I agree they can't, but you can exercise for a very long time.. Not only that, but after you're done it's rather difficult to study because you are so exhausted mentally.
I don't know much about football but I used to compete in badminton and played with many professional players. Most people playing internationally train 6 days a week, 3 times a day. Even when I was only training twice a day, after I was done I would not be able to do anything because of the fatigue, I'd probably just eat and sleep.
I feel much the same way about working nowadays; even though I do have some spare time where I'm not working, the time is less productive than if I were in school where I would be doing nothing but studying. I certainly still learn new things, but it takes me much longer because my mental state is not fresh.
I wonder if this would be alleviated by studying before work instead of after, though, which is something I'm experimenting with. The only issue is that I already have trouble waking up for work, and yet somehow am unable to sleep early despite being so tired.
