Generally, we feel good when we increase our fitness potential (i.e. the chances of survival and reproduction). The good or ‘positive’ emotions are sent by our subconscious mind so that we’re motivated to repeat the activity that is highly beneficial for us.
This is why activities like eating, sex, and gaining social approval make us feel good because they’re critical from the purely biological standpoint of enabling you to survive and reproduce.
On the contrary, we feel bad or ‘negative’ emotions when we do something (or something happens to us) that reduces our potential fitness.
This is why the financial crisis makes us feel terrible and breakups leave us depressed (see Where do good and bad moods come from?).
Applying this principle to exercise
We’ve evolved to feel good after a session of exercise because, for our ancestors, strenuous exercise (especially running) was critical for their survival. In many situations, it could’ve meant the difference between life and death.
But exercise puts the body under significant stress which isn’t a healthy state to be in. Moderate to high-intensity exercise releases the stress hormone cortisol which, if present in large amounts for a prolonged time in the body, can cause ill health effects. Lactic acid is produced in the body for anaerobic respiration and the body is effectively ‘in pain’.
To counter this undesirable effect, the body has evolved to release certain painkillers as soon as we’re done with a strenuous exercise session. This not only alleviates pain but also motivates us to repeat the activity in the future.
For our ancestors, running and chasing must have been the norm. They just wouldn’t have been able to survive if it wasn’t so. But today, strenuous exercise isn’t critical for our survival at all and this mismatch causes several health problems in those who lead sedentary lifestyles.
If exercise feels good, why don’t people exercise?
Since exercise makes us feel good, it has the potential of becoming addictive. There are indeed people who admit they’re exercise addicts or gym rats. However, if you take a sample of the population anywhere on earth, you’ll probably find that most people don’t exercise.
The first reason is, of course, that it’s no longer critical for survival and the negative health consequences of not exercising regularly are usually experienced later in life.
The second reason is that, unlike an addiction to drugs, binge eating, video games, etc., the ‘good’ feelings that result from exercise are not experienced immediately but after a fairly long session of exercise.
This time lag is what demotivates people from exercising. Had exercise felt good while you were doing it, I bet a large percentage of the population would have no problems with exercising regularly.
Assuming you’re in a neutral mood before exercise, it simply makes no sense to put your body through the pain of exercise. We’re primarily pleasure-driven organisms. In the short run, the disadvantages of exercise outweigh the advantages.
But in the long run, feeling good is a preferred mood state over feeling neutral. So, in the long run, the advantages of exercise outweigh its disadvantages when we speak purely in terms of the pleasure or pain we experience.
It’s this long-term view that one needs to adopt if they’re seeking to make exercise a regular part of their lives.