2max, power output, heart rate, respiratory exchange ratio, respiratory rate, rating of perceived exertion, blood lactate concentration), the power outputs associated with the gas exchange threshold and respiratory compensation point, critical power, work capacity above critical power, time trial mean power output, and estimated vastus lateralis adipose tissue thickness as fixed effects. The best model was selected based on Akaike information criteria. Significance was set at P ≤ 0.05.
RESULTS:
The best model revealed that HIIT power output, V̇O2max, and maximal respiratory exchange ratio (RERmax) are all determinants of TTE, with the first two emerging as primary factors. Specifically, with an intercept of 11.309 (SE = 3.292), a unit increase in power output reduces the log transformed TTE by 0.032 (SE = 0.003). Conversely, a unit increase in V̇O2max extends the log transformed TTE by 2.267 (SE = 0.277). A decimal unit increase in RERmax reduces the log transformed TTE by 0.277 (SE = 2.621). The model indicated considerable inter-individual differences, with a SD of 0.460 for the intercept. The SD for the residual variability was estimated as 0.318.
CONCLUSION:
Besides the expected effect of the power output target for HIIT, it seems that individuals with higher V̇O2max, attained with lower RERmax, are more likely to produce longer TTEs. A complex interplay of attributes, possibly involving unexplored factors, complicates the individualisation of HIIT prescription.
REFERENCE:
Bossi et al. (2023) Eur J Appl Physiol 123, 1655–1670