Author(s): REBIS, K., KOWALSKI, T., KLUSIEWICZ, A., Institution: INSTITUTE OF SPORT - NATIONAL RESEARCH INSTITUTE IN WARSAW, Country: POLAND, Abstract-ID: 813

INTRODUCTION:
Ski-mountaineering (SKIMO) is an endurance winter sport that combines skiing and mountaineering. As the participants ascend and descend snow-covered mountains, it requires continuous effort in various hypoxic conditions. The frequent changes in altitude and oxygen levels limit the practical application of traditionally derived thresholds or training zones based on heart rate (HR) or lactate concentration (bLa). The state-of-the-art literature reports that the maximal metabolic steady state may also be identified based on the muscle oxygenation (SmO2) kinetics during exercise (Cayot et al., 2021), providing a foundation to define exercise intensity. However, research regarding practical applications of SmO2-derived thresholds and training zones remains scarce. Therefore, we investigated the transferability of SmO2-based intensity prescription between different hypoxic conditions to assess the suitability of real-time SmO2 measurements for SKIMO athletes.
METHODS:
A group of well-trained male SKIMO athletes (n=15, age 29.7±11.5 years, VO2max 60.9±8.1 mL/kg/min) participated in the study. In normoxia (87m ASL, FiO2=20.8%), they performed a graded-intensity run test on a treadmill to determine the anaerobic threshold (AnT) with the mod-Dmax method. The following week, they performed maximal lactate steady state (MLSS) run assessments in acute normobaric hypoxia (3000m ASL, FiO2=14.4%) with the intensity aligned to 90-105% of SmO2 at the normoxia-determined AnT. SmO2 (Moxy Monitor at the vastus lateralis, Moxy Monitors, USA), HR (Polar H10 chest strap, Polar Electro Oy, Finland), and bLa (Super GL 2, Dr. Müller Gerätebau GmbH, Germany) were monitored during both efforts. The number and percentage of MLSS assessments without bLa increase over 1 mmol/L were reported. Paired t-tests with Cohen’s d effect sizes and ICC were computed to compare bLa and HR at AnT in normoxia and MLSS averages in hypoxia, as both corresponded to equivalent SmO2.
RESULTS:
11 out of 15 MLSS assessments (73.3%) were performed without bLa increase over 1 mmol/L. Statistically significant differences at equivalent SmO2 in normoxia and hypoxia were found for HR (175±11.7 vs 160±14.2 bpm, p=0.005, d=1.02), but not for bLa (4.9±1.2 vs 5.1±2.4 mmol/L, p=0.845, d=-0.05). ICC(2,k) for HR and bLa were 0.56 (95% CI: -0.24, 0.85) and 0.40 (95% CI: -0.75, 0.80), respectively.
CONCLUSION:
The results indicate fair transferability of SmO2-based intensity prescription between different hypoxic conditions in well-trained SKIMO athletes. The practical significance of our observations depends on the required accuracy of the exercise intensity determination. Considering the exploratory design of the study and substantial individual variability in analyzed indices, further research is necessary. All the participants were accustomed to exercise in hypoxia, therefore our findings may not apply to different populations, ie. recreationally active tourists.