IOPI Northwest

Why Measure Lip Strength?

Inadequate lip strength may contribute to problems with deglutition, such as food containment during chewing. If lip weakness is severe, it also may interfere with the production of plosive speech sounds. Such weakness would probably be obvious, but being able to accurately "track" the degree of weakness would enable the clinician to determine whether the weakness is getting better or worse, and/or see if training improves lip strength. Additionally, observing lip weakness in a patient may help identify abnormalities within the nervous system such as subtle cortical dysfunction, or disease processes gradually affecting the function of the facial nerve.

Cheek Method of Measurement

There are two ways the IOPI can be used to measure the strength of the lips. In the first method, an IOPI bulb is placed inside the cheek just lateral to the corner of the mouth and the patient squeezes the IOPI bulb against the buccal surface of the teeth by pursing the lips as hard as possible. Although the bulb is not directly between the lips, it is valid because the pressure developed in the bulb depends upon the strength of obicularis oris, the circumferential muscle complex that surrounds the mouth. It is tension in this muscle that allows the lips to be compressed against one another.

Lip Method of Measurement

The second method involves placing the IOPI bulb directly between the upper and lower lip with the long axis of the IOPI bulb parallel to the lips, and then the patient/subject is asked to compress the lips as hard as possible. If the bulb is placed to the side, rather than in the midline of the lips, one may obtain a comparison of the lip strength on the two sides of the body, a measurement that might be of interest in the case of a patient with known or suspected neurological damage.

Comparison of Lip and Cheek Methods

Some Speech Pathology researchers have directly evaluated both of these methods in normal subjects. The general impression is that the cheek method, with the bulb under the cheek, gives more reliable measures than the first method (personal communication from Drs. Pamela Mathy and Heather Clark). The problem with the lip method is that the bulb tends to roll around between the lips and feels unstable to the subject. Subjects also unconsciously try to "trick" the measurement by folding the lips back over the teeth, which of course lets the jaws exert the pressure on the bulb.

Lip Normal Values

There is one published study so far (Clark et al., 2009 -Ref #1) that has presented data for lip strength measured with the IOPI. In addition to reporting the effect of directional tongue exercise on tongue strength, the main purpose of the study, Dr. Clark and colleagues used the "under the cheek" method to measure lip strengh in 39 normal adults and found maximum pressures of about 30 ± 10 kPa for this population. The lip was not exercised, and did not significantly change in strength over the 9-week exercise period.