Experimental Model of Trigger Points Using Eccentric Exercise

Abstract

Objectives: To introduce the experimental model of trigger point [TrP] induced by repeated eccentric contractions [REC] in humans, rabbits, and rats, and to suggest a generalized hypothesis of the TrP formation in various tissues.

Methods: In human subjects, REC of the extensor digitrum muscle of forearm were done with a load set on the middle fingers. In animal experiments [rabbit and rat], passive stretching during REC induced by electrical stimulation of the nerve was done using gastrocnemius muscle. Amplitude of reflex EMG of biceps femoris muscle was used for nociceptive response. Local ischemia was made by ligation of blood vessels.

Results: After REC, a sensitive spot and palpable band appeared, and pressure-pain threshold was restrictedly reduced at the center of palpable band. Measurements of deep pain by focal current stimulation, pain sensation in human, and reflex electromyogram of biceps femoris were elicited by only at the depth of fascia. Electrical activities also recorded from the sensitive spot at the depth of fascia, and they were suppressed by acupuncture. Ischemic condition elongated the existence of sensitive spot and palpable band, and windup phenomena also observed.

Conclusions: The tissue injuries and subsequent inflammation processes produced by the REC play an important role in the development of TrP, and ischemic condition could induce synaptic changes in the spinal cord. Sensitization of peripheral sensory receptors presumably polymodal receptors of the fascia and plastic changes and central sensitization might be a possible underlying mechanism of the TrP formation and referred pain phenomena.

KEYWORDS:

• Trigger point model
• rat
• rabbit
• human
• eccentric contraction
• sensitized nociceptor