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Shika Igaku (Journal of the Osaka Odontology Society) 2000 Mar; 63 (1): 23-32.
Evaluation of muscle fatigue in the masseter muscle using a tactile sensor
Hiroshi Katayama and Joji Inada
Department of Physiology, Osaka Dental University, 8-1 Kuzuhahanazono-cho, Hirakata-shi, Osaka 573-1121, Japan
Abstract To establish an effective method for evaluating muscle fatigue after mastication, we measured stiffness and elasticity in the masseter muscle after experimental induction of fatigue by mastication using a newly developed tactile sensor. Among the masticatory muscles, the masseter is thought to create the greatest forces of mastication and occlusion. We compare the results of the tactile sensor and the frequency analysis of the electromyogram with conventional methods of evaluating muscle fatigue.
The tactile sensor indicated that increases in stiffness (decreases in the slope of the tangent of the hysteresis curve) and decreases in elasticity (increase in the residual deformation) of the masseter muscle on the mastication side were proportional to the number of masticatory cycles, which were measured at 0, 50, and 100 cycles. Increases in muscle stiffness and decreases in muscle elasticity associated with an increase in the number of masticatory cycles were also observed on the non-mastication side, although they were not as pronounced as on the mastication side. A frequency analysis of simultaneously recorded electromyograms of the masseter muscle showed a decrease in the higher frequency components (300-500 Hz). However, this parameter was proportional to the number of mastication cycles in only a small number of the subjects on either the mastication or non-mastication side (2/6 and 1/6, respectively). It was unclear in the other subjects.
These results suggest that muscle stiffness and elasticity measured with the tactile sensor more accurately reflect muscle fatigue than conventional parameters.
Key words: Masseter muscle; Fatigue; (Stiffness); Electromyography
[NOTE: The remainder of this publication is in Japanese, except for the Tables and Figures which are provided below.]
| Table 1 Changes in stiffness (Df/Dx) and elasticity (Hz) for the masseter muscle on the mastication side under various conditions | ||||||||
| Subject | Resting | 50 cycles | 100 cycles | Clenching | ||||
| Df/Dx | Hz | Df/Dx | Hz | Df/Dx | Hz | Df/Dx | Hz | |
| A | 1.8 | 75 | 1.1 | 85 | 0.8 | 98 | 0.6 | 12 |
| B | 1.6 | 95 | 0.9 | 112 | 0.8 | 118 | 0.5 | 21 |
| C | 3.5 | 92 | 1.7 | 97 | 0.4 | 112 | 0.1 | 32 |
| D | 1.2 | 83 | 0.9 | 95 | 0.7 | 110 | 0.4 | 13 |
| E | 3.1 | 86 | 1.6 | 100 | 1.5 | 106 | 1.1 | 23 |
| F | 2.4 | 73 | 1.2 | 83 | 1.0 | 98 | 0.8 | 14 |
| Table 2 Changes in stiffness (Df/Dx) and elasticity (Hz) for the masseter muscle on the non-mastication side under various conditions | ||||||||
| Subject | Resting | 50 cycles | 100 cycles | Clenching | ||||
| Df/Dx | Hz | Df/Dx | Hz | Df/Dx | Hz | Df/Dx | Hz | |
| A | 1.7 | 73 | 1.5 | 80 | 1.3 | 84 | 0.5 | 14 |
| B | 1.5 | 93 | 1.3 | 98 | 1.2 | 100 | 0.4 | 26 |
| C | 3.6 | 88 | 3.1 | 92 | 2.8 | 102 | 0.1 | 35 |
| D | 1.1 | 86 | 1.0 | 90 | 0.8 | 94 | 0.3 | 15 |
| E | 2.8 | 87 | 2.2 | 93 | 2.2 | 94 | 1.0 | 22 |
| F | 2.2 | 75 | 2.0 | 79 | 1.7 | 81 | 0.6 | 16 |
| Table 3 Analysis of the frequency components of the masseter muscle electromyogram during the 1st to 5th cycles, 46th to 50th cycles, and 96th to 100th cycles of mastication | |||||
| Subject | Cycles | Mastication side | Non-mastication side | ||
| 100-200 Hz | 300-500 Hz | 100-200 Hz | 300-500 Hz | ||
| A | 1-5 | -0.1 (121.1) | -17.1 (424.2) | -1.1 (160.2) | -14.4 (377.3) |
| 46-50 | -2.2 (128.9) | -22.0 (478.9) | -1.5 (105.5) | -17.3 (338.3) | |
| 96-100 | -6.3 (175.8) | -30.5 (385.2) | -4.0 (105.5) | -19.7 (322.7) | |
| B | 1-5 | -0.1 (144.5) | -15.1 (314.8) | -0.6 (160.2) | -24.2 (330.5) |
| 46-50 | -0.1 (175.8) | -19.4 (393.0) | -0.8 (160.2) | -30.5 (346.1) | |
| 96-100 | -0.1 (125.3) | -24.6 (322.7) | -9.9 (128.9) | -37.1 (322.7) | |
| C | 1-5 | -0.1 (160.2) | -18.6 (361.7) | -0.1 (136.7) | -25.5 (314.8) |
| 46-50 | -6.2 (168.0) | -26.4 (346.1) | -0.1 (168.0) | -26.2 (369.5) | |
| 96-100 | -0.1 (183.6) | -27.7 (307.0) | -0.6 (121.1) | -26.9 (353.9) | |
| D | 1-5 | -0.1 (175.8) | -25.5 (346.1) | -3.0 (113.3) | -26.6 (324.2) |
| 46-50 | -0.1 (168.0) | -26.0 (338.5) | -6.1 (144.5) | -25.0 (330.5) | |
| 96-100 | -1.7 (199.2) | -26.7 (322.7) | -8.8 (136.7) | -28.0 (346.1) | |
| E | 1-5 | -0.1 (121.1) | -26.0 (322.7) | -0.1 (121.1) | -22.7 (361.7) |
| 46-50 | -3.7 (131.4) | -30.2 (463.3) | -0.1 (136.7) | -24.3 (338.3) | |
| 96-100 | -1.6 (121.5) | -30.5 (307.0) | -0.1 (152.3) | -24.9 (338.3) | |
| F | 1-5 | -1.1 (144.5) | -22.9 (322.7) | -0.1 (191.4) | -14.9 (369.5) |
| 46-50 | -0.1 (128.9) | -23.2 (486.7) | -0.1 (190.5) | -18.1 (416.4) | |
| 96-100 | -1.4 (152.3) | -27.3 (369.5) | -0.1 (198.3) | -19.3 (322.7) | |
| dB (Hz) | |||||
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