So you worked out hard, and now you’re sore the next day (or more likely, 48 hours after your workout). It hurts to move, and your muscles ache. The last thing you want to do is workout again, but that is exactly what you need.
Our bodies work based on simple physics and chemistry. Transport through the body mostly relies on diffusion, a slow process of molecules moving through a solvent (usually a liquid) from an area of high concentration to low concentration.
Post workout, your body needs to repair: it needs to remove waste products and replace them with nutrients. If left to itself, the diffusion of waste and nutrients will take longer due to the slow nature of the process.
Imagine in the picture above that you utilize a stirring rod to mix the dye through the water. With stirring or perturbation of the liquid, you get uniform color within seconds, as opposed to the minutes or hours it takes for it to happen by itself.
A workout aimed at alleviating soreness serves as the stirring rod for diffusion in your body and tissues. It should be strenuous enough to increase the exchange of waste products for nutrients but not so much that it strains the muscles again.
That is the cure. Despite the ache, do the same type of exercise that started the soreness to, in actuality, alleviate it. Simply change the intensity: do half the weight and double the number of repetitions. The exercise should be easy to perform. By doing this, you increase the rate of recovery and will actually decrease the muscle ache and soreness.