In all studies related to measuring the strength of neck extensor muscles the level of thoracic support has been adjusted differently. This may provide different results from different studies in which the level of lever arm has been set differently. Objective: The aim of this study was to measure and compare the isometric force and the isometric torque of neck extensor muscles at different levels of thoracic supports. Methods: Twenty healthy women volunteered in the study. The isometric force of neck extensor muscles was measured while the thoracic support was located at five different levels. The highest level was set at the level of spine of scapula (level I) and the other levels were located 2.5 cm lower from the previous one. The lowest level was set at 10 centimeter lower than the highest one. The isometric torque for each level was calculated from the multiplication of isometric force by the length of the lever arm measured from the upper tip of thoracic support to the center point of the cell load at the occiput. Results: The amount of isometric force and isometric torque of neck extensor muscles were increased step by step from 130.5, 138.9, 141.9, 147.9 to 155.4 N and from 33.7, 38.7, 42.5, 47.2 to 52.7 Nm respectively. Except for the isometric force of cervical extensor muscles measured at the level of II and III, the differences between the other levels were significant (P< 0.05). There was a high significant correlation between isometric force and isometric torque measurements of neck extensor muscles at different levels (0.81 < r < 0.96). Conclusion: In this study, by changing the length of lever arm, the isometric force and isometric torque measurements of neck extensor muscles were varied accordingly. Therefore, it is strongly recommended to set a certain level of thoracic support in follow up and interventional studies. To set the level of thoracic support at a certain level may provide the possibility to compare the strength of neck extensor muscles from different studies. The measurements at the level of spine of scapula appeared to be an easy method and less time consuming. Key Words – neck, isometric, force, torque, support
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