title: Acute experimental hip muscle pain alters single-leg squat balance in healthy young adults.
abstract: BACKGROUND
  Clinical musculoskeletal pain commonly accompanies hip pathology and can impact balance performance. Due to the cross-sectional designs of previous studies, and the multifactorial nature of musculoskeletal pain conditions, it is difficult to determine whether pain is a driver of balance impairments in this population. This study explored the effects of experimentally induced hip muscle pain on static and dynamic balance.
  
  
  METHODS
  Twelve healthy adults (4 women, mean[SD]: 27.1[3] years) performed three balance tasks on each leg, separately: single-leg standing (eyes closed), single-leg squat (eyes open), forward step (eyes open); before and after hypertonic saline injection (1ml, 5% NaCl) into the right gluteus medius. Range, standard deviation (SD), and velocity of the centre of pressure (CoP) in medio-lateral (ML) and anterior-posterior (AP) directions were considered.
  
  
  RESULTS
  During the single-leg squat task, experimental hip pain was associated with significantly reduced ML range (-4[13]%, P=0.028), AP range (-14[21]%, P=0.005), APSD (-15[28]%, P=0.009), and AP velocity (-6[13]%, P=0.032), relative to the control condition, in both legs. No effect of pain was observed during single-leg standing and forward stepping. Significant between-leg differences in ML velocity were observed during the forward stepping task (P=0.034).
  
  
  CONCLUSIONS
  Pain is a potentially modifiable patient-reported outcome in individuals with hip problems. This study demonstrates that acute hip muscle pain alone, without interference of musculoskeletal pathology, does not lead to the same impairments in balance as exhibited in clinical populations with hip pathologies. This is the first step in understanding how and why balance is altered in painful hip pathologies.
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: a.hatton1@uq.edu.au.
authors.forename: Anna L
authors.initials: AL
authors.lastname: Hatton
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: k.crossley@uq.edu.au.
authors.forename: Kay M
authors.initials: KM
authors.lastname: Crossley
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia; Laboratory EA 4334, University of Nantes, Nantes, France. Electronic address: f.hug@uq.edu.au.
authors.forename: François
authors.initials: F
authors.lastname: Hug
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: jamesbouma@gmail.com.
authors.forename: James
authors.initials: J
authors.lastname: Bouma
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: ha.bonnie@gmail.com.
authors.forename: Bonnie
authors.initials: B
authors.lastname: Ha
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: karaspaulding@hotmail.com.
authors.forename: Kara L
authors.initials: KL
authors.lastname: Spaulding
authors.affiliation: School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia. Electronic address: k.tucker1@uq.edu.au.
authors.forename: Kylie
authors.initials: K
authors.lastname: Tucker
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D064368:Healthy Volunteers; D006615:Hip / Q000503:physiopathology; D006801:Humans; D007866:Leg / Q000503:physiopathology*; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D063806:Myalgia / Q000503:physiopathology*; D011187:Posture / Q000502:physiology*
keywords: Balance performance; Hip muscle pain; Hypertonic saline