Jumping

I remember a fellow Kung Fu practitioner talking about when he was younger and doing Karate. He said they would warm up with 40 jumps where the knees hit the chest alternating with light hops. I was doing this on the basketball court while Noah dribbled and shot around and noticed that I was pretty much done when I got to 30. I think I will start to do this at some point every day. I mean why try doing all those jump kicks like I do if I can only do 30 regular jumps? I hope they help build back the small muscles I have probably lost. I mean I can still do the jump kicks, but I suspect not as well.