The patterns of activation of splenius capitis, semispinalis capitis, transversospinalis, and levator scapulae muscles were studied during various head-neck positions, movements, and isometric tests in 19 healthy human subjects. Myoelectric activities were recorded with intramuscular bipolar wire electrodes. Cervical computerized tomography of each subject was performed before the electromyography session in order to guide electrode insertion. Head motion was recorded using an electromechanical device. This report demonstrates that head motion results from a complex interaction of active muscular forces, passive ligamentous forces, and gravity. Splenius capitis has two main functions, i.e., cervical extension and ipsilateral rotation. Semi spinalis capitis and the transversospinalis are mainly extensors, and levator scapulae acts primarily on the shoulder girdle. Splenius capitis, semispinalis capitis, and transversospinalis play a subordinate part in ipsilateral tilting. In addition, most subjects' semispinalis capitis were gradually recruited during ipsilateral rotation. No signal was detected from the transversospinalis during rotation tests.