AbstractAim: The present study examined the effects of 10 x 30-second and 8 x 20-second supramaximal interval training (SIT) on maximal oxygen consumption (VO2max), running economy (RE), lactate threshold (LT), anaerobic capacity (AC) and running performance (300- and 3000m) in a group of moderately trained females. The rating of perceived exhaustion (RPE) was also addressed during training. Methods: 23 healthy, non-smoking, moderately endurance-trained females (52.4 ± 3.9 mL·kg-1·min-1 VO2max) were randomized to run either 10 x 30-second all-out sprints interspersed by 3.5 min of low intensity (< 70 % HRmax) active recovery (Sprint, n = 10) or 8 x 20-second sprints at ~ 150 % of maximal aerobic speed (MAS) separated by 10 seconds of static recovery (Tabata, n = 13), 3 times a week for 8 weeks. Results: VO2max remained unchanged in both training groups. Tabata improved RE (mL·kg-0.75·m-1) by 2.3 % and velocity at LT by 1.2 %. AC (O2 deficit, mL·kg-1) increased by 9.6 and 8.4 % for Tabata and Sprint, respectively. 300m performance improved by 5.6 % following Tabata and 6.7 % following Sprint. Performance on 3000m improved by 4.6 % for the Tabata group and 4.0 % for the Sprint group. There was no significant difference in change for any physiological or performance variable between groups. Tabata participants reported a significantly higher RPE (Borg scale) of 18.5 ± 0.7 versus 17.6 ± 1.1 reported by the Sprint group. Conclusion: 10 x 30-second and 8 x 20-second SIT are inefficient strategies at improving VO2max for moderately trained females, likely due to lack of taxation on the central cardiovascular system. However, both SIT protocols are effective choices if the goal is to improve AC and running performance. Due to a significantly lower time commitment and injury risk, Tabata would be the recommended alternative despite being the more exhausting of the two.