The Reliability of a 90-minute Preloaded Treadmill Time-Trial in Hot and Moderate Ambient Temperatures

Abstract

Exercise tests to exhaustion have been shown to have poor test-retest reliability and high levels of within-subject variation (Jeukendrup et al., 1996) as well as lacking direct comparison to sporting events (Hopkins et al., 2001). This has lead to interest in alternative methods of endurance performance assessment such as time-trials (TT) and, for longer protocols, preloaded time-trials (TTpre). Both have been shown to be reproducible methods of endurance assessment in ambient conditions for cycling and running (Doyle and Martinez, 1998; Jeukendrup et al., 1996) however the reliability of such performance tests is unknown in elevated temperatures. PURPOSE: To investigate the reliability of a 90-min treadmill-based TTpre in elevated and moderate temperatures. METHODS: Seven well-trained males (31 ± 8 yrs; 73.5 ± 5.6 kg; 57.68 ± 6.29 ml.kg-1.min-1) completed six 90-min TTpre, three in hot (H) ambient conditions (30.5 ± 0.1°C, 53 ± 2% relative humidity (RH)) and three in moderate (M) ambient conditions (14.4 ± 0.1°C, 59 ± 4% RH). Trials were separated by 7–14 days and conducted on a motorised treadmill. The order of the environmental conditions was randomised. The TTpre consisted of 75-min at ∼60% VO2max immediately followed by a self-paced 15-min TT. During the TT section subjects were instructed to run as far as possible within the 15-min and were given visual feedback of the time remaining. Reliability was assessed via coefficient of variation (CV). The distances covered were compared using paired t-tests. Trial 1 in each condition was considered a familiarisation. Results are presented as percentages for CV and mean ± standard deviation for distances. RESULTS: Subjects ran further in the M than the H trials (90-min TTpre: 16,072 ± 1,366 km vs 15,753 ± 1,307 km, P<0.01; 15-minTT: 3,519 ± 460 km vs 3,213 ± 516 km, P<0.001). The CV for the 90-min protocol was 0.69% (M) and 0.58% (H) which increased to 2.53% (M) and 2.32% (H) when calculated for the 15-min TT section alone. CONCLUSIONS: The 90-min TTpre is a reliable test for the assessment of endurance performance in prolonged treadmill running in males in H and M conditions. Reliability is enhanced in H compared to M conditions.