^Heavy-, Moderate-Intensity ^{Severe-, and}Exercise ^Extreme-, Increase ^{but Not} Vo ^‧_2max and Thresholds after 6 wk of Training

INGLIS, E. C., D. IANNETTA, L. RASICA, M. Z. MACKIE, D. A. KEIR, M. J. MACINNIS, and J. M. MURIAS. Heavy-, Severe-, and Extreme-, but Not Moderate-Intensity Exercise Increase Vo ^‧_2max and Thresholds after 6 wk of Training. Med. Sci. Sports Exerc., Vol. 56, No. 7, pp. 1307- 1316, 2024. Introduction: This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (VO ^‧_2max) and submaximal thresholds. Methods: Eighty-four young healthy participants (42 females, 42 males) were randomly assigned to six age, sex, and VO ^‧_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. Results: Compared with the change in VO ^‧_2max (ΔVO ^‧_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 (θ_LT) was similar across HVY1, HVY2, HIIT, and SIT, which were all greater than CON (P < 0.05). The ΔVO ^‧₂ and ΔPO at θ_LT 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). Conclusions: This study demonstrated that i) exercise intensity is a key component determining changes in VO ^‧_2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals.