You don't have to be an exercise scientist, however, to know about DOMS. We've all felt the nice sore you get after a good workout, but I had DOMS once, and it felt like the muscular ache you can get from the flu and lasted for almost two weeks. This is common, but a huge bummer. The reason I got it may perhaps be why you got it as well-- while this condition can be triggered by the start of a new workout, it is exceedingly well-correlated with so-called eccentric contractions, or the type of work you do in letting down a weight slowly. These contractions work fewer fibers, including those located at the junction where muscles meet tendons--all possible reasons for the injury.
The extreme soreness I felt occurred after trying a trick employed by the US Ski Team known as eccentric leg-press overload workouts, where you basically push up the weight with two legs and let it down with one. (It's difficult to isolate your eccentric movements, but incredibly useful. To learn more, read the Bodywork section of the forthcoming May issue of Outside.)
Your muscles are weaker when healing from DOMS, so working through the pain won't earn you any strength gains, and may delay healing. The use of lighter weights, stretching, and massage have also been shown to be of little help. A study from Greece that was published in the Journal of Strength and Conditioning Research did show a reduction in pain by taking ibuprofen, but it didn't help the subjects return to normal strength any sooner. The good news is that you will be less likely to get so sore the next time you try an eccentric workout.
Filed To: Strength and Power Training