Sprint interval training is a powerful tool that gives you back considerably more in terms of health and performance than the effort required. This makes sprinting, and the related high-intensity protocols, the most effective way to get in shape as quickly as possible.
Now, sprinting can be a bit unpleasant. It is mentally challenging due to the physiological stress it causes, but it’s well worth the effort. It takes much less time than slower, aerobic protocols and gives you the following greater benefits:
Better body composition with more lean muscle and less body fat
Increased power and strength capacity
Improved metabolism and mitochondrial density
Greater work capacity and resistance to stress
Better heart, lung function, and circulation
Improved insulin sensitivity and ability to oxidize (burn) fat for energy
Better brain function and enhanced learning potential
The intriguing thing about interval training is that it requires a relatively small dose to convey these pretty incredible health effects. It works like this:
The harder you work, the less time you need to work for. If you prefer your pain to be intense but short, maximal sprints will be amazingly beneficial. For example, performing 4 to 6 all-out sprints 3 times a week can provide all the benefits listed above.
However, the reality for a lot of people is that they’re under enough “maximal” stress in their daily life. Moderate intensity intervals are more realistic. An example, is intervals of 1 minute or longer that are performed at 80 to 90 percent of maximal with an equal or 2:1 work-to-rest ratio.
This article will provide examples of both so that you can pick your poison based on your lifestyle and training goals.
#1: Use short all-out sprints to lose body fat, build muscle, and improve metabolism.
Short all-out sprints can help women who are fairly new to exercise to lose body fat and improve health. For instance, a study of 45 young women found that 15 weeks of interval training three times a week produced an impressive average loss of 2.5 kg of body fat and increase in lean mass of 0.6 kg. The women also lost 0.15 kg of belly fat, which looks like a small amount but is significant due to its location around the organs.
This study was noteworthy because it compared interval cycle sprints (8-second sprint followed by 12 seconds of low-intensity cycling, repeated 60 times for a total of 20 minutes) with steady-state cycling for 40 minutes. In half the training time, the interval group improved body composition, whereas the steady-state group gained an average of 0.4 kg, or about a pound.
Within the interval training group, the leaner women lost less body fat than those who originally had more body fat. With the four leanest women removed from calculations, average fat loss was 4 kg, suggesting that sprint training is well worth the effort if you’re overweight and want to improve health.
The interval trainees’ metabolism was also revved up by the end of the study as seen by lower fasting insulin levels and decreases in concentration of the hormone leptin.
Use It: An 8-seconds on, 12-seconds off interval protocol done three times a week is ideal for women who are new to interval training or have not been engaged in intense training recently. Longer intervals are indicated for trained women and athletes, although that doesn’t mean they couldn’t use this protocol for a few weeks for variety.
#2: Try a Wingate protocol (4 to 6 x 30s. all-out sprints) to improve conditioning and endurance.
The well-known Wingate protocol, which uses 30-second maximal intervals, can help athletes get in shape and everyday folks improve body composition and health.
For instance, a study of female soccer players who did Wingate running intervals improved high-intensity work capacity and overall conditioning by 42 percent more than a group of players who did endurance running. The interval training took about half the training time as the endurance workouts.
What about losing body fat with the Wingate protocol?
It’s possible, however results from studies are mixed. One trial found that compared to men, women lost no body fat but men lost 3 kg from doing the same interval workout for 6 weeks.
Scientists think the discrepancy in body fat loss may be due to the small study size or the fact that the women were already fairly lean at the beginning of the study.
Another possibility is that Wingate is not the best choice for women who want to lose fat because they seem to rely on aerobic pathways for energy production more than men do. This means that maximal intensity training may not by the best choice for women who don’t need to be able to produce explosive strength for sports.
Use It: The best interval protocol will be unique to the individual. Female athletes will benefit from higher intensity repeats with 2 to 4 minutes rest, whereas women who are fairly lean and in shape may want to opt for longer, more moderate intervals to improve body composition.
#3: High but not maximal intensity intervals may yield better results for trained women to improve body composition and health.
Comparison studies of how men and women respond to interval training show that men achieve higher peak power but women achieve higher heart rate maximum values, which they are able to maintain over the course of a workout.
Women also deplete ATP more slowly and appear to recover more quickly than men. Scientists suggest longer, submaximal intervals of 1 minute or longer at a 2:1 work-to-rest ratio may be most appropriate for eliciting gains in trained women.
Other benefits of studies using longer, more moderate intervals include better heart rate variability, decreased blood pressure, improved lung function and better overall heart function. Intervals also shift the body into fat burning mode, while increasing insulin sensitivity and blood sugar tolerance. Finally, intervals have even been shown to decrease inflammation in the brain and improve brain volume for mental quickness.
Use It: Try 1 to 2 minute intervals at 80 to 90 percent of maximal with a 2:1 or 3:1 work-to-rest ratio. A place to start is with 1-minute intervals with 30 seconds active rest.
Use a larger ratio with shorter rest to produce greater metabolic stress if the goal is fat loss. A smaller ratio with longer rest will be a bit less mentally challenging but is still enormously effective for improving health.
#4: Work hard, but don’t over do it. Research suggests 2 to 4 high-intensity workouts a week may be optimal for women.
Training too hard too frequently is an increasingly common pitfall to high-intensity training. Humans tend to think that if a little is good, more will be better. Not so.
In theory, high-intensity training requires 48 to 72 hours for the central nervous system to recover. Training frequency should be 2 to 4 days a week, depending on the exact intensity of the workouts.
For instance, a recent study found that high-intensity training leads to fatigue of the sympathetic nervous system and reduced ability of the body to regulate blood pressure and heart rate for optimal function.
If you allow adequate rest, the nervous system will rebound and recover, making you stronger in the long run. But with daily high-intensity workouts, or worse, two-a-days, the nervous system becomes suppressed. Cortisol and the other stress hormones are dysregulated, and you experience diminishing returns or actual harm to the body.
Too frequent training may have other negative effects. A recent study of older women compared the effect of doing a combined strength and endurance program either 2, 4, or 6 times a week. Results showed that all groups lost body fat, but there was almost no difference in fitness gains among the groups.
However, the women exercising four times a week increased total energy expenditure the most (by about 225 calories a day), whereas the group that trained six times a week had reduced their energy expenditure (by about 200 calories a day).
Scientists believe that the high frequency training led the women to be less active overall because it was too stressful. The women didn’t say they were more tired, but they did feel that 6-day-a-week training took too much time.
This wasn’t an interval training study, but it lends caution to anyone who thinks that more is always better. The key is to find that sweet spot of a potent dose of intensity that you apply with as much effort and intention as possible a few days a week.
Use It: Interval training should be done 2 to 4 times a week, depending on intensity. For example, pairing two strength training workouts with two interval workouts should leave adequate time for recovery. Keep 48 to 72 hours between workouts that tax the neuromuscular system (strength workouts with low reps and heavy loads) or muscle damaging workouts (eccentric training).
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Sewright, K., et al. Sex Differences in Response to Maximal Eccentric Exercise. Medicine and Science in Sports and Exercise. 2008. 40(2). 242-251.
Flores, D., et al. Dissociated Time Course of Recovery Between Genders after Resistance Exercise. Journal of Strength and Conditioning Research. 2011. 25(11). 3039-3044.
Rowan, A., Kueffner, T., et al. Short Duration High-Intensity Interval Training Improves Aerobic Conditioning of Female College Soccer Players. International Journal of Exercise Science. 2012. 5(3), 232-238.
Laurent, M., et al. Sex Specific Responses to Self-Paced, High-Intensity Interval Training with Variable Recovery Periods. Journal of Strength and Conditioning Research. 2013. Published Ahead of Print.
Heydari, M., Freud, J., et al. The Effect of High-Intensity Intermittent Exercise on Body Composition of Overweight Young Males. Journal of Obesity. 2012. Published Ahead of Print.
Macpherson, R., Hazell, T., et al. Run Sprint Interval Training Improves Aerobic Performance but Not Maximal Cardiac Output. Medicine and Science in Sports and Exercise. 2011. 43(1), 115-121.
Trapp, E., Chisholm, D., et al. The Effects of High-Intensity Intermittent Exercise Training on Fat Loss and Fasting Insulin Levels of Young Women. International Journal of Obesity. 2008. 32(4), 684-691.