Hypertonicity is too much resting tone in a muscle. The muscle becomes rigid and fixed in a short or long position and can often create a deviation in posture such as a change in stance or roaching of the back. 

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A hypertonic muscle can feel hard to the touch and can produce a pain response as well as chronic aching. Because the muscles are ridge they can restrict movement in the limbs and inhibit normal movement. Hypertonic muscles are often associated with and caused by Myofascial pain, Injury, Repetitive activities, lack of rest between exercise or training, orthopaedic conditions and trigger points.