CL&R had an article about how Fischer trained at a spa in the Adirondacks for an upcoming match.
One thing he did was swim and also hold his breath for as long as he could. Not sure that latter was good.
Recent reports have Caruana and Chirila going for long runs, playing tennis, basketball, and also swimming.
Anand does 2 hours of cardio each night to help stop him from dreaming about chess.
Carlsen went to the Olympic center with his father and they had him change his diet. Less orange juice with sugar and substitute a mix of chocolate/regular milk. He also trained by skiing and hired a personal chef to balance his carbs protein, and calcium.
Carlsen even optimized his sitting position.
Further he reduced his schedule to about 7 tournaments a year instead of about 13. And took time off after each to recuperate.
So GMs do many things other than study chess. Are there any books or good articles prescribing what would be best for training our bodies to play tournaments not just learning chess more itself.