Please state why your knees hurt? Is it an injury? Is it arthritis? It makes a huge difference, so please rephrase your question.
As long as you keep their head above your knees, it won't hurt them.
its fun but ur worn out after and knees hurt
Yes
because when u run for a long time the nerves start getting over active and they hurt
Your knees are for prayin.
To be honest the answer to your question is that this product might hurt your knees based on my experience with ankle weights, I did feel pain and soreness on my knees as well as my ankles and calf muscles.
For very flexible people,no for beginners yes. its all about the bone. beginners dont have flexible knees but flexible people do and it is fine for your knees to hurt. mine do when i do a middle split cause im good at the regular split so its perfectlly normal!
the ones in there knees, shoulders, and elbows.
Well they most likely hurt or gash it or something.
no
Your question ... the way you wrote it ... really doesn't make sense. I think you meant the second choice to be "legs straight and knees locked". That configuration is more likely to hurt you, because your knees can't absorb any of the impact, and the shock is transmitted up into your hips and spine.