E. Flood1, I. Matthews1, L. Heenan1, K. Fisher1, B.J. Winn2, B.S. Kirby2, B.W. Wilkins1

1Gonzaga University, Spokane, WA.

2Nike Sport Research Lab, Nike Inc., Portland, OR.

Mental stress has a significant neuro-excitatory effect on the cardiovascular system and the maximal sustainable metabolic rate (critical intensity; CI) appears predicated on adequate oxygen supply to match demand. PURPOSE: To determine if mental stress alters the parameters of the power-duration relationship (CI) and if mental stress during exercise alters the balance between oxygen supply and demand. METHODS: 14 young (8 male, 6 female) participants completed five study days. Day 1: a three minute all out cycling (3MT) to determine baseline CI and maximal oxygen uptake. Days 2 & 3: a 3MT preceded by either a 2-min Color Word Stroop Test (Stroop) or a control test (counterbalanced order). Days 4 & 5: constant work-rate cycling trials at either 5% above or 5% below CI (counterbalanced order) as determined by the 3MT; a Stroop was performed while participants exercised at the prescribed work-rate. Oxygen uptake (VO2), heart rate (HR), and muscle oxygenation (%SmO2, thigh and shoulder sites) were assessed throughout exercise and venous blood lactate was determined before and after the 3MT’s and every 5 min during constant work-rate trials. Blood pressure was monitored continuously throughout the control and Stroop conditions which preceded the 3MT’s (Days 2 & 3). RESULTS: Blood pressure dynamics verified a robust pressor response to the Stroop, not observed in control (p<0.05). The pressor response increased the dynamic %SmO2 response (P<0.05) to the Stroop test. End test power (from 3MT) was similar following control (261±76 W) and Stroop (254±80 W) conditions. This was also true for maximal VO2 (50.7± 4.9 vs 50.9±3.8 ml/kg/min for control vs Stroop) and venous blood lactate (16.2±1.3 vs 17.2±1.9 mmol/L for control vs Stroop). There was a clear increase in %SmO2 to the Stroop (p<0.05), but only in the non-exercising muscle (shoulder site) and only during exercise at 5% below CI. CONCLUSIONS: Despite a clear pressor response leading to altered oxygen supply relative to demand, mental stress does not alter CI determined from a 3MT. However, there is a clear mismatch in oxygen supply relative to demand in non-exercising muscle during exercise below CI. This suggests a different exercise intensity and non-exercising muscle interaction in the control of blood flow during combined exercise and mental stress. Supported by Nike, Inc.

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