How Much Exercise is Enough?

If a little exercise is good than more is better right?  Not so fast.  Like most things in life there does appear to be a sweet spot when it comes to exercise.   To understand this, it is important to keep in mind that the human body is all about homeostasis.  Homeostasis refers to the ability of the body to maintain a balance within its internal environment while being faced with constant changes in the external environment.     

For example, the body tightly regulates many factors such a temperature.  Regardless of outside temperature the body will adjust heat production to maintain a body temperature of about 98.6 degrees.  There are many other examples including blood sugar regulation, ph regulation, AND caloric expenditure!

For example, during conditions of low food intake the body will slow down the metabolism to maintain caloric equilibrium in terms of the energy the body is using and taking in.  This ability is known at metabolic adaptation and allows us to survive during famine.

At the same time the body also adjusts to energy production demands to try to maintain balance between calories in and calories out.   Research has shown that there is an activity/exercise threshold, and when we go above this threshold of exercise the body adjusts by minimizing movement and slowing metabolic rate when NOT exercising.

A great example can be seen in elite level swimmers who spend up to 7 hours per day in vigorous exercise.  Anyone who has spent a few days with these folks will notice that when they are not exercising they are sitting or lying down and tend to sleep a lot between workouts.

This explains why several very well-designed research studies show that total daily energy expenditure is NOT always higher in groups who exercise a lot!     At the low range of physical activity/exercise more activity and exercise IS associated with higher total daily calorie burn, but for people in the upper range of physical activity and exercise total daily calorie burn plateaued.   Body fat levels and activity levels modulate metabolic rate aka totally daily calorie burn.

This fits the metabolic adaptation theory perfectly!   More fat and less overall movement and the body will allow you to “waste” more calories in movement.   However as fat mass becomes very low and/or activity levels become very high the body becomes stingier in allowing energy output so makes adjustments to prevent total daily energy usage from going higher!

Other studies have shown that maximum health and longevity benefits appear to max out at about 500 calories per day in formal exercise activity.   This is not to say more is bad, but rather points out that with exercise there is clearly a point of diminishing returns.    

So more is NOT always better when it comes to exercise!