Faster \dot{V}{\text{O}}_{ 2} kinetics after eccentric contractions is explained by better matching of O2 delivery to O2 utilization

Purpose

This study examined the impact of eccentric exercise-induced muscle damage on the rate of adjustment in muscle deoxygenation and pulmonary O₂ uptake ( \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ) kinetics during moderate exercise.

Methods

Fourteen males (25 ± 3 year; mean ± SD) completed three step transitions to 90 % θ_L before (Pre), 24 h (Post24) and 48 h after (Post48) eccentric exercise (100 eccentric leg-press repetitions with a load corresponding to 110 % of the participant’s concentric 1RM). Participants were separated into two groups: phase II \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) time constant (τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ) ≤ 25 s (fast group; n = 7) or τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\)  > 25 s (slow group; n = 7). \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) and HHb] responses were modeled as a mono-exponential.

Results

In both groups, isometric peak torque (0°/s) at Post24 was decreased compared to Pre (p < 0.05) and remained depressed at Post48 (p < 0.05). τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) was designed to be different (p < 0.05) at Pre between the Fast (τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ; 19 ± 4 s) and Slow (32 ± 6 s) groups. There were no differences among time points (τ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) : Pre, 19 ± 4 s; Post24, 22 ± 3 s; Post48, 20 ± 4 s) in the Fast group. In Slow, there was a speeding (p < 0.05) from the Pre (32 ± 6 s) to the Post24 (25 ± 6) but not Post48 (31 ± 6), resulting in no difference (p > 0.05) between groups at Post24. This reduction of τ \(\dot{V}{\text{O}}_{{2{\text{p}}}} \,\) was concomitant with the abolishment (p < 0.05) of an overshoot in the HHb]/ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ratio.

Conclusion

We propose that the sped \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) kinetics observed in the Slow group coupled with an improved HHb]/ \(\dot{V}{\text{O}}_{{2{\text{p}}}}\) ratio suggest a better matching of local muscle O₂ delivery to O₂ utilization following eccentric contractions.