The aim of this study was to assess the influence of head position on dorsal neck muscle efficiency in the sagittal plane. Fifteen subjects participated. The EMG versus isometric extension moment of dorsal neck muscles was studied in neutral (with subject gazing on a horizontal plane), cervical flexed, and cervical extended positions. A vectorial construction was created by means of photographs to calculate the extension moment which balances measured pulling force and gravitational force in isometric conditions. The maximum extension was highest in neutral position. The EMG/moment relationship was non-linear. The ratio between the EMG and the generated moment differed significantly in the three positions (p < 0.01) and was lower in neutral position. These results demonstrate the influence of head position on dorsal neck muscle efficiency; muscles appeared most efficient in neutral position. Muscle length, depending on head position, is probably the main influencing factor.