November 2020

The Reliability of MyotonPRO in Assessing Masseter Muscle Stiffness and the Effect of Muscle Contraction

Authors: Jia-Feng Yu 1, Tian-Tian Chang 2, Zhi-Jie Zhang 3


  1. Department of Rehabilitation Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, China (mainland)
  2. Department of Sport Rehabilitation, Shanghai University of Sport, Shanghai, China (mainland)
  3. Luoyang Orthopedic Hospital of Henan Province, Orthopedic Hospital of Henan Province, Luoyang, Henan, China (mainland)

Journal: Medical Science Monitor - November 2020, 26: e926578 (DOI: 10.12659/MSM.926578)

Background: Temporomandibular disorders (TMD) are accompanied by masticatory muscle-related pain, making it meaningful to assess the stiffness of the masticatory muscles. The present study investigated the intra- and inter-operator reliabilities of MyotonPRO for assessing the elasticity of masseter muscles, to determine minimal detectable changes, and to quantify changes in stiffness from conditions of relaxation to maximal contraction.

Material and Methods: Twenty healthy subjects (10 men and 10 women) were recruited. The stiffness of their masseter muscles was quantified with MyotonPRO in both relaxed and maximal contraction conditions. Two experienced operators (A and B) measured stiffness on the same day, and operator A repeated this procedure 5 days later.

Results: Intra-rater reliability was good (ICC=0.78) and inter-operator reliability was excellent (ICC=0.95) for assessing masseter muscle stiffness with MyotonPRO. The mean stiffness of the masseter muscle on the dominant side was 369.5 N/m under relaxed conditions and 618.3 N/m at maximum bite force, an increase of 67.4%. Stiffness on the dominant and non-dominant sides did not differ significantly under both conditions (P>0.05).

Conclusions: MyotonPRO is a reliable method for quantifying the stiffness of the masseter muscle and monitoring its changes under different contraction conditions.


Keywords: Elasticity, Isometric Contraction, Masseter Muscle, Reproducibility of Results

In conclusion, MyotonPRO is a novel technique with high reliability in quantifying masseter muscle stiffness under both relaxed conditions and at maximum bite force. The finding that stiffness was similar on both sides provides a reference for future studies.