Association between V ˙ O₂ kinetics and V ˙ O_2max in groups differing in fitness status

Purpose: This study evaluated (i) the relationship between oxygen uptake (V ˙ O₂) kinetics and maximal V ˙ O₂ (V ˙ O_2max) within groups differing in fitness status, and (ii) the adjustment of V ˙ O₂ kinetics compared to that of central [cardiac output (Q̇), heart rate (HR)] and peripheral (deoxyhemoglobin over V ˙ O₂ ratio ([HHb]/V ˙ O₂)] 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. Q̇ and HR kinetics were measured in 18 participants (9 untrained; 9 trained). Results: No significant correlation between τ̇V ˙ O₂ and V ˙ O_2max 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). τQ̇ (18.8 ± 5.5 s) and τHR (20.1 ± 6.2 s) were significantly greater than τV ˙ O₂ (13.9 ± 2.7 s) for trained (p < 0.05). No differences were found between τQ̇ (22.8 ± 8.45 s), τHR (21.2 ± 8.3 s) and τV ˙ O₂ (28.9 ± 5.7 s) for untrained (p > 0.05). τQ̇ 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]/V ˙ O₂ 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 V̇O_2max values are not accompanied by faster V ˙ O₂ kinetics; (ii) central delivery of O₂ does not seem to limit the kinetics of V ˙ O₂; and (iii) O₂ delivery within the active tissues might contribute to the slower V ˙ O₂ kinetics response in untrained participants.