Couch potatoes don’t need to exercise like mad

December 21, 2012 - 06:32

Scientists have studied whether couch potatoes aged between 20 and 40 really need to exercise 60 minutes a day.

You need to get your heart rate up for 30 minutes almost every day to optimally reduce your risk of diabetes and cardiovascular disease. (Photo: Colourbox)

You’re wasting your time if you exercise for more than 30 minutes a day in an effort to become healthy. At least if you’re a moderately overweight man aged between 20 and 40.

This is revealed in a new study, which has examined how 30 and 60-minute daily exercise sessions over 11 weeks affect young men’s risk of developing cardiovascular disease and type 2 diabetes.

“We have studied a group of overweight young men, who do not lead very active lives – the couch potatoes. They actually make up about 40 percent of all Danish men in the 20-40 age bracket,” says Michala Holm Reichkendler, MD, who is currently putting the finishing touches on her PhD thesis.

“They often have a little trouble getting started with their exercise. But the good news from our study is that they get the same health benefits regardless of whether they exercise for 30 or 60 minutes a day.”

Men felt healthy – but were in the danger zone

The study consisted of 53 young men from a variety of social backgrounds. They were all at risk of developing lifestyle diseases later on in life. They were selected to help the researchers examine how exercise can improve the mechanisms in the body that doctors normally check when they diagnose diabetes and cardiovascular disease.

Around a third of the men already suffered from ‘metabolic syndrome’, which is characterised by problems with blood pressure, cholesterol levels, blood sugar and/or waist circumference.
”We first screened the participants so that we could pick out some that were slightly overweight and untrained,” explains Reichkendler.

“They all felt healthy and were not taking any medication, nor did they have high blood pressure or close relatives with diabetes.”

No rest for the couch potatoes

Facts

The men in the study were moderately overweight.

Their BMI scores ranged from 25 to 30 and their body fat percentage was above 25. They were not used to exercising and had fitness ratings of below 45.

The exercise reduced the metabolic syndrome by 78 percent in the 30-minute group and by 80 percent in the 60-minute group.

The men were divided randomly into three groups:

  • One that exercised for 30 minutes a day over 11 weeks
  • One that exercised for 60 minutes a day over 11 weeks
  • One that continued the inactive lifestyle.

The researchers tested the participants throughout the study, including measuring their heart rate and taking blood samples.

”They exercised 6-7 days a week, and at least three of these days the exercise left them short of breath. So we’re not talking about a quiet stroll in the park. They were running and cycling pretty fast,” says Reichkendler.

Highly effective against diabetes

The researchers found that, in general, the exercise benefited the men equally, regardless of the length of their exercise session. The reduced risk of developing cardiovascular disease was the same for all.

”Our main discovery was that the insulin sensitivity, both in the liver and in the muscles, improved significantly – and it didn’t make a difference whether they exercised for 30 or 60 minutes a day,” says the researcher.

”The insulin sensitivity in the muscles improved by about 30 percent, and in the liver by about 20 percent. This significantly reduced the men’s diabetes risk. Similarly, their fitness improved by some 18 percent.”

Thirty minutes is the magic point

The Danish health authorities have long recommended 30 minutes of daily exercise. But it isn’t until now that a scientific study demonstrates that 30 minutes is the magic point at which further exercise doesn’t make us significantly healthier.

Facts

The exact figures for the men’s improved insulin sensitivity and fitness rating:

  • Fitness rating: 18 percent in the 30-minute group and 17 percent in the 60-minute group
  • Skeletal muscle insulin sensitivity: 28 percent in the 30-minute group and 36 percent in the 60-minute group
  • Hepatic (liver) insulin resistance: 17 percent in the 30-minute group and 18 percent in the 60-minute group.

”There are only a few so-called cross-sectional studies that the Danish health authorities are basing their assessment on,” she says.

In these studies, researchers examined a sample of the population and compared the participants’ health with their level of physical activity. They then combined this data with existing knowledge about how the body responds to exercise for up to 30 minutes a day.

“Against this background, the Danish health authorities – along with the World Health Organization – reckon that 30 minutes is enough, but that there are further health gains in exercising even more.”

The new study is a subproject of the research project FINE, is published in the journal Obesity. The study also forms part of Reichkendler’s PhD thesis,

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Read the Danish version of this article at videnskab.dk

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Translated by
Dann Vinther