Comparison of Abdominal Muscle Activity in Relation to Knee Angles during Abdominal Drawing-in Exercises Using Pressure Biofeedback

[Purpose] The leg angles that are the most effective for abdominal muscle activation were investigated by performing abdominal drawing-in exercises at different leg angles with a biofeedback pressure unit. [Methods] Subjects were asked to adopt a supine position, and the tip of the biofeedback pressure unit was placed under the posterior superior iliac spine. Then, the pressure was adjusted to 40 mmHg while referring to the pressure gauge connected to the biofeedback pressure unit. Subjects were instructed to increase the pressure by 10 mmHg using the drawing-in technique upon the oral instruction, "Start," and to maintain the drawn-in state. The time during which the pressure was maintained within an error range of ±1-2mmHg was measured in seconds. [Result] During the abdominal drawing-in exercises, the activity of the rectus abdominis, the internal and external obliques, and the transverse abdominis increased as the knee joint flexion angle increased from 45° to 120°. [Conclusion] When trunk stabilization exercises are performed at the same pressure to reduce damage after the acute phase of low back pain, trunk muscle strength can be efficiently increased by increasing the knee joint angle gradually, while performing abdominal drawing-in exercises with a biofeedback pressure unit.