Author(s): NIVET, M., REBULL-BARRERA, J., LE-FUR, Y., VILMEN, C., MILLET, G.P., BEN DAHAN, D., RUPP, T. , Institution: UNIVERSITÉ SAVOIE MONT BLANC, Country: FRANCE, Abstract-ID: 1991

INTRODUCTION:
Ageing is associated with impaired neuromuscular function, force production, and exercise tolerance, contributing to functional impairment in older adults (1). While moderate-intensity exercise is commonly recommended, high-intensity exercise has been reported to be more effective to counteract age-related functional decline (2). Hypoxic conditioning has emerged as a strategy to potentiate exercise-induced stimuli (3), but its combination with high-intensity exercise remains poorly investigated, particularly in older adults.
This study aimed to compare force production and fatigability during high-intensity localized exercise, performed under hypoxic and normoxic conditions in young and older adults. We hypothesized that (i) force production would be lower in older adults regardless of condition, and that (ii) hypoxia would impair performance and affect force production kinetic in both groups during repeated high-intensity exercise.

METHODS:
Twenty-two healthy participants matched on body-weight and physical activity (young: 18-25 years, n = 11; older: >65 years, n = 11) completed a familiarization session followed by two randomized experimental trials under normoxic (FiO2 = 20.9%) and hypoxic (FiO2 = 13.0%) conditions. After warmup, each trial consisted of repeated sets of high-intensity intermittent isometric quadriceps contractions performed until task-failure, defined as two consecutive sets showing a >= 20% reduction in force relative to the maximal force produced at the beginning of the task. Force production and fatigability were assessed throughout each trial. Repeated-measures ANOVAs with Bonferroni post hoc tests were conducted on the number of sets completed in each condition and on average force responses throughout the common number of completed sets across participants and conditions (i.e. 6 sets).

RESULTS:
Hypoxia significantly reduced exercise tolerance during repeated high-intensity contractions, as evidenced by a lower number of completed sets compared with normoxia (9 ± 4 vs 14 ± 5; p < 0.001), with no difference between age-groups (p = 0.47). Across the first six sets, mean force production was significantly higher in young compared with older adults (170 ± 49 vs 119 ± 47 N; p = 0.02). Although no significant main effect of condition was observed (p = 0.051), force production tended to be lower under hypoxia compared to normoxia.

CONCLUSION:
Our results indicated age-related differences in force production, between young and older adults, regardless of condition. In addition, hypoxia reduced exercise tolerance and tended to affect force production during the first six sets of repeated high-intensity exercise in either age group. Additional participants are currently being recruited to further evaluate this trend.

REFERENCES.
1. Hunter SK et al. J Appl Physiol. 1 oct 2016;121(4):982‑95.
2. Coswig VS, et al. J Transl Med. déc 2020;18(1):88.
3. Burtscher J et al. J Physiol. nov 2024;602(21):5757‑83.