ROM or Range Of Motion is both flexion (bending) AND extension (straightening) Range of motion or ROM is a medical/anatomical definition not a mathematical one. The range of 180-360 degrees is not factored in, presumably because the lower leg cannot move in an entire circle! To measure degrees of flexion using the goniometer, the zero is on the ankle and the 180 on the hip. Thus full extension is 0 degrees. As the foot moves towards to hip, so the numbers go up - the right angle at the knee being (hardly surprisingly) 90 degrees, and so on. Any extension with the knees going backwards (hyper-extension) uses the 0-180 degrees on the opposite arc so a knee is said to have (for instance) -5 degrees of hyper-extension. Here are examples of what (extreme) hyper-extension can look like. Standing hyper-extension Laying hyper-extension These degrees of flexion are required for the following activities: - 65° to walk, - 70° to lift an object from the floor, - 85° for stair climbing, - 95° for comfortable sitting and standing - 105° for tying shoelaces.