Because you move your legs so much and they are not used to the pressure.
by getting your legs pumped by sprinting in place
stop being lazy and start sprinting go lakers
Cheetahs can climb but not well as they do not have retractable claws and their legs are designed more for sprinting than climbing.
Your legs may hurt when you sleep because you are experiencing growing pains. You may also have restless leg syndrome which can cause sore legs.
Does it hurt?
Sprinting is correct.
You've probably slept with you legs in an awkward position.
lay down and alleviate your legs
Look up sciatica.
I would suggest running on the bottoms as I would think that running on the tops would hurt very much.
sprinting started in 1708