title: Retest reliability of force-time variables of neck muscles under isometric conditions.
abstract: BACKGROUND
  Proper conditioning of the neck muscles may play a role in reducing the risk of neck injury and, possibly, concussions in contact sports. However, the ability to reliably measure the force-time-based variables that might be relevant for this purpose has not been addressed.
  
  
  OBJECTIVE
  To assess the between-days reliability of discrete force-time-based variables of neck muscles during maximal voluntary isometric contractions in 5 directions.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  University research center.
  
  
  METHODS
  Twenty-six highly physically active men (age  =  21.6 ± 2.1 years, height  =  1.85 ± 0.09 m, mass  =  81.6 ± 9.9 kg, head circumference  =  0.58 ± 0.01 m, neck circumference  =  0.39 ± 0.02 m).
  
  
  METHODS
  We used a custom-built testing apparatus to measure maximal voluntary isometric contractions of the neck muscles in 5 directions (extension, flexion, protraction, left lateral bending, and right lateral bending) on 2 separate occasions separated by 7 to 8 days.
  
  
  METHODS
  Variables measured were peak force (PF), rate of force development (RFD), and time to 50% of PF (T(50)PF). Reliability indices calculated for each variable comprised the difference in scores between the testing sessions, with corresponding 95% confidence intervals, the coefficient of variation of the typical error of measurement (CV(TE)), and intraclass correlation coefficients (ICC [3,3]).
  
  
  RESULTS
  No evidence of systematic bias was detected for the dependent measures across any movement direction; retest differences in measurements were between 1.8% and 2.7%, with corresponding 95% confidence interval ranges of less than 10% and overlapping zero. The CV(TE) was lowest for PF (range, 2.4%-6.3%) across all testing directions, followed by RFD (range, 4.8%-9.0%) and T(50)PF (range, 7.1%-9.3%). The ICC score range for all dependent measures was 0.90 to 0.99.
  
  
  CONCLUSIONS
  Discrete variables representative of the force-generating capacity of neck muscles under isometric conditions can be measured with an acceptable degree of reliability. This finding has possible applications for investigating the role of neck muscle strength-training programs in reducing the risk of injuries in sport settings.
authors.affiliation: School of Kinesiology and Health Studies, Queen's University, Kingston, ON, Canada.
authors.forename: Sivan
authors.initials: S
authors.lastname: Almosnino
authors.forename: Lucie
authors.initials: L
authors.lastname: Pelland
authors.forename: Joan M
authors.initials: JM
authors.lastname: Stevenson
mesh_terms: D001924:Brain Concussion / Q000209:etiology; D015331:Cohort Studies; D016001:Confidence Intervals; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009333:Neck / Q000502:physiology*; D019838:Neck Injuries / Q000209:etiology*; D015203:Reproducibility of Results; D013334:Students; D011795:Surveys and Questionnaires; D013997:Time Factors; D014495:Universities; D055815:Young Adult