A Correction Method for Muscle Stiffness Sensors to Measure Transversus Abdominis Activity

The transversus abdominis muscle is important for various human functions, including the prevention of back pain and the use of muscle activity values as an indicator for the treatment of urinary incontinence. Measuring muscle activity is an effective means of evaluating whether correct training has been performed. The transversus abdominis muscle stiffness sensor developed in a previous study used a method in which a belt with a sensor attached was wrapped around the lower back, which made measurement simple but also caused problems owing to the influence of phenomena other than muscle activity on the measurement data. Therefore, we propose a novel correction method to calculate the muscle activity of this sensor accurately, which can be used for simple measurements. We propose a formula to compensate for effects other than muscle activity based on a model equation that includes contact conditions and belt tension, which affect the muscle stiffness sensor value. We evaluated the validity of the correction equation from simulations and the change in similarity owing to the correction by simultaneously measuring the muscle action potentials and muscle stiffness sensor values during breathing movements with muscle activity. The proposed correction method improved the muscle stiffness data during respiration and contraction. It is possible to improve the measurement accuracy by improving the calibration method and hardware.