The effects of the low recumbent body position in muscle deoxygenation during ramp incremental exercise

Exercising in the supine position whereby the active muscles are held above the level of the heart compromises performance when compared with upright cycling. The lack of gravitational assist to muscle blood flow, results in a reduction of muscle perfusion pressure and subsequently oxygen delivery (Egaña et al., 2013; DiMenna et al., 2010). In the present study we investigated the impact of the low recumbent cycling position on cycling performance, muscle fractional O2 extraction (estimated using deoxygenated haemoglobin), and rate of increase of pulmonary oxygen uptake (VO2) during incremental cycling exercise. Eleven young healthy male participants (mean ± SD; 22 ± 3years; 181.5 ± 4.7cm; 78.4 ± 10.5kg) performed a ramp incremental cycling test to exhaustion in four cycling positions; upright, 30° recumbent (R), 15°R, and supine. Exercise was performed initially for 2-min at 10W, followed by 20 or 25 W/min increments on an electrically braked cycle ergometer, with pedal frequency held constant at an individually selected rpm. VO2 was measured on a breath-by-breath basis using an online metabolic system, while the rate of muscle deoxygenation (deoxygenated haemoglobin/myoglobin, deoxy[Hb + Mb]) of the vastus lateralis (VL) muscle was continuously measured using near infrared spectroscopy (NIRS). Deoxy[Hb + Mb] responses displayed a sigmoidal shape across the four cycling positions. The slope of deoxy[Hb + Mb] / %workloadpeak was significantly (P<0.05) lower in the upright position (0.037±0.017) compared with the three other positions (30°R = 0.055±0.022; 15°R = 0.054±0.020;supine = 0.053±0.009), but was not different among the 30°R, 15°R and supine positions. These findings suggest that the reductions in cycling performance observed between the upright and low-recumbent (30°R & 15°R), and supine postures can be partially attributed to greater oxygen extraction levels in the 30°R, 15°R and supine postures, possibly due to a gravity-induced reduction in muscle oxygen delivery. However, factors affecting the differences in cycling performance between low recumbent and supine postures are less clear.References: DiMenna F, Bailey S & Jones A (2010). Influence of body position on muscle deoxy[Hb + Mb] during ramp cycle exercise. Respir Physiol Neurobiol 173, 138-145. Egaña M, Columb D & O’Donnell S (2013). Effect of low recumbent angle on cycling performance, fatigue, and VO2 kinetics. Med Sci Sports Exerc 45, 663-673