title: Effects of Prolonged and Acute Muscle Pain on the Force Control Strategy During Isometric Contractions.
abstract: Musculoskeletal pain is associated with multiple adaptions in movement control. This study aimed to determine whether changes in movement control acquired during acute pain are maintained over days of pain exposure. On day 0, the extensor carpi radialis brevis muscle of healthy participants was injected with nerve growth factor (NGF) to induce persistent movement-evoked pain (n = 13) or isotonic saline as a control (n = 13). On day 2, short-lasting pain was induced by injection of hypertonic saline into extensor carpi radialis brevis muscles of all participants. Three-dimensional force components were recorded during submaximal isometric wrist extensions on day 0, day 4, and before, during, and after saline-induced pain on day 2. Standard deviation (variation of task-related force) and total excursion of center of pressure (variation of force direction) were assessed. Maximal movement-evoked pain was 3.3 ± .4 (0-10 numeric scale) in the NGF-group on day 2 whereas maximum saline-induced pain was 6.8 ± .3 cm (10-cm visual analog scale). The difference in centroid position of force direction relative to day 0 was greater in the NGF group than in the control group (P < .05) on day 2 (before saline-induced pain) and day 4, reflecting changes in tangential force direction used to achieve the task. During saline-induced pain in both groups, tangential and task-related force variation was greater than before and after saline-induced pain (P < .05).
  
  
  
  Persistent movement-evoked pain changes force direction from the pain-free direction. Acute pain leads to increased variation in force direction irrespective of persistent movement-evoked pain preceding the acutely painful event. These differences provide novel insight into the search for and consolidation of new motor strategies in the presence of pain.
authors.affiliation: Center for Neuroplasticity and Pain, SMI, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Christian A
authors.initials: CA
authors.lastname: Mista
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, Queensland, Australia.
authors.forename: Michael J G
authors.initials: MJG
authors.lastname: Bergin
authors.affiliation: Center for Neuroplasticity and Pain, SMI, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Rogerio P
authors.initials: RP
authors.lastname: Hirata
authors.affiliation: Center for Neuroplasticity and Pain, SMI, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Steffan W
authors.initials: SW
authors.lastname: Christensen
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, Queensland, Australia; University of Queensland, School of Biomedical Sciences, Queensland, Australia.
authors.forename: Kylie
authors.initials: K
authors.lastname: Tucker
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, Queensland, Australia.
authors.forename: Paul
authors.initials: P
authors.lastname: Hodges
authors.affiliation: Center for Neuroplasticity and Pain, SMI, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark. Electronic address: tgn@hst.aau.dk.
authors.forename: Thomas
authors.initials: T
authors.lastname: Graven-Nielsen
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D063806:Myalgia / Q000503:physiopathology; D020932:Nerve Growth Factor; D010147:Pain Measurement; D011312:Pressure; D019415:Torque; D014953:Wrist / Q000503:physiopathology
chemical_list: D020932:Nerve Growth Factor
keywords: Force; NGF; muscle pain; persistent pain