The reliability of a handheld dynamometer in measuring maximal isometric neck strength
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Neck pain is the fourth leading cause of disability worldwide, and is a burden to both the affected individual and the society. Several studies have documented decreased neck strength in patients with chronic neck pain. However, there is a need for a practical and reliable device to measure neck strength in clinical practice. The main objective of this study was to determine the reliability of a handheld dynamometer in measuring maximal isometric neck strength in flexion, extension and lateral flexion. A second objective was to determine whether neck extension/flexion ratio was altered in patients with chronic neck pain, compared to healthy controls. The reliability study included 50 healthy participants tested in flexion, extension and lateral flexion on three different occasions. To determine any differences in extension/flexion strength ratio, 19 patients with chronic neck pain were tested in flexion and extension. The intraclass correlation coefficient (ICC) indicated excellent reliability in all movement directions tested (mean ICC ranged from 0.89 to 0.96). Moreover, the results also indicated a reduction in within-subject variation between test days 2-3, compared to test days 1-2. The extension/flexion ratio was similar in both healthy controls and patients with chronic neck pain (1.59±0.5 vs 1.57±0.38), i.e., both patients and controls were approximately 60% stronger in extension than flexion. In conclusion, a handheld dynamometer is a reliable tool to measure maximal isometric neck strength in flexion, extension and lateral flexion in healthy subjects. There is no difference in the extension/flexion strength ratio in patients with chronic neck pain, compared to healthy controls.