Sexual dimorphism of murine masticatory muscle function.
ABSTRACT To determine if gender distinctions of force generating capacity existed in murine masticatory muscles.
In order to investigate the effect of sex on force generating capacity in this muscle group, an isolated muscle preparation was developed utilising the murine anterior deep masseter. Age-matched male and female mice were utilized to assess function, muscle fibre type and size in this muscle.
Maximum isometric force production was not different between age-matched male and female mice. However, the rate of force generation and relaxation was slower in female masseter muscles. Assessment of fibre type distribution by immunohistochemistry revealed a three-fold decrease in the proportion of myosin heavy chain 2b positive fibres in female masseters, which correlated with the differences in contraction kinetics.
These results provide evidence that masticatory muscle strength in mice is not affected by sex, but there are significant distinctions in kinetics associated with force production between males and females.
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ABSTRACT: Rotator cuff tears are one of the most common tendon disorders found in the healthy population. Tendon tears not only affect the biomechanical properties of the tendon, but can also lead to debilitation of the muscles attached to the damaged tendons. The changes that occur in the muscle after tendon detachment are not well understood. A rat rotator cuff model was utilized to determine the time course of changes that occur in the supraspinatus muscle after tendon detachment. It was hypothesized that the lack of load on the supraspinatus muscle would cause a significant decrease in muscle mass and a conversion of muscle fiber properties toward those of fast fiber types. Tendons were detached at the insertion on the humerus without repair. Muscle mass, morphology and fiber properties were measured at one, two, four, eight, and 16 weeks after detachment. Tendon detachment resulted in a rapid loss of muscle mass, an increase in the proportion of fast muscle fibers, and an increase in the fibrotic content of the muscle bed, concomitant with the appearance of adhesions of the tendon to surrounding surfaces. At 16 weeks post-detachment, muscle mass and the fiber properties in the deep muscle layers returned to normal levels. However, the fiber shifts observed in the superficial layers persisted throughout the experiment. These results suggest that load returned to the muscle via adhesions to surrounding surfaces, which may be sufficient to reverse changes in muscle mass.Journal of Orthopaedic Research 04/2005; 23(2):259-65. · 2.81 Impact Factor
Journal of the American Dental Association (1939) 11/1993; 124(10):115-21. · 1.77 Impact Factor