Effects of masticatory muscle fatigue without and with experimental pain on jaw-stretch reflexes in healthy men and women.
OBJECTIVE
To examine the effects of experimentally evoked masticatory muscle fatigue, without and with experimental muscle pain, on the short-latency jaw-stretch reflex, using a randomised crossover design.


METHODS
Reflexes were evoked in both the masseter and temporalis muscles in 15 men and 13 women. The study was performed in two blocks, both containing 3 experimental conditions (before, directly after, and 15 min after provocation). Provocation consisted of a fatiguing chewing test, followed by an intramuscular injection of either isotonic saline (IS; non-painful) or hypertonic saline (HS; painful).


RESULTS
No significant effects of the experimental condition 'fatigue+IS' were found for any of the reflex outcome variables. For each muscle, the 'fatigue+HS' condition yielded significantly higher normalized reflex amplitudes than the other conditions. Several muscles displayed gender differences regarding both onset latency and normalized reflex amplitude.


CONCLUSIONS
Experimentally evoked mild-to-moderate muscle fatigue does not modulate the human jaw-stretch reflex. On the other hand, experimental muscle pain, evoked after the performance of a fatiguing chewing test, does yield a facilitation of this reflex. The gender differences found in both onset latency and peak-to-peak amplitude stress the need to take gender into consideration in future jaw reflex studies.


CONCLUSIONS
The sensitivity of the human jaw-stretch reflex can be modulated by HS-induced muscle pain; not by muscle fatigue that is provoked by intense chewing.
Department of Oral Function, Academic Centre for Dentistry Amsterdam, Louwesweg 1, 1066 EA Amsterdam, The Netherlands.
M K A
MK
van Selms
K
K
Wang
F
F
Lobbezoo
P
P
Svensson
L
L
Arendt-Nielsen
M
M
Naeije
D000328:Adult; D000704:Analysis of Variance; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007568:Jaw / Q000503:physiopathology*; D008297:Male; D008410:Masticatory Muscles / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D012026:Reflex, Stretch / Q000502:physiology*; D012462:Saline Solution, Hypertonic / Q000009:adverse effects; D012727:Sex Characteristics
D012462:Saline Solution, Hypertonic