Impact of Stress on Resting Skeletal Muscle Oxygen Consumption with and without Prior Exercise

Abstract

The effects of acute exercise on muscle metabolism are well established, however the impact of mental stress (MS) on muscle metabolism is not well understood. PURPOSE: To assess muscle oxygen consumption (mVO2) after acute MS and evaluate the effect of acute exercise prior to MS on mVO2. METHODS: Participants (N=15 males, 22± 2 yr, VO2peak 40.8 ± 5.7 ml/kg/min) served as their own control in a randomized counter balanced design. Participants completed a total of three visits over 3-5 weeks. On the initial visit, a maximal oxygen uptake test on a cycle ergometer was performed. Near-infrared spectroscopy (NIRS) was used during a five-minute cuff occlusion and the initial slope during the occlusion was used to assess mVO2 in the gastrocnemius muscle. mVO2 was assessed at baseline (BL), after rest (CON) or exercise (EX), and after mental stress (MS). On two separate days, participants either rested for 25 minutes (CON) or completed 25 minutes of exercise (EX) at 90% ventilatory threshold on cycle ergometer. MS was evoked by a serial subtraction test administered by two research assistants dressed in white lab coats. Data were analyzed using a 2x3 repeated measures ANOVA with Fishers LSD post hoc tests, and are presented as mean percent change +/- SD. RESULTS: A significant interaction effect of Condition x Time on mVO2 was observed(F=6.3 p<0.05,η2=0.326). Post hoc comparisons indicated mVO2 was significantly increased after EX compared to CON by 21.8+/- 26.0% (p<0.05). Within CON, MS increased mVO2 by 12.6 +/- 10.2% (p<0.001). In EX, there was an increase in mVO2 from BL to after EX by 12.6 +/- 16.0% (p<0.05) and from BL to after MS by 18.2 +/- 64.1% (p=0.053). CONCLUSION: To our knowledge, these data are the first to suggest that acute MS increases the metabolic rate of resting skeletal muscle. Interestingly, the combination of prior EX and MS does not further augment metabolic activity beyond MS alone.