This study compared the effects of 12-week sprint interval training (SIT), high-intensity interval training (HIIT), and moderate-intensity continuous training (MICT) on cardiorespiratory fitness (VO2peak), body mass and insulin sensitivity in overweight females. Forty-two overweight women (age 21.2 +/- 1.4 years, BMI 26.3 +/- 2.5 kg/m2) were randomized to the groups of SIT (80 x 6-s sprints plus 9-s rest), and isoenergetic (300KJ) HIIT (approximately 9 x 4-min cycling at 90% VO2peak plus 3-min rest) and MICT (cycling at 60% VO2peak for approximately 61-min). Training intervention was performed 3 d/week for 12 weeks. After intervention, all three groups induced the same improvement in VO2peak (approximately +25%, p < 0.001) and a similar reduction in body mass (approximately -5%, p < 0.001). Insulin sensitivity and fasting insulin levels were improved significantly on post-training measures in SIT and HIIT by approximately 26% and approximately 39% (p < 0.01), respectively, but remain unchanged in MICT. In contrast, fasting glucose levels were only reduced with MICT (p < 0.01). The three training strategies are equally effective in improving VO2peak and reducing body mass, however, the SIT is time-efficient. High-intensity training (ie, SIT and HIIT) seems to be more beneficial than MICT in improving insulin sensitivity.

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