The Scientist: Jordan D. Metzl, M.D., is a sports medicine physician at New York City’s Hospital for Special Surgery and author of “The Athlete’s Book of Home Remedies.” He has run 29 marathons and completed 10 Ironman triathlons.

The Answer: There’s good soreness and there’s bad soreness. The trick is knowing the difference. If you do feel a generalized achiness in your muscles 24 to 48 hours after a hard enough workout, that’s healthy muscle soreness. Nice work.

But if you’re so sore that it impedes your joint function, or if a very specific part of your muscle hurts—the top of your hamstring, say—you’ve pushed it too far.

You may have heard that muscle soreness is a result of lactic acid buildup, but doctors are increasingly suspicious of this explanation. Another theory floating around is that it has to do with ripping the muscle fibers, which, when they heal, result in a stronger muscle. This might be a myth, too.

One thing we do know is that when you work out a muscle, it starts a cascade of inflammatory chemicals. Hormones tell white and red blood cells, platelets and growth factors to rush to the tired muscle. It’s the same thing that happens when you cut your finger, and the reaction is stronger when you overuse your muscle than when you work out correctly. The jury’s still out, however, on just why this inflammatory response results in soreness.

Strength training is a trial-and-error activity. You should calibrate your next workout according to how you felt after the last one. Two to three sessions a week will help you build up your muscles, so you won’t be quite as achy the next day. But remember that if you don’t get sore at all, you’re not working hard enough!

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