Asked by: Solang Uk, Switzerland
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.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.