Association between V̇O2max and the kinetics of V̇O2 in groups differing in fitness status

Purpose This study evaluated (i) the relationship between oxygen uptake ( ̇VO2) kinetics and maximal ̇VO2 ( ̇VO2max) within groups differing in fitness status, and (ii) the adjustment of ̇VO2 kinetics compared to that of central [cardiac output (Q), heart rate (HR)] and peripheral (deoxyhemoglobin over ̇VO2 ratio ([HHb]/̇VO2)] O2 delivery, during step-transitions to moderate-intensity exercise. Methods Thirty-six young healthy male participants (18 untrained; 18 trained) performed a ramp-incremental test to exhaustion and 3 step-transitions to moderate-intensity exercise. Q and HR kinetics were measured in 18 participants (9 untrained; 9 trained). Results No significant correlation between τ̇VO2 and ̇VO2max was found in trained participants (r = 0.29; p > 0.05) whereas a significant negative correlation was found in untrained (r = − 0.58; p < 0.05) and all participants (r = − 0.82; p < 0.05). τQ (18.8 ± 5.5 s) and τHR (20.1 ± 6.2 s) were significantly greater than τ ̇VO2 (13.9 ± 2.7 s) for trained (p < 0.05). No differences were found between τQ (22.8 ± 8.45 s), τHR (21.2 ± 8.3 s) and τ ̇VO2 (28.9 ± 5.7 s) for untrained (p > 0.05). τQ demonstrated a significant strong positive correlation with τHR in trained (r = 0.76; p < 0.05) but not untrained (r = 0.61; p > 0.05). A significant overshoot in the [HHb]/̇VO2 ratio was found in the untrained groups (p < 0.05) but not in the trained groups (p > 0.05) Conclusion The results indicated that when comparing participants of different fitness status (i) there is a point at which greater VO2max values are not accompanied by faster ̇VO2 kinetics; (ii) central delivery of O2 does not seem to limit the kinetics of ̇VO2; and (iii) O2 delivery within the active tissues might contribute to the slower ̇VO2 kinetics response in untrained participants.