A Validation Study Of A Treadmill Speed Incline Conversion Chart

Abstract

PURPOSE: To investigate the accuracy of the Hillrunner.com treadmill speed incline conversion chart using ventilatory data, heart rate, subjective perceived effort, and blood lactate. METHODS: Two groups of experienced runners, divided based on their self-reported easy run pace, ran at 6 different speed/incline combinations for 5 minutes each. All stages were equivalent according to the HillRunner.com chart, and 1 minute standing rest was given between stages. Group 1 (n=11) ran at inclines up to 4%, while Group 2 (n=22) ran at inclines up to 10%. Oxygen consumption (VO2), respiratory exchange ratio (RER), heart rate (HR), blood lactate (BL), overall rate of perceived exertion (RPE), and leg RPE (LRPE) were measured for each stage. VO2 was compared against the VO2 predicted by the ACSM equation (ACSM.VO2). Stage order was randomized, and repeated-measures ANOVA was used to detect differences between stages and inclines. RESULTS: Measures of exercise intensity did not change as incline rose from 0% to 4% in Group 1 (p>.05). Increases in VO2 (42.2±3.6 to 45.9±4.0 mL.kg-1.min-1; p<.05), HR (146±12 to 151±12 bpm; p<.05), BL (1.4±0.9 to 1.9±1.2 mM; p<.05) and LRPE (10±2 to 12±2; p<.05) were found as incline increased from 0% to 10% in Group 2. When compared with VO2, ACSM.VO2 underestimated oxygen consumption at all inclines up to 8% (p<.05). ACSM.VO2 was similar to VO2 at an incline of 10% in Group 2 (45.9±4.0 vs. 46.7±2.4 mL.kg-1.min-1; p>.05). Within subjects, pooled results show moderate correlations between HR and BL at 0% and 2% (R=0.478, R=0.587; p<.01) but not at 4% (R=0.309; p>.05). Statistically significant correlations were also found between HR and BL at 6%, 8%, and 10% (R=0.601, R=0.560, R=0.600; p<.01) in the Group 2 participants. CONCLUSIONS: The HillRunner.com chart appears valid at relatively low inclines. However, at higher inclines, the decreases in speed may not prevent increases in exercise intensity as measured with VO2, HR, BL, and LRPE. The ACSM VO2 prediction equation underestimates oxygen consumption in a trained population at inclines up to 8%.