Cardiorespiratory and Neuromuscular Improvements Plateau after Two Weeks of Sprint Interval Training in Sedentary Individuals.

INTRODUCTION: Previous studies ranging from 2 to 12 weeks of sprint interval training (SIT) have reported improvements in maximal oxygen uptake (V̇O2max) and neuromuscular function in sedentary populations. However, whether the time course of the changes in these variables correlate with greater training volumes, is unclear.

METHODS: 13 sedentary participants performed three all-out training weekly sessions involving 15-s sprints interspersed with 2 minutes of recovery on a cycle-ergometer. The 6-week training program was composed of three identical blocks of 2-weeks in which training volume was increased from 10 to 14 repetitions over the first four sessions and reduced to 8 in the last session. The power output and the heart rate (HR) were monitored during the sessions. The V̇O2max, the power-force-velocity profile (PFVP) and the isometric force were assessed every two weeks from baseline.

RESULTS: A significant increase in V̇O2max was observed from the second week plateauing thereafter despite four additional weeks of training. The dynamic force production increased from the second week and the speed production decreased by the end of the protocol. The isometric force and the maximal power output from the PFVP did not change. Importantly, the time spent at high percentages of the maximal HR during the training sessions was lower in the second and third training block compared to the first.

CONCLUSIONS: SIT resulted in a effective approach for rapidly increasing V̇O2max and, no change in the isometric force was found, cycling-specific neuromuscular adaptations were observed from the second week of training. SIT may be useful in the short-term but further improvement of overall physical fitness might need other training modalities like endurance and/or resistance training.