The tolerable duration of continuous high-intensity exercise is determined by the hyperbolic Speed-tolerable duration (S-t LIM ) relationship. However, application of the S-t LIM relationship to normalize the intensity of High-Intensity Interval Training (HIIT) has yet to be considered, with this the aim of present study. Subjects completed a ramp-incremental test, and series of 4 constant-speed tests to determine the S-t LIM relationship. A sub-group of subjects (n = 8) then repeated 4 min bouts of exercise at the speeds predicted to induce intolerance at 4 min (WR 4 ), 6 min (WR 6 ) and 8 min (WR 8 ), interspersed with bouts of 4 min recovery, to the point of exercise intolerance (fixed WR HIIT) on different days, with the aim of establishing the work rate that could be sustained for 960 s (i.e. 4x4 min). A sub-group of subjects (n = 6) also completed 4 bouts of exercise interspersed with 4 min recovery, with each bout continued to the point of exercise intolerance (maximal HIIT) to determine the appropriate protocol for maximizing the amount of high-intensity work that can be completed during 4x4 min HIIT. For fixed WR HIIT t LIM of HIIT sessions was 399±81 s for WR 4 , 892±181 s for WR 6 and 1517±346 s for WR 8 , with total exercise durations all significantly different from each other (P < 0.050). For maximal HIIT, there was no difference in t LIM of each of the 4 bouts (Bout 1: 229±27 s; Bout 2: 262±37 s; Bout 3: 235±49 s; Bout 4: 235±53 s; P > 0.050). However, there was significantly less high-intensity work completed during bouts 2 (153.5±40. 9 m), 3 (136.9±38.9 m), and 4 (136.7±39.3 m), compared with bout 1 (264.9±58.7 m; P > 0.050). These data establish that WR 6 provides the appropriate work rate to normalize the intensity of HIIT between subjects. Maximal HIIT provides a protocol which allows the relative contribution of the work rate profile to physiological adaptations to be considered during alternative intensity-matched HIIT protocols. © 2013 Ferguson et al.
Ferguson, C., Wilson, J., Birch, K. M., & Kemi, O. J. (2013). Application of the speed-duration relationship to normalize the intensity of high-intensity interval training. PLoS ONE, 8(11). https://doi.org/10.1371/journal.pone.0076420