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Hank: Alright. Let's face it. We've all mostly given up on our New Year's Resolutions by now. But if you are one of the few people who recently started hitting the gym on a regular basis, you've probably experienced the muscle pain and stiffness that shows up over the first few days after you work out. It's known as "delayed onset muscle soreness," and it probably has to do with tiny rips in your muscles. But while muscle growth does seem to be related to damaged cells repairing themselves, more pain doesn't necessarily mean more gain.
See, when you work your muscles harder than usual, it can cause micro-trauma, or microscopic tears. Now, that's more likely to happen after particular kinds of exercise, like when you're doing what's called eccentric contractions: when your muscles are contracting and lengthening at the same time. For example, bringing a dumbbell down during a bicep curl? Your bicep is sort of slowly relaxing, but it's still contracting to hold the weight up. These kind of motions put extra tension on the proteins within the muscles, and cause tiny tears that trigger inflammation. That swelling, along with the tears themselves, activates nociceptors, the neurons responsible for sensing pain; as time passes, your muscles heal, and the pain goes away.
But: are your muscles stronger now? Well, maybe.
We know that building muscle does involve minor damage and healing. But it isn't totally clear if muscle soreness and growth use the same mechanism, especially because researchers have found that feeling extra-sore doesn't necessarily mean you're growing more muscle. Either way, though, the next time you work out should be easier, thanks to the so-called "repeated bout effect." Since muscle soreness mainly comes from exercises your muscles aren't used to, after a while, they'll start to adapt, and you won't be in as much pain. It's almost like your body wants you to get back to the gym.
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