To be honest, whenever I find myself stuck into a long study session at my flat, especially during exam revision, my go-to activity is doing a brisk routine of mobility stretches and skipping with a jump rope. I usually spend hours hunched over my laptop or textbooks at my desk, so every couple of hours I force myself to step away and get moving for about ten to fifteen minutes.
I don't really need a gym or a massive space for this, which makes it super convenient. I just clear a bit of floor space in my living room or, if the weather is decent, I nip out into the small garden at the back of my building. In terms of equipment, it's pretty minimal. I keep a simple leather skipping rope beside my study desk, and occasionally I might roll out a cushioned yoga mat if I'm doing core stretches or floor work. I usually do it in my normal lounge clothes, though I make sure to put on trainers so I don't hurt my ankles on the hard floor.
The main reason this helps me is that it gives both my body and mind a complete reset. Sitting still for hours makes me feel really sluggish and prone to losing concentration. By getting my heart rate up and stretching out my neck and lower back, I release all that built-up tension. It sort of clears the cobwebs, so to speak. When I sit back down at my desk, I notice an immediate boost in my mental clarity and stamina, which means I can tackle the next few hours of revision far more effectively rather than just staring blankly at the screen.