Elevated muscle pain induced by a hypertonic saline injection reduces power output independent of physiological changes during fixed perceived effort cycling

Abstract

Pain is a naturally occurring phenomenon that consistently inhibits exercise performance by imposing unconscious, neurophysiological alterations (e.g., corticospinal changes) as well as conscious, psychophysiological pressures (e.g., shared effort demands). Although, several studies indicate that pain would elicit lower task outputs for a set intensity of perceived effort, no study has tested this. Therefore, this study investigated the impact of elevated muscle pain through a hypertonic saline injection on the power output, psychophysiological, cerebral oxygenation, and perceptual changes during fixed perceived effort exercise. Ten participants completed three visits (one familiarisation + two fixed perceived effort trials). Fixed perceived effort cycling corresponded to 15% above gas exchange threshold (mean RPE = 15; hard). Before the 30-minute fixed perceived effort exercise, participants received a randomised, bilateral hypertonic or isotonic saline injection in the vastus lateralis. Power output, cardiorespiratory, cerebral oxygenation, and perceptual markers (e.g., affective valence) were recorded during exercise. Linear mixed model regression assessed the condition and time effects and condition × time interactions. Significant condition effects showed that power output was significantly lower during hypertonic conditions (t_107= 2.08,p=.040,β=4.77 Watts,95%CI [0.27 to 9.26 Watts]). Meanwhile all physiological variables (e.g., heart rate, oxygen uptake, minute ventilation) demonstrated no significant condition effects. Condition effects were observed for deoxyhaemoglobin changes from baseline (t_107= -3.29,p=.001,β=-1.50 ΔµM,95%CI [-2.40 to-0.61 ΔµM]) and affective valence (t_127= 6.12,p=.001,β=0.93,95%CI [0.63,1.23]). Results infer that pain impacts the self-regulation of fixed perceived effort exercise, as differences in power output mainly occurred when pain ratings were higher after hypertonic versus isotonic saline administration.