That depends on your goals! You can use it before exercise to help warm up and increase your mobility, and after exercise to reduce soreness and increase blood flow to the muscles that were just exercised.If you are using the Rehab Roller as a warm-up tool: Shorter duration and quick moving rolling is best. You should focus on rolling for around 20-30 seconds of foam rolling per muscle group, but certainly less than 120-seconds per muscle group. This will simply get the blood flowing to the muscles that are about to be used, which has tremendous benefit to using the muscles without them cramping up.Post workout, the Rehab Roller is used as a muscle recovery tool and it is ideally suited for after exercise and heavy activity. According to a recent PubMed Study, “foam rolling, as a recovery tool, substantially reduces muscle soreness caused by activity.” and additional PubMed Study went on to prove that “foam rolling substantially increases range of motion without a decrease of muscle activation or force.” It is a great tool for decreasing immediate muscle soreness, as well as delayed onset muscle soreness, the type of soreness that lasts for days after your workout. For example, I felt pretty sore and stiff after painting my basement one day. I got on the Rehab Roller after my shower and I felt like new.PubMed.gov References:http://www.ncbi.nlm.nih.gov/pubmed/25415413http://www.ncbi.nlm.nih.gov/pubmed/26618062