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A Taxonomy of Functional Upper Extremity Motion

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A Taxonomy of Functional Upper Extremity Motion

Heidi M Schambra et al. Front Neurol.

Abstract

Background: Functional upper extremity (UE) motion enables humans to execute activities of daily living (ADLs). There currently exists no universal language to systematically characterize this type of motion or its fundamental building blocks, called functional primitives. Without a standardized classification approach, pooling mechanistic knowledge and unpacking rehabilitation content will remain challenging. Methods: We created a taxonomy to characterize functional UE motions occurring during ADLs, classifying them by motion presence, temporal cyclicity, upper body effector, and contact type. We identified five functional primitives by their phenotype and purpose: reach, reposition, transport, stabilize, and idle. The taxonomy was assessed for its validity and interrater reliability in right-paretic chronic stroke patients performing a selection of ADL tasks. We applied the taxonomy to identify the primitive content and motion characteristics of these tasks, and to evaluate the influence of impairment level on these outcomes. Results: The taxonomy could account for all motions in the sampled activities. Interrater reliability was high for primitive identification (Cohen's kappa = 0.95-0.99). Using the taxonomy, the ADL tasks were found to be composed primarily of transport and stabilize primitives mainly executed with discrete, proximal motions. Compared to mildly impaired patients, moderately impaired patients used more repeated reaches and axial-proximal UE motion to execute the tasks. Conclusions: The proposed taxonomy yields objective, quantitative data on human functional UE motion. This new method could facilitate the decomposition and quantification of UE rehabilitation, the characterization of functional abnormality after stroke, and the mechanistic examination of shared behavior in motor studies.

Keywords: dose; function; primitive; rehabilitation; stroke; upper extremity.

Figures

Figure 1
Figure 1
Functional motion hierarchy, adapted from Fanti (16). Functional motion can be broken down into levels of motion with decreasing durations and complexity. Activities are long-duration motions with many goals, functional movements are moderate-duration motions with a few goals, and functional primitives are short-duration motions or minimal-motions with one goal. A sequence of functional primitives combine to make a functional movement, and a sequence of functional movements combine to make an activity.
Figure 2
Figure 2
Functional UE motion taxonomy. The taxonomy is meant for application in humans using their upper body to perform functional activities. Classes of functional motion are characterized by the presence of motion, the temporal cyclicity of motion, the upper body segment primarily translating the UE, and the type of object contact. Importantly, grasp may occur anywhere on the UE, not just at the hand. Functional primitives are identified by their motion and contact type. The primitives are reach (motion to move into contact with a target object), reposition (motion to move near to a target object), transport (motion to convey a target object), stabilize (minimal-motion to keep a target object still), and idle (minimal-motion to stand at the ready).
Figure 3
Figure 3
Primitive composition of activities. Primitives were summed within activity irrespective of temporal cyclicity or upper body segment. Their average proportional contribution to each activity is shown. Overall, transports (38.7%) and stabilizations (26.0%) predominated across activities, while reaches (12.5%), idles (15.0%), and repositions (7.3%) were less prevalent.
Figure 4
Figure 4
Motion characteristics of activities. Primitive features were used to characterize the proportional contribution of motion, temporal cyclicity, and upper body segment to the execution of the activities. (A) Presence of motion: activities were executed with modestly more functional motion (58.5%) than minimal-motion (41.0%). (B) Temporal cyclicity of functional motion: activities were primarily executed with discrete motions (91.0%) and less commonly with rhythmic motions (9.0%). (C) Upper body segment effecting functional motion: activities were primarily executed by the proximal segment (80.4%), and less by the distal (7.4%), proximal-distal (6.7%), axial-proximal (5.5%), or axial (0%) segments. (D) Grasp use in transports and stabilizations: activities were primarily executed with prehensile grasps (94.5%) and uncommonly with non-prehensile grasps (5.5%).
Figure 5
Figure 5
Impairment effects on primitive composition and motion characteristics. Patients with mild (average FMA 59.5) and moderate (average FMA 41.6) impairment were compared. (A) Primitive execution: Mildly impaired subjects used more transports, whereas moderately impaired patients used more reaches. There was a trend for more idles and stabilizes in the moderately impaired group. (B) Motion use: mildly impaired patients used more functional motion to execute the activities, whereas moderately impaired patients used more minimal-motion. (C) Segmental use: mildly impaired patients more often used their proximal and distal segments to execute the activities, whereas moderately impaired patients more often used their axial and proximal segments in combination. (D) Grasp use: mildly impaired patients more often used prehensile grasps whereas moderately impaired patients more often used non-prehensile grasps. Mildly and moderately impaired patients had comparable use of discrete and rhythmic motion (not shown). *p < 0.05.

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