Characterization of normative hand movements during two functional upper limb tasks

Abstract

Background: Dexterous hand function is crucial for completing activities of daily living (ADLs), which typically require precise hand-object interactions. Kinematic analyses of hand trajectory, hand velocity, and grip aperture provide valuable mechanistic insights into task performance, but there is a need for standardized tasks representative of ADLs that are amenable to motion capture and show consistent performance in non-disabled individuals. Our objective was to develop two standardized functional upper limb tasks and to quantitatively characterize the kinematics of normative hand movement.

Methods: Twenty non-disabled participants were recruited to perform two tasks: the Pasta Box Task and Cup Transfer Task. A 12-camera motion capture system was used to collect kinematic data from which hand movement and grip aperture measures were calculated. Measures reported for reach-grasp and transport-release segments were hand distance travelled, hand trajectory variability, movement time, peak and percent-to-peak hand velocity, number of movement units, peak and percent-to-peak grip aperture, and percent-to-peak hand deceleration. A between-session repeatability analysis was conducted on 10 participants.

Results: Movement times were longer for transport-release compared to reach-grasp for every movement. Hand and grip aperture measures had low variability, with 55 out of 63 measures showing good repeatability (ICC > 0.75). Cross-body movements in the Pasta Box Task had longer movement times and reduced percent-to-peak hand velocity values. The Cup Transfer Task showed decoupling of peak grip aperture and peak hand deceleration for all movements. Movements requiring the clearing of an obstacle while transporting an object displayed a double velocity peak and typically a longer deceleration phase.

Discussion: Normative hand kinematics for two standardized functional tasks challenging various aspects of hand-object interactions important for ADLs showed excellent repeatability. The consistency in normative task performance across a variety of task demands shows promise as a potential outcome assessment for populations with upper limb impairment.

Fig 1. Functional tasks.

Sequence of the Pasta Box Task (A) and Cup Transfer Task (B). During the Pasta Box Task, the participant moved the box of pasta from a lower side table to two shelves of different heights in front of them (Movements 1 and 2) and back again to the start position (Movement 3). Tasks were completed using three distinct movements, with standardized placement positions, including returning the hand to a standard “home” position at the end of each movement. During the Cup Transfer Task, the participant moved two compliant cups filled with therapeutic beads over a partition to a target location using a top grasp for the first cup and a side grasp for the second cup (Movements 1 and 2). These movements were followed by a return of the hand to the “home” position, and then by moving the cups back to their initial positions using respective types of grasps (Movements 3 and 4).

Fig 2. Pasta Box Task hand trajectory.

Hand trajectories for the Pasta Box Task. The group average hand trajectory is plotted as a dark line, and the standard deviation of participant means as three-dimensional shading. Movement 1 (A), Movement 2 (B), and Movement 3 (C) are segmented into reach (red), grasp (orange), transport (blue), and release (green) phases. The maximum of the mean three-dimensional standard deviation was calculated for reach-grasp and transport-release segments in each movement to quantify variability, reported in Table 2.

Fig 3. Cup Transfer Task hand trajectory.

Hand trajectories for the Cup Transfer Task. The group average hand trajectory is plotted as a dark line, and the standard deviation of participant means as three-dimensional shading. Movement 1 (A), Movement 2 (B), Movement 3 (C), and Movement 4 (D) are segmented into reach (red), grasp (orange), transport (blue), and release (green) phases. The maximum of the mean three-dimensional standard deviation was calculated for reach-grasp and transport-release segments for each movement to quantify variability, reported in Table 3.

Fig 4. Hand velocity.

Hand velocity graphs for Pasta Box Task (A) and Cup Transfer Task (B). The solid line represents the group average, and grey shading the standard deviation of participant means. The task is segmented into reach (red), grasp (orange), transport (blue), and release (green) phases for each movement, with light grey representing the return to “home” phase. Kinematics of the reach-grasp segment and the transport-release segment were analyzed together.

Fig 5. Grip aperture.

Grip aperture graphs for Pasta Box Task (A) and Cup Transfer Task (B). The solid line represents the group average, and grey shading represents the standard deviation of participant means. The task is segmented into reach (red), grasp (orange), transport (blue), and release (green) phases for each movement, with light grey representing the return to “home” phase. Kinematics of the reach-grasp segment and the transport-release segment were analyzed together.