I found zero pain at all while using the Exogen Sys. Sometimes, I even forgot I had it on. I used it for 65 treatments, which is about 2 1/2 months. The pain I had initially experienced (before the Exogen treatment) was quite severe. I would rank it a 8/10, where it was localized on the lower left side of my back. This type of injury is usually caused by an increase in training intensity, or overuse. Many gymnasts, kick boxers/karate practitioners develop this type of injury. With my case, it was an overuse injury where I was using poor technique and relying on other muscles to compensate. In addition I was still working out which involved skipping and jumping and kicking a heavy bag which was 'dumb' to say the least. My injury was unable to heal for the longgest time because I kept on re-injuring it. The cycle continued until a sports doctor finally told me that if I dont stop and take 3 months off, I can have a complete fracture on my L5, in which it would never heal. He then ordered the Exogen, and 3 moths after, I experienced no pain. Sometimes, it will creep up on me if I train really hard but the pain level is so minimal. I am also taking care of it now with monthly massage therapy to break up the scar tissue as a result from the trauma, yoga (to increase my range of motion), and listening to my body (something which is new to me).
I wish your son all the best, and hope he can put this behind him. Best of Luck