May 7, 2015

Hazell, T. J., Hamilton, C. D., Olver, T. D. and Lemon, P. W. 2014. Running sprint interval training induces fat loss in women. Appl Physiol Nutr Metab. 39(8): 944-950.

Over the past decade, an extreme form of high-intensity interval exercise training known as sprint interval training (SIT) has gained popularity. This form of exercise has participants complete repeated, brief, but intense exercise durations separated by a short recovery period (typically 4-6, 30 s maximal efforts with ~4 min recovery between each bout), at a frequency of 3 times per week for 4-6 weeks. Interestingly, studies on SIT have demonstrated similar cellular and aerobic performance adaptations as well as greater losses of body fat vs traditional endurance exercise (30-60 min at low to moderate exercise intensities). Further, all of this with a fraction of the time commitment. With overweight or obesity reaching epidemic proportions among Canadians and because of the associated adverse health consequences, the role of SIT as a method to reduce body fat is intriguing. This is especially so with women because, without significant changes in dietary habits, endurance exercise is relatively ineffective at improving body composition when compared to men.

In this study, we assessed body composition in young, healthy recreationally active (but not systematically exercise-trained) women (body fat = 25% of body mass). The women completed 4-6 repeated 30 sec maximal exercise efforts on a self-propelled treadmill, 3 times per week for 6 weeks. This training induced an 8% (1.2 kg) reduction in fat mass, a 3.5% (2.8 cm) reduction in waist circumference, and a small 1.3% (0.6 kg) increase in fat-free mass (likely muscle) in addition to several exercise performance-enhancing effects. While it is currently unknown exactly how the brief but very intense exercise bouts that characterize SIT result in these body fat losses, other research from our group has demonstrated a small and prolonged increase in post-exercise metabolism, a tendency for an increased post-exercise fat metabolism, minimal changes in appetite or satiety, and a greater adherence rate compared to endurance exercise. Further study is needed to sort out the details but it appears SIT leads to significant improvements in body composition in as little a time period as 4-6 weeks.

Today, many Canadians are searching for time-efficient ways to improve their body composition, with a primary desire to decrease fat mass. In this regard, our data suggest that SIT may be a suitable exercise prescription to achieve these goals, especially as it requires very little time commitment. Importantly, many of our participants have continued this type of training long after the completion of our studies suggesting it is not difficult to make this part of one’s long term routine. Finally, although these effects are considerable and exercise should be a part of any healthy lifestyle, it is important to appreciate that SIT involves maximal exercise efforts that may not be best for everyone. Consequently, starting with a more moderate approach is recommended for those who have not been exercising in the recent past. Finally, the optimal length of the SIT exercise bouts is unclear as there is evidence that shorter (10-15 sec) and longer (45-60 sec) bouts are effective, though the total calorie expenditure varies, suggesting that the stimulus is more related to exercise intensity than duration.


Hazell, T. J., Hamilton, C. D., Olver, T. D. and Lemon, P. W. 2014. Running sprint interval training induces fat loss in women. Appl Physiol Nutr Metab. 39(8): 944-950.

If you intend citing any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.