If you were reading a health or medical journal, you might suspect the acronym SIT had something to do with obesity and sedentary lifestyles. It doesn’t, at least not directly. SIT stands for “Sprint Interval Training,” and it’s become a hot topic in discussions of efficient exercise and healthier lifestyles.
Interest in SIT reached a new high this week with publication of the latest study by Martin Gibala, Ph.D., an expert in muscle metabolism, and colleagues from McMaster University. The new paper received additional coverage in the New York Times.
Gibala has been at the forefront of SIT investigations for the last decade. (SIT is also known as High Intensity Training, HIT, and High Intensity Interval Training, HIIT.) His new paper, published by PLOS One, has a says-it-all title: “Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment.”
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That’s right: Gibala is claiming that a SIT workout—10 minutes of easy exercise with three 20-second sprints interspersed—is as effective as 50 minutes of continuous, moderate effort. This may sound too good to be true, but Gibala is a highly regarded physiologist, and he performed careful calculations of VO2 max, insulin sensitivity, and mitochondrial content on his subjects. On all three fronts, the 10-minute SIT workout produced results at least as good as the 50-minute continuous moderate workout.
The subjects were mostly men in their late 20s who were healthy and modest-weight, but untrained. Given their lack of fitness at the beginning of the 12-week trial, it’s not surprising that three workouts a week increased their VO2 max by 19 percent. The surprise is that the SIT trainers gained as much as the continuous trainers on all measures, despite logging just one-fifth the training minutes.
The subjects in the study rode stationary bikes, but the study's conclusion uses the broader term “exercise,” which suggests that running sprints would have the same effects. Below, we answer questions about SIT training as they relate to our sport.
Wait a minute, aren’t sprinting and endurance running polar opposites? How can sprints enhance endurance?
One sprint is just one sprint, obviously. However, multiple sprints separated by several minutes of easy running actually constitute a very effective endurance workout, as SIT studies have consistently shown. The sprint/rest, sprint/rest nature of interval training might produce greater skeletal muscle and heart adaptations than continuous running.
I'm interested in weight control. Won’t I burn fewer calories with SIT running versus continuous running?
Yes, probably, given that you are only running about one-fifth the time. On the other hand, you’ll be burning more calories per minute, and might have a greater post-exercise calorie burn, due to the intermittent sprints. Also, as Mayo Clinic endurance exercise expert Michael Joyner, M.D., told Runner's World Newswire, “Higher intensity exercise might also suppress appetite more after running than a more modest-paced run.” Joyner and colleagues recently published a meta-analysis of SIT studies among humans, concluding, generally, that SIT training can produce positive physiological and health benefits where less vigorous training sometimes does not.
Will SIT training make me a faster runner?
It’s possible, though there is little research in this area. The new Gibala study didn’t measure performance, just certain physical markers. It didn’t aim for “optimal” improvement; it simply compared two protocols, roughly 10 minutes of SIT versus 50 minutes of moderate running. Four years ago, a study published in the Journal of Applied Physiology did measure robust 5K improvements among veteran runners who followed a 30-20-10 SIT program for seven weeks. On average, the runners dropped their 5K times from 23:03 to 22:16.
Interval training dates back to the 1940s and is no big secret among runners. Indeed, it has long been the approach of choice when runners are “peaking” for a big event. “I think every runner has known for 50 years that five or six weeks of interval training helps you prepare for races,” notes Mark Tarnopolsky, Ph.D., a coauthor of the new paper and a world class ski orienteering performer. “Intervals will ‘top up’ an already well-trained system, but you can’t keep them going for long or you get injured or flat.”
Are 20- to 30-second sprints the best way to improve running fitness?
Probably not. SIT training can give you a big bang for your buck, especially when you don’t have much time to train. However, a number of running-performance studies point to four- and five-minute intervals as the best way to increase aerobic capacity and running efficiency. In other words, run several 800- to 1600-meter repeats at about your 5K racing speed, or slightly faster.
“It would be ludicrous to train for half-marathons and longer events with just SIT workouts,” says Tarnopolsky. “You get many other adaptations from longer continuous runs that you can’t get from just intervals.”
How does SIT training fit in with public health guidelines that advise 150 minutes of exercise a week?
Actually, those guidelines acknowledge that 75 minutes of more vigorous exercise, like running at any intensity, is equivalent to 150 minutes of gentler exercise like walking. Now Gibala appears to have pared down the 75 minutes to 30 minutes. Too good to be true? There’s no way to know at this time. "We don’t have a clue about the long-term health benefits,” says Tarnopolsky. “All the exercise epidemiology studies have been done with populations working at the level of a fast walk or an easy peasy run—quite different from SIT training.”
Are there risks involved with SIT training?
Of course. Continuous running produces enough injuries on its own; faster sprint training is likely to increase the risk of injury. Though there is scant research on cardiac risks of high-intensity exercise, doctors are cautious about advising SIT workouts to their older patients. “Middle aged and sedentary people with risk factors need to be screened before doing anything high intensity,” says Joyner. “With moderate intensity exercise, most people can just start.”
Running coach Greg McMillan says he has used SIT workouts successfully with novice runners—the types who run three miles, three times a week, always at the same pace—but that he is very cautious about potential injuries. “I encourage these runners to add a pace-change run, though a little gentler than all-out sprinting, and they generally get a nice fitness boost from this,” he says. (Several SIT studies have shown that longer, slower sprints, such as 60 seconds at a time versus 20 to 30 seconds, can also lead to significant improvements in VO2 max.)
What’s the bottom line on SIT training for runners?
It has its place—a modest place, perhaps. And it's probably most useful in special situations—like for example, long trips when you don’t have much time to train but want to maintain as much fitness as possible. “I tell people all the time that they’d be amazed by what they can get from a 20-minute run that varies 60 seconds hard with 60 seconds easy,” says Joyner.
That said, few individuals can continue doing SIT workouts for long. In one seven-week study of hard intervals, the researchers wanted to add more weeks. The subjects refused to go on. The training was just too hard for them to tolerate any more. “SIT training looks great for the short term, but if you try to extrapolate to a longer term, I doubt anyone could keep up this kind of training for very long without getting injured, bored, stale,” says Tarnopolsky.
He continues: “Endurance runners need to log the miles to build tenacity, ligament and muscle toughness under fatigue, cardiac adaptations, mitochondrial biogenesis, capillary adaptations, and ability to use lipids. Then they should titrate to higher intensities to top up mitochondrial function and lactate tolerance at the speeds of their races.”
McMillan summarizes: “Ultimately, training should be well-rounded so you don’t miss any of the benefits that come from different types of endurance running. It's also important to focus on avoiding injury, so the runner can keep training and building toward their ultimate running success.”
