Flexibility is a derivative of strength. Muscle tightness is secondary to muscle weakness. Wherever you see a limitation in motion is an indicator that one or more of the muscles that cross that axis cannot contract efficiently. When a muscle, or group of muscles, cannot contract efficiently it means that they cannot effectively shorten. When a muscle or group of muscles cannot effectively shorten, then the muscles on the opposite side of the axis cannot fully lengthen. This inefficiency in muscle contraction is expressed as muscle tightness. Whenever you see a limitation in motion (muscle tightness), it is a representation that one or more of the muscles on the opposite side of the axis cannot contract efficiently (weakness).
Therefore, Muscle Activation Techniques (MAT™) assesses Range of Motion in order to determine which muscles are potentially weak.