Just about anyone can benefit from a quick and effective way of reducing body fat. With sprint interval training, you get a fantastic return on a small investment of time and effort.
Not only is it a research-proven method of helping you trim your waistline, but sprint training improves overall fitness, boosts mood, increases insulin sensitivity, lowers blood pressure, and enhances brain function.
This article will give you a quick peek at the research into sprinting, explain why it works, and give you protocols to get started shredding the fat for a lean and healthy body composition.
It might seem like common sense that sprint interval training would be great for getting lean based on the typical physique of your competitive sprinter, but science didn’t catch on until a 1994 study that found that adding short (15-30 second) and long (60-90 second) intervals to a traditional aerobic program leads to significantly greater fat loss compared to 30 minutes of steady state aerobic exercise alone (1).
Most intriguing: The total amount of calories expended during the sprint program was half that of the aerobic program, but fat loss was nine times greater, based on skinfold measurements!
Does this mean that calories are irrelevant when it comes to fat loss? Not exactly!
Achieving an energy deficit is always necessary to lose body fat, but it does mean that the calories burned during your workout don’t matter all that much. Instead, excess post-exercise oxygen consumption (EPOC) plays a primary role in producing greater fat loss in response to sprint training. EPOC is a fancy way of saying “afterburn,” or the amount of energy you burn in the 24 to 48 hours of recovery after a tough workout.
The intensity of exercise plays a major role in elevating EPOC, which means that because interval training is often performed at “all-out” intensities, it triggers an afterburn that can make up and surpass the greater amount of energy burned during steady-state exercise.
For instance, a 2012 study compared energy expenditure following 30 minutes of aerobic exercise with four 30-second sprints and found that the amount of calories burned during the workout was 150 percent greater with the aerobic protocol than the sprints (2). However, when researchers looked at the 24-hour period that included the workouts, the sprint group had “caught up” with the aerobic group and energy expenditure was equal between them. A number of reasons contribute to the elevation in metabolism that occurs following sprinting:
Body temperature is elevated
Lung and heart activity are increased as the body recovers
Lactate and hydrogen must be removed
Energy stores in muscle must be restored
Fat burning hormones like epinephrine are increased
This was followed by two studies (one on men (3) and one using women (4)) that found that 20 minutes of short, all-out intervals (8 seconds on, 12 seconds active rest) on a stationary bike produced significant fat loss. In the men’s study, subjects lost 2 kg of body fat, gained 1.2 kg of lean muscle mass, and reduced body fat percentage by 5.7 percent.
In the women’s study, subjects lost 2.5 kg of body fat and lost a significant amount of belly fat. Most important: The women’s study also had a group that did 40 minutes of aerobic exercise for comparison. The aerobic training group actually gained 0.44 kg of body fat. Despite exercising for half the time, the sprint group lost 11.2 percent of total fat mass whereas the aerobic group gained fat.
Now, don’t get confused and conclude that aerobic exercise leads to fat gain!
That’s certainly not what happened here. Rather, it’s much more likely that the women in the aerobic training group started eating more and gained fat because they were “compensating” for energy burned during workouts. An increased appetite is one documented effect of some exercise programs, and it seems to be more common in response to aerobic than anaerobic forms such as weight training or intervals.
In fact, one reason that sprint training is thought to be so effective is that it may reduce perceptions of hunger so that you eat less. Unfortunately, due to the inherent problems with diet journals (people hopelessly mis-record how much they eat) studies haven’t been able to nail down how much of a role reduced appetite factors into fat loss from interval training.
However, we do know from animal studies that intense exercise leads to the release of appetite suppressing hormones such as corticotropin-releasing hormone. Additionally, during exercise you experience a decrease in blood flow to the GI tract, which may lower hunger in the few hours post-workout (5).
A third factor that plays a role in the fat loss effect is the release of fat burning hormones. A study from Canada found that normal-weight women who did 6 weeks of sprint training (4 to 6 maximal 30 second running sprints on a treadmill) lost 1.2 kg of body fat, shrank their waistlines by 3.5 percent, and gained 0.6 kg of lean muscle (6).
Researchers point to the fact that sprints are a catalyst for improving the body’s ability to burn fat. Higher intensity exercise requires more energy, which leads to the release of growth hormone and the catecholamines, both of which drive fat burning in the body (7). Fat burning is key because if you eat a high-carb diet, your body won’t have the enzymes and other “metabolic machinery” to burn fat effectively, which makes you more prone to food cravings and increased appetite. This is most true if you are sedentary or don’t exercise frequently.
Best of all: Sprints are thought to increase activity of one type of fat receptors (B-adrenergic receptors) that are localized in the abdominal region. This means that sprinting has a much greater effect on reducing belly fat than more moderate forms of exercise like aerobic training!
So there you have it: The three mechanisms behind the fat loss effect of sprint training are:
#1: Increased EPOC: Elevated metabolism and greater calorie burn in the extended recovery period after your workout.
#2: Increased fat burning due to greater release of catecholamines and growth hormone.
#3: Reduced appetite, allowing for lower food intake.
You’re probably wondering how you can get started with sprint training. What follows are protocols and tips for getting the best results:
#1: If you’re overweight and sedentary, start with stationary bike sprints. Try repeated 8-second sprints followed by 12 seconds easy pedaling. Start with 5 minutes of this, working up to 20 minutes total.
#2: Another option for novices is to try high-intensity efforts of 1 minute followed by 1-minute rest repeated 10 times for a total of 20 minutes.
#3: If you’re fit but need to lose fat, try the Wingate protocol, which is 30 seconds of all-out effort followed by 4 minutes of recovery. Repeat 4 to 6 times. This protocol can be done on a stationary bike, on a track (intervals can be 200 meters), or pushing a weighted sled.
#4: If you like to take things a little slower, try 5 repeats of 3 minutes at a moderate intensity interspersed with 1 to 3 minutes of active rest (8).
#5: You can also try a descending distance protocol: Run 400 meters, then rest 4 minutes, run 300 meters, rest 3 minutes, sprint 200 meters, rest 2 minutes, and sprint 100 meters.
#6: Remember to always start with a quick 5-minute warm-up to raise body temperature and prime the muscles for the intense effort.
#7: Do sprints 2 to 4 days a week on alternate days. If you’re also doing strength training, 2 days of sprinting is sufficient. If sprints are you primary form of exercise 3 to 4 days a week is ideal.
#8: Best results will come if you are consistent with workouts. Significant body composition changes should be visible within 6 weeks.
#9: Sprint against resistance whenever possible. Use a resisted bike, rowing machine, hills, stairs, or a weighted sled. This will provide sufficient overload to trigger an increase in lean muscle mass.
#10: Sprinting is a highly effective training model for reducing body fat without the need to diet or cut calories. That said, it’s still important to watch out that you aren’t eating more calories than normal, either as a “reward” to yourself or because you’re not recovering optimally and stress hormones are becoming elevated, increasing hunger.