Metabolic and performance adaptations to interval training in endurance-trained cyclists

Abstract

This study examined the effects of sustained high-intensity interval training (HIT) on the athletic performances and fuel utilisation of eight male endurance-trained cyclists. Before HIT, each subject undertook three baseline peak power output ${\dot W}_{\rm peak}$ tests and two simulated 40-km time-trial cycling performance (TT₄₀) tests, of which the variabilities were 1.5 (1.3)% and 1.0 (0.5)%, respectively [mean (SD)]. Over 6 weeks, the cyclists then replaced 15 (2)% of their 300 (66) km · week⁻¹ endurance training with 12 HIT sessions, each consisting of six to nine 5-min rides at 80% of ${\dot W}_{\rm peak}$, separated by a 1-min recovery. HIT increased ${\dot {W}}_{\rm peak}$ from 404 (40) to 424 (53) W (P < 0.01) and improved TT₄₀ speeds from 42.0 (3.6) to 43.0 (4.2) km · h⁻¹ (P < 0.05). Faster TT₄₀ performances were due to increases in both the absolute work rates from 291 (43) to 327 (51) W (P < 0.05) and the relative work rates from 72.6 (5.3)% of pre-HIT ${\dot {W}}_{\rm peak}$ to 78.1 (2.8)% of post-HIT ${\dot {W}}_{\rm peak}$ (P < 0.05). HIT decreased carbohydrate (CHO) oxidation, plasma lactate concentration and ventilation when the cyclists rode at the same absolute work rates of 60, 70 and 80% of pre-HIT ${\dot {W}}_{\rm peak}$ (P < 0.05), but not when they exercised at the same relative (% post-HIT ${\dot { W}}_{\rm peak}$) work rates. Thus, the ability of the cyclists to sustain higher percentages of ${\dot {W}}_{\rm peak}$ in TT₄₀ performances after HIT was not due to lower rates of CHO oxidation. Higher relative work rates in the TT₄₀ rides following HIT increased the estimated rates of CHO oxidation from ≈ 4.3 to ≈ 5.1 g · min⁻¹.