Heavy-, Severe-, and Extreme-, but Not Moderate-Intensity Exercise Increase V̇o 2max and Thresholds after 6 wk of Training

This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (V̇O 2max ) and submaximal thresholds. Eighty-four young healthy participants (42 females, 42 males) were randomly assigned to six age, sex, and V̇O 2max -matched groups (14 participants each). Groups performed continuous cycling in the 1) moderate (MOD), 2) lower heavy (HVY1), and 3) upper heavy-intensity (HVY2) domain; interval cycling in the form of 4) high-intensity interval training (HIIT) in the severe-intensity domain, or 5) sprint-interval training (SIT) in the extreme-intensity domain; or no exercise for 6) control (CON). All training groups, except SIT, were work-matched. Training participants completed three sessions per week for 6 wk with physiological evaluations performed at PRE, MID, and POST intervention. Compared with the change in V̇O 2max (∆V̇O 2max ) in CON (0.1 ± 1.2 mL·kg -1 ·min -1 ), all training groups, except MOD (1.8 ± 2.7 mL·kg -1 ·min -1 ), demonstrated a significant increase ( P < 0.05). HIIT produced the highest increase (6.2 ± 2.8 mL·kg -1 ·min -1 ) followed by HVY2 (5.4 ± 2.3 mL·kg -1 ·min -1 ), SIT (4.7 ± 2.3 mL·kg -1 ·min -1 ), and HVY1 (3.3 ± 2.4 mL·kg -1 ·min -1 ), respectively. The ΔPO at the estimated lactate threshold ( θLT ) was similar across HVY1, HVY2, HIIT, and SIT, which were all greater than CON ( P < 0.05). The ΔV̇O 2 and ΔPO at θLT for MOD was not different from CON ( P > 0.05). HIIT produced the highest ΔPO at maximal metabolic steady state, which was greater than CON, MOD, and SIT ( P < 0.05). This study demonstrated that i) exercise intensity is a key component determining changes in V̇O 2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals.