From Ergo Log
For healthy but slightly overweight people in their twenties and thirties half an hour of cardio training a day has almost the same positive health effects as a full hour. Danish sports scientists at the University of Copenhagen will soon publish an article on this in Obesity.
Intensive exercise is healthy. It improves cardiovascular health, insulin sensitivity and body composition. But exactly how much is the optimal amount of intensive exercise? We don't yet know that much about this.
In 2012 the Danes published the results of a human study in which subjects who did half an hour of cardio training daily lost about the same amount of fat as subjects who did twice the amount of training per day. [Am J Physiol Regul Integr Comp Physiol. 2012 Sep 15;303(6):R571-9.]
The group who trained 30 minutes a day lost 83 percent more fat than the researchers had expected; the subjects who trained for an hour each day lost 20 percent less body fat than the researchers had calculated.
In the study that will appear soon in Obesity, the Danes looked closely again at what happens if sedentary plump but healthy men train for 30 minutes a day, doing a workout that burns 300 kcal [High].
The figure below shows that after 11 weeks the High group had gained 1.2 kg lean body mass and had lost 3.7 kg fat. In the Mod group the figures were 0.6 and 4.2 kg respectively. The differences between the two groups were not very large.
The figures below show the effect on 'bad cholesterol' LDL, 'good cholesterol' HDL and the triglycerides in the blood. The High group did slightly better than the Mod group.
The researchers also looked at the effect on maximal oxygen uptake. This increased by a negligibly larger amount in the Mod group than in the High group.
And finally, above you can see the effect of the daily 30 and 60-minute cardio training sessions on the HOMA-IR [insulin insensitivity]. Insulin functioning improved by about the same amount in both groups.
Taken altogether the health of the subjects in the High group increased more than that of the subjects in the Mod group, but by much less than you'd expect.
"Only minor additional health benefits were found when exercising 3,800 as opposed to 2,000 kcal/week for 11 weeks in young, healthy, moderately overweight Caucasian men", the researchers conclude. "A small dose of physical exercise is healthier than none, and a moderate dose of exercise is better than a small dose, but a moderate dose of daily physical exercise appears to be nearly or just as good as a high dose. This new knowledge is important for a better understanding of the pathophysiology of the metabolic syndrome in relation to physical exercise and has important public health implications."
Obesity (Silver Spring). 2012 Dec 12. doi: 10.1002/oby.20226. [Epub ahead of print].