title: Acute Responses of Strength and Running Mechanics to Increasing and Decreasing Pain in Patients With Patellofemoral Pain.
abstract: BACKGROUND
  Patellofemoral pain (PFP) is typically exacerbated by repetitive activities that load the patellofemoral joint, such as running. Understanding the mediating effects of changes in pain in individuals with PFP might inform injury progression, rehabilitation, or both.
  
  
  OBJECTIVE
  To investigate the effects of changing pain on muscular strength and running biomechanics in those with PFP.
  
  
  METHODS
  Crossover study.
  
  
  METHODS
  University research laboratory.
  
  
  METHODS
  Seventeen participants (10 men, 7 women) with PFP.
  
  
  METHODS
  Each participant completed knee pain-reducing and pain-inducing protocols in random order. The pain-reducing protocol consisted of 15 minutes of transcutaneous electric nerve stimulation (TENS) around the patella. The pain-inducing protocol was sets of 20 repeated single-legged squats (RSLS). Participants completed RSLS sets until either their pain was within at least 1 cm of their pain during an exhaustive run or they reached 10 sets.
  
  
  METHODS
  Pain, isometric hip and trunk strength, and running mechanics were assessed before and after the protocols. Dependent variables were pain, normalized strength (abduction, extension, external rotation, lateral trunk flexion), and peak lower extremity kinematics and kinetics in all planes. Pain scores were analyzed using a Friedman test. Strength and mechanical variables were analyzed using repeated-measures analyses of variance. The α level was set at P < .05.
  
  
  RESULTS
  Pain was decreased after the TENS (pretest: 3.10 ± 1.95, posttest: 1.89 ± 2.33) and increased after the RSLS (baseline: 3.10 ± 1.95, posttest: 4.38 ± 2.40) protocols (each P < .05). The RSLS protocol resulted in a decrease in hip-extension strength (baseline: 0.355 ± 0.08 kg/kg, posttest: 0.309 ± 0.09 kg/kg; P < .001). Peak plantar-flexion angle was decreased after RSLS (baseline: -13.97° ± 6.41°, posttest: -12.84° ± 6.45°; P = .003). Peak hip-extension (pretest: -2.31 ± 0.46) and hip-abduction (pretest: -2.02 ± 0.35) moments decreased after both the TENS (extension: -2.15 ± 0.48 Nm/kg, P = .015; abduction: -1.91 ± 0.33 Nm/kg, P = .015) and RSLS (extension: -2.18 ± 0.52 Nm/kg, P = .003; abduction: -1.87 ± 0.36 Nm/kg, P = .039) protocols.
  
  
  CONCLUSIONS
  This study presents a novel and effective method of increasing pain in persons with PFP. Functionally increased pain after RSLS coincides with reduced hip-extensor muscle strength and decreased plantar-flexion angle during running. The TENS treatment decreased pain during running in those with PFP but failed to influence strength. Hip moments were reduced by both protocols, which may demonstrate that acute increases or decreases in pain cause runners to change their mechanics.
authors.affiliation: Carroll University, Waukesha, WI.
authors.forename: David M
authors.initials: DM
authors.lastname: Bazett-Jones
authors.affiliation: University of Wisconsin-Milwaukee.
authors.forename: Wendy
authors.initials: W
authors.lastname: Huddleston
authors.affiliation: University of Wisconsin-Milwaukee.
authors.forename: Stephen
authors.initials: S
authors.lastname: Cobb
authors.affiliation: University of Wisconsin-Milwaukee.
authors.forename: Kristian
authors.initials: K
authors.lastname: O'Connor
authors.affiliation: University of Wisconsin-Milwaukee.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Earl-Boehm
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D019637:Orthopedic Procedures / Q000379:methods*; D017063:Outcome Assessment, Health Care; D059408:Pain Management / Q000379:methods; D010147:Pain Measurement / Q000379:methods; D057071:Patellofemoral Joint / Q000293:injuries / Q000503:physiopathology; D046788:Patellofemoral Pain Syndrome / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy; D016059:Range of Motion, Articular / Q000502:physiology; D012420:Running / Q000502:physiology
keywords: kinematics; kinetics; knee; transcutaneous electric nerve stimulation