Differences in multi-degrees-of-freedom coordination of reaching between non-neurologically impaired adults and stroke survivors

The work of this dissertation attempted to further our understanding of multi-degree of freedom coordination of reaching within and beyond a person's functional arm length. With the first two studies of this dissertation, the mechanism of interjoint coordination in reaching was systematically addressed. First, differences in coordination among joints of the arm between young and older adults were related specifically to their potential effect on the consistency of the hand path during reaching to targets. Second, comparisons of interjoint coordination were made between older adults and stroke survivors to identify the extent to which deficits in coordination in stroke survivors are due to aging versus the stroke, and how this differed between right-brain and left-brain strokes.;In line with our prediction for the first study, the elbow and wrist distal joints covaried with other joints to stabilize the hand's path more during the late than the early phase of reaching. In contrast, the shoulder joint's covariation with other joints was similar for both phases of reaching. In addition, the shoulder's coordination with other joints had more of an impact on hand path variability than did either the elbow's or the wrist's coordination with the other joints. Young adults exhibited better interjoint coordination, evidenced by a larger increase in "bad" variance after simulated removal of joint covariation than older adults. Also, interjoint coordination was better for the right than the left arm for young but not for older adults, but this was the case only for the late phase of the reach and moreover for distal joints only. Thus, the results from the first study indicated age-related changes in joints' coordination related to the consistency of the hand path during reaching. In the second study, simulated removal of a joints' covariation led to less change in the magnitude of "bad" variance for the paretic arm as compared to the comparable arm of the controls, confirming poorer coordination of joints of the paretic arm irrespective of the lesion side.;The third study of this dissertation investigated differences in muscle synergies of the trunk in relation to its control during reaching beyond functional arm length between stroke survivors and age-matched control subjects. Many functional reaching activities that involve the arm also require the control of varying degrees of trunk excursion, depending on the distance to be reached. Post-stroke survivors struggle more with tasks that involve reaching upwards, typically requiring lower-trunk initiated movements, including anterior pelvic tilt, compared to downward reaches initiated primarily from the upper-trunk. The former movements have remained largely uninvestigated in stroke survivors. Therefore, the third study of this dissertation addressed this gap in knowledge about differences between reaches to different heights by investigating the coordination of trunk muscles when reaching upward or downward to targets located beyond the subjects' functional arm length for stroke survivors and healthy control subjects. Principal component analysis was used to identify combinations of ten trunk muscles, or muscle mode vectors. Flexibility in coordinating these muscle-modes to stabilize the trunk's motion was investigated using uncontrolled manifold analysis (UCM). It was hypothesized that there would be diminished coordination among muscle modes in stroke-survivors compared to controls, resulting in a less consistent trunk movement path, especially when reaching upwards.;For control subjects, during both reaching up and reaching down, the muscle mode variance across repetitions of the task was associated more with stable trunk motion, i.e., "good" variance was greater than muscle-mode variance resulting in variable trunk motion, or "bad" variance. In contrast, stroke survivors showed greater "bad" variance and smaller "good" variance than controls, especially when reaching upward. This result suggests a poorer ability of stroke survivors to decouple subspaces of muscle mode space related to trunk motion, which is necessary for variance of muscle mode combinations leading to an inconsistent trunk path to be restricted while variance of those combinations consistent with a flexible muscle synergy, i.e., allowing for "good" variance, is allowed. Moreover, the poorer ability of stroke survivors to reach upward toward a target appears to be related to even poorer muscle mode coordination compared to reaching downward.;This dissertation improves our knowledge about the control of multi DOFs in reaching for both within and beyond functional arm length. The method employed in this dissertation provides novel means to identify underlying mechanisms that account for functional performance differences between neurologically impaired individuals and matched control subjects. (Abstract shortened by UMI.).