A foam roller is a self-massage tool that can be used pre-run to increase mobility and after the run to speed up recovery. By decreasing muscle tension in chronically tight spots, a foam roller and similar tools can provide some of the benefits of deep-tissue massage.
Using a foam roller is a way to perform myofascial release around muscles. "Myofascial" refers to fascia, the connective tissue that surrounds your muscles and other body parts and allows for movement. This internal webbing can stiffen with repetitive motions such as distance running.
Foam rollers can also target trigger points, which are areas in muscles where knots have developed over time. It's possible to have excellent range of motion but still have trigger points that create pain and tightness. Trigger points start as micro-tears that become chronic through a tear-and-repair repetitive cycle, leading to increased tension in the affected muscle.
Stretching a muscle with a knot or trigger point generally addresses only the healthy muscle tissue. Trigger points respond much better to direct pressure; a foam roller is one way to safely apply that pressure.
Among the most common spots for runners to foam roll are the quadriceps, calves, hamstrings, and iliotibial band.
Research on foam rollers has found they can increase range of motion and speed recovery by reducing pain and soreness. Although there isn't large-scale direct evidence of foam rollers' effectiveness in preventing injury, it stands to reason that decreasing the muscle tension caused by trigger points should lower injury risk and allow for more consistent training.