Maintenance of internal load despite a stepwise reduction in external load during moderate intensity heart rate clamped cycling with acute graded normobaric hypoxia in males

Siu Nam Li, Peter Peeling, Brendan R. Scott, Jeremiah J. Peiffer, Alex Shaykevich, Olivier Girard

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Objectives: To investigate the acute effects of graded hypoxia on external and internal loads during 60 min of endurance cycling at a clamped heart rate. Design: Repeated measures. Methods: On separate visits, 16 trained males cycled for 60 min at a clamped heart rate corresponding to 80 % of their first ventilatory threshold at sea-level and 2500 m, 3000 m, 3500 m and 4000 m simulated altitudes (inspired oxygen fractions of 20.9 %, 15.4 %, 14.5 %, 13.6 % and 12.7 %, respectively). Markers of external (power output) and internal (blood lactate concentration, tissue saturation index, cardio-respiratory and perceptual responses) loads were measured every 15 min during cycling. Neuromuscular function of knee extensors was characterised pre- and post-exercise. Results: Compared to sea-level (101 ± 22 W), there was a stepwise reduction in power output with increasing hypoxia severity (− 17.9 ± 8.9 %, − 27.1 ± 10.7 %, − 34.2 ± 12.0 % and − 44.6 ± 15.1 % at 2500 m, 3000 m, 3500 m, and 4000 m, respectively, all p < 0.05). Blood lactate and tissue saturation index were not different across hypoxia severities, and perceptual responses were exacerbated at 4000 m only, with increased breathing difficulty. Knee extensor torque decreased post-exercise (− 14.5 ± 9.0 %, p < 0.05), independent of condition. Conclusions: Increasing hypoxia severity reduces cycling power output and arterial oxygen saturation in a stepwise fashion without affecting exercise responses between sea-level and simulated altitudes up to 3500 m despite breathing difficulty being elevated at 4000 m.

Original languageEnglish
Pages (from-to)628-635
Number of pages8
JournalJournal of Science and Medicine in Sport
Volume26
Issue number11
Early online date2023
DOIs
Publication statusPublished - Nov 2023

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