Why do we stretch when we wake up?

Why do we stretch when we wake up?

When we wake up every morning or after having a nap, normal person will stretch. Why this happen? Is this cause by the position of sleeping or what?

When you sleep, your muscles lose tone and fluid tends to pool along your back. Stretching helps to massage fluid gently back into the normal position. Also, your muscles protect themselves from over-extension by inhibiting the nerve impulses as they approach their limit. Over time, this safety mechanism becomes increasingly restrictive. Stretching briefly takes your muscles outside their normal range. This recalibrates the feedback mechanisms that determine their normal amount of motion. LV

BBC.Knowledge.July.2013