title: Is synergistic organisation of muscle coordination altered in people with lateral epicondylalgia? A case-control study.
abstract: Lateral epicondylalgia is a common musculoskeletal disorder and is associated with deficits in the motor system including painful grip. This study compared coordination of forearm muscles (muscle synergies) during repeated gripping between individuals with and without lateral epicondylalgia.
  
  
  
  Twelve participants with lateral epicondylalgia and 14 controls performed 15 cyclical repetitions of sub-maximal (20% maximum grip force of asymptomatic arm), pain free dynamic gripping in four arm positions: shoulder neutral with elbow flexed to 90° and shoulder flexed to 90° with elbow extended both with forearm pronated and neutral. Muscle activity was recorded from extensor carpi radialis brevis/longus, extensor digitorum, flexor digitorum superficialis/profundus, and flexor carpi radialis, with intramuscular electrodes. Muscle synergies were extracted using non-negative matrix factorisation.
  
  
  
  Analysis of each position and participant, demonstrated that two muscle synergies accounted for >97% of the variance for both groups. Between-group differences were identified after electromyography patterns of the control group were used to reconstruct the patterns of the lateral epicondylalgia group. A greater variance accounted for was identified for the controls than lateral epicondylalgia (p=0.009). This difference might be explained by an additional burst of flexor digitorum superficialis electromyography during grip release in many lateral epicondylalgia participants.
  
  
  
  These data provide evidence of some differences in synergistic organisation of activation of forearm muscles between individuals with and without lateral epicondylalgia. Due to study design it is not possible to elucidate whether changes in the coordination of muscle activity during gripping are associated with the cause or effect of lateral epicondylalgia.
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Science, Brisbane, Australia; Central Queensland University, School of Human, Health and Social Sciences, Division of Physiotherapy, Rockhampton, Australia. Electronic address: l.heales@uq.edu.au.
authors.forename: Luke James
authors.initials: LJ
authors.lastname: Heales
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Science, Brisbane, Australia; University of Nantes, Laboratory EA, 4334, Nantes, France. Electronic address: f.hug@uq.edu.au.
authors.forename: François
authors.initials: F
authors.lastname: Hug
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Science, Brisbane, Australia. Electronic address: d.macdonald1@uq.edu.au.
authors.forename: David Alan
authors.initials: DA
authors.lastname: MacDonald
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Science, Brisbane, Australia. Electronic address: b.vicenzino@uq.edu.au.
authors.forename: Bill
authors.initials: B
authors.lastname: Vicenzino
authors.affiliation: University of Queensland, NHMRC Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Science, Brisbane, Australia. Electronic address: p.hodges@uq.edu.au.
authors.forename: Paul William
authors.initials: PW
authors.lastname: Hodges
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016022:Case-Control Studies; D004551:Elbow Joint / Q000502:physiology; D004576:Electromyography; D005260:Female; D005542:Forearm / Q000502:physiology*; D006225:Hand / Q000502:physiology; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010147:Pain Measurement; D011403:Pronation; D016059:Range of Motion, Articular / Q000502:physiology; D013716:Tennis Elbow / Q000503:physiopathology*
keywords: Electromyography; Muscle synergies; Non-negative matrix factorization; Tennis elbow