Spontaneous electrical activities at myofascial trigger points at different stages of recovery from injury in a rat model.

BACKGROUND: Spontaneous electrical activity (SEA) is a feature of myofascial trigger points (MTrPs), which can either be latent or active. However, SEA at different stages of recovery from MTrPs remains unclear. OBJECTIVE: To investigate the temporal changes in the nature of SEA after generation of MTrPs in a rat model. METHODS: 32 rats were divided into four groups: 24 rats were assigned to experimental groups (EGs), which underwent the MTrP modelling intervention and 8 were allocated to a control group (CG). All EG rats received a blunt strike to the left vastus medialis combined with eccentric exercise for 8 weeks. After modelling, the EG rats were subdivided into three groups with total recovery times of 4, 8 and 12 weeks (EG-4w, EG-8w and EG-12w, respectively). Taut bands (TBs) with and without the presence of active MTrPs were identified in the left hind limb muscles of all rats, verified by SEA and further examined with electromyography recordings. Myoelectrical signals were also categorised into one of five types. RESULTS: CG rats had fewer TBs than EG rats and EGs showed variable frequencies of SEA. SEA frequencies were higher in EG-4w than in EG-8w and EG-12w groups (240.57±72.9 vs 168.14±64.5 and 151.63±65.4, respectively, p<0.05) and were significantly greater in all EGs than in the CG (55.75±21.9). Relative to CG rats, amplitudes and durations of electrical potentials in the EG were only increased in the EG-8w and EG-12w groups. Types IV and V myoelectrical signals were never seen in latent MTrPs and type V signals did not occur in EG-4w rats. CONCLUSIONS: Increasing recovery periods following a MTrP modelling intervention in rats are characterised by different frequencies and amplitudes of SEA from TBs. TRIAL REGISTRATION NUMBER: 2014012.

Myoelectrical activity and muscle morphology in a rat model of myofascial trigger points induced by blunt trauma to the vastus medialis.

OBJECTIVES: To explore myoelectrical activity and muscle morphology of myofascial trigger points (MTrPs) in an injury model of rats. METHODS: A total of 24 male SD rats were randomly divided into a control group (group A) and model group (group B). A blunt striking injury and eccentric exercise were applied to the vastus medialis (VM) of rats in group B for 8 weeks. Later, the palpable taut band (TB), local twitch response, myoelectrical activities and morphology in the two groups were examined. RESULTS: An average of 2.5 (30/12) palpable TBs were detected in the VM in group B compared with none in group A. The MTrPs had two types of abnormal potential. Their amplitudes were significantly higher than those in the control group (p<0.01) but their durations showed no significant differences. A series of reflex contractions appeared in groups A and B in response to external stimulation to the ear. Their amplitude and duration in group B were significantly lower than those in group A. A series of lower fibrillation potentials repeatedly occurred in model MTrPs in group B. The morphology of MTrPs showed abnormal muscle fibres with large round or ellipse shapes in cross-section and enlarged tapering shapes in longitudinal section. CONCLUSIONS: Active MTrPs can be provoked by repeated blunt injury. Active MTrPs are a group of muscle fibres with abnormal shapes and abnormal myoelectrical potentials. External stimulation provokes low-voltage responses in MTrPs, which is different from the response of normal muscle fibres.