Synchronization of human finger movements: delays and sex differences with isotonic 'antiphase' motion

The interval between the operation of two Morse keys, or the moments at which fingers touched or broke contact with electrical conductors, has been measured, the subjects making the movements as synchronously as possible. The data obtained deal with timings when two fingers flexed or extended together ('in phase') and when one finger extended whilst the other flexed ('antiphase'). For antiphase movements of the index fingers with the conductors, flexion usually occurred before extension so there was 'overlap'. Statistically, this period was greater in women and unusually high values were found in one subject with mild cerebral palsy. Overlap was not found using the keys. Using conductors, the timing of antiphase movements for the index and middle fingers of the right and left hand showed overlap again. No significant relationships were found with handedness. When the conductors were placed above the fingers, and the contact was thus with the dorsum, extension took place before flexion: both fingers were extended for a while, with overlap occurring again. The significance of these findings for the understanding of motor control is discussed.