Short Bursts or Steady Miles? Interval Training and Body Fat

Interval training, short hard efforts mixed with rest, is one of the most popular ways to exercise. Steady, moderate cardio has been around much longer. If your goal is to lose body fat, does it matter which you choose? This guide looks at a well-known review that compared them. It is general education, not medical advice.

What was compared

A 2017 meta-analysis in Obesity Reviews by Wewege and colleagues looked for trials comparing high-intensity interval training with moderate-intensity continuous training in overweight or obese adults aged 18 to 45. It screened 1,334 articles and included 13 studies. On average the programs lasted about 10 weeks with three sessions a week.

How they compared

• Both worked. Both types of training significantly reduced whole-body fat mass and waist size.
• No clear winner. The reviewers found no significant difference between the two on any body composition measure. For running, the effect sizes for fat mass were almost identical: -0.82 for interval training and -0.85 for continuous training.
• Time was the difference. Interval training took about 40 percent less training time.
• The type of exercise mattered. The cycling studies did not show a fat loss effect in this review.

The authors concluded that short-term moderate to high-intensity exercise can modestly improve body composition, even without a change in body weight, and that interval training may be a time-efficient part of a weight management plan.

What that means for choosing

• Pick what you will keep doing. If you enjoy short bursts, they fit a busy day. If you prefer a steady walk, jog or ride, that works as well for body fat in these studies.
• Time is a real factor. Fitting in 20 minutes of intervals can be easier than 35 minutes of steady effort.
• Mix them. Many people alternate, and variety can keep exercise interesting.

Limits to keep in mind

• The programs were short. About ten weeks is a good start, but it does not show what happens over years.
• The changes were modest. The reviewers describe modest improvements in body composition, and nutrition has a large effect on weight.
• The people studied were adults under 45. The results may not apply the same way to older adults.
• Intense exercise is not for everyone. If you have heart disease, high blood pressure, joint problems or have been inactive for a long time, talk with a clinician before starting high-intensity workouts. Beginning gently is fine.

Putting it into practice

• Try a simple pattern. For example, a minute of brisk effort followed by a minute or two of easy walking, repeated several times, with a warm-up before and a cool-down after.
• Use the talk test. A hard effort should leave you breathing quickly but not struggling.
• Add strength work. Cardio does not replace muscle building. Our guide to strength training for beginners explains why it matters.
• Keep the easy days easy. Our guides to zone 2 cardio and how much exercise helps with weight cover the steadier side.

In short

For body fat, short bursts and steady miles did about equally well in these studies, and the bursts took less time. That means the best exercise is often the one that fits your life and that you enjoy enough to repeat.

Sources

• Wewege M, van den Berg R, Ward RE, Keech A. The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis. Obesity Reviews, 2017;18(6):635-646.