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. The authors sought to determine the reliability of 4- 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] y; = 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- and 20-min TTs. The typical error of the mean (TEM) and intraclass correlation coefficient (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 [49] W, P = .25; TEM = 8.1 W; ICC = .98), 20-min TTs (342 [36] W vs 344 [33] W, P = .41; TEM = 4.6 W; ICC = .99), and CP estimates (323 [35] W vs 328 [32] W, P = .25; TEM = 6.5; ICC = .98) were reliable. The 4-min MPO (R2 = .95), 20-min MPO (R2 = .92), estimated CP (R2 = .82), and combination of the 4- and 20-min MPO (adjusted R2 = .98) were strongly associated with the 60-min MPO (309 [26] W). Conclusion: The 4- and 20-min TTs appear useful for assessing performance in trained, if not elite, cyclists.
MacInnis is with the University of Calgary, Calgary, AB, Canada. Thomas and Phillips are with the Dept of Kinesiology, McMaster University, Hamilton, ON, Canada.
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