'Resistance Training' Better for Weight Loss
Resistance training increases type II muscle fibers for picking up heavy loads.
When it comes to losing weight, and preventing diabetes, pumping iron could play a much more important role than previously recognized.
The discovery that "resistance training" such as weightlifting is as significant in helping obese people to shed pounds as "endurance training", such as running, has been made with mice genetically altered to be strong and muscular.
The discovery, which also suggests why aging makes it harder to lose weight, builds upon the fact that there are two types of muscle fiber.
Endurance training such as running increases the amount of type I muscle fibers, linked with endurance, while resistance training such as weightlifting increases type II muscle fibers that help us pick up heavy loads, and quickly.
Now, using genetically altered mice, a team at Boston University reports in the journal Cell Metabolism that an increase in type II muscle mass linked with pumping iron can reduce body fat which in turn reduces overall body mass and risk of adult diabetes.
The team used a genetic trick in obese mice that caused the mice's muscles to bulk up with type II muscle as though they had been lifting weights and found that the "genetically reprogrammed" mice, as well as being stronger, lost fat and showed other signs of metabolic improvement throughout the body, such as less fatty livers.
What's more, those benefits were seen even though the mice continued eating a diet high in both fat and sugar and didn't increase their physical activity at all.
"We've shown that type II muscle does more than allow you to pick up heavy objects," says Prof Kenneth Walsh of Boston University School of Medicine, who developed the "MyoMouse". "It is also important in controlling whole-body metabolism."
"Resistance training builds the white meat," Prof Walsh says, referring to the relatively mitochondria-poor type II muscle. "There is some evidence it's good for you, but it's not immediately clear why. Now, we've provided a scientific rationale."
"These findings indicate that type II muscle has a previously unappreciated role in regulating whole-body metabolism through its ability to alter the metabolic properties of remote tissues," the researchers concluded.
"These data also suggest that strength training, in addition to the widely prescribed therapy of endurance training, may be of particular benefit to overweight individuals."
The study also sheds new light on middle age spread and sag. "Beyond the age of 30, humans lose approximately six lbs of muscle mass per decade. Surprisingly, ageing individuals predominantly lose type II muscle.
"Thus a 50 year old may be relatively good at playing tennis or jogging because type I muscle is preserved, but a measurement of grip strength or core body strength could show appreciable declines," explains Prof Walsh. Therefore, this new study suggests that the loss of type II muscle contributes to the development of obesity and diabetes as we age.
The team suspects that the beneficial effects of muscle growth seen in the MyoMouse are controlled by the production and secretion of a variety of signaling factors. Prof Walsh and his colleagues are currently identifying the novel proteins in muscle that communicate with other tissues.
These new proteins, referred to as "myokines" from the Greek words "muscle" and "motion," may represent new targets for therapies that mimic the benefits of weight training for the treatment of obesity and diabetes as well as muscle wasting disorders.
"The work shows that boosting muscles in "at-risk" human populations may prove to be critical weapons in the fight against obesity and obesity-related co-morbidities including diabetes, heart disease, stroke, hypertension, and cancer," say Brooke Harrison and Leslie Leinwand of the University of Colorado at Boulder in a commentary.
Obesity rates in the UK have quadrupled over the past 25 years. In England alone, 22 per cent of men and 23 per cent of women were classified as obese in 2002, according to figures from the Economic and Social Research Council. A total of 43 per cent of men and 34 per cent of women met the lesser criteria for being overweight.
By Roger Highfield, Science Editor
Published: 5:00PM GMT 05 Feb 2008