Exercise-Induced Cardiac Fatigue is Similar Across Increasing Trail-Running Race Distances

Abstract

A transient reduction in cardiac function following prolonged endurance exercise, termed exercise-induced cardiac fatigue, has previously been reported following events ranging from 2-40hrs. Right-ventricular dysfunction has been demonstrated to occur prior to left-ventricular dysfunction and, similarly, diastolic impairments may occur prior to systolic impairments. While highly-trained athletes are more fatigue-resistant than lesser-trained subjects, the timing and magnitude of cardiac alterations following prolonged racing is unclear. PURPOSE: The aim of this study was to investigate the effects of varying distance trail running races on cardiac function in recreational runners of varying fitness levels, to determine the dose-response of cardiac fatigue. METHODS: Forty-three distance runners competing in the Sulphur Springs trail races (25k,n=9; 50k,n=13; 80k,n=13; 160k,n=8) completed pre and post testing measures including resting echocardiography, and an incremental running test to determine maximal oxygen consumption (VO2max). RESULTS: Mean race durations were as follows; 25k:2.5±0.3hrs, 50k: 6.0±2.0hrs, 80k: 11.6±1.8, and 160k: 25.2±3.6hrs (all P<0.001). Echocardiographic results indicated diastolic impairments of both ventricles, with minimal systolic impairments, across all race distances post-race. Of the parameters investigated, only early-to-late diastolic filling ratio (E/A) was different between groups such that the 160k racers did not have as great of a reduction (mean Δ-0.51±0.50, 160k Δ-0.20±0.45, P=0.02). All racers had decreased blood pressure (MAP pre: 94±10 vs post: 83±9mmHg, P<0.0001), and elevated heart rates (pre:55±8 vs post:78±12b/min, P<0.0001) post-race. Fitness (VO2max) and age were not related to changes in cardiac function, whereas race duration was related to changes in E/A ratio (r=0.37, P=0.02) only. Changes in diastolic blood pressure were related to many changes in cardiac function including peak longitudinal strain (r=0.34, P=0.03). CONCLUSIONS: Prolonged trail-races appear to alter diastolic function regardless of race duration, and fitness, likely due to similar reductions in blood pressure post-race. A clear relationship between race duration and level of cardiac impairment is not apparent.