Adaptations to 4weeks of high-intensity interval training in healthy adults with different training backgrounds.

Abstract

This study investigated the physical fitness and oxygen uptake kinetics ([Formula: see text]) along with the exercise-onset O2 delivery (heart rate kinetics, τHR; changes in normalized deoxyhemoglobin/[Formula: see text] ratio, Δ[HHb]/[Formula: see text]) adaptations of individuals with different physical activity (PA) backgrounds responding to 4weeks of high-intensity interval training (HIIT), and the possible effects of skeletal muscle mass (SMM) on training-induced adaptations. Twenty subjects (10 high-PA level, HIIT-H; 10 moderate-PA level, HIIT-M) engaged in 4weeks of treadmill HIIT. Ramp-incremental (RI) test and step-transitions to moderate-intensity exercise were performed. Cardiorespiratory fitness, body composition, muscle oxygenation status, VO2 and HR kinetics were assessed at baseline and post-training. HIIT improved fitness status for HIIT-H ([Formula: see text], + 0.26 ± 0.07L/min; SMM, + 0.66 ± 0.70kg; body fat, -1.52 ± 1.93kg; [Formula: see text], -7.11 ± 1.05s, p < 0.05) and HIIT-M ([Formula: see text], 0.24 ± 0.07L/min, SMM, + 0.58 ± 0.61kg; body fat, -1.64 ± 1.37kg; [Formula: see text], -5.48 ± 1.05s, p < 0.05) except for visceral fat area (p = 0.293) without between-group differences (p > 0.05). Oxygenated and deoxygenated hemoglobin amplitude during the RI test increased for both groups (p < 0.05) except for total hemoglobin (p = 0.179). The Δ[HHb]/[Formula: see text] overshoot was attenuated for both groups (p < 0.05) but only eliminated in HIIT-H (1.05 ± 0.14 to 0.92 ± 0.11), and no change was observed in τHR (p = 0.144). Linear mixed-effect models presented positive effects of SMM on absolute [Formula: see text] (p < 0.001) and ΔHHb (p = 0.034). Four weeks of HIIT promoted positive adaptations in physical fitness and [Formula: see text] kinetics, with the peripheral adaptations attributing to the observed improvements. The training effects are similar between groups suggesting that HIIT is effective for reaching higher physical fitness levels.