Endurance athletes often undertake periods of intense training with the aim of improving performance. This increased stress can lead to a deterioration in performance and alteration in physiological systems – a functional state sometimes called ‘overreaching’.
Among these changes, the autonomic nervous system, which can regulate bodily functions such as heart rate and blood pressure, may be disturbed. In this study, the investigators assessed the effects of 3-weeks of overload training at 150% of the athletes’ normal load and compared the effects with those following a regular training program in a control group.
Subjects were well trained male and female triathletes or cyclists between 18-50 years of age who were randomly assigned either to the overload or regular training groups; a total of 17 individuals completed the study. Athletes who completed overload training had a decrease in cycling performance, in parallel with an increase in resting muscle sympathetic activity.
The control group improved their performance; they demonstrated no changes to sympathetic activity, but improvements in the tonic and reflex control of heart rate. This study demonstrates that overload training may blunt the beneficial autonomic effects of regular training, and that increased sympathetic activity may be involved in the observed performance decline.
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