Objective: To evaluate the reproducibility of measurement for maximum voluntary isometric contractions of the cervical musculature in different movements.
Design: Repeated test-retest measurements.
Setting: A department of physiotherapy.
Participants: Thirty-three healthy subjects (17 men, 16 women; age range, 19-63 y) for the intraexaminer study and 10 healthy subjects (4 men, 6 women; age range, 20-37 y) for the interexaminer study.
Interventions: Maximum isometric strength in sitting and standing for flexion, extension, lateral flexion, and rotation using a custom isomyometer device. Three tests, performed 5 to 8 days apart, to assess intraexaminer reliability. Two examiners, each performing 1 trial, measuring on the same day to assess interexaminer reliability.
Main outcome measures: Intraexaminer and interexaminer reliability of neck muscle strength.
Results: The standing position showed better reproducibility than the sitting position. The intraclass correlation coefficient (ICC1,3) was above .84 for all tests in any movement and position and above .93 when the first test was excluded. The standard error (SE) of measurement (<16.5 N; <.13 N-m for rotation) and smallest detectable difference (SDD) (<20.1%) were also small. For interexaminer reliability, the ICC(2,1) ranged from.88 to.94 and the SE from 10.7 to 20.8 N (<1.15 N-m for rotation); the SDD was less than 29.8% (except right rotation, which was 38.8%).
Conclusions: A reliable protocol for measuring neck strength has been developed. Standing position and a full practice session produces more reliable measurements.