Influence of vision and posture on grip-lift task parameters in healthy adults

The grip-lift task enables a quantitative assessment of grasping ability. Patients are regularly assessed in a supine position, which offers a different view of the grasped object from that in the sitting position. To our knowledge, no data are currently available on the influence of posture and vision on grip-lift task parameters. We therefore aimed to determine the effects of posture and vision on these parameters. Twenty-six healthy right-handed adults performed grip-lift tasks with a manipulandum that measured different temporal and dynamic parameters in four conditions: sitting eyes open, sitting blindfolded, lying down eyes open and lying down blindfolded. A repeated-measures analysis of variance with two factors (vision and position) showed that the absence of vision affected all the parameters measured. The lying down position increased the time between the first contact with the object and the modification of the vertical force as well as the delay between the first increase of the horizontal force and the increase of the vertical force. In addition, there was a lower adaption of the horizontal force, required to squeeze the object, to the vertical force. Finally, the interaction of position and vision was associated with significant differences in the delay between the contact of each digit with the object, the maximum horizontal force and the ratio between the horizontal and vertical force during a static holding period. Both position and vision appear to affect the grip-lift task. Consequently, sequential assessments should be performed in the same condition to obtain reliable data.