title: EFFECT OF RESTRICTED HIP FLEXOR MUSCLE LENGTH ON HIP EXTENSOR MUSCLE ACTIVITY AND LOWER EXTREMITY BIOMECHANICS IN COLLEGE-AGED FEMALE SOCCER PLAYERS.
abstract: BACKGROUND
  Hip flexor tightness is theorized to alter antagonist muscle function through reciprocal inhibition and synergistic dominance mechanisms. Synergistic dominance may result in altered movement patterns and increased risk of lower extremity injury.
  
  
  OBJECTIVE
  To compare hip extensor muscle activation, internal hip and knee extension moments during double-leg squatting, and gluteus maximus strength in those with and without clinically restricted hip flexor muscle length.
  
  
  METHODS
  Causal-comparative cross-sectional laboratory study.
  
  
  METHODS
  Using a modified Thomas Test, female soccer athletes were assigned to a restricted (>0 ° of sagittal plane hip motion above the horizontal; n=20, age=19.9 ± 1 years, ht=167.1 ± 6.4 cm, mass=64.7 ± 8.2kg) or normal (>15 ° of sagittal plane hip motion below horizontal; n=20, age=19.4 ± 1 years, ht=167.2 ± 5.5 cm, mass=61.2 ± 8.6 kg) hip flexor muscle length group. Surface electromyographic (sEMG) activity of the gluteus maximus and biceps femoris, and net internal hip and knee extension moments were measured between groups during a double-leg squat. Isometric gluteus maximus strength was assessed using handheld dynamometry.
  
  
  RESULTS
  Individuals with restricted hip flexor muscle length demonstrated less gluteus maximus activation (p=0.008) and a lower gluteus maximus : biceps femoris co-activation ratio (p=0.004). There were no significant differences (p>0.05) in hip or knee extension moments, isometric gluteus maximus strength, or biceps femoris activation between groups.
  
  
  CONCLUSIONS
  Female soccer athletes with hip flexor muscle tightness exhibit less gluteus maximus activation and lower gluteus maximus : biceps femoris co-activation while producing similar net hip and knee extension moments. Thus, individuals with hip flexor muscle tightness appear to utilize different neuromuscular strategies to control lower extremity motion.
  
  
  METHODS
  3.
authors.affiliation: Stanford University - Sports Medicine, Serra Mall, Stanford, CA, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Mills
authors.affiliation: The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Barnett
authors.initials: B
authors.lastname: Frank
authors.affiliation: Fusionetics Performance Healthcare System, Alpharetta, GA, USA.
authors.forename: Shiho
authors.initials: S
authors.lastname: Goto
authors.affiliation: The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Troy
authors.initials: T
authors.lastname: Blackburn
authors.affiliation: The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Samantha
authors.initials: S
authors.lastname: Cates
authors.affiliation: Fusionetics Performance Healthcare System, Alpharetta, GA, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Clark
authors.affiliation: The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Alain
authors.initials: A
authors.lastname: Aguilar
authors.affiliation: Emory University, School of Allied Health, Atlanta, GA, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Fava
authors.affiliation: The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Darin
authors.initials: D
authors.lastname: Padua
keywords: ACL Injury; Electromyography; Hamstring Injury; Musculoskeletal Injury; Neuromuscular Control