Effects of continuous and interval training on the parameters of the power-endurance time relationship for high-intensity exercise

The purpose of this study was to evaluate the effects of 6 weeks of low-intensity continuous exercise training (CE; 40 min at 50% V̇O₂(peak), 3 days/week) and high-intensity interval exercise training (IE: 10 x 2 min at V̇O₂(peak), 3 days/week) on the parameters of the power-endurance time relationship for cycle ergometry. The hyperbolic relationship between power and endurance time was linearized by expressing the power against the inverse of time, as described by Whipp et al. (22). This model consists of two parameters: Θf, a fatigue threshold reflecting the capability for sustained aerobic power, and W', a constant postulated to reflect a finite energy store (i.e., those factors comprising the O₂ deficit: Phosphagen stores, anaerobic glycogenolysis, myoglobin O₂ stores). Prior to training, test-retest reliability coefficients (r²) for Θf and W' were 0.92 and 0.62, respectively (P<0.01). Training resulted in significant (P<0.01) increases in Θf for both CE [27 ± 3 W (13.4%) increase] and IE [33 ± 5 W (15.0%) increase], with no difference between groups. Increases in Θf were not dependent upon improvements in V̇O₂(peak). W' was not changed significantly in either group after training. However, a significant negative correlation abetween the training-induced changes in Θf and W' (R=-0.76; P<0.01) was obtained. The minimum intensity threshold for exercise training necessary to elicit increases in Θf has yet to be identified, but is at least as low as 50% of V̇₂(peak).