The Reliability of 4-Minute and 20-Minute Time Trials and Their Relationships to Functional Threshold Power in Trained Cyclists
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PURPOSE: The mean power output (MPO) from a 60-min time trial (TT) - also known as "functional threshold power" or "FTP" - is a standard measure of cycling performance; however, shorter performance tests are desirable to reduce the burden of performance testing. We sought to determine the reliability of 4-min and 20-min TTs and the extent to which these short TTs were associated with 60-min MPO. METHODS: Trained male cyclists (n = 8; age = 25 ± 5 years; VO2max = 71 ± 5 mL/kg/min) performed two 4-min TTs, two 20-min TTs, and one 60-min TT. Critical power (CP) was estimated from 4-min and 20-min TTs. The typical error of the mean (TEM) and intraclass correlation (ICC) were calculated to assess reliability, and R2 values were calculated to assess relationships with 60-min MPO. RESULTS: Pairs of 4-min TTs (Mean: 417 [SD: 45] W vs. 412  W, p. = 0.25; TEM = 8.1 W; ICC = 0.98), 20-min TTs (342  W vs. 344  W, p = 0.41; TEM = 4.6 W; ICC = 0.99), and CP estimates (323  W vs. 328  W, p = 0.25; TEM = 6.5; ICC = 0.98) were reliable. The 4-min MPO (R2 = 0.95), 20-min MPO (R2 = 0.92), estimated CP (R2 = 0.82), and combination of the 4-min and 20-min MPO (adj. R2 = 0.98) were strongly associated with the 60-min MPO (309  W). CONCLUSION: The 4-min and 20-min TTs appear useful for assessing performance in trained, if not elite, cyclists.
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