Eccentric Exercise And Microvascular Function

Abstract

Exercise involving eccentric contractions results in reduced muscle function. Blood oxygen level dependent (BOLD) MR imaging has demonstrated slowed microvascular reactivity in eccentrically exercised tibialis anterior (TA) muscle. While the mechanism is unclear, exercise-induced inflammation and oxidative stress may reduce nitric oxide (NO) bioavailability, and consequently slow microvascular reactivity. PURPOSE: To test the hypotheses that ingestion of dietary nitrate or antioxidants preserve microvascular reactivity following eccentric exercise. METHODS: Thirty young men and women were randomized into three groups, who ingested a single dose of: i) beetroot juice (BR, 8.4mmol NO3-), ii) antioxidants (AO, Vitamin C and E, alpha-lipoic acid), or iii) placebo (PLA, fruit juice) at 46 hours after an exercise protocol. The protocol consisted of eccentric contractions of the TA in one leg, while the contralateral leg served as control. At baseline, and 48h after eccentric exercise, participants were positioned in a 3T magnet, and BOLD images were acquired bilaterally in TA muscle during i) brief maximal contractions (MVC), and ii) cuff occlusion (5 min, 260mmHg) to monitor the hyperemic responses. The time-to-peak (TTP, s) of the hyperemic response was used as an index of microvascular reactivity. Data were analyzed using mixed model, three-way (Leg, Group, Session (0h, 48h)) repeated measures ANOVA. RESULTS: The ANOVA revealed leg-by-session interactions for TTP following brief MVCs and cuff occlusion (P < 0.001), with no main or interaction effects of group. Specifically, 48h after eccentric exercise, TTP (MVC) was prolonged in all groups compared with baseline (BR: 8.6±1.0 vs.10.9±1.0 s; AO: 8.4±0.4 vs.10.1±0.4 s, PLA: 9.0±0.9 vs.11.0±0.8 s), with no changes in control leg. Similarly, 48h after eccentric exercise, TTP (cuff) was prolonged in all groups compared with baseline (BR: 45.5±4.7 vs.68.6±7.7 s; AO: 36.8±5.7 vs.54.5±8.5 s, PLA: 42.1±6.4 vs.68.1±7.1 s), with no changes in control leg. CONCLUSION: Ingestion of BR and AO do not preserve microvascular reactivity after eccentric exercise, indicating that elevated oxidative stress and lower NO bioavailability do not contribute to altered microvascular function after eccentric exercise. Supported by Danish Ministry of Culture grant.