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11.06.2009

Stressed out? Your cortisol level will explode after training

If you are experiencing a lot of psychological stress in your life – for example because there's been a death in your close family, you're going through a divorce or are in a conflict situation – your body's cortisol production increases exponentially after training. This fact emerged from what has now become a classic study of forty top American athletes done by Frank Perna and Sharon McDowell. The results of the study were published in 1995 in the International Journal of Behavioral Medicine.

Cortisol, the major stress hormone, makes sure that the body directs as much effort as possible towards generating energy. This occurs at the expense of muscle build up and the immune system. That's why athletes fall ill or incur injuries more often if they are under stress or are overtraining. The researchers, who worked at the University of Miami and the US Olympic Training Center, decided to examine whether cortisol production is only determined by training. They suspected that life stress – in the form of life-changing events in the athletes' lives – might also be a factor.

To find out, the researchers performed a trial with forty cyclists and rowers, all of whom were Olympic athletes for the US. The researchers asked the athletes about potential stress-causing events in their lives. On the basis of their findings they divided the athletes into two groups: a high-stress and a low-stress group. Then they got all the subjects to cycle. The researchers gradually increased the resistance against which the test subjects had to cycle, until the subjects could go no further.

The researchers measured the cortisol level in the test subjects just before and just after the training session, and also a day later. The figure below shows what happened to the cortisol level as a result of the session.

In the athletes who were experiencing low levels of stress, the training session reduced the cortisol level. In the athletes with a lot of life stress, exactly the opposite occurred. "Perhaps the most interesting finding was that the low-LES group experienced a rapid significant decrease in cortisol after exercise, whereas the high-LES group experienced a significant increase in cortisol level, which remained elevated one day later", the researchers write. The phrase 'one day later' refers to the post-test (2) measurement.

If you're having a tough time outside the field, gym or athletics track, it might be an idea not to train every day, but to build in at least one rest day between training sessions. That way your body has time for its raised cortisol level to return to normal.

Last year sports scientists at the University of Texas at Austin discovered that life stress reduces power athletes' progression, but doesn't reduce it to nil.

Source:
Int J Behav Med. 1995;2(1):13-26.