Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans

Parra et al. ( Acta Physiol. Scand 169: 157 - 165, 2000) showed that 2 wk of daily sprint interval training ( SIT) increased citrate synthase ( CS) maximal activity but did not change anaerobic work capacity, possibly because of chronic fatigue induced by daily training. The effect of fewer SIT sessions on muscle oxidative potential is unknown, and aside from changes in peak oxygen uptake ((V) over dot O-2 peak), no study has examined the effect of SIT on aerobic exercise capacity. We tested the hypothesis that six sessions of SIT, performed over 2 wk with 1 - 2 days rest between sessions to promote recovery, would increase CS maximal activity and endurance capacity during cycling at similar to 80% (V) over dot O-2 peak. Eight recreationally active subjects [ age = 22 +/- 1 yr; (V) over dot O-2 peak = 45 +/- 3 ml center dot kg(-1) center dot min(-1) ( mean +/- SE)] were studied before and 3 days after SIT. Each training session consisted of four to seven all-out 30-s Wingate tests with 4 min of recovery. After SIT, CS maximal activity increased by 38% (5.5 +/- 1.0 vs. 4.0 +/- 0.7 mmol center dot kg protein(-1) center dot h(-1)) and resting muscle glycogen content increased by 26% ( 614 +/- 39 vs. 489 +/- 57 mmol/kg dry wt) ( both P < 0.05). Most strikingly, cycle endurance capacity increased by 100% after SIT ( 51 +/- 11 vs. 26 +/- 5 min; P < 0.05), despite no change in (V) over dot O-2 peak. The coefficient of variation for the cycle test was 12.0%, and a control group ( n = 8) showed no change in performance when tested similar to 2 wk apart without SIT. We conclude that short sprint interval training ( similar to 15 min of intense exercise over 2 wk) increased muscle oxidative potential and doubled endurance capacity during intense aerobic cycling in recreationally active individuals.