Prisoners will not only be encouraged to become more powerful, but barbells and weights make excellent weapons. There is no real benefit to the prisoners by doing this. If they really want to stay in good shape, they can anyway. If they really want to stay in shape, they shouldn't have become criminals. We pay for a lot of luxuries for prisoners. I'm not saying that we should have french prisons, but that would be better than what we do have.
Every prison seems to have weightlifting equipment in the yard. I find this very disturbing that they would be giving prisoners a way to increase their strength. This means they will build that strength to use it on themselves or to attack prison guards. Nothing should be given to prisoners to make them stronger.
Allowing convicted criminals to use their extensive free time to get stronger is just begging for more effective violent criminals. We would never think it a good idea to train them in martial arts, cyber security/computer hacking, physical security systems/safe-cracking, pharmaceutical chemistry, or marksmanship. I fail to see how this is different.
Prisoners should be allowed to be healthy and fit like the rest of us. Weightlifting is a fine way for them to spend there time and relatively inexpensive compared to other free time options in prison. You are more at risk of dying in city streets than in prison (see sources). Once they get out physical strength will hardly make them better criminals as it is made obsolete by many readily available weapons.
The point of prisons seems to me to be a time for self-reflection to be to reintegrate people back into society. Otherwise wouldn't we be using death penalties if they were simply expensive holding cells? If this is truly the intent behind prisons then it would make sense to allow them to exercise. It helps people deal with anger or sadness (emotions probably contributing to their convictions). It could give them tools to help them along.
If we aren't planning to release them, it still doesn't change the fact that it's beneficial to their physical and mental health which makes them more stable. They are in a state where they would be less violent. Having calm prisoners who are happier seems better to me.
It's not as if prison guards are incapable of dealing with prisoners who might be violent. And being stronger doesn't make you immune to a taser.
I have a theory that a fair percentage of crime could be prevented by better equipping those involved with stronger coping mechanisms. Exercise has been shown to not only improve physical health, but mental health as well, therefore allowing prisoners a means of venting their anger in a productive way. Denying them this coping mechanism only prevents them from pursing another healthy path towards becoming a productive citizen, and barring a prisoner from his chosen means of healthy expression of anger won't make said anger disappear. I'm much more comfortable with releasing a prisoner who's been given the opportunity to deal with his anger in a productive way than releasing one whose anger has simply been left to fester.
But I am a personal trainer for a living with a long background and I would be REALLY punished if I couldn't at least stay healthy/fit/expend energy at some point of the day. Old school ideas to make the majority in prison this hardcore "punishment" don't help anything. Put these types back into society after no exposure to anything and see how likely they are to end up back with the damage prison has done. There isn't ENOUGH resources in prison our goal shouldn't be to keep everyone in there.