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muscle soreness

WHAT CAUSES MUSCLE SORENESS?

Gabe Mirkin, M.D.

Your muscles should feel sore on some days after you exercise. If you go out and

jog the same two miles at the same pace, day after day, you will never

become faster, stronger or have greater endurance. If you stop lifting weights

when your muscles start to burn, you won't feel sore on the next day and

you will not become stronger. All improvement in any muscle function comes from

stressing and recovering. On one day, you go out and exercise hard enough

to make your muscles burn during exercise. The burning is a sign that you are

damaging your muscles. On the next day, your muscles feel sore because they

are damaged and need time to recover. Scientist call this DOMS, delayed onset

muscle soreness.

It takes at least eight hours to feel this type of soreness. You finish a

workout and feel great; then you get up the next morning and your exercised

muscles

feel sore. We used to think that next-day muscle soreness is caused by a buildup

of lactic acid in muscles, but now we know that lactic acid has nothing

to do it. Next-day muscle soreness is caused by damage to the muscle fibers

themselves. Muscle biopsies taken on the day after hard exercise show bleeding

and disruption of the z-band filaments that hold muscle fibers together as they

slide over each other during a contraction.

Scientists can tell how much muscle damage has occurred by measuring blood

levels of a muscle enzyme called CPK. CPK is normally found in muscles and is

released into the bloodstream when muscles are damaged. Those exercisers who

have the highest post-exercise blood levels of CPK often have the most muscle

soreness. Using blood CPK levels as a measure of muscle damage, researchers have

shown that people who continue to exercise when their muscles feel sore

are the ones most likely to feel sore on the next day.

Many people think that cooling down by exercising at a very slow pace after

exercising more vigorously, helps to prevent muscle soreness. It doesn't.

Cooling

down speeds up the removal of lactic acid from muscles, but a buildup of lactic

acid does not cause muscle soreness, so cooling down will not help to prevent

muscle soreness. Stretching does not prevent soreness either, since

post-exercise soreness is not due to contracted muscle fibers.

Next-day muscle soreness should be used as a guide to training, whatever your

sport. On one day, go out and exercise right up to the burn, back off when

your muscles really start to burn, then pick up the pace again and exercise to

the burn. Do this exercise-to-the-burn and recover until your muscles start

to feel stiff, and then stop the workout. Depending on how sore your muscles

feel, take the next day off or go at a very slow pace. Do not attempt to train

for muscle burning again until the soreness has gone away completely. Most

athletes take a very hard workout on one day, go easy for one to seven days

afterward, and then take a hard workout again. World-class marathon runners run

very fast only twice a week. The best weightlifters lift very heavy only

once every two weeks. High jumpers jump for height only once a week. Shot

putters throw for distance only once a week. Exercise training is done by

stressing

and recovering.