title: Experimental knee pain impairs submaximal force steadiness in isometric, eccentric, and concentric muscle actions.
abstract: BACKGROUND
  Populations with knee joint damage, including arthritis, have noted impairments in the regulation of submaximal muscle force. It is difficult to determine the exact cause of such impairments given the joint pathology and associated neuromuscular adaptations. Experimental pain models that have been used to isolate the effects of pain on muscle force regulation have shown impaired force steadiness during acute pain. However, few studies have examined force regulation during dynamic contractions, and these findings have been inconsistent. The goal of the current study was to examine the effect of experimental knee joint pain on submaximal quadriceps force regulation during isometric and dynamic contractions.
  
  
  METHODS
  The study involved fifteen healthy participants. Participants were seated in an isokinetic dynamometer. Knee extensor force matching tasks were completed in isometric, eccentric, and concentric muscle contraction conditions. The target force was set to 10 % of maximum for each contraction type. Hypertonic saline was then injected into the infrapatella fat pad to generate acute joint pain. The force matching tasks were repeated during pain and once more 5 min after pain had subsided.
  
  
  RESULTS
  Hypertonic saline resulted in knee pain with an average peak pain rating of 5.5 ± 2.1 (0-10 scale) that lasted for 18 ± 4 mins. Force steadiness significantly reduced during pain across all three muscle contraction conditions. There was a trend to increased force matching error during pain but this was not significant.
  
  
  CONCLUSIONS
  Experimental knee pain leads to impaired quadriceps force steadiness during isometric, eccentric, and concentric contractions, providing further evidence that joint pain directly affects motor performance. Given the established relationship between submaximal muscle force steadiness and function, such an effect may be detrimental to the performance of tasks in daily life. In order to restore motor performance in people with painful arthritic conditions of the knee, it may be important to first manage their pain more effectively.
authors.affiliation: Health and Rehabilitation Research Institute, Auckland University of Technology, Private Bag 92006, Auckland, 1142, New Zealand. drice@aut.ac.nz.|Waitemata Pain Service, Department of Anaesthesia and Perioperative Medicine, North Shore Hospital, Private Bag 93-503, Takapuna, Auckland, New Zealand. drice@aut.ac.nz.
authors.forename: David A
authors.initials: DA
authors.lastname: Rice
authors.affiliation: Health and Rehabilitation Research Institute, Auckland University of Technology, Private Bag 92006, Auckland, 1142, New Zealand. peter.mcnair@aut.ac.nz.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: McNair
authors.affiliation: Health and Rehabilitation Research Institute, Auckland University of Technology, Private Bag 92006, Auckland, 1142, New Zealand. gwyn.lewis@aut.ac.nz.
authors.forename: Gwyn N
authors.initials: GN
authors.lastname: Lewis
authors.affiliation: Unitec Institute of Technology, Private Bag 92025, Victoria St West, Auckland, New Zealand. jaymannion@gmail.com.
authors.forename: Jamie
authors.initials: J
authors.lastname: Mannion
mesh_terms: D000293:Adolescent; D000328:Adult; D018771:Arthralgia / Q000139:chemically induced / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009048:Motor Skills / Q000502:physiology; D053581:Muscle Strength Dynamometer; D052097:Quadriceps Muscle / Q000503:physiopathology*; D012462:Saline Solution, Hypertonic; D055815:Young Adult
chemical_list: D012462:Saline Solution, Hypertonic