SMR (self myofascial release) is an important part of NASM’s 4 step rationale to corrective exercise. As part of the inhibitory phase, SMR is meant to relax overactive muscles fibers that may be present within the muscle.
The rationale behind it is that by using the clients body weight over a semi hard object, the client can control the amount of pressure they need to apply mechanical forces over the adhesions within the muscle and by doing so cause the adhesion in the muscle tissue to relax. Tools that suit this need can range from soft foam rollers to PVC piping, flexible plastic or metal sticks, or even tennis or golf balls.
Having used foam rollers myself I can attest to their beneficial effects at inhibiting overactive muscle tissue. The only limiting factor is the pain level that may be involved. Some clients do not have a high threshold for pain and therefore do not always perform SMR either correctly or at all.
When faced with this the best encouragement to offer is that it may hurt now, but it will feel better later, and after every use it will hurt less. I personally use the same principle of SMR in trigger point release massages that I perform on certain areas that are harder for clients to hit on their own such as the upper back and traps.