M.R. Ely1, D.C. Sieck1, J.E. Mangum1, E.A. Larson1, L.C. Brito2, C.T. Minson1FACSM, J.R. Halliwill1FACSM

1University of Oregon. Eugene, OR; 2University of Sao Paulo, Sao Paulo, Brazil

Histamine, commonly associated with allergies and immune responses is released/produced within skeletal muscle during exercise. In humans, blocking histamine’s actions via antihistamines did not influence speed, power, or time to completion of short-duration, high-intensity exercise. Conversely, in rodents, antihistamines decreased the speed and duration components of endurance tasks. It is unknown if the differential exercise outcomes between humans and rodents from antihistamines is species specific or related to exercise intensity/duration. PURPOSE: To test the effects of antihistamines on cycling time trial performance preceded by rest or exercise. It was hypothesized that H1/H2antihistamines would slow the time to completion of a fixed-distance time-trial compared to placebo, and the effect would be greater following an endurance-exercise bout. METHODS: Eleven (3F) competitive cyclists (Cat 1-3) performed six 10km time-trials on separate days. The first two trials served as a familiarization and repeatability was assessed by calculating a coefficient of variation (CV). The next four trials were performed in a randomized-block order. Two were preceded by 120 min of seated rest and two by 120 min of steady-state cycling at 50% VO2peak. Within those blocks, volunteers consumed either antihistamines (540 mg fexofenadine; H1receptor blocker, and 300 mg of ranitidine; H2receptor blocker) or placebo 60 min prior to the start of rest/exercise. Two-Way RMANOVA, effect size (ES = Cohen’s dz), 95% CI, and CV from familiarization trials were used to determine the presence, strength, and meaningfulness of differences between the trials. RESULTS: A reduction in time to completion occurred with antihistamines compared to placebo (+10.5 ± 3.8 s, mean ± SEM, drug effect p=0.002), the reduced performance tended to be exacerbated by prior exercise (p=0.057) but there was no drug by prior exercise interaction (p=0.716). The day-to-day 10 km variability (CV) was 0.98%. The percent change in time-to-completion between placebo and antihistamine was likely trivial following rest (mean -0.87%, 95%CI -2.02 to 0.29%) (ES=0.505) and potentially harmful following exercise (mean -1.2%, 95%CI -2.45 to 0.05%) (ES=0.646). CONCLUSION: Antihistamines slowed 10km time-trials in highly competitive cyclists.

Support provided by: The Eugene & Clarissa Evonuk Memorial Graduate Fellowship & The ACSM Northwest Student Research Award.

This document is currently not available here.