The Resting Tone of the Nervous System

In the previous post we discussed neuroception and the subconscious evaluation of threat by the sensory systems and the brain. Our ability to accurately appraise the environment — including sensory input, context, past history and future expectations, etc. — dictates the baseline or resting tone of the nervous system.  As we age, these environmental influences on the system (and our cognitive appraisal of them) add up and shape how we perceive ourselves and the world around us. If stressors accumulate, both physical and psychological, and become more chronic without sufficient adaptation the resting tone of the nervous system is likely to increase. 

Why does this matter? It matters for all the toned up, tweaked, anxious athletes/execs as well as the persistent pain and chronic fatigue people. So basically everyone. As resting system tone increases one becomes more rigid, disengaged, and invariant, with a limited ability to adapt and grow. Think of it as a spectrum between an open and flexible system vs a closed and rigid system (more on that in a minute). So how do we define resting tone and is it fixed?

The baseline tone of the nervous system is the starting point of the autonomic nervous system. It’s the outlook or, maybe, the rhythmic midpoint. This tone determines how much tension we move with, how we interact with others, and our reactions/adaptability to stressors. Tone seems to be dictated by our perceptions of threat and the ability to cope with external demands. Too much threat and the reflexive, subcortical limbic system is lit up. Specifically, the amygdala gets sensory information from the autonomic nervous system and once sufficiently conditioned by prior experiences of threat or expectations (cognitive pre-experiences) the sympathetic nervous system is facilitated. The amygdala happens to connect directly to the hypothalamus-pituitary-adrenal axis (the birthplace of the stress response!) and in turn is highly sensitive to stress hormones creating a vicious cycle of increased neural tone. Repeat this sequence often enough and thru the wonders of neuroplasticity this tone becomes the resting state of the nervous system. 

Obviously, the opposite is true as well in that those with a healthy, capable vagus nerve (remember it’s cranial nerve X, the rest and digest one that decreases breathing rate and increases heart-rate variability) are able to engage with the environment in an open way that allows for flexibility and variance. There needs to be a healthy spectrum along which the person can function and meet all demands.

So the idea here is that there is a spectrum between an open, engaging baseline and a closed, disengaged baseline. On the open end, resting tone is low with a higher parasympathetic presence. On the closed end, sympathetic state dominates. Where we are on this spectrum is essentially a glimpse at the resting state of the nervous system. 

A few key points:

• This is not necessarily a good vs bad spectrum. Athletes need to be able to quickly go from one end of the spectrum to the other depending on the task. However…
• In order to engage in the environment, make sound decisions, and be adaptable the athlete/client needs to be towards the open end. My argument is that the resting tone needs to be towards the open end in order to self-regulate and adapt. But…
• In order to perform and concentrate on a task there needs to be a certain level of stress – one cannot learn and perform a skilled movement without some degree of arousal and filtering of sensory input. Moderate, transient stress improves memory and plasticity. Higher sympathetic tone necessary for concentration and motor control – but may come at a cost if over-used (the far right of this spectrum).

This is what I see all too often: clients are chronically on the closed end of the spectrum, flooring it to a red light and losing the ability to oscillate across the spectrum. This limits the ability to engage in and improve with training. Those who are more open with higher parasympathetic tone at rest are better able to concentrate and use stress to their advantage when high performance and reactivity is needed.

So as coaches and physios we need to promote a sustainably low resting tone of the nervous system that is able to meet demands and respond to challenges in order to grow. How do we do this? Reduce threat and then work on these points I made in a prior post on high-tension movement strategies. More on this to come…

– Seth

* I also highly recommend reading this amazing text by Robert Sapolsky, PhD as we’ll continue to integrate much of his work going forward: