title: Muscular mechanical hyperalgesia after lengthening contractions in rats depends on stretch velocity and range of motion.
abstract: The current study investigated stretch variables and mechanical factors of lengthening contractions (LC) in the processes leading to muscular mechanical hyperalgesia in rats to understand mechanisms underpinning delayed onset muscle soreness (DOMS).
  
  
  
  Under isoflurane anaesthesia, ankle extensor muscles were loaded with repetitive LC with angular stretch velocities (50°, 100°, 200° and 400°/s) at a fixed range of motion (ROM) of 90°, and with ROMs (30°, 60°, 90° and 120°) at a fixed velocity of 200°/s.
  
  
  
  Mechanical hyperalgesia was observed in a velocity- and ROM-dependent manner. Under the fixed ROM, integrated torque generated during LC (iTq[max]) was inversely correlated with the velocity, but the rate of torque increase during LC (rTq[max]) was positively and significantly correlated with the velocity, and the magnitude of hyperalgesia was correlated with rTq[max](p < 0.001). When the velocity was fixed, iTq[max]was significantly correlated with ROM, and the magnitude of hyperalgesia was correlated with iTq[max](p < 0.01). Necrotic myofibres were observed only sparsely (<0.8%) after any of the LC protocols tested. Up-regulation of nerve growth factor and glial cell line-derived neurotrophic factor mRNA in the muscle was positively correlated with the increases in the LC velocity and ROM (p < 0.05~0.001).
  
  
  
  Both velocity and ROM are pivotal variables determining the initiation of mechanical hyperalgesia. Neurotrophic factor-mediated peripheral mechanisms, but apparently not inflammatory changes caused by myofibre damage, are responsible for the mechanical hyperalgesia.
  
  
  
  Mechanical hyperalgesia appears after LC in a stretch velocity- and range of motion-dependent manner. The rate of torque increase and integrated torque are the crucial factors. Neurotrophic factor-mediated peripheral pain mechanisms without robust inflammatory changes caused by myofibre damage were required for this mechanical hyperalgesia.
authors.affiliation: Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hayashi
authors.affiliation: Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University, Kasugai, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Katanosaka
authors.affiliation: Medical Information Department, Vitacain Pharmaceutical Co. Ltd., Osaka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Abe
authors.affiliation: Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Yamanaka
authors.affiliation: Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, Joondalup, WA, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Nosaka
authors.affiliation: Department of Physical Therapy, College of Life and Health Sciences, Chubu University, Kasugai, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mizumura
authors.affiliation: Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Taguchi
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000378:metabolism; D006930:Hyperalgesia / Q000209:etiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000503:physiopathology*; D063806:Myalgia / Q000209:etiology*; D020932:Nerve Growth Factor / Q000378:metabolism; D016059:Range of Motion, Articular / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D051100:Glial Cell Line-Derived Neurotrophic Factor; D020932:Nerve Growth Factor