Validation of a Novel device for Assessing Neck Muscle Strength

Abstract

Background: The Neuromuscular Cranio-Cervical Device (NOD) was originally designed to evaluate Cranio-Cervical Flexion Test performance but can also be used as a handheld dynamometer for testing other muscle groups, including neck muscle strength. It offers a potential alternative to the Multi-Cervical Unit (MCU), a fixed dynamometer, more closely aligned with isokinetic dynamometry, the gold standard. However, its validity and reliability need to be established. This study aimed to evaluate concurrent validity compared to the MCU and inter- and intra-rater reliability of the NOD for measuring neck flexion and extension muscle strength.

Methods: Twenty participants were assessed for neck flexion/extension strength whilst in a seated position, with the measurements repeated over three sessions. Concurrent validity was assessed by comparing NOD measurements to the MCU using Pearson correlation coefficients, and reliability was determined using Intraclass Correlation Coefficients (ICCs).

Results: Concurrent validity was strong for extension (r = 0.954) but lower for flexion (r = 0.705), indicating some variability in flexion measurements. Inter-rater reliability was good to excellent for both flexion (ICC = 0.931) and extension (ICC = 0.896). Intra-rater reliability for extension was good to excellent (ICC = 0.893), while flexion ranged from moderate to excellent (ICC = 0.844).

Conclusions: The NOD is a valid tool, particularly for extension measurements, although further refinement of testing is needed to improve the accuracy for flexion strength measurements. It is also reliable for both extension and flexion, showing promise as a practical, affordable, portable tool with real-time feedback for the assessment of neck muscle strength in clinical settings.

Keywords: Concurrent Validity; Handheld Dynamometer; Inter-rater Reliability; Intra-rater Reliability; Multi-Cervical Unit; Neck Muscle Strength.

FIGURE 1 -

Neck muscle strength testing for flexion and extension using two different methods: a handheld dynamometer (NOD) (A, B) and the Multi-Cervical Unit (MCU) (C, D). In panels A and B, the individual was seated with their arms crossed and a belt around the waist to stabilize the trunk, minimizing compensatory movements. The experimenter held the handheld dynamometer (NOD) on the forehead (A) for flexion and on the occiput (B) for extension, applying force while ensuring consistent contact with the head. In panels C and D, the individual is seated with their arms crossed and secured at the waist and chest with belts to stabilize the trunk and prevent extraneous movement. The head is positioned within the adjustable frame of the MCU, with the device set to the appropriate attachment for each movement. For extension (D), the attachment is tilted 15 degrees so that the point of force application is correctly aligned on the occiput.

FIGURE 2 -

Scatter plots with regression lines (A, B) and Bland-Altman plots (C, D) comparing NOD measurements with MCU for both neck flexion (A, C) and neck extension (B, D). In panels A and B, the x-axis represents the NOD measurements, and the y-axis represents the MCU measurements. The solid black lines indicate the regression lines, while the shaded areas represent the 95% CIs. These plots illustrate the relationship between the two methods, highlighting the strength and direction of their correlation for both flexion (A) and extension (B). In panels C and D, the x-axis represents the average of the measurements from the NOD and MCU methods, while the y-axis shows the difference between the NOD and MCU measurements. The red dashed line indicates the mean bias, reflecting the average difference between the two methods, and the black dotted lines represent the 95% limits of agreement, showing the range within which most differences are expected to fall. These plots assess the validity of the NOD method by comparing its measurements to the MCU for both flexion (C) and extension (D), highlighting any systematic bias and the level of agreement between the two methods.

FIGURE 3 -

Bland-Altman plots for inter-rater (A, B) and intra-rater (C, D) measurements of neck flexion and extension. In panels A and B, the x-axis represents the average of the two raters’ measurements, while the y-axis indicates the difference between their measurements. The red dashed line represents the mean bias, showing the average difference between raters, and the black dotted lines indicate the upper and lower 95% limits of agreement, outlining the range within which most of the differences between the raters are expected to fall. In panels C and D, the x-axis represents the average of the measurements taken by the same rater across sessions 1 and 3, while the y-axis represents the difference between those repeated measurements. The red dashed line represents the mean bias, indicating the average difference between the repeated measurements by the same rater, and the black dotted lines mark the upper and lower 95% limits of agreement, showing the range within which most differences are expected to fall. Panels A and C correspond to neck flexion measurements, while panels B and D correspond to neck extension measurements.