“If done properly, it can be safe for the vast majority of people,” says Dr. Meagan Wasfy, an instructor in medicine at Harvard Medical School and a cardiologist at Massachusetts General Hospital.
The trick is to define “high intensity” based on your fitness. For an elite athlete, high intensity might mean gruelling wind sprints, but if you’re not that fit, it might be as simple as incorporating a few brief periods of speed walking or slow jogging into your morning walk.
Getting started with interval training
While interval training is safe for most people, it might not be appropriate for those with heart problems, breathing disorders, or other medical conditions. So, as with any new exercise regimen, it’s always a good idea to get clearance from your doctor before you begin. Once you get the go-ahead, you can start incorporating intervals into your fitness program a little at a time.
Your goal should be to perform at least a half-hour exercise session five times a week, with the first five and last five minutes devoted to warm-up and cool-down, says Dr. Wasfy. The actual workout should last 20 minutes, alternating between high and low intensity for whatever activity you are performing. For example, you might swim or cycle more intensely for 30 seconds, and then slow back down for 30 seconds to recover before speeding up again. You can use longer recovery periods initially if you need to.
While these high-intensity intervals that get your heart rate up can be as short as 30 seconds, the goal should be to extend them over time, eventually working up to high-intensity intervals that are at least two minutes long.
Those short bursts of activity can considerably improve the benefits of your workout. Ultimately, “during a 30-minute workout, including warm-up and cool-down, between 10 and 15 minutes will be at high intensity,” says Dr. Wasfy. But it will be a more productive 30 minutes than it would have been using a traditional workout format. “If you think about exercise volume as calories burned or steps taken, you will get more done in the same period of time,” she says. “This is appealing to people who are fitting exercise into a busy schedule.”
Initially, you may not have the endurance to perform interval training during all your weekly workout sessions, but you can slowly build up on that end as well.
Taking cues from your body
In order to successfully incorporate interval training, you have to listen to your body and respond to it accordingly. “The downside of interval training is that any time you are pushing your body to high intensity, you may unmask symptoms of underlying health problems,” says Dr. Wasfy. For example, a heart blockage that might not bother you on a regular walk could produce symptoms during interval training. The same could be true of musculoskeletal problems — a budding knee problem could get worse quickly when you are doing high-intensity intervals. So, be certain to pay attention to your physical needs. If you notice a problem, talk with your doctor.
Fostering fitness gains
Studies show that interval training, performed safely and correctly, may help you achieve more rapid fitness gains. Those short, high-intensity bursts help your body get used to exercising at a higher level, which makes it easier for you to do more at that level over time. If you’re not getting into that zone on a regular basis, your functional fitness will stagnate, says Dr. Wasfy. For example, a brisk daily walk is great, but it won’t improve your fitness beyond a certain point if you’re not moving your body into that higher-intensity range. Challenge yourself to help increase capacity. You’ve got to feel a little uncomfortable to ratchet up your fitness level, she says. Interval training allows you to do this incrementally.
In addition to its other benefits, interval training can reduce blood pressure and other cardiovascular risk factors, as well as improve blood sugar control, research shows. The American Society of Sports Medicine says the practice can also help you lose weight — particularly that troublesome abdominal fat — and maintain muscle mass.
In addition to squeezing a better workout into a shorter period of time, interval training can jolt you out of an exercise slump by adding a little interest and excitement to a stale routine.
So, next time you work out, try incorporating intervals and take your old workout to new levels.