The Physiological and Self-Perceived Determinants of Fatigue Development during Upright Versus Supine Cycling

Background: Supine cycling is a commonly used form of exercise to study skeletal muscle bioenergetics (Goulding et al., 2020; Goulding et al., 2021). Compared to upright cycling, the supine variant is characterized by slower oxygen transport, greater skeletal muscle deoxygenation amplitude (Goulding et al., 2020), and a greater type II fiber activation (Goulding et al., 2021). This typically results in excessive energy cost of supine exercise, and subsequently earlier exercise termination when compared to the classical upright cycling. However, the underlying mechanisms causing earlier exercise termination during supine cycling require further clarification.

Aim: The purpose of this investigation was to determine whether differences in body position (upright versus supine) govern the physiological performance indicators, including time to exhaustion (TTE), maximal heart rate (HR), peak power output (PPO), as well as the self-reported rate of perceived exertion (RPE), in healthy young men.

Methods: Nineteen participants (age 22±3) completed three experimental sessions, including one preliminary medical screening visit, and two ramp incremental tests (random order, in upright and supine positions, within 48 hours) until voluntary exhaustion. All tests were performed on an electronically braked cycle ergometer (Ergoline 900, Hamburg, Germany), and HR responses were monitored with a Garmin monitor (HRM-3 SS, Kansas, USA). The self-reported RPE scale (1 - 10) was administered following both upright and supine protocols, and participants were asked wheatear they stopped the ramp test due to leg pain or dyspnea.

Results: Significant differences were observed between the supine versus upright cycling. Lower PPO (-15%, p=.001) and HR (-17 bpm, p=.001) accompanied by shorter TTE (2 min, p=.001) were found in the supine cycling compared to upright cycling. The self-reported RPE data suggest that exercise termination was predominantly associated with perception of pain in the leg muscles, as compared to dyspnea (9.1±1.2 vs 7.6±1.1, p=.001, respectively), with no differences between the two exercise variants.

Conclusion: The present findings suggest that during supine cycling fatigue develops more rapidly when compared to the upright protocol. Interestingly, there were no differences observed in the self-reported RPE in upright versus supine cycling, with all participants consistently reporting leg pain as the main reason for exercise termination. Future studies should provide the context for the interplay between physiological response and the self-reported exertion during similar exercise protocols.

References:

Goulding, R.P., Okushima, D., Marwood, S., Poole, D.C., Barstow, T.J., Lei, T.H., Kondo, N., & Koga, S. (2020). Impact of supine exercise on muscle deoxygenation kinetics heterogeneity: mechanistic insights into slow pulmonary oxygen uptake dynamics. Journal of Applied Physiology (1985), 129(3), 535-546.

Goulding, R.P., Okushima, D., Fukuoka, Y., Marwood, S., Kondo, N., Poole, D.C., Barstow, T.J., & Koga, S. (2021). Impact of supine versus upright exercise on muscle deoxygenation heterogeneity during ramp incremental cycling is site specific. European Journal of Applied Physiology, 1-14. (epub ahead of print) doi: 10.1007/s00421-021-04607-6