White, A. T., VanHaitsma, T. A., Light, A. R., Light, K. C., Hughen, R. W., & Yenchik, S. (2012). Effect of short vs. longer duration strenuous exercise on afferent fatigue signaling. Presentation 1153 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

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"Metabolite-detecting receptors on Group IV afferents influence exercise performance and fatigue perception." This study determined the effects of short versus longer duration exercise on post-exercise expression of sensory and indolamine receptors and immune markers associated with fatigue. Cyclists (N = 12) performed a graded maximal-exercise test and a 40 km time-trial one week apart. Blood draws and fatigue ratings were obtained at baseline and 0.5, 8, and 24 hours after exercise. "Leukocytes were separated for RNA extraction and quantitative real-time polymerase chain reaction (qPCR) analysis of 4 metabolite-detecting genes (acidsensing, ASIC3; purinergic 2X sensing, P2X4; and 2 transient vanilloid receptors, TRPV1 and TRPV4); 2 indolamine receptors (dopamine, DRD4; and serotonin, HTR1D) and 3 immune markers (IL-10, IL-6 and Toll-like receptor 4, TLR4)". Fingerstick lactates were obtained at one and five minutes post-exercise.

Exercise time was longer and mean power was lower for the time-trial compared to the graded-exercise test. Blood lactate at one minute post-exercise was significantly higher after the graded-exercise test compared to the time-trial. Five-minute lactates were not different. Fatigue ratings increased significantly above baseline at 0.5, 8, and 24 hours after the time-trial but not the graded-exercise test. More changes in post-exercise expression of metabolite-detecting genes were observed after the time-trial, with significant decreases in ASIC3, TRPV1, TRPV4, and P2X4 seen at 0.5 hour. ASIC3 and TRPV1 remained significantly lower at 8 and 24 hours post-exercise, respectively. After the graded-exercise test, TRPV1 decreased at 0.5 hour but to a lesser degree than after the time-trial. After both exercise trials, decreases in IL10 were seen at 0.5 hour followed by significant increases at eight hours. After the time-trial, IL10 remained elevated at 24 hours. DRD4 expression decreased after both trials at 8 hours, but HTR1D changed only after the time-trial, with significant increases observed at 8 hours.

Implication. Both a graded-exercise test and a time-trial condition resulted in increased fatigue and changes in metabolite-detecting, immune, and indolamine gene expressions. The time-trial produced greater and longer lasting fatigue that was associated with greater changes in metabolite detecting and indolamine receptor expression and immune responses. Short-duration interval training performances promote quicker recovery while working at a higher intensity than a continuous time-trial activity.

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