Kinematic Analysis Using 3D Motion Capture of Drinking Task in People With and Without Upper-extremity Impairments

Kinematic analysis describes the movements of the body through space and time, including linear and angular displacements, velocities, and accelerations. The optoelectronic motion capture systems use multiple high-speed cameras that either send out infra-red light signals to capture the reflections from passive markers placed on the body or transmit the movement data from active markers containing infrared emitting diodes. These systems are considered as 'gold standard' for the acquisition of kinematic data¹. These systems are valued for their high accuracy and flexibility in measurements of diverse tasks. Kinematic measures have shown to be effective in capturing smaller changes in movement performance and quality that may be undetected with traditional clinical scales^2,3. It has been suggested that kinematics should be used for distinction between true recovery (restoration of premorbid movement characteristics) and the use of compensatory (alternative) movement patterns during the accomplishment of a task^4,5.

Upper extremity movements can be quantified using end-point kinematics, generally obtained from a hand marker, and angular kinematics from joints and segments (i.e., trunk). End-point kinematics provide information about trajectories, speed, temporal movement strategies, precision, straightness, and smoothness, while angular kinematics characterize movement patterns in terms of temporal and spatial joint and segment angles, angular velocities, and interjoint coordination. End-point kinematics, such as, movement time, speed, and smoothness are effective to capture the deficits and improvements in movement performance after stroke^6,7,8 and angular kinematics show whether the movements of joints and body segments are optimal for a specific task. Kinematics from people with impairments are often compared with movement performance in individuals without impairments^8,9. End-point and angular kinematics are correlated in a way that a movement performed with effective speed, smoothness, and precision will require good movement control, coordination, and use of effective and optimal movement patterns. For example, a patient with stroke who moves slowly usually also shows decreased smoothness (increased number of movement units), lower maximum velocity, and increased trunk displacement⁸. On the other hand, improvements in endpoint kinematics, such as movement speed and smoothness might occur independently from the changes of compensatory movement strategies of trunk and arm¹⁰. It has been established that kinematic analysis may provide additional and more precise information about how the task is accomplished after an injury or disease, which in turn is essential for individualized effective treatment to reach optimal motor recovery¹¹. Kinematic analysis is increasingly used in clinical studies to describe the movements in people with upper extremity impairments after stroke^8,9, to evaluate motor recovery^7,12,13 or to determine the effectiveness of therapeutic interventions^10,14.

Movement tasks often studied in stroke are pointing and reaching, although the use of functional tasks that incorporate manipulation of real everyday objects is increasing¹. Since kinematics of reaching depend on the experimental constraints such as the selection of objects and the goal of the task¹⁵, it is essential to assess movements during purposeful and functional tasks in which the real difficulties in individual's daily life will be reflected more closely.

Thus, the aim of this paper is to provide a detailed description of a simple standardized protocol used for kinematic analysis of a purposeful and functional task, drinking task, applied to individuals with upper extremity impairments in acute and chronic stages after stroke. Results from the validation of this protocol for individuals with moderate and mild stroke impairment will be summarized.