Background: In all studies in which the strength of the neck extensor muscles has been measured, the level of thoracic support has been adjusted differently so direct comparison of the results is not possible.
Objective: To measure and compare the isometric force and isometric torque of neck extensor muscles at different levels of thoracic support.
Methods: Twenty healthy women volunteered for the study. The maximum isometric force of the neck extensor muscles was measured with the thoracic support located at five different levels. The highest level was set at the level of the spine of the scapula (level I) and the other levels were located 2.5 cm lower than the previous one, with the lowest level set 10 cm below the highest level. The maximum isometric torque for each level was calculated by multiplying the isometric force by the length of the lever arm measured from the upper tip of the thoracic support to the centre point of the cell load at the occiput.
Results: The maximum isometric force and maximum isometric torque of the neck extensor muscles were increased step by step from 130.5 N to 138.9 N, 141.9 N, 147.9 N and 155.4 N and from 33.7 Nm to 38.7 Nm, 42.5 Nm, 47.2 Nm and 52.7 Nm, respectively. Except for the isometric force of the cervical extensor muscles measured at levels II and III, the differences between the other levels were significant (p<0.05). There was a significant correlation between isometric force and isometric torque measurements of the neck extensor muscles at different levels (0.81<r<0.96).
Conclusion: Maximum isometric force and maximum isometric torque measurements of the neck extensor muscles vary with the length of the lever arm. It is recommended that a specific level of thoracic support should be used in follow-up and intervention studies. Setting the level of thoracic support at a specific level will make it possible to compare the strength of the neck extensor muscles in different studies. Measurements at the level of the spine of the scapula were easier and less time consuming.
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Competing interests: None.
Ethics approval: Informed consent was given by all subjects prior to the study and the study was approved by the ethical committee of the Medical University of Shahid Beheshti (Medical Sciences), Tehran, Iran.
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