The influence of high-intensity exercise training on the Wlim-Tlim relationship

JENKINS, D. G. and B. M. QUIGLEY. The influence of high intensity exercise training on the Wlim-Tlim relationship. Med Sci. Sports Exerc., Vol. 25, No. 2, pp. 275–282, 1993. When exercise to exhaustion is performed using at least two different intensities, work to fatigue (Wlim) can be expressed as a linear function of time to fatigue (Tlim). Whereas the slope of this function is related to endurance ability, the y-intercept is associated with the potential to perform high intensity interval exercise. The purpose of the present investigation was to determine the influence of 8-wk intermittent high-intensity exercise training on the y-intercept derived from the Wlim-Tlim relationship. Eight healthy, untrained male students (19.1 ± 0.6 yr) completed five 60-s bouts of maximal exercise on the cycle ergometer, three times a week, for 8 wk. Seven controls avoided regular activity for the same period. Prior to and immediately following the training period, the Wlim-Tlim relationship, VO2max, and total work completed in five 60-s exercise bouts on the cycle ergometer were determined. Correlational analysis established relationships between the y-intercept and total work accomplished in the interval test pre- (r = 0.90; P < 0.01; N = 15) and post-training (r = 0.92; P < 0.01; N = 15), confirming that the y-intercept is related to the ability to perform exercise of this nature. Moreover, the “anaerobic” energy yield, calculated from total work and oxygen consumed during the interval exercise, was also related to the y-intercept (r = 0.78; P < 0.01). Interval training significantly increased both the y-intercept (P = 0.0015) and total work accomplished in the interval test (P = 0.001), while the slope of the Wlim-Tlim relationship (critical power) remained unchanged. Changes in the y-intercept were correlated to changes in total work accomplished (r = 0.85; P <0.01). Furthermore, peak post-exercise plasma lactate concentration resulting from the interval task increased from 12.2 ± 1.6 to 16.3 ± 0.9 mmol.−1 (P = 0.003), while oxygen consumed during this exercise demand was not significantly changed with training (P = 0.166). The present study has demonstrated that not only does the y-intercept of the Wlim-Tlim relationship provide a measure of the ability to undertake repeated bouts of maximal, high intensity exercise, but that this particular characteristic is also responsive to exhaustive interval training.