Question

why do we fell muscle cramps after a fast running?

Answer 1

IT can happen for no reason, it seems, taking you completely by surprise. And it can be excruciating. Suddenly, a muscle contracts violently, as if it had been prodded with a jolt of electricity. And it remains balled in a tight knot as painful second after painful second drags on.

A seized calf muscle or a hamstring can be frightening. Swimmers fear they will drown. Cyclists nearly fall off their bikes. Runners drop to the ground, grimacing, gritting their teeth.

The contraction is so strong that you could not will yourself to ball your muscle that tightly. And your muscle is likely to feel sore the next day.

Answer 2

When we run a lot a lot of oxygen is used up and as a result the muscles contract in order to carry out anaerobic respiration to produce lactic acid which is a substitute for oxygen. This is why we feel muscle cramps.
HOPE IT HELPS!!
PLEASE MARK MY ANSWER AS THE BRAINLIEST!!