Yesterday I did Jumping jacks without a timer. I was trying to handle chores while exercising and filming. It's very easy for me to do all three because I have automated the habit of doing jumping jacks to a large extent.
To automate jumping jacks is easy, just start. Jump and clap/scissors above your head. It might start to hurt your calves but that's when you start to build endurance.
It is also best that if you want to protect yourself you do it on mats or with shoes or stockings. It all depends on your comfort level really. I remember when I first started doing jumping jacks and I would feel blisters underneath my feet.
The more I've done this exercise, the better I've become at it and it seems like it doesn't hurt as much as it did when I first started doing it.
I've built more shoulder endurance and calf endurance. Some pages also say that it helps build glutes and quadriceps, but I don't feel it as much as I feel it on my calves.
