System and method for measuring body joint range of motion

A method for measuring body joint range of motion using by a joint rotation measurement device that communicates with inertial measurement unit (IMU) sensors capable of measuring the IMUs' orientations relative to Earth, the method comprising:

• receiving, at the joint rotation measurement device, orientation data from a primary IMU sensor mounted on a proximal body segment and a secondary IMU sensor mounted on a distal body segment connected to the proximal body segment via a joint;
• measuring, at the joint rotation measurement device, a sensor orientation relationship between the primary IMU sensor and the secondary IMU sensor using the orientation data received from the primary and secondary IMU sensors;
• and
• converting, by a conversion application stored at a memory of the joint rotation measurement device, the sensor orientation relationship into at least one physiologically modeled constituent joint rotation relationship between the proximal body segment and the distal body segment, where a constituent joint rotation relationship is defined in no more than two dimensions of three-dimensional space,
• wherein converting the sensor orientation relationship into the physiologically modeled constituent joint rotation relationship includes defining a constituent radial axis composite rotation of the distal body segment measured with respect to the proximal body segment, where the radial axis intersects the joint connecting the distal body segment to the proximal body segment, is orthogonal to an axial axis of the distal body segment, is orthogonal to an axial axis of the proximal body segment, where an axial axis intersects the joint connecting the distal body segment to the proximal body segment and is parallel to a major axis of a smallest rectangular cuboid enclosing a body segment, and where a major axis is a line passing through the center of two opposing sides of the cuboid that are farthest apart from each other.