Good health and fitness is essential for riding. I go to the gym about 3x/week on average and do cardio, (basically treadmill or stair stepper), strength training, (various machines with weights, balance training (my balance is bad due to my head injury).
I had initially lost 27 lbs. in the hospital after my injury; when I had passed the swallowing studies and no longer aspirated (food went down the right way, through my esophagus to my stomach rather down my trachea to my lungs), I was told to "eat everything." Ultimately I regained about 37 lbs, so I intentionally lost 10 back to about 109-110.
Currently I try to limit any sweets or fried food & eat mostly protein, veggies & fruit, which keeps me strong and gives me the energy I need to train myself and my horse.