Detection of muscle fatigue caused by repeated posterior tongue lift movement from neck surface EMG: a pilot study.

BACKGROUND: Fatigue is an important factor for muscle strengthening in rehabilitation medicine. Frequency analysis has been regarded as the gold standard for muscle fatigue assessment in surface electromyography (EMG). However, there are no experiments quantifying fatigue with grouped discharge (GD), which is one of the historical phenomena observed in patients having fatigue, by using high sampling rate recording of EMG. OBJECTIVE: To investigate the effect of fatigue, which is induced by repeated posterior tongue lift movement (TLM), on the occurrence of GD peaks, thus, to provide possible basis as a parameter for future fatigue evaluation. METHODS: Nineteen healthy adults (9 men and 10 women) participated in this study. The muscle fatigue protocol consisted of repetitive posterior TLM and maximum voluntary contractions (MVC). Bilateral N-EMG (Neck surface EMG for measuring the muscle activity of the posterior tongue) was recorded. RESULTS: Subjective tongue fatigue at the end of the protocol was significantly higher than at beginning throughout the muscle fatigue protocol (p < .01). The frequency of occurrence of GD peaks was 0.9 ± 1.2 (per second) at the baseline in 33 of 38 subject sides, and significantly increased depending on fatigue progression (p < .01). CONCLUSION: It was shown that fatigue due to repetitive posterior tongue lifting resulted in significant increase in the frequency of occurrence of GD peaks. Especially, the nature of GD, showing very few occurrences at non-fatigue condition, might work as an advantageous property for its use in future absolute evaluation of fatigue phenomena.

Characteristics of Grouped Discharge Waveforms Observed in Long-term Masseter Muscle Electromyographic Recording: A Preliminary Study.

We investigated the characteristics of grouped discharge (GD) waveforms obtained from long-term masseter electromyogram (EMG) recording in 6 female temporomandibular disorder (TMD) patients with myofascial pain and 6 healthy females. The EMG measurement was performed from the morning of the experiment day until the subject woke up the next day. We observed a significantly larger number of GD waveforms in the TMD group compared to the control group (p=0.002). Our results indicate that the existence of GD waveforms in masseter EMGs might be a predictor of future TMD with myofascial pain.

Specific diurnal EMG activity pattern observed in occlusal collapse patients: relationship between diurnal bruxism and tooth loss progression.

AIM: The role of parafunctional masticatory muscle activity in tooth loss has not been fully clarified. This study aimed to reveal the characteristic activity of masseter muscles in bite collapse patients while awake and asleep. MATERIALS AND METHODS: Six progressive bite collapse patients (PBC group), six age- and gender-matched control subjects (MC group), and six young control subjects (YC group) were enrolled. Electromyograms (EMG) of the masseter muscles were continuously recorded with an ambulatory EMG recorder while patients were awake and asleep. Diurnal and nocturnal parafunctional EMG activity was classified as phasic, tonic, or mixed using an EMG threshold of 20% maximal voluntary clenching. RESULTS: Highly extended diurnal phasic activity was observed only in the PBC group. The three groups had significantly different mean diurnal phasic episodes per hour, with 13.29±7.18 per hour in the PBC group, 0.95±0.97 per hour in the MC group, and 0.87±0.98 per hour in the YC group (p<0.01). ROC curve analysis suggested that the number of diurnal phasic episodes might be used to predict bite collapsing tooth loss. CONCLUSION: Extensive bite loss might be related to diurnal masticatory muscle parafunction but not to parafunction during sleep. CLINICAL RELEVANCE SCIENTIFIC RATIONALE FOR STUDY: Although mandibular parafunction has been implicated in stomatognathic system breakdown, a causal relationship has not been established because scientific modalities to evaluate parafunctional activity have been lacking. PRINCIPAL FINDINGS: This study used a newly developed EMG recording system that evaluates masseter muscle activity throughout the day. Our results challenge the stereotypical idea of nocturnal bruxism as a strong destructive force. We found that diurnal phasic masticatory muscle activity was most characteristic in patients with progressive bite collapse. PRACTICAL IMPLICATIONS: The incidence of diurnal phasic contractions could be used for the prognostic evaluation of stomatognathic system stability.