Muscle Pain and Muscle Spindles

Abstract

Muscle pain is a common symptom associated with, for example, myofascial syndrome, fibromyalgia and polymyalgia rheumatica.

Hyperexcitability of muscle spindle afferents in jaw‐closing muscles in experimental myalgia: Evidence for large primary afferents involvement in chronic pain

“…Muscle pain is a perplexing common condition that can, at times, arise from inflammation caused by minor injuries, strain, exercise, fatigue or stress, whereas at other times, pain can be completely absent in some muscle diseases associated with important inflammatory histopathological signs (Partanen, 2018). It is usually localized and resolves spontaneously or after simple treatments (Tantanatip & Chang, 2023).…”

“…A typical feature of muscle pain syndromes is that pain is not spread uniformly across the muscle but is triggered at some specific points (Partanen, 2018). Trigger points are spots of hardening in the muscle tissue that are painful on compression (Simons et al., 1999).…”

“…Typically, trigger points are a hallmark of myofascial pain syndrome (Money, 2017 ; Saxena et al., 2015 ), but they can also impact fibromyalgia by adding to the level of central sensitization that characterizes this condition (Ge, 2010 ). Even in EMG studies of healthy muscles, pain caused by the insertion of the EMG needle is elicited in small spots where spontaneous electric activity is encountered, but outside of these spots, there is no pain and no spontaneous activity (Lavelle et al., 2007 ; Partanen, 2018 ). Electrical stimulation near these spots is extremely painful even if no visible contraction can be detected, and because the same stimulation elsewhere in the muscle is painless, it has been proposed that pain spots occur when the needle touches an intramuscular nerve terminal (Partanen, 2018 ).…”

“…Even in EMG studies of healthy muscles, pain caused by the insertion of the EMG needle is elicited in small spots where spontaneous electric activity is encountered, but outside of these spots, there is no pain and no spontaneous activity (Lavelle et al., 2007 ; Partanen, 2018 ). Electrical stimulation near these spots is extremely painful even if no visible contraction can be detected, and because the same stimulation elsewhere in the muscle is painless, it has been proposed that pain spots occur when the needle touches an intramuscular nerve terminal (Partanen, 2018 ). Furthermore, these pain spots have been found often to coincide with increased resistance to the advancement of the needle, which has led to the suggestion that these terminals are located inside muscle spindle capsules (Partanen, 2018 ).…”

“…Electrical stimulation near these spots is extremely painful even if no visible contraction can be detected, and because the same stimulation elsewhere in the muscle is painless, it has been proposed that pain spots occur when the needle touches an intramuscular nerve terminal (Partanen, 2018 ). Furthermore, these pain spots have been found often to coincide with increased resistance to the advancement of the needle, which has led to the suggestion that these terminals are located inside muscle spindle capsules (Partanen, 2018 ). These capsules are lamellated structures of connective tissue that enclose the intrafusal muscle fibers, around which coil the mechanosensitive sensory endings of large‐diameter primary afferents (PAs) of group Ia and II (Banks & Barker, 2004 ; Hulliger, 1984 ).…”