Measurement of the thicknesses of the Transverse abdominis and multifidus muscles was performed in a resting position and during the tasks with submaximal muscle contraction on both sides. To record the thicknesses of the Transverse abdominis and multifidus muscles, we used an LA523 linear probe (set to 12 MHz) and a CA431 convex array probe (set to 7.5 MHz). In order to measure Transverse abdominis muscle thickness, the subjects were set in crook-lying position. The ultrasound probe was placed midway between the iliac crest and costal margin, on the midaxillary line, about 10 cm off the midline of body at the level of umbilicus. Transverse abdominis muscle thickness was measured in millimeters between the fascial lines, one centimeter away from the muscle junction in the direction of the thoracolumbar fascia18). The two submaximal tasks were performed for the Transverse abdominis muscle, the abdominal draw-in maneuver (ADIM) and active straight leg raising (ASLR).