Three-dimensional isometric strength of neck muscles in humans.

STUDY DESIGN Three-dimensional moments were measured experimentally during maximum voluntary contractions of neck muscles in humans. OBJECTIVES To characterize the maximum moments with attention paid to subject size and gender, to calculate moments at different locations in the neck, and to quantify the relative magnitudes of extension, flexion, lateral bending, and axial rotation moments. SUMMARY OF BACKGROUND DATA Few studies of neck strength have measured moments in directions other than extension, and it is difficult to compare results among studies because moments often are resolved at different locations in the cervical spine. Further, it is not clear how subject size, gender, and neck geometry relate to variations in the moment-generating capacity of neck muscles. METHODS Maximum moments were measured in 11 men and 5 women with an average age of 31 years (range, 20-42 years). Anatomic landmarks were digitized to resolve moments at different locations in the cervical spine. RESULTS When moments were resolved about axes through the midpoint of the line between the C7 spinous process and the sternal notch, the maximum moments were as follows: extension (men, 52 +/- 11 Nm; women, 21 +/- 12 Nm), flexion (men, 30 +/- 5 Nm; women, 15 +/- 4 Nm), lateral bending (men, 36 +/- 8 Nm; women, 16 +/- 8 Nm), and axial rotation (men 15 +/- 4; women, 6 +/- 3) Nm). The magnitudes of extension, flexion, and lateral bending moments decreased linearly with vertical distance from the lower cervical spine to the mastoid process. CONCLUSIONS Moments in three dimensions were quantified with regard to subject size and location along the cervical spine. These data are needed to characterize neck strength for biomechanical analysis of normal and pathologic conditions.