Soreness Doesn't Equal A Good Workout, And Feeling Good Doesn't Mean You're A Slacker
A friend is visiting from out of town and suggests the two of you go hiking. You haven't hiked in years, but it sounds like fun, so you go for a five-miler along the trails of a local forest preserve. The next morning, you wake up—and you can't move. Wow, that hike didn't seem that tough, but it must have been a better workout than you thought! We hate to break it to you, but no: pain does not equal gain, and soreness does not mean you got a good workout. The good news? The reverse is also true.
Why Do My Muscles Get Sore?
Not because they're growing, that's for sure. The technical term for that sore feeling is delayed onset muscle soreness (DOMS), which generally rears its ugly head 24–72 hours after a workout. Though we still don't totally understand what causes it, it's most likely because exercise causes microscopic tears in your muscles, which cause inflammation and a heightened sensation of pain. (By the way, it's not because of a buildup of lactic acid. That theory has long been debunked.) Most exercises can result in DOMS, but the biggest culprit is anything that requires eccentric contraction—that is, the lengthening phase of a movement, like when you lower a weight or run down a hill. Another big cause is simply doing an exercise you're not used to doing, like starting a new workout program or going on a five mile hike with no experience.
Here's the thing: inflammation around those microscopic tears are one sign that muscles are rebuilding themselves and getting stronger. Doesn't that mean that soreness does equal muscle growth? Not necessarily, for two reasons: muscle damage isn't the only way that muscles grow, and DOMS isn't even a very good indicator of muscle damage anyway. A paper in Strength and Conditioning Journal pointed out that study subjects who performed different kinds of eccentric exercises they weren't used to experienced DOMS afterward even though there wasn't evidence of muscle damage. (Talk about adding insult to injury).
The Repeated Bout Effect (A.K.A. The Good News)
Here's what should make you pause: the more you do an exercise, the less sore you feel afterward. If soreness meant muscle growth, wouldn't that mean that you'd get all the benefits of an exercise the first few times you do it? In that case, why would bodybuilders continue to bench press and marathoners continue to run? No, the reason you don't get as sore the more you do an exercise is the repeated bout effect: an adaptation your body makes after the very first workout to make sure that your muscles aren't as damaged the next time. (And as we've already learned, damage isn't the only path to a stronger muscle).
Feeling great the day after a workout doesn't necessarily mean you slacked off—it could mean you're getting fitter. As much as some fitness buffs love to "hurt so good," it's not always necessary, and feeling too sore to work out is a guaranteed way to slow your progress. The key, as with most things, is balance.