Six high-intensity interval training sessions over 5 days increases maximal oxygen uptake,endurance capacity,and sub-maximal exercise fat oxidation as much as 6 high-intensity interval training sessions over 2 weeks

Background:High-intensity interval training(HIIT)induces similar or even superior adaptations compared to continuous endurance training.Indeed,just 6 HIIT sessions over 2 weeks significantly improves maximal oxygen uptake(VO_(2max)),submaximal exercise fat oxidation,and endurance performance.Whether even faster adaptations can be achieved with HIIT is not known.Thus,we aimed to determine whether 2 sessions of HIIT per day,separated by 3 h,every other day for 5 days(double HIIT(HIIT-D),n=15)could increase VO_(2max),submaximal exercise fat oxidation,and endurance capacity as effectively as 6 sessions of HIIT over 2 weeks(single HIIT(HIIT-S),n=13).Methods:Each training session consisted of 10×60 s of cycling at 100%of VO_(2max)interspersed with 75 s of low-intensity cycling at 60 watt(W).Pre-and post-training assessments included VO_(2max),time to exhaustion at-80%of VO_(2max),and 60-min cycling trials at-67%of VO_(2max).Results:Similar increases(p<0.05)in VO_(2max)(HIIT-D:7.7%vs.HIIT-S:6.0%,p>0.05)and endurance capacity(HIIT-D:80.1%vs.HIIT-S:79.2%,p>0.05)were observed.Submaximal exercise carbohydrate oxidation was reduced in the 2 groups after exercise training(HIIT-D:9.2%,p=0.014 vs.HIIT-S:18.8%,p=0.012)while submaximal exercise fat oxidation was significantly increased in HIIT-D(15.5%,p=0.048)but not in HIIT-S(9.3%,p=0.290).Conclusion:Six HIIT sessions over 5 days was as effective in increasing VO_(2max)and endurance capacity and was more effective in improving submaximal exercise fat oxidation than 6 HIIT sessions over 2 weeks.