thats even worse!!! so when the momentum transfer changes back with gravity to the vertical DOWN...your muscles have to go from no load to max gravity acceleration load?
And you people think this is safe?
Nah, the weight-less description was a poor description. If done correctly, the motion should look similar to a pendulum. That's what most people who initially try kipping pull-ups don't realize. They try to just implement the kip and it will throw their pull-ups completely off-kilt.
While you do have to add in a kip, you also have to add in a press at the top of your pull to push your upper body away from the bar while your legs kip forward. Your center of gravity should always remain roughly at the same location relative to the bar. At the bottom of your pull your legs are back and you bring your chest to the bar, then as you continue your pull you add in the kip, swing your legs forward and push your upper body back. There should never be a true weightless feel.
However, you do realize that almost every single explosive, Olympic lift is designed on a jump-catch cycle right? In the snatch you throw a weight over your head and then catch it. In a jerk you take a bar from a rack position and explosively press it overhead before catching it. How is this any different.
Olympic lifts are shown to increase bone strength, core stability and promote maximum oxygen uptake which is the most important aspect of cardiovascular fitness.