Bodies need ways to regulate themselves to keep us alive. Getting hungry so that we eat. Getting tired so that we sleep. Previous scientific thought was that our bodies are reactive to the environment around us, correcting the balance after the demands have happened similar to a thermostat adjusting to changes in temperature. Newer developments in neuroscience show that might not be the case. Instead, it is now thought that the brain uses sensory inputs from the world to make predictions about what is likely to happen next to organise resources in order to meet the expected demands. An example of how this works, most of the time the brain will know when you are about to stand up and make a prediction to adjust blood pressure to be ready for when you stand, but occasionally when standing up very suddenly you might feel lightheaded as your blood pressure is momentarily too low when the brain has. This concept is known as 'allostasis' and has been used in particular by scientists who study stress.
It was developed further (by Lisa Barrett-Feldman in her book 'How Emotions Are Made') into the idea of a 'body budget' using a financial analogy. The brain acts as book keeper, predicting withdrawals that will be made and keeping track of deposits, with the goal of keep things balanced so that we have resources available to us as and when we need them. Central to this idea is that our brains are wired around interpretation of the physical world around us, more like an impressionist painting rather than a photograph, and that interpretation is in part shaped by how we feel internally at a given moment which in turn is related to the balance of our body budget. There is naturally fluctuation of the budget throughout the day as the brain allocates resources for digesting food or instead for running.
How is this concept relevant to us in the world of health and fitness?
All being well resources are maintained more or less in balance but it is possible for the body budget to get out of balance, for example staying awake later than usual and being underslept the next day, leaving the body lower on resources. Returning to a normal sleep time over the following nights will allow the to restore normal balance. Most people could easily list a handful of things that count as withdrawals and as deposits to budgets. Draining resources are things like alcohol, late nights, getting sick, having a stressful day. Restoring resources are things like eating well, regular sleep schedule, spending time in nature and with friends whose company we enjoy.
Exercise sits mainly on the restorative side. Although it does take effort, and a harder workout will leave us fatigued, it usually also enhances mood and is recovered from easily. Chronic life stresses can also lead to a depleted body budget. Such as living through the COVID-19 pandemic. When there is more uncertainty predicting becomes less accurate and the body is more likely to end up in a resource debt and leave us feeling more and more run down over time. Then, as the fatigue tempts us to skip a workout or choose the ready meal over the fresher home made option or avoid social contact, neglecting the things that would help to restore our body budgets we get stuck feeling crappy without the energy to shift things back to a more balanced state. Over a period of time this can it's toll on the body in a deeper way as inflammation can build up. In small doses inflammation is a good thing, it's a reaction that helps the body heal (e.g. the swelling when you get an insect bite), but excessive amounts of anything will end up being harmful. An immune system that's out of balance is linked to things like obesity, diabetes, heart disease, insomnia, and can affect memory and cognitive function.
Without wanting to cause anyone stress by reading this I think it's useful to have an understanding of the way the body responds to our environments and behaviours and the benefits of staying committed to maintaining healthy habits. Everyone reading this is probably familiar with that feeling when workout we didn't want to do ends up leaving us feeling much better than missing it would have done. I think this concept gives a neat way of understanding that. Moving your body, especially if you can get outdoors or be around other people, helps to restore your body budget to a more balanced state. Often when we've exercised it's then easier to make healthier food choices, we tend to sleep better and be in a more positive mood. It could also be applied more broadly as a way to think activities outside of the health and fitness space and work life. Are they adding to or detracting from your energy overall? Would doing more of this and less of that help you feel more balanced? How do you want to spend your precious energy resources and what helps to fill you back up again?
Further reading more specifically on emotion: