Body builders’ muscles show surprising benefits
PUMPING iron could play a previously unrecognised role in preventing obesity and diabetes, new research suggests. Scientists made the surprise discovery that body builders’ ‘‘ type II’’ muscle helps to reprogram the whole body’s metabolism.
The findings suggest that resistance training gym sessions may be part of the answer to keeping people trim and healthy.
It had been widely assumed that only aerobic endurance exercise, such as running or swimming, had any significant influence on the body’s energy balance.
This kind of exercise produces ‘‘ type I’’ muscle containing ‘‘ slow’’ fibres full of mitochondria, the tiny powerhouses in cells that burn fuel to generate energy.
Type I muscle enables marathon runners to keep going without getting tired.
In contrast, type II muscle produces the ability to lift heavy loads or show a sprinter’s short burst of speed, but little staying power.
Scientists in the US created a mouse dubbed ‘‘ MyoMouse’’ that could be made to bulk up with type II muscle simply by switching on a growth-regulating gene called Akt1.
When the switch was turned off, and the mice were fed an eight-week sugary diet with a caloric composition similar to human ‘‘ fast food’’, they grew obese.
The animals also became insulin resistant, an early sign of diabetes, and developed fatty deposits in their livers — a condition seen in humans and known as fatty liver disease.
Activating the Akt1 gene immediately led to the growth of type II muscle fibres.
But instead of producing strong and fat ‘‘ sumo’’ mice, as many of the researchers had expected, the switch resulted in animals that lost weight.
Blood tests showed that the mice also became metabolically normal, and they were cured of fatty liver disease.
The beneficial changes occurred even when the mice continued to eat a high calorie diet without taking extra exercise.
‘‘ This work shows that type II muscle doesn’t just allow you to pick up heavy objects, it is also important in controlling whole body metabolism,’’ says study leader Professor Kenneth Walsh, from Boston University School of Medicine in Massachusetts.
Further analysis revealed that the physiology and gene activity of fat and liver cells in the mice had been altered.
The researchers suspect that signalling molecules secreted by muscles may be involved.
They are currently in the process of identifying novel proteins in muscle that communicate with other tissues.
The proteins, referred to as ‘‘ myokines’’ from the Greek words ‘‘ muscle’’ and ‘‘ motion’’, may provide new targets for obesity and muscle wasting drug treatments.
Reporting their findings in the journal Cell Metabolism, the researchers concluded: ‘‘ These data... suggest that strength training, in addition to the widely prescribed therapy of endurance training, may be of particular benefit to overweight individuals.’’
The results may also provide new insight into certain aspects of ageing.
‘‘ Beyond the age of 30, humans lose approximately six pounds (2.7 kg) muscle mass per decade,’’ says Professor Walsh.
‘‘ 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.’’ PA