Biology subjects

McKay, J. L.

Publications and source records attributed to McKay, J. L..

3 recordsLinked to original sources

bioRxiv2018

Antagonist muscle activity during reactive balance responses is elevated in Parkinson’s disease and in balance impairment

BACKGROUND: Abnormal antagonist leg muscle activity could indicate increased muscle co-contraction and clarify mechanisms of balance impairments in Parkinsons disease (PD). Prior studies in carefully selected patients showed PD patients demonstrate earlier, longer, and larger antagonist muscle activation during reactive balance responses to perturbations. RESEARCH QUESTION: Here, we tested whether antagonist leg muscle activity was abnormal in a group of PD patients who were not selected for phenotype, and most of whom had volunteered for exercise-based rehabilitation. METHODS: We compared antagonist activation during reactive balance responses to multidirectional support-surface translation perturbations in 31 patients with mild-moderate PD (age 68{+/-}9; H&Y 1-3; UPDRS -III 32{+/-}10) and 13 matched individuals (age 65{+/-}9). We quantified modulation of muscle activity (i.e., the ability to activate and inhibit muscles appropriately according to the perturbation direction) using modulation indices (MI) derived from minimum and maximum EMG activation levels observed across perturbation directions. RESULTS: Antagonist leg muscle activity was abnormal in unselected PD patients compared to controls. Linear mixed models identified significant associations between impaired modulation and PD (P<0.05), PD severity (P<0.01), and balance ability (P<0.05), but not age (P=0.10). SIGNIFICANCE: Antagonist activity is increased during reactive balance responses in PD patients of varying phenotypes who are candidates for rehabilitation. Abnormal antagonist activity may contribute to balance impairments in PD and be a potential rehabilitation target or outcome measure.\n\nFunding SourcesThis work was supported by the National Institutes of Health (NIH) KL2 TR000455, K25 HD086276, R01 HD46922, R21 HD075612, TL1TR000456, and UL1 TR000424. The study sponsors had no role in study design; in the collection, analysis and interpretation of data; in the writing of the report; or in the decision to submit the article for publication.\n\nDeclaration of InterestConflicts of interest: None.\n\nAuthor ContributionsResearch project: Conception, JLM, LHT, MEH; Organization, JLM, KCL, LHT, MEH; Execution, JLM, KCL, LHT, MEH.\n\nStatistical Analysis: Design and Execution, JLM, KCL; Review and Critique, LHT, MEH. Manuscript Preparation: Writing of the first draft, KCL; Review and Critique: JLM, LHT, MEH.\n\nHighlights O_LIWe quantified abnormal antagonist muscle activation during balance in PD.\nC_LIO_LIAbnormalities were related to PD severity as well as to overall balance ability.\nC_LIO_LIAbnormalities were similar across PD phenotypes with and without tremor.\nC_LIO_LIBalance antagonist activation may be a useful rehabilitative outcome measure.\nC_LI

neuroscience↗

bioRxiv2017

The Influence of Parkinson’s Disease and Neurotypical Aging on Cognitive Performance Among Volunteers for an Exercise-based Rehabilitative Intervention

PURPOSETo determine the impact of aging versus combined aging and disease on cognition in older adults with and without Parkinsons disease (PD) who were volunteers for exercise based rehabilitation research.\n\nMETHODSWe used a multiple linear regression approach to analyze cognitive outcome measures of rehabilitation volunteers with and without PD.\n\nRESULTSSignificant associations were identified between increased age and decreased performance on 8 of the 14 outcomes analyzed after controlling for false discovery rate. Of those 8 outcomes, multivariate regression analyses demonstrated an effect of disease on performance in only 4/8. In all cases, PD was associated with superior, rather than decreased performance after controlling for age. Results were unaffected by sex and education. Post-hoc comparison with available age norms demonstrated that differences between PD and Non-PD volunteers could be primarily attributed to the Non-PD group substantially underperforming versus age norms.\n\nCONCLUSIONSIn rehabilitative exercise studies using volunteers, many cognitive domains decline with increasing age, consistent with previous neuropsychological studies without a rehabilitation component. However, older \"neurotypical\" volunteers may potentially underperform PD volunteers after controlling for age. This may be an important design consideration for rehabilitation studies with cognitive outcomes.\n\nIMPLICATIONS FOR REHABILITATIONO_LIAn increasing number of rehabilitation studies incorporate cognitive outcomes.\nC_LIO_LIWhether the overall cognitive profile of rehabilitation volunteers differs from that of neurotypical aging remains to be established.\nC_LIO_LIRehabilitation volunteers with Parkinsons disease may outperform putatively neurotypical volunteers after controlling for covariates.\nC_LIO_LICognitive impairments associated with PD in neuropsychological studies may not generalize to exercise rehabilitation volunteers.\nC_LI

neuroscience↗

bioRxiv2017

Agreement between measurements of stance width using motion capture and center of pressure in individuals with and without Parkinson’s disease

BackgroundMany individuals with Parkinsons disease exhibit narrow stance width during balance and gait. Because of this, stance width is an important biomechanical variable in many studies. Measuring stance width accurately using kinematic markers in parkinsonian patients can be problematic due to occlusions by research staff who must closely guard patients to prevent falls.\n\nMethodsWe investigated whether a measure of stance width based on the mediolateral distance between the center of pressure under each foot could approximate stance width measured with kinematic data. We assessed the agreement between estimates of stance width obtained from simultaneous kinematic and center of pressure measures during quiet standing in 15 individuals (n=9 parkinsonian, n=6 age-similar neurotypical). The source data (1363 unique trials) contained observations of stance width varying between 75-384 mm ({approx}25-150% of hip width).\n\nFindingsStance width estimates using the two measures were strongly correlated (r = 0.98). Center of pressure estimates of stance width were 48 mm wider on average than kinematic measures, and did not vary across study groups (F2,12=1.81, P<0.21). The expected range of differences between the center of pressure and kinematic methods was 14-83 mm. Agreement increased as stance width increased (P<0.02).\n\nInterpretationIt is appropriate to define stance width based on center of pressure when it is convenient to do so in studies of individuals with and without Parkinsons disease. When comparing results across studies with the two methodologies, it is reasonable to assume a bias of 48 mm.

neuroscience↗