Changes in V̇O2max after 6 Weeks of Intensity Domain-Specific Training: Role of Central and Peripheral Adaptations.

Abstract

Purpose: This study characterized central and peripheral adaptations to domain-specific endurance exercise training.

Methods: Eighty-four young healthy participants were randomly assigned to age- and sex-matched groups of: continuous cycling in the 1) moderate (MOD)-, 2) lower heavy (HVY1)-, and 3) upper heavy-intensity (HVY2)- domain; interval cycling in the 4) severe-intensity domain (i.e., high-intensity interval training (HIIT), or 5) extreme-intensity domain (i.e., sprint-interval training (SIT)); or 6) control (CON). Two 3-week phases of training (three sessions per week) were performed. All training protocols, except SIT, were work-matched.

Results: Maximal oxygen uptake (V̇O2max), maximal cardiac output (Q̇max), derived maximal arterial-venous oxygen difference (a-vO2diff), blood volume (BV), plasma volume (PV), and near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity (τOxCap) were measured and compared at PRE and POST. The largest change in V̇O2max occurred in HIIT (0.43 ± 0.20 L·min-1), which was greater than CON (0.02 ± 0.08 L·min-1), MOD (0.11 ± 0.19 L·min-1), HVY1 (0.24 ± 0.18 L·min-1) and SIT (0.28 ± 0.21 L·min-1) (p < 0.05) but not HVY2 (0.36 ± 0.14 L·min-1) (p > 0.05). Changes in Q̇max were observed in HVY1 (1.6 ± 0.5 L·min-1), HVY2 (3.0 ± 0.6 L·min-1), HIIT (2.9 ± 1.2 L·min-1) and SIT (1.8 ± 1.4 L·min-1) (p < 0.05) but not in MOD (1.2 ± 0.3 L·min-1) and CON (0.1 ± -0.5 L·min-1) (p > 0.05). HVY2 and HIIT produced significant changes in BV ((438 ± 101 mL, and 302 ± 38 mL) and PV (198 ± 92 mL, and 158 ± 51 mL), respectively (p < 0.05) whereas other groups did not.

Conclusions: No significant peripheral adaptations (i.e., τOxCap and a-vO2diff) were observed in any group (p > 0.05). The results indicate that higher training intensities (i.e., HVY2 and HIIT) produces larger changes in V̇O2max which is supported predominantly by central adaptations. Additionally, results suggest that, despite non-significant changes, the contribution of peripheral components to changes in V̇O2max should not be dismissed.