PMC

Grip force magnitude decreased with increase in handle diameter (p<0.05) except when comparing force magnitudes for handle 1 and handle 2, and handle 1 and handle 3. Grip force vector direction decreased with increase in handle diameter (p<0.05) except when comparing force directions for handle 2 and handle 3. A decrease in force vector direction corresponds to clockwise rotation in force vector toward the thumb-tip ().

Schematic diagram of the experimental handles used for the prehension experiment. (a) Experimental handle utilized for experiments 1 and 2. The mass of the handle, including the counter-weight, was 0.535 kg. In the case of experiment 1, only two horizontal lines were drawn: one at the center of the thumb platform and the other at the midway between middle and ring fingers (HOME position). For experiment 2, in addition to the two horizontal lines, two more lines were drawn (1.5 cm above from HOME and 1.5 cm below from HOME). The dimensions of the handle frame of the handle used for the first and second experiment is (20 × 1 × 3) cm (b) Experimental handle utilized for experiment 3 and 4. The total mass of the handle, excluding the external load, was 0.450 kg. An external load of any of the mass 0.150 kg, 0.250 kg, 0.350 kg, and 0.450 kg was attached at the bottom of the handle below the center of mass of the handle (represented with symbol ‘X’) depending on the condition in the case of experiment 3. For both the conditions of experiment 4, an external load of mass 0.250 kg was attached at the bottom of the handle. The dimensions of the handle frame of the handle used for the third experiment are (21 × 1 × 3) cm. I, M, R, L, T represents index, middle, ring, little, and thumb.

A: male and female segments; B: inner surface; C: interlocked handle

A: male and female segments; B: inner surface; C: interlocked handle