European Journal of Applied Physiology

, Volume 113, Issue 3, pp 567–575

Variability of three-dimensional forces increase during experimental knee pain

  • Sauro E. Salomoni
  • Ashir Ejaz
  • Anders C. Laursen
  • Thomas Graven-Nielsen
Original Article

DOI: 10.1007/s00421-012-2461-2

Cite this article as:
Salomoni, S.E., Ejaz, A., Laursen, A.C. et al. Eur J Appl Physiol (2013) 113: 567. doi:10.1007/s00421-012-2461-2

Abstract

Knee pain is a common symptom of different knee pathologies, affecting muscle strength and force generation. Although the control of precise three-dimensional forces is essential for the performance of functional tasks, current evidence of pain effects in force variability is limited to single-directional assessments of contractions at moderate force levels. This study assessed the effects of experimental knee joint pain in the three-dimensional force variability during isometric knee extensions at a wide range of target forces (2.5–80 % of maximal voluntary contraction, MVC). Fifteen healthy subjects performed contractions before, immediately following, and after injections of hypertonic (painful) or isotonic (control) saline into the infrapatellar fat pad. Pain intensity was measured on a 10-cm visual analogue scale. Force magnitude, direction, and variability were assessed using a six-axis force sensor while activity of quadriceps and hamstring muscles was recorded by surface electromyography. Significant correlation was found between tangential force displacements and variability of quadriceps muscle activity. Experimental knee pain increased the variability of the task-related force component at all force levels, while variability of tangential force components increased at low forces (≤5 % of MVC). The mean quadriceps activity decreased during painful contractions only at 80 % of MVC. Pain adaptations underlying increased force variability at low contraction levels probably involve heterogeneous reorganization of muscle activity, which could not be detected by surface electrodes. These findings indicate a less efficient motor strategy during knee joint pain, suggesting that pain relief may enhance training for the control of smooth forces by knee pain patients.

Keywords

Knee pain Force variability Motor control Adaptation Isometric force 

Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Sauro E. Salomoni
    • 1
  • Ashir Ejaz
    • 2
  • Anders C. Laursen
    • 2
  • Thomas Graven-Nielsen
    • 1
  1. 1.Laboratory for Musculoskeletal Pain and Motor Control, Department of Health Science and Technology, Faculty of Medicine, Center for Sensory-Motor Interaction (SMI)Aalborg UniversityAalborg EDenmark
  2. 2.Orthopaedic DepartmentAalborg HospitalAalborg EDenmark

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