Aerobic high-intensity intervals improve (V)over dotO2max more than supramaximal sprint intervals in females, similar to males

Introduction: Maximal oxygen uptake ((V)over dotO(2max)) is a pivotal factor for aerobic endurance performance. Recently, aerobic high-intensity interval training (HIIT) was documented to be superior to sprint interval training (SIT) in improving (V)over dotO(2max) in well-trained males. However, as mounting evidence suggests that physiological responses to training are sex-dependent, examining the effects of HIIT versus SIT on (V)over dotO(2max), anaerobic capacity, and endurance performance in females is warranted. Methods: We randomized 81 aerobically well-trained females (22 +/- 2 years, 51.8 +/- 3.6 mL center dot kg(-1)center dot min(-1) (V)over dotO(2max)), training three times weekly for 8 weeks, to well-established protocols: (1) HIIT 4 x 4 min at similar to 95% of maximal aerobic speed (MAS), with 3 min active recovery (2) SIT 8 x 20 s at similar to 150% of MAS, with 10 s passive recovery (3) SIT 10 x 30 s at similar to 175% of MAS, with 3.5 min active recovery. Results: Only HIIT 4 x 4 min increased (V)over dotO(2max) (7.3 +/- 3.1%), different from both SIT groups (all p < 0.001). Anaerobic capacity (maximal accumulated oxygen deficit) increased following SIT 8 x 20 s (6.5 +/- 10.5%, p < 0.05), SIT 10 x 30 s (14.4 +/- 13.7%, p < 0.05; different from HIIT 4 x 4 min, p < 0.05). SIT 10 x 30 s resulted in eight training-induced injuries, different from no injuries following HIIT 4 x 4 min and SIT 8 x 20 s (p < 0.001). All groups improved long-distance (3000-meter) and sprint (300-meter) running performance (all p < 0.001). SIT protocols improved sprint performance more than HIIT 4 x 4 min (p < 0.05). Compared to previous male results, no increase in (V)over dotO(2max) following SIT 8 x 20 s (p < 0.01), and a higher injury rate for SIT 10 x 30 s (p < 0.001), were evident. Conclusions: In aerobically well-trained women, HIIT is superior to SIT in increasing (V)over dotO(2max) while all-out treadmill running SIT is potentially more harmful.