I used to do alot of leg work like rope jumping and bike riding, and also do side to side push-offs to improve my ankles and
lower legs. I also did tons of push-ups and would also use weights on my wrist while looping. weight training with 15lbs bar bells
and shoulder shrugs and rolls. High repeatition with lighter weights. Stay below 15lbs and let it burn. I ran track in high school
and played softball 3 night a week so running was not an isssue. Also try at least 1hr -1.5 hr of cardio 3 times a week helps.
I can say at 62 I can play 3-4 hours with little rest. This was after doing a 3-4 month cardio work out 3-4 days a week.