Performance and physiological responses during a sprint interval training session: relationships with muscle oxygenation and pulmonary oxygen uptake kinetics

The purpose of this study was to examine the cardiorespiratory and muscle oxygenation responses to a sprint interval training (SIT) session, and to assess their relationships with maximal pulmonary O₂ uptake \( (\dot{V}{\text{O}}_{{ 2 {\text{p}}}} {\text{max)}} \), on- and off- \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \) kinetics and muscle reoxygenation rate (Reoxy rate). Ten male cyclists performed two 6-min moderate-intensity exercises (≈90–95% of lactate threshold power output, Mod), followed 10 min later by a SIT session consisting of 6 × 30-s all out cycling sprints interspersed with 2 min of passive recovery. \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \) kinetics at Mod onset (\( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{on}} \)) and cessation (\( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{off}} \)) were calculated. Cardiorespiratory variables, blood lactate ([La]_b) and muscle oxygenation level of the vastus lateralis (tissue oxygenation index, TOI) were recorded during SIT. Percentage of the decline in power output (%Dec), time spent above 90% of \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } \) (t > 90% \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } \)) and Reoxy rate after each sprint were also recorded. Despite a low mean \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \) (48.0 ± 4.1% of \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } \)), SIT performance was associated with high peak \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \) (90.4 ± 2.8% of \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } \)), muscle deoxygenation (sprint ΔTOI = −27%) and [La]_b (15.3 ± 0.7 mmol l⁻¹) levels. Muscle deoxygenation and Reoxy rate increased throughout sprint repetitions (P < 0.001 for both). Except for t > 90% \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } \) versus \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{off}} \) [r = 0.68 (90% CL, 0.20; 0.90); P = 0.03], there were no significant correlations between any index of aerobic function and either SIT performance or physiological responses [e.g., %Dec vs. \( \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{off}} \): r = −0.41 (−0.78; 0.18); P = 0.24]. Present results show that SIT elicits a greater muscle O₂ extraction with successive sprint repetitions, despite the decrease in external power production (%Dec = 21%). Further, our findings obtained in a small and homogenous group indicate that performance and physiological responses to SIT are only slightly influenced by aerobic fitness level in this population.