If your endurance work wears you out enough that hgh helps recovery I could see it being beneficial, in my experience the extra water weight and bit of joint tightness I get only takes away from my endurance goals even at 3 ius a day. The best thing I have found is just generous trt 175-250, maybe some carnitine if your into that and eating to get the body composition that is conducive for your goals, swimmer vs cyclist vs climber vs grappler will all be slightly different body comps to maximize endurance for said task. Taurine helps with pumps and cramps, make sure your electrolytes are topped off. Id hold off on cardarine until you get a cardio progression plan dialed in and you progress a little bit. If you save it till you hit a plateau and then remove it later on I find you can still make progress without relying on it all the time.