title: Low back and lower-limb muscle performance in male and female recreational runners with chronic low back pain.
abstract: METHODS
  Controlled laboratory study, cross-sectional.
  
  
  OBJECTIVE
  To compare lumbar extensor muscle fatigability, lumbar stabilizing muscle activation, and lower-limb strength between male and female runners with chronic low back pain (LBP) and healthy runners.
  
  
  BACKGROUND
  Little is known about muscle performance in runners with chronic LBP.
  
  
  METHODS
  Eighteen recreational runners with chronic LBP (9 men, 9 women; mean age, 27.8 years) and 18 healthy recreational runners (9 men, 9 women; mean age, 24.6 years) were recruited. The median frequency slopes for bilateral iliocostalis and longissimus were calculated from electromyographic signals captured during a 2-minute Sorensen test. The thickness changes of the transversus abdominis and lumbar multifidus between resting and contraction were measured using an ultrasound scanner. Peak concentric torques of the bilateral hip extensors, hip abductors, and knee extensors were measured using an isokinetic dynamometer at 60°/s. The average values for both sides were used for statistical analysis.
  
  
  RESULTS
  When averaged across sexes, peak knee extensor torque was 12.2% lower in the LBP group compared to the healthy group (mean difference, 0.29 Nm/kg; 95% confidence interval: 0.06, 0.53; P = .016). Male runners with chronic LBP exhibited smaller lumbar multifidus thickness changes compared to healthy male runners (mean difference, 0.13 cm; 95% confidence interval: 0.01, 0.25; P = .033). No other group differences were observed.
  
  
  CONCLUSIONS
  Runners with chronic LBP exhibited diminished knee extensor strength compared to healthy runners. Male runners with chronic LBP demonstrated additional deficits in lumbar multifidus activation.
authors.affiliation: Physical Education and Sports Science Academic Group, National Institute of Education, Nanyang Technological University, Singapore.
authors.forename: Congcong
authors.initials: C
authors.lastname: Cai
authors.forename: Pui W
authors.initials: PW
authors.lastname: Kong
mesh_terms: D000328:Adult; D064131:Back Muscles / Q000502:physiology*; D002908:Chronic Disease; D003430:Cross-Sectional Studies; D004576:Electromyography; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology*; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D019415:Torque; D055815:Young Adult
keywords: electromyography; isokinetic strength; muscle activation; rehabilitative ultrasound image