Very short (15s - 15s) interval-training around the critical velocity allows middle-aged runners to maintain V̇O₂ max for 14 minutes

The purpose of this study was to compare the effectiveness of three very short interval training sessions (15-15 s of hard and easier runs) run at an average velocity equal to the critical velocity to elicit V̇O₂ max for more than 10 minutes. We hypothesized that the interval with the smallest amplitude (defined as the ratio between the difference in velocity between the hard and the easy run divided by the average velocity and multiplied by 100) would be the most efficient to elicit V̇O₂ max for the longer time. The subjects were middle-aged runners (52±5 yr, V̇O₂ max of 52.1±6 mL × min^-1 × kg^-1, vV̇O₂ max of 15.9±1.8 km × h^-1, critical velocity of 85.6±1.2% vV̇O₂ max) who were used to long slow distance-training rather than interval training. They performed three interval-training (IT) sessions on a synthetic track (400 m) whilst breathing through the COSMED K4b² portable metabolic analyser. These three IT sessions were: A) 90-80% vV̇O₂ max (for hard bouts and active recovery periods, respectively), the amplitude = (90-80/85) 100=11%, B) 100-70% vV̇O₂ max amplitude=35%, and C) 60 × 110% vV̇O₂ max amplitude = 59%. Interval training A and B allowed the athlete to spend twice the time at V̇O₂ max (14 min vs. 7 min) compared to interval training C. Moreover, at the end of interval training A and B the runners had a lower blood lactate than after the procedure C (9 vs. 11 mmol × l^-1). In conclusion, short interval-training of 15 s-15 s at 90-80 and 100-70% of vV̇O₂ max proved to be the most efficient in stimulating the oxygen consumption to its highest level in healthy middle-aged long-distance runners used to doing only long slow distance-training.