Rate dependent influence of arterial desaturation on self-selected exercise intensity during cycling

Abstract

The purpose of this study was to clarify if Ratings of Perceived Exertion (RPE) and self-selected exercise intensity are sensitive not only to alterations in the absolute level of arterial saturation (SPO2) but also the rate of change in SPO2. Twelve healthy participants (31.6 ± 3.9 y, 175.5 ± 7.7 cm, 73.3 ± 10.3 kg, 51 ± 7 mL·kg-1·min-1 [Formula: see text]) exercised four times on a cycle ergometer, freely adjusting power output (PO) to maintain RPE at 5 on Borg's 10-point scale with no external feedback to indicate their exercise intensity. The fraction of inspired oxygen (FIO2) was reduced during three of those trials such that SPO2 decreased during exercise from starting values (>98%) to 70%. These trials were differentiated by the time over which the desaturation occurred: 3.9 ± 1.4 min, -8.7 ± 4.2%•min-1 (FAST), 11.0 ± 3.7 min, -2.8 ± 1.3%•min-1 (MED), and 19.5 ± 5.8 min, -1.5 ± 0.8%•min-1 (SLOW) (P < 0.001). Compared to stable PO throughout the control condition (no SPO2 manipulation), PO significantly decreased across the experimental conditions (FAST = 2.8 ± 2.1 W•% SPO2-1; MED = 2.5 ± 1.8 W•% SPO2-1; SLOW = 1.8 ± 1.6 W•% SPO2-1; P < 0.001). The rates of decline in PO during FAST and MED were similar, with both greater than SLOW. Our results confirm that decreases in absolute SPO2 impair exercise performance and that a faster rate of oxygen desaturation magnifies that impairment.

Fig 1. Representative data from one subject illustrating changes in S_PO₂ (%) over time (min) (top) and PO (W) over time (min) (bottom).

Constant RPE exercise was performed for 30 min. The subject was breathing normoxic gas for the first 5 min during the exercise period so that they could establish a level of voluntary effort that corresponded to a RPE of 5. The desaturation procedure was initiated at 0 min, which was the official start of the experimental trials.

Fig 2. Representative data from one subject illustrating the time delay between the start of arterial desaturation and the subsequent decrease in PO.

Dashed lines indicate when FAST, MED, and SLOW began to deviate from CON. The shaded area represents the lag time between the start of arterial desaturation and the ensuing decrease in PO.