Author(s): ROUSSEAU, Q., RABITA, G., SIBLOT, A., BRUNET, E., MORALES-ARTACHO, A.J., Institution: INSEP, Country: FRANCE, Abstract-ID: 2606

INTRODUCTION:
The capacity to maintain physiological stability during exercise is defined as “durability” (1). Previous investigations have reported that prolonged exercise bouts may decrease maximal oxygen uptake (V̇O2peak), exercise economy, or metabolic thresholds (2). The Step-Ramp-Step (SRS) protocol (3) allows to identify metabolic thresholds and retrieve the constant-work rate (CWR) V̇O2-power output (PO) relationship (4). Although it has never been used for that purpose, this protocol may be suitable to track changes in physiological parameters and hence evaluate changes in durability within a 1.5-h single session. Therefore, the purpose of this study was to evaluate the effect of a 30-minute fatiguing effort performed in the high-end of the heavy-intensity domain on physiological parameters – namely the Gas Exchange Threshold (GET), the Respiratory Compensation Point (RCP), V̇O2peak and time-to-exhaustion (TTE) – using a recently validated modified SRS (mod-SRS) protocol (5).
METHODS:
Eleven trained male triathletes (V̇O2peak = 67.0 mL.min-1.kg-1) attended the laboratory 3 times to conduct a cycling mod-SRS protocol in a “fresh” state (mod-SRSFRESH, visit 1) and a mod-SRS protocol following a 30-min cycling bout at 95% PORCP (mod-SRSFATIGUED, test in visit 2 and retest in visit 3). TTE was computed as the time sustained during the CWR final step of the mod-SRS. Separate one-way repeated-measures ANOVA were used to compare POGET, PORCP, V̇O2 at GET and RCP, V̇O2peak and TTE across visits. Test-retest reliability was computed with the Coefficient of Variation (CV).
RESULTS:
POGET was higher in mod-SRSFRESH than in mod-SRSFATIGUED in trial 1 and trial 2 (bias = 20 and 10 W, bias CI95% : [8, 32] and [1, 18] W, p = 0.002 and 0.028, respectively). PORCP was not statistically different between mod-SRSFRESH and mod-SRSFATIGUED either in trial 1 or trial 2 (bias = 11 and 4 W, bias CI95% : [-4, 25] and [-14, 23] W, respectively). The V̇O2 at GET and RCP as well as V̇O2peak were not statistically different between mod-SRSFRESH and mod-SRSFATIGUED in trial 1 (bias = -0.04 to 0.08 L·min-1, bias CI95% : [-0.24, 0.17] to [-0.07, 0.23] L·min-1) or trial 2 (bias = -0.13 to -0.03 L·min-1, bias CI95% : [-0.39, 0.14] to [-0.16, 0.11] L·min-1). TTE was not statistically different between mod-SRSFRESH and mod-SRSFATIGUED either in trial 1 or trial 2 (bias = 66 and 50 s, bias CI95% : [-21, 154] and [-19, 119] s, respectively). CV for V̇O2 variables were within a range of 3.5 to 5.0 %, for POGET and PORCP 5.0 to 6.0 % and for TTE 29.5 %.
CONCLUSION:
Collectively, these results showed an overall leftward shift in the V̇O2-PO relationship due to the CWR heavy-intensity bout which affected the PO at thresholds but not the V̇O2 or V̇O2peak. TTE, albeit reduced in the fatigued state, presents a high intra-individual variability.

1 : Maunder et al., Sports Med, 2021.
2 : Hunter et al., Exp Phys, 2025.
3 : Iannetta et al., MSSE, 2020.
4 : Iannetta et al., MSSE, 2023.
5 : Rousseau et al., MSSE, 2026.