Supplementary Electronic Material
Statistical analysis of movement kinematics and finger forces
The range of wrist flexion-extension motion (ROM) varied across subjects. The minimum ROM was 66.6 4.9 (mean SD), and the maximum ROM was 124.7 9.2. For four subjects, the ROM did not vary with frequency. For the other four, the ROM means were significantly different for some frequencies, but the size of these differences was small (the largest difference was 8).
The subjects moved faster for higher FREQUENCY without reducing their ROM. The oscillatory movement of the handle creates radial and tangential accelerations (along directions in Fig. 2) proportional to the object’s angular velocity and acceleration, respectively. Hence, it was expected that the amplitudeof accelerations, defined as the difference between peaks and valleys of tangential acceleration () and the maximum peak height for radial acceleration (), will change with the prescribed movement FREQUENCY. The amplitudes of both tangential and radial accelerations were significantly different for the three FREQUENCIES for all subjects (data pooled across WEIGHT). Across subjects and frequencies, the radial acceleration amplitude varies from 7.9 1.9 rad/s2 to 64.7 14.0 rad/s2 and the tangential acceleration amplitude varies from 40.9 5.1 rad/s2 to 125.4 15.7 rad/s2.
The changes in radial and tangential accelerations with FREQUENCY translated to concomitant changes in handle accelerations along and for most cases. The inertial accelerations and along and , respectively, are estimated separately for flexion and extension movement cycles using Equations 1 and 2. Their amplitudes were computed as the difference between the minimum and the maximum values for a cycle. The amplitude of increased with FREQUENCY for flexion and extension and for all subjects. Across all cases, ranged from 2.3 0.5 m/s2 to 11.3 1.4 m/s2. The amplitude of increased significantly with FREQUENCY in all cases for four subjects. For the other four subjects, the change was not significant in seven out of 24 (3 pairs 2 directions 4 subjects) pair-wise comparisons. The actual values ranged from 1.5 0.6 m/s2 to 8.1 1.2 m/s2.
Changes in object acceleration with FREQUENCY and WEIGHT corresponded to significant changes in TH and VF normal forces. The mean values of these forces computed over the individual movement half cycle were significantly affected by FREQUENCY and WEIGHT for 184 out of 192 (8 subjects 2 variables 2 movement directions 6 pair-wise comparisons) pair-wise post-hoc comparisons. In no case were the means of both the TH and VF forces simultaneously unaffected by any factor. There were three cases wherein the TH and VF normal-force amplitudes were simultaneously unaffected by FREQUENCY. There were 11 other cases wherein a factor had no significant effect on the amplitude of the TH or the VF normal force.
We conclude that the task design successfully resulted in the desired mechanical effects on the handle kinematics and finger forces.
1