Multi-muscle synergies in preparation for gait initiation in Parkinson's disease.

OBJECTIVE: We investigated changes in indices of muscle synergies prior to gait initiation and the effects of gaze shift in patients with Parkinson's disease (PD). A long-term objective of the study is to develop a method for quantitative assessment of gait-initiation problems in PD. METHODS: PD patients without clinical signs of postural instability and two control groups (age-matched and young) performed a gait initiation task in a self-paced manner, with and without a quick prior gaze shift produced by turning the head. Muscle groups with parallel scaling of activation levels (muscle modes) were identified as factors in the muscle activation space. Synergy index stabilizing center of pressure trajectory in the anterior-posterior and medio-lateral directions (indices of stability) was quantified in the muscle mode space. A drop in the synergy index in preparation to gait initiation (anticipatory synergy adjustment, ASA) was quantified. RESULTS: Compared to the control groups, PD patients showed significantly smaller synergy indices and ASA for both directions of the center of pressure shift. Both PD and age-matched controls, but not younger controls, showed detrimental effects of the prior gaze shift on the ASA indices. CONCLUSIONS: PD patients without clinically significant posture or gait disorders show impaired stability of the center of pressure and its diminished adjustment during gait initiation. SIGNIFICANCE: The indices of stability and ASA may be useful to monitor pre-clinical gait disorders, and lower ASA may be relevant to emergence of freezing of gait in PD.

Synergic control in asymptomatic welders during multi-finger force exertion and load releasing while standing.

Motor synergies, i.e., neural mechanisms that organize multiple motor elements to ensure stability of actions, are affected by several neurological condition. Asymptomatic welders showed impaired synergy controlling the stability of multi-finger action compared to non-welders and this impairment was associated with microstructural damage in the globus pallidus. We further explored the effect of welding-related metal exposure on multi-finger synergy and extended our investigation to posture-stabilizing synergy during a standing task. Occupational, MRI, and performance-stabilizing synergies during multi-finger accurate force production and load releasing while standing were obtained from 29 welders and 19 age- and sex-matched controls. R2* and R1 relaxation rate values were used to estimate brain iron and manganese content, respectively, and diffusion tensor imaging was used to reflect brain microstructural integrity. Associations of brain MRI (caudate, putamen, globus pallidus, and red nucleus), and motor synergy were explored by group status. The results revealed that welders had higher R2* values in the caudate (p = 0.03), putamen (p = 0.01), and red nucleus (p = 0.08, trend) than controls. No group effect was revealed on multi-finger synergy index during steady-state phase of action (ΔVZss). Compared to controls, welders exhibited lower ΔVZss (-0.106 ± 0.084 vs. 0.160 ± 0.092, p = 0.04) and variance that did not affect the performance variable (VUCM, 0.022 ± 0.003 vs. 0.038 ± 0.007, p = 0.03) in the load releasing, postural task. The postural synergy index, ΔVZss, was associated negatively with higher R2* in the red nucleus in welders (r = -0.44, p = 0.03), but not in controls. These results suggest that the synergy index in the load releasing during a standing task may reflect welding-related neurotoxicity in workers with chronic metals exposure. This finding may have important clinical and occupational health implications.

Immediate Effects of Arm Reaching Training in Standing on Postural Control Differ between Right and Left Stroke Individuals.

BACKGROUND: Arm reaching training in standing for several weeks affects the postural control of individuals recovering from cerebrovascular accident (CVA). Whether these effects differ with the side of the brain lesion are unknown. OBJECTIVES: To examine the immediate effects of a training session of arm reaching movements on the balance and trunk motion of individuals who suffered a right or left CVA. MATERIALS AND METHODS: Thirty-six adults divided into four groups (i.e., right CVA, left CVA, right control, and left control) performed 120 reaches in a standing position toward one of three target heights. Before and after the reaching trials, participants stood as quiet as possible on two force plates and had their postural sway, trunk motion, and body weight distribution assessed. RESULTS: CVA groups showed greater postural sway regardless of the brain lesion's side compared to the control groups. After the session of reaching movements, the left stroke group reduced the postural sway and trunk displacements. Larger ranges of weight-bearing asymmetry were more frequent after the training session, mainly for the right stroke group. CONCLUSIONS: A single session training of reaching movements affects mostly the postural control of left stroke survivors. More training sessions may be needed for individuals after right stroke to show balance improvements. The current findings support the hemispheric specialization for postural control and suggest that the training involving arm movements in standing can benefit the motor rehabilitation of stroke individuals.

Asymmetry of Body Weight Distribution During Quiet and Relaxed Standing Tasks.

The goal of this work was to investigate body weight distribution during relaxed and quiet (constrained) standing tasks. Forty-one healthy, young adults performed relaxed and quiet standing tasks, and they stood with each leg on a separate force plate. The weight distribution asymmetry across time was computed as the difference between the right and left vertical force time series. The subjects presented a small average across time asymmetry during relaxed and quiet standing. However, during relaxed standing, the subjects alternated between postures, and, as a result, they were largely asymmetrical over time (instant by instant). Two unexpected results that the authors found for the relaxed standing task were that women were more asymmetrical over time than men and that there were two preferential modes of weight distribution.

From One to Two: Can Visual Feedback Improve the Light Touch Effects on Postural Sway?

The postural control is improved by implicit somatosensory information from lightly touching a rigid bar or explicit visual information about the postural sway. Whether these two additional sources provided at the same time further reduce the postural sway is still unknown. Participants stood on a force plate as quiet as possible lightly touching the bar while received or not visual feedback of the center of pressure position on a monitor screen. Postural sway reduced similarly with the light touch regardless of the additional visual feedback. The findings suggested that providing explicit visual feedback of the center of pressure does not increase the light touch effects on the postural sway. The importance of the implicit somatosensory information on postural control is discussed.

Métodos qualitativos e quantitativos de avaliação do alinhamento postural / Qualitative and quantitative methods of postural assessment

Introduction: Postural alignment has been studied by health professionals over the years. Due to technological advances, the use of quantitative methods for postural evaluation became more common in clinical practice. Objectives: To present different methods of postural assessment used by health professionals in the last decade. Methods: A literature review in the databases Lilacs, Medline, Pubmed, Cochrane and CAPES from 2000 to 2012 was made, in English, Spanish and Portuguese languages, and the following descriptors were used: posture, evaluation, motor activity, equipment, supplies, avaliación, actividad motora, equipos e suministros. Results: We found 33 papers published in refereed journals, however, only 25 references used qualitative or quantitative instruments for postural evaluation. Conclusion: In the past few years the use of softwares for quantitative postural assessment has been frequently adopted in clinical practice, in addition to the qualitative method. The adoption of these technological tools will allow health professionals to develop more accurate evaluations to determine the magnitude of postural changes. (AU)

Introdução: O alinhamento postural tem sido objeto de estudo de profissionais da saúde ao longo dos anos. Graças aos avanços tecnológicos, o uso de métodos quantitativos para avaliação da postura tem se tornado mais frequente na prática clínica.Objetivos: Apresentar os diferentes métodos de avaliação postural adotados por profissionais da saúde na última década. Métodos: Realizou-se uma revisão de literatura de artigos nas bases de dados Lilacs, Medline, Pubmed, Cochrane e CAPES, no período entre 2000 e 2012, nos idiomas inglês, espanhol e português, utilizando-se os seguintes descritores: postura, avaliação, atividade motora, equipamentos, provisões, posture, evaluation, motor activity, equipment, suplies, avaliación, actividad motora, equipos e suministros. Resultados: Foram encontrados 33 artigos científicos publicados em revistas indexadas, porém somente 25 referências utilizaram instrumentos qualitativos ou quantitativos de avaliação postural. Conclusão: Nos últimos anos o uso de softwares para realização de avaliação postural quantitativa tem se mostrado cada vez mais frequente na prática clínica, como complemento ao método qualitativo. A adoção dessas ferramentas tecnológicas permitirá ao profissional da saúde desenvolver avaliações mais acuradas e determinar a magnitude das alterações posturais. (AU)