Why do I sometimes feel more sore, or sore in different muscles, two days after a workout, as opposed to the day right after?
There's a name for this type of delayed onset muscle soreness, and -- surprise! -- it's delayed onset muscle soreness (or DOMS).
DOMS usually sets in one to three days after your tough workout, but it may persist for up to 10. There are a number of theories as to what's really going on at the muscular level to create pain so far after the fact, including lactic acid buildup and inflammation, not to mention real damage to muscles and/or tendons. Experts say it's likely, however, that a combination of two or more of the going theories are probably at work.
One thing seems pretty certain, at least, and that's that DOMS is likely the result of a specific type of muscle movement or contraction called eccentric muscle contractions, Dr. Steven Stovitz, M.D., MS, associate professor in the department of family medicine and community health and a team physician at the University of Minnesota, writes to HuffPost Healthy Living in an email. Eccentric contractions occur when the muscle is contracting at the same time as it is lengthening, like in the biceps during the downward-moving portion of a curl or in the quads while running down hills, he explains.
Typically, it's "untrained" muscles that ache days later, says Stovitz, which is why you might be more likely to feel sore the second or third day after a workout you've never done before, or why athletes experience DOMS at the beginning of their seasons, says Dr. William Briner, M.D., sports medicine physician at the Hospital for Special Surgery in New York City.
"A muscle that is to perform excessive work in a concentric fashion (i.e. contracting while shortening) may fatigue and suffer immediate pain that resolves within a day," says Stovitz. "Also, a muscle that works eccentrically, but has been trained to do so, may also be sore for only a day and not suffer the delayed soreness." Therefore, your muscles that contracted eccentrically and are the least trained are the ones that are going to chime in a couple of days after the fact.
It's not all bad news, though: "It's not like pain in a tendon or a joint," Briner tells HuffPost Healthy Living. "It may mean you've pushed a little harder, but it's part of the process and it will go away." You might feel like taking a day off to give those sore muscles a little time to recover, but you don't have to, unless the pain is limiting your range of motion. In fact, a little light exercise may even help you heal, Men's Health reported, since exercise boosts blood flow. Massage or some anti-inflammatories can also help.
The best news is that after that first bout of DOMS, "it is likely that you will be better prepared to repeat the exercise without suffering the soreness," says Stovitz. Stick with that new move or routine, and you'll eventually be able to do it pain-free -- and you'll likely get stronger in the process.