Relationship between isometric cervical extension strength based on a cervical extension machine and the cross-sectional area of neck muscles

The purpose of this study was to examine the relationship between isometric cervical extension strength and the cross-sectional area (CSA) of neck extensor muscles in order to obtain fundamental data for conducting neck muscle training to prevent neck injuries. Subjects were 8 males belonging to the judo or American football club in N University. Isometric cervical extension strength was measured at eight positions (0 degrees, 18 degrees, 36 degrees, 54 degrees, 72 degrees, 90 degrees, 108 degrees, maximum flexion) using a cervical extension machine (Medx Inc., USA). A transaxial magnetic resonance imaging (MRI) image of neck muscles was obtained at the intervertebral disk between C4 and C5 (using an MRI machine made by Hitachi medical Corp., JAPAN). The findings were as follows. 1. The correlation between isometric cervical extension strength at 36 degrees, 54 degrees and 72 degrees in a neutral position (60.8+/-1.4 degrees) and the CSA of neck extensor muscles were higher than at other degrees (0 degrees, 18 degrees, 90 degrees, 108 degrees, maximum flexion). In particular, there was a significant linear relationship at 54 degrees (slightly extended position). 2. A significant linear relationship was observed between the neck girth and CSA of neck extensor muscles. In conclusion, there was a closer relationship between isometric cervical extension strengths at certain angles in a neutral position and the CSA of neck extensor muscles. Therefore, it was shown that isometric cervical extension strengths at certain angles in a neutral position mainly represented the CSA of neck extensor muscles.