I have heard of and even seen peope make big changes to their body and health with only 15, 30, or 60 minutes of exercise a day. It doesn’t even seem like much.
Whether it’s cardio or lifting weights, why do people only need that much time a day to improve? In fact, why does MORE time with exercise (like 3 hours or more) even seem harmful?
I know diet plays a big role but still. Like I started strength training for only 15 minutes a day and I see some changes in my body physically.
In: Biology
The first thing to understand is that in nature most animals don’t spend a lot of time being active, there is a lot of down time. If you think of lions, certainly they have periods of high activity, but they also have 15-20 hour periods of resting. For most mammals, the period of their day taken up by high intensity work is pretty small.
There are different ways to come at this question, but the most basic is that 30-60 minutes is usually enough time to signal to your body to adapt. In the case of muscle building, its enough to signal to your body that it should be building muscle.
It’s not really the exercise itself that causes the benefits, but all of the subsequent processes it kicks off. Another way to put it is that our body has evolved its signaling around the average day, and the average day for humans probably only had 30-60 minutes of high intensity work.
Because its all mostly signaling, once the body has got the signal, well doing more isn’t going to do anything extra. It’s like if you are pouring water into a cup, maybe the more and more you pour into it the better, but once it starts pouring over you’re not getting any more benefit.
To continue with the cup analogy, you can also fill that cup more slowly and get a similar signal. The 30-60 minutes usually refers to moderate to high intensity activity, but low intensity can work if done long enough, within reason.
With exercise, going too far beyond can be harmful because the body only has so much recovery capacity. Running a 25k can provide a lot of signal, but it can also put a toll on your body.
Really, the reverse of that question is probably more illuminating, if our bodies can kick of these signals whenever they want, why not just do it without exercise? The basic answer is that those adaptations are very expensive to maintain and that in an environment with poor resources those adaptations may be more of a hindrance. Excess muscle mass is a good example, it can provide a lot of benefit, but it is very costly in terms of energy so the body is stingy with how much it can grow. The body in general tries to adapt to the stress that is put on it.
As a side example, there are some genetic mutations that cause an animal to grow excess muscles.
[https://en.wikipedia.org/wiki/Belgian_Blue](https://en.wikipedia.org/wiki/Belgian_Blue)
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