What’s wrong with me if i come out out of a cold shower and my legs won’t hold me up and feel like i’m gunna fall back but catch myself like my legs are in fire

I think, it is because u took a cold shower so u couldn't move ur legs. The blood of ur leg freezed so... u couldn't move but there's no way u to felt like ur legs are in a fire cause u didn't take a hot shower.

c. the runner should sprint as fast as possible to the finish line.

the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.