Open Mouth-Maximal Isometric Press (OM-MIP)

Suprahyoid and infrahyoid ('perihyoid') muscles are two groups of muscles that are important for swallowing physiology and function. One way to assess periphyoid muscle strength within the context of a clinical swallow evaluation is with the open mouth-maximal isometric press (OM-MIP).

The OM-MIP is a simple and objective way to quantify perihyoid muscle strength. OM-MIP has age- and sex-based normative data to assist in determining if a patient is presenting with perihyoid strength values that are within or outside of normal limits. OM-MIP involves using a handheld dynamometer. Handheld dynamometers require a one-time purchase (i.e., no continuous upkeep, unlike IOPI or Tongueometer, which require purchasing new tongue bulbs), with analogue dynamometers (e.g., Jamar) typically costing $150-$300 USD.

To measure OM-MIP, the examinee leans forward from their waist, rests their elbows on their knees, holds on to the handheld dynamometer, and tucks their chin with maximum force against the dynamometer while maintaining an isometric open mouth posture of 2–5 mm . "Press your chin down as hard as you can without letting your mouth close or your teeth touch." Verbal encouragement is provided by the clinical to achieve maximal effort (e.g., "Go go go!").

Normative data were collected using the technique described above. However, alternative methods for obtaining OM-MIP can include having the patient rest their elbows on a table rather than their knees, or using a clinician-administered approach. This may affect measures slightly, though seemingly not a lot. These alternatives may be necessary for people with mobility challenges.

A more detailed description of OM-MIP is outlined in the original publication (see below references - and the 'Free Publications' section of my website for a free, self-archived version of the manuscript). Chin tucking is used for OM-MIP because it has been found to engage the suprahyoid and infrahyoid muscles. However, because chin tucking against resistance can involve recruitment of the accessory and suboccipital muscles, an isometric open mouth posture is incorporated into the OM-MIP. The isometric open mouth serves two functions. First, it is designed to limit maximal strength measures to the jaw-stabilizing muscles (i.e., perihyoid muscles), rather than the accessory and suboccipital muscles, which may also be active during chin tucking. Second, research indicates that jaw opening against resistance elicits greater suprahyoid and infrahyoid muscle activity than chin tucking without an open mouth posture.

Normative data were developed from >200 healthy males and females across the age continuum. OM-MIP norms are outlined below. By determining if a patient has 'weak' OM-MIP strength, a clinician can provide some objective data in support of potentially incorporating strength-based exercises targeting the perihyoid musculature (e.g., chin tuck against resistance/CTAR). By determining if a patient has normal/strong OM-MIP strength, a clinician would have data to suggest that targeting perihyoid strength may not be warranted (i.e., focusing on other exercises).

Interestingly, recent research has found significant relationships between OM-MIP with superior hyoid displacement, anterior hyoid displacement, and maximal opening of the pharyngeal-esophageal segment. Therefore, if a patient presents with changes in these kinematic events during videofluoroscopy while also having reduced OM-MIP, then a clinician may consider that perhaps reduced perihyoid strength is contributing to these impairments.

Using OM-MIP to Personalized Chin Tuck Against Resistance (CTAR)

OM-MIP can be used to provide rationale that Chin Tuck Against Reistance (CTAR) may be of benefit for your patient. Before recommending CTAR for a patient, I like to ask myself the following:

Do you think changes in peripheral muscle strength (as opposed to changes in skill, sensation, tissue pliability, anatomy) is one of the primary causes of the person's impaired swallowing physiology?
Does the patient have reduced perihyoid (OM-MIP) strength?
Are the primary and most impactful physiologic impairments swallowing movements most associated with hyoid strength (i.e., base of tongue retraction, hyoid displacement, thyrohyoid approximation)?

If you answered yes to all of the above, then CTAR 'may' be a viable treatment option. OM-MIP can help to answer one of those questions. If the person's OM-MIP is WNL, then I would likely consider another strength-based swallowing therapy for the patient. If recommending CTAR, then consider measuring the person's OM-MIP and then prescribing CTAR as a percentage of the person's OM-MIP. For light intensity, consider training at 30-50% of the person's OM-MIP. For moderate internsity, consider training at 60-80% of the person's OM-MIP. See below video for more details.

References

Curtis, J. A., Langenstein, J., Troche, M. S., Laus, J., & Schneider, S. L. (2019). Open mouth-maximal isometric press: Development and norms for clinical swallowing evaluations and treatment. American journal of speech-language pathology, 28(1), 148-154.

Curtis, J. A., Laus, J., Schneider, S. L., & Troche, M. S. (2021). Examining the Relationships Between Lingual Strength, Perihyoid Strength, and Swallowing Kinematics in Dysphagic Adults: A Retrospective Cross-Sectional Analysis. Journal of Speech, Language, and Hearing Research, 64(2), 405-416

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