Science of Sport: Risks of long-term detraining for endurance athletes

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Endurance-trained athletes should avoid long detraining periods because the resultant metabolic changes might prove difficult to reverse. That’s the clear message from a French study on rowers – the first to study the effects of long-term detraining in highly trained endurance athletes.

The metabolic adaptations to endurance training are well understood; essentially, it induces a sparing of carbohydrate stores by increasing the contribution of fatty acid metabolism to the overall supply of energy to working muscles through enhanced glycogen creation and increased amino acid availability. These adaptations contribute collectively to enhanced endurance performance.

But what happens when the stimulus to the adaptations disappears not just for a few weeks but for months? That’s what the French researchers set out to investigate with 10 male national and international rowers who had announced their intentions of training hard for one year before bringing their sporting careers to a close.

The study started after an off-season of six weeks, during which the athletes were asked to avoid any physical exercsie. There then followed a 47-week training period, during which the athletes trained for a total of 1,046 hours (more than 22 per week) undergoing extensive performance and metabolic testing in weeks 1, 24 and 47. After another off-season they embarked on a detraining year, during which physical activity averaged 1.1 hours per week, with testing in weeks 52, 76 and 99.

Key findings were as follows:

• Short-term detraining (five weeks) induced significant changes in the metabolic response to exercsie, with decreased fat breakdown during exercise and increased reliance on glucose. These changes did not represent a direct metabolic limit to exercise, with no alterations in acute responses to exercise;
• However, long-term detraining produced more significant and dramatic changes, with lower fatty acid availability giving rise to an even higher reliance on glucose during exercise. Additionally, destruction of red blood cells (haemolysis) was observed during exercise, probably as a result of lower efficiency of the body’s systems for protecting the blood against oxidative damage.

‘Therefore, endurance-trained athletes should avoid detraining periods longer than a few weeks (notably during off-season)’, conclude the researchers, ‘since alterations of the metabolic adaptations to training may become rapidly chronic after such a delay.’

Int J Sports Med 2003; 24:320-325

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