The autonomic nervous system or ANS is made up of sympathetic and parasympathetic nerves. The sympathetic nerves speed up various physiological processes such as heart rate and the parasympathetic nervous system slows down physiological processes.

It is possible to measure sympathetic and parasympathetic responses to exercise using heart rate variability. Heart rate variability is the time interval between heart beats and is usually measured in ms.

Scientists use heart rate variability information to study what happens to the ANS during and after exercise.

One particular interesting study is that of Buchheit et al. (2007) . These researchers studied a phenomenon known as parasympathetic reactivation.  

When we are at rest the parasympathetic nervous system is the predominant system we use to control normal bodily functions. However, when we exercise the sympathetic nervous system increases its activity and reduces the effect of the parasympathetic nervous system.

So, parasympathetic reactivation is the study of how long the parasympathetic nervous system takes to recover from exercise and return to baseline or near baseline measures.

What Buchheit et al. (2007) looked at was which type of training affected parasympathetic reactivation the most. The type of training looked at was repeated all-out sprints, continuous running or an intermittent exercise session.

The results showed that the activities that placed the highest demand on the anaerobic energy system ie. repeated sprints had the slowest parasympathetic reactivation.

This study really backs up what coaches have thought for a while, that anaerobic exercise places a considerable demand on the human nervous system.

What’s important is that we recognise that it’s not just muscles that need to recover from exercise but the nervous system too. This means we need to take into account rest periods during exercise and throughout training cycles in order to optimise training adaptations.

This point is especially valid when we are competing in sprint and intermittent type activities.

Alan Ruddock CSCS, YCS