Exercise intensity and body composition

Low intensity exercise is best for overall weight loss, while high intensity exercise is best for maintaining muscle mass, according to a new study from Greece.

The researchers set out to compare the effects of two exercise training programmes (both expending equal amounts of energy but one of low and one of high intensity) on 14 healthy untrained women.

The women were divided into two equal groups, which exercised on a treadmill at 45 or 72% of VO2max four times a week for three months, expending 370 calories (kcal) per exercise session – a total of 18,500 kcal – while maintaining their normal diets.

Key findings were as follows:

  • Body mass (weight) decreased significantly in all participants, with an average weight loss of 2.6kg, but the loss was most marked in the low intensity group, who lost 1.4kg more than their high intensity counterparts on average;
  • Percentage body fat and fat mass decreased significantly in the whole sample, with no significant differences between the groups;
  • Fat-free mass (muscle) decreased in most (five) of the members of the low intensity group but increased in most (six) of those in the high intensity group.

Commenting on the increased weight loss in the low intensity group, the researchers speculate that ‘high intensity exercise might more effectively stimulate appetite and/or encourage relaxation after exercise periods’.

They add that the difference in fat-free mass change between the groups ‘either suggests that high intensity endurance exercise elicits some degree of muscle hypertrophy in untrained women or simply reflects the fact that it was less effective in reducing body weight, or is due to a combination of the two’.

They conclude that ‘both programmes may prove useful in eliciting favourable changes depending on which target (weight loss or maintenance of fat-free mass) is of higher priority’.

Int J Sports Med DO1: 10.1055/s-2005-865625

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