Between the mind and its own body there is naturally an even more intimate connection than between the rest of the external world and mind. Just because of this necessary connection of my body with my soul, the activity immediately exerted on the soul by the body is not a finite [that is, limited and contained], not a merely negative, activity. First of all, then, I have to maintain myself in this immediate harmony of my soul and my body; true, I do not have to make my body an end in itself as athletes and tightrope walkers do, but I must give my body its due, must take care of it, keep it healthy and strong, and must not therefore treat it with contempt or hostility. It is just by disregard or even maltreatment of my physical body that I would make my relationship to it as one of dependence and externally necessary connection; for in this way I would make it into something - despite its identity with me - negative towards me and consequently hostile, and would compel it to rise up against me, to take revenge on my mind. If, by contrast, I conduct myself in accordance with the laws of my bodily organism, then my soul is free in its physical body.A clearer exhortation to lift weights or do HIIT won’t be found in the pages of any other philosopher. G W F Hegel, it turns out, was a Bro. He understood that when we eat crap, drink too much, take drugs, leave the iron un-lifted and generally treat our bodies badly, we end up feeling bad and our judgement and thoughts will be clouded if not turned off. Think hangover. By eating well, exercising, not drinking too much and leaving the drugs alone, we not only prevent the bad stuff, but also, and this is important, feel free in [our] physical body, that is, our body is no longer an obstruction, as it is with a hangover, but a resource for us. We are not constrained by its sickness or poor condition, but free within it.
In plain English experience: I get one of my darn colds, I feel trapped inside it. When it goes, and I recover, I feel free again.
Notice also that Hegel takes for granted that, not only are the body and mind intimately connected, but also the external world and mind are connected. He was the first philosopher to reject the idea that all we can know of the world is what gets to us through our failing senses, and that the mind rattles around, unconnected to the world, even to the body of the person whose mind it is.
The quote is from Hegel's Philosophy of Mind, part of his Encyclopedia of Philosophy, translated by Wallace and Miller. Lots of goodness in there - check it out.