Weight Training and Metabolism

By Miranda Hitti

WebMD Health News
Reviewed by Louise Chang, MD

Feb. 5, 2008 -- Weight training may be a health boon for overweight people, new research shows.

Boston University scientists report that "strength training, in addition to ... endurance training, may be of particular benefit to overweight individuals."

The researchers aren't talking about fitting into a smaller-sized pair of jeans or shrinking the numbers on the scale. Instead, they're focused on the metabolism benefits of getting stronger at any size.

Here's their key finding from lab tests on mice: Stronger muscles means more fat burned and a perkier metabolism, even with less-than-stellar diet and exercise habits.

But there's a catch. Muscles don't stay that way without work, so you've got to be in it for the long haul to keep reaping the benefits.

Yasuhiro Izumiya, MD, PhD, and colleagues used genetic engineering to turn a certain muscle gene off and on in mice.

When the gene was on, the mice got a lot more muscular and stronger, mimicking the effects of weight training.

But when the gene was switched off, the mice lost their buff physiques, as if they'd slacked off a strength-training program.

Those mice shed more fat, had livelier metabolisms, and responded better to insulin (a hormone made by their bodies to control blood sugar) when they were muscular.

That pattern held even when the mice ate fatty, sugary chow and didn't get much exercise. However, those mice did wind up fatter than active mice on a healthier diet.

The mice's metabolic benefits stemmed from their type 2 muscle fibers, which are strengthened by weight training, Izumiya's team notes in Cell Metabolism.

But strength training is just one part of fitness. In Izumiya's study, when the mice got very muscular, their grips became stronger, but they didn't fare too well on a treadmill test. So while weight training may help with weight loss, endurance training is still important.