Exercise Intensity in Track and Level-grade Treadmill Running: A Cross-over Longitudinal Study in Well-trained Athletes

Heart rate is a conventional indicator of exercise intensity. Diverse studies have reported results of the comparison between the heart rate responses attained during running overground and on a treadmill; non-unanimous conclusions have emerged. The intention of this study was to compare the exercise intensity through heart rate between progressive running tests performed on track and level-grade treadmills. The heart rate responses of twelve highly trained male athletes were analyzed (Age = 24.3±2.7 years). The running protocol had initial and final speeds of 11 km·h−1 and 18 km·h−1, and increments of 0.5 km·h−1 every 200 m. Two tests were performed: on an outdoor 400 m track, and a level-grade motorized treadmill under laboratory conditions. An innovative data analysis approach was proposed, by using a linear mixed-effects model, with the Test and Speed stage and their interaction as fixed factors, and the Subject as a random factor; a suitable correlation structure was also specified. The statistical significance level was set at p < 0.05. The difference between tests was not significant (F = 0.06, p = 0.81). The interaction effect between the Test and Speed stage was also not significant (F = 1.32, p = 0.19). Exercise intensity as measured by heart rate showed similar mean responses in track and level-grade treadmill running across a wide range of speeds in well-trained athletes.