Effect of Muscle Energy Technique on Hamstring Muscle for the Trigger Points of Muscle of Mastication

The primary muscles of mastication (chewing food) are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. The masticatory muscles are divided into elevator and depressor groups. The collective term 'hamstrings' refers to four muscles- semimembranosus (SM), semitendinosus (ST), biceps femoris long head (BFlh) and biceps femoris short head (BFsh). The hamstring muscles are the major flexors of the knee and also aid hip extension. Trigger point is classically defined as a hyperirritable spot in the skeletal muscle that is associated with a hypersensitive palpable nodule in a taut band which is painful on compression and can give rise to characteristic referred pain, motor dysfunction, and autonomic phenomena. Latent trigger points located in the muscles can interfere with muscular movement patterns, cause cramps, and reduce muscle strength. Active MTrPs can be associated with a reduced range of motion through muscle dysfunction and muscle weakness, causing orefacial pain, MTrPs in the masticatory muscles may restrict active maximum mouth opening (MMO).

It is possible that stretching the hamstring muscles may activate the dorsal periaqueductal grey area of the midbrain [PAG], and activate descending inhibitory control pathways. It is known that descending projections from the PAG to the medulla have collateral branches that terminate in various areas including the upper cervical spinal cord. Convergence of the nociceptive afferents from the receptive fields of cervical roots C1-C3 and those of the trigeminal nerve, which include the masseter muscle, occurs in the nucleus caudalis. If hamstring muscle stretching is capable of activating the PAG, then decreased sensitivity should affect a greater number of muscles, including the remaining masticatory muscles.

Muscle energy technique (MET) is a manual technique developed by osteopaths that is now used in many different manual therapy professions. It is claimed to be effective for a variety of purposes, including lengthening a shortened or contractured muscle, strengthening muscles, as a lymphatic or venous pump to aid the drainage of fluid or blood, and increasing the range of motion (ROM) of a restricted joint. MET may influence pain mechanisms and promote hypoalgesia.