Author(s): KUORELAHTI, T., BADENHORST, C., IHALAINEN, J.K., LINNAMO, V., HYNYNEN, E., MIKKONEN, R.S., Institution: UNIVERSITY OF JYVÄSKYLÄ, Country: FINLAND, Abstract-ID: 970

INTRODUCTION:
Acute hypoxia is widely reported to compromise both maximal and submaximal endurance performance,(1,2) although a large variation exists between individuals. Sex and training status have been suggested to partly explain the interindividual differences in physiological responses to hypoxia,(1,3) but research remains limited. This study investigated the effects of acute normobaric hypoxia on submaximal endurance performance and whether the physiological responses, such as blood lactate (La), peripheral oxygen saturation (SpO2), and perceived exertion, are influenced by sex or training status. In addition, we assessed whether heart rate is sufficient for monitoring exercise intensity during submaximal exercise in acute hypoxia, as athletic training monitoring often relies on lactate threshold specific heart rates determined in normoxic conditions.
METHODS:
Endurance trained males (n=20; Age=30 ± 5) and females (n=20; Age=27 ± 7) were recruited for the study and classified as Recreational to Trained (Tier 1-2; M=10, F=8) and Highly Trained athletes (Tier 3-4; M=8, F=12).(4) All participants performed an incremental running test in normoxia, from which VO2max and heart rates at first (HRLT1) and second lactate thresholds (HRLT2) were determined. Two running interval sessions were then completed in a randomized, single-blind study design, with participants completing 2 x 4 min at HRLT1 and 5 x 4 min at HRLT2 in normoxia (NORM) and hypoxia (HYP). Running speed, rating of perceived exertion (RPE), and SpO2 were assessed during each interval. La was collected after the second interval at HRLT1 and second and fourth interval at HRLT2.
RESULTS:
During the interval sessions, no significant interactions between the environment and sex or training status were detected (p>0.05). Instead, hypoxia had significant effects on running speed, La, and SpO2 (F=100.1, p<0.001; F=32.7, p<0.001; F=420.0, p<0.001), while RPE remained unaffected. Running speed and SpO2 were 6.7 ± 5.3 % and 10.2 ± 4.8 % lower throughout the hypoxic interval session in all participants, while La increased by 30.0 ± 40.0 % across HRLT1 and HRLT2.
CONCLUSION:
The results of the present study demonstrated comparable physiological responses to submaximal exercise in acute hypoxia between training status groups and sex. Interestingly, the observed elevation in La during the hypoxic exercise may suggest an elevated relative exercise intensity when using normoxic lactate threshold heart rates to monitor training in acute hypoxia. As such, lactate, instead of heart rate, may be a preferred training intensity monitoring method for endurance athletes in acute hypoxic conditions.

REFERENCES:
1. Deb et al. 2018. DOI: 10.1080/17461391.2017.1410233
2. Faulhaber et a. 2021. DOI: 10.3390/ijerph18147573
3. Raberin et al. 2024. DOI: 10.1123/ijspp.2021-0451
4. McKay et al. 2022. DOI: 10.1007/s40279-023-01954-6