Biomechanics of the human hand during suspensory locomotion: a combined pressure and kinematic approach.

The human hand is a key anatomical area for understanding behavioural transitions in fossil hominins, particularly in relation to the evolution of human locomotion. Previous studies have examined the pressure distribution in non-human primate arboreal and terrestrial locomotion although pressure in relation to human arboreal locomotion remains unstudied. A novel combined pressure and kinematic approach is used to quantify for the first time pressure and the location of peak pressure experienced by the human hand across a range of diameters and hand postures during static and dynamic suspension activities. Significant differences were found in normalised peak pressure between the 45mm and 105mm diameters when all activity categories were combined (thumb adducted, thumb abducted, and dynamic suspension). Further analysis showed that for separate activity categories there were significant differences in normalised peak pressure between the 45mm and 105mm diameters for both the thumb adducted and abducted activities. In all cases the 45mm diameter had a greater normalised peak pressure value. The location of peak pressure has been shown to be significantly affected by diameter on the third digit and fourth proximal phalanx when the thumb is abducted. The mode locations for all activities and diameters were on the fourth-to-second digits and moved distally as the diameter increased from 45mm to 105mm. These results suggest that increasing the diameter of a superstrate [support positioned above the body: Hunt K D, Cant J G H, Gebo D L, Rose M D, Walker S E, and Youlatos D (1996) Standardized descriptions of primate locomotor and postural modes. Primates. 37: 363-387] decreases the normalised peak pressure and that diameter size affects the location of peak pressure when the thumb is abducted during suspension. There was a significant preference for the 45mm diameter out of all three diameter sizes. These results are consistent with ergonomic studies of grasping by human hand during daily manipulative activities.