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Revised:  24 Nov 05

COOL-DOWN

The justification for a cool-down period after any vigorous workout is quite simple.  Blood returns to the heart through a system of veins; the blood is pushed along by heart contractions, and the milking action of the veins is assisted by muscle contractions during exercise.  Veins contract, or squeeze, and move the blood forward against gravity while valves prevent the blood from backing up.  If you stop exercising suddenly, this milking action also ceases, and blood return will stop quickly.  This may cause blood pooling (blood remaining in the same area) in the legs, leading to deep breathing, which may in turn lower carbon dioxide levels and produce muscle cramps.  At this point, blood pressure drops precipitously and causes functional problems.  The body compensates for unexpected drop in pressure by secreting as much as 100 times the normal amount of a hormone called norepinephrine.  This high level of norepinephrine  can cause cardiac problems for some individuals during the recovery phase of vigorous exercises.  The final three to eight minutes of a workout should involve a period of slowly diminishing intensity through the use of a slow jog for three quarters of a mile at a pace of three to four minutes per quarter mile, each quarter mile slower than the previous one.  Stretching during the final phase of the cool-down period helps fatigued muscles return to normal resting length and a more relaxed state, reducing the chance of muscle soreness the following day.

Source:  Sports Speed, Third Edition