T. Gay et al., CHARACTERISTICS OF MUSCLE FATIGUE IN PATIENTS WITH MYOFASCIAL PAIN-DYSFUNCTION SYNDROME, Archives of oral biology, 39(10), 1994, pp. 847-852
The purpose of this study was to compare the properties of muscle fati
gue in the masseter and temporalis muscles of normal individuals and t
hose with myofascial pain-dysfunction syndrome (MPD). The MPD muscle i
s presumed to have different characteristics of fatigue than its healt
hy counterpart; these characteristics can be quantitated using standar
d electromyogram (EMG) signal-processing techniques. A total of 18 pat
ients diagnosed as having MPD comprised the experimental group and 15
adults with no history or present symptoms of temporomandibular joint
pain and dysfunction served as controls. Surface EMG recordings were m
ade for both the masseter and anterior temporalis muscles while the su
bject held an incisal bite force level of 10N for as long as possible.
The EMG data were transferred to a microcomputer where the power-dens
ity spectrum of the signals were calculated for 2-s samples at 10-s in
tervals. The mean power frequency (MPF) and power (root mean square, r
.m.s.) of the signals were calculated from the power-density spectra.
Results showed: (1) the endurance times were significantly shorter for
the MPD patients; (2) the masseter was not active in three of 17 MPD
patients; (3) decreases in MPF over time were significantly greater fo
r the MPD patients than normal subjects; (4) increases in r.m.s. power
were significantly greater over time for the MPD patients; (5) bandwi
dths of the power-density spectra were similar for the two groups. The
implication of these results is the MPD muscle is not in a state of c
onstant fatigue, as is currently believed, but rather demonstrates acc
elerated fatigue.