Surface electromyography of abdominal and back muscles in patients with active scars.

Among the clinical symptoms caused by active scars in the abdominal region, back pain is very frequent. The muscles underneath such a scar appear to be less active on palpation than on the opposite side. To confirm this, 13 patients and 13 healthy controls were examined by surface electromyography (SEMG). We proceeded with SEMG of the straight abdominal muscles on both sides on lifting the head and the shoulders with the subject supine, and of the erector spinae with the patient prone. The patients with active scars were examined before and immediately after soft tissue treatment. SEMG examination showed increased muscle activity of the rectus abdominis in 6 cases on the side of the active scar and in 7 cases on the opposite side. This asymmetry decreased in 7 cases (p=0.045). Asymmetry was also found in the controls. This asymmetry was, however, significantly lesser than in the patients with an active scar (p=0.029). The discrepancy between palpatory and EMG findings is due to hypotony of the soft tissues on the side of the scar, giving the impression (illusion) that muscular activity is diminished on that side.