Aerobic capacity and (V) over dotO2 kinetics adaptive responses to short-term high-intensity interval training and detraining in untrained females

Purpose This study investigated the physical fitness and oxygen uptake kinetics (tau(V) over dotO(2p)) along with the O-2 delivery and utilization (heart rate kinetics, tau HR; deoxyhemoglobin/(V) over dotO(2) ratio, Delta[HHb]/(V) over dotO(2)) adaptations of untrained female participants responding to 4 weeks of high-intensity interval training (HIIT) and 2 weeks of detraining. Methods Participants were randomly assigned to HIIT (n = 11, 4 x 4 protocol) or nonexercising control (n = 9) groups. Exercising group engaged 4 weeks of treadmill HIIT followed by 2 weeks of detraining while maintaining daily activity level. Ramp-incremental (RI) tests and step-transitions to moderate-intensity exercise were performed. Aerobic capacity and performance (maximal oxygen uptake, (V) over dotO(2max); gas-exchange threshold, GET; power output, PO), body composition (skeletal muscle mass, SMM; body fat percentage, BF%), muscle oxygenation status (Delta[HHb]), (V) over dotO(2), and HR kinetics were assessed. Results HIIT elicited improvements in aerobic capacity ((V) over dotO(2max), + 0.17 +/- 0.04 L/min; GET, + 0.18 +/- 0.05 L/min, P < 0.01; PO-(V) over dotO(2)max, +/- 23.36 +/- 8.37 W; PO-GET, + 17.18 +/- 3.07 W, P < 0.05), body composition (SMM, + 0.92 +/- 0.17 kg; BF%, - 3.08% +/- 0.58%, P < 0.001), and speed up the tau(V) over dotO(2p) (- 8.04 +/- 1.57 s, P < 0.001) significantly, extending to better Delta[HHb]/(V) over dotO(2) ratio (1.18 +/- 0.08 to 1.05 +/- 0.14). After a period of detraining, the adaptation in body composition and aerobic capacity, as well as the accelerated tau(V) over dotO(2p) were maintained in the HIIT group, but the PO-(V) over dotO(2max) and PO-GET declined below the post-training level (P < 0.05), whereas no changes were reported in controls (P > 0.05). Four weeks of HIIT induced widespread physiological adaptations in females, and the majority of improvements were preserved after 2 weeks of detraining except for power output corresponding to (V) over dotO(2max) and GET.