Voluntary Posture Research Articles

Relative contribution of muscle strength, lean mass, and lower extremity motor function in explaining between-person variance in mobility in older adults

BackgroundApproximately 35% of individuals > 70 years have mobility limitations. Historically, it was posited lean mass and muscle strength were major contributors to mobility limitations, but recent findings indicate lean mass and muscle strength only moderately explain mobility limitations. One likely reason is that lean mass and muscle strength do not necessarily incorporate measures globally reflective of motor function (defined as the ability to learn, or to demonstrate, the skillful and efficient assumption, maintenance, modification, and control of voluntary postures and movement patterns). In this study we determined the relative contribution of lean mass, muscle strength, and the four square step test, as an index of lower extremity motor function, in explaining between-participant variance in mobility tasks.MethodsIn community-dwelling older adults (N = 89; 67% women; mean 74.9 ± 6.7 years), we quantified grip and leg extension strength, total and regional lean mass, and time to complete the four square step test. Mobility was assessed via 6-min walk gait speed, stair climb power, 5x-chair rise time, and time to complete a complex functional task. Multifactorial linear regression modeling was used to determine the relative contribution (via semi-partial r2) for indices of lean mass, indices of muscle strength, and the four square step test.ResultsWhen aggregated by sex, the four square step test explained 17–34% of the variance for all mobility tasks (p < 0.01). Muscle strength explained ~ 12% and ~ 7% of the variance in 6-min walk gait speed and 5x-chair rise time, respectively (p < 0.02). Lean mass explained 32% and ~ 4% of the variance in stair climb power and complex functional task time, respectively (p < 0.02). When disaggregated by sex, lean mass was a stronger predictor of mobility in men.ConclusionThe four square step test is uniquely associated with multiple measures of mobility in older adults, suggesting lower extremity motor function is an important factor for mobility performance.Trial registrationNCT02505529–2015/07/22.

Chapter 14 - Motor functions

Motor development includes the evolution from reflexive to voluntary and goal-directed motor actions. These motor actions are never performed in isolation but always in a varying physical environment, often requiring object and social interaction. For a child to function within this context, they require the ability to demonstrate skillful, efficient, and voluntary postures and movement patterns. Furthermore, these movement patterns or motor skills need to be performed in interaction with the environment and in response to diverse stimuli, an ability that is defined as praxis. In this chapter, definitions are provided for the different components of motor function, motor skills, and praxis. The close interaction between perception, cognition, and (motor) action is discussed. Furthermore, crucial periods of typical development of motor and praxis abilities are highlighted, by means of the metaphorical "mountain of motor development," that is rooted in the dynamic systems perspective on motor development, as a starting point. The chapter ends with a discussion on the evaluation of motor function and praxis, highlighting benefits, and possible pitfalls.

Essential tremor quantification during activities of daily living

BackgroundEssential tremor (ET), characterized primarily by postural and kinetic tremor, is typically measured in the clinic with subjective tremor rating scales. These ratings are often used to adjust medications and assess efficacy in clinical trials. However, tremor ratings require the presence of a clinician and do not necessarily capture tremor fluctuations throughout the day during activities of daily living (ADL). ObjectiveTo evaluate the ability of motion sensors to discriminate tremor from voluntary posture and motion, classify tremor as postural or kinetic, and rate tremor severity during standardized tasks and non-standardized activities of daily living. MethodsTen subjects with ET wore motion sensors on the index finger and performed standardized motor tasks from the Washington Heights-Inwood Genetic Study of Essential Tremor (WHIGET) tremor rating scale (wTRS) and non-standardized ADL tasks. Four movement disorder specialists independently rated video segments of the standardized tasks but not the ADL tasks. Quantitative features were extracted from the motion sensors and used to develop mathematical models for predicting rating scores from kinematic data. ResultsThe quantitative motion features were highly correlated with wTRS ratings for postural (r = 0.90) and kinetic (r = 0.80) tremors. Mathematical models produced tremor ratings that correlated strongly with clinician ratings of the wTRS tasks (mean r = 0.80) and also produced ADL task ratings that correlated well with the most recent clinician wTRS ratings (mean r = 0.72). ConclusionsRecordings from motion sensors can be used to classify tremor as postural or kinetic and quantify tremor severity during both standardized and non-standardized activities.

Contexts and Corporate Voluntary Environmental Behaviors

Why do an increasingly large number of firms choose to spend their own money and resources to protect the environment beyond the extant regulatory requirements? This article addresses this question by examining the EPA's Green Lights (GL) voluntary program in which a firm's policy makers made an early commitment to limiting greenhouse gases through the installation of energy-e ficient lighting technology in its facilities. Two theoretical perspectives—resource-based theory and neo-institutional theory—are adopted to investigate the contexts by which a firm is encouraged to undertake voluntary environmental actions and evaluate environmental strategies associated with them. Accordingly, the authors focus on two major contexts: market contexts in which a firm adopts voluntary actions as a strategic response to market pressures and to advance competitiveness; and institutional contexts in which a firm takes voluntary postures as a strategic response to institutional pressures, to obtain institutional legitimacy and weaken regulatory scrutiny. The research results partially support both contexts and their associated strategic behaviors.

Definition and Classification of Negative Motor Signs in Childhood

In this report we describe the outcome of a consensus meeting that occurred at the National Institutes of Health in Bethesda, Maryland, March 12 through 14, 2005. The meeting brought together 39 specialists from multiple clinical and research disciplines including developmental pediatrics, neurology, neurosurgery, orthopedic surgery, physical therapy, occupational therapy, physical medicine and rehabilitation, neurophysiology, muscle physiology, motor control, and biomechanics. The purpose of the meeting was to establish terminology and definitions for 4 aspects of motor disorders that occur in children: weakness, reduced selective motor control, ataxia, and deficits of praxis. The purpose of the definitions is to assist communication between clinicians, select homogeneous groups of children for clinical research trials, facilitate the development of rating scales to assess improvement or deterioration with time, and eventually to better match individual children with specific therapies. "Weakness" is defined as the inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint. "Reduced selective motor control" is defined as the impaired ability to isolate the activation of muscles in a selected pattern in response to demands of a voluntary posture or movement. "Ataxia" is defined as an inability to generate a normal or expected voluntary movement trajectory that cannot be attributed to weakness or involuntary muscle activity about the affected joints. "Apraxia" is defined as an impairment in the ability to accomplish previously learned and performed complex motor actions that is not explained by ataxia, reduced selective motor control, weakness, or involuntary motor activity. "Developmental dyspraxia" is defined as a failure to have ever acquired the ability to perform age-appropriate complex motor actions that is not explained by the presence of inadequate demonstration or practice, ataxia, reduced selective motor control, weakness, or involuntary motor activity.

Wachholder and Altenberger 1927: foundational experiments for current hypotheses on equilibrium-point control in voluntary movements.

Between 1923 and 1927 Kurt Wachholder and his assistant and collaborator Hans Altenburger published an impressive series of 11 papers on electrophysiological and kinematic studies on voluntary human movements in Pfluger s Archive, the leading journal for physiological studies in Germany at the time. Unfortunately, these excellent studies have remained largely unnoticed, partly because they are written in German and therefore inaccessible to many people in the post–World War II research community in motor control. Wachholderʼs name is sometimes only vaguely acknowledged as a pioneer in electromyography, as he was the first to report the tri-phasic pattern in discrete single-joint movements (Wachholder & Altenburger, 1926b). This study and one other paper on rhythmic movements have been recently translated, and their close reading provided astonishing insights, not only in an historical sense but also with respect to present-day research (Sternad, 2001; Sternad & Corcos, 2001; Wachholder & Altenburger, 1926a). The two studies gave a first impression of Wachholderʼs rigorous methodology, stringent logic, and far-reaching conclusions about the nature of movement generation that are more than just historical precursors but indeed of contemporary interest. At the end of this series of papers in Pfluger s Archive is the present study, unnumbered, but with an eye-catching title about the change of rest length in muscles. The topic of a changeable and controllable rest length in muscles has been a focus of attention in motor control since Feldmanʼs seminal studies in the 1960s that gave rise to the equilibrium-point hypothesis (Feldman, 1966a, 1966b). To what degree is Wachholder and Altenburgerʼs contribution a precursor to these thoughts? A few remarks about Wachholderʼs perspective should provide a suitable backdrop to the present paper. After all, this paper is only one of the building blocks for Wachholder s comprehensive work on voluntary posture and movements, which culminated 1928 in a monograph (Wachholder, 1928). This book provides a well-rounded perspective on, effectively, motor control. An outstanding characteristic of the physiologist Wachholder is that he combined his meticulous physiological experiments with a more encompassing psychological perspective, leading to broader-scale theorizing about the generation of human voluntary posture and movements. How does the nervous system control Motor Control, 2002, 6, 299-318

Motor coordination in weightless conditions revealed by long-term microgravity adaptation

The functional approach to studying human motor systems attempts to give a better understanding of the processes behind planning movements and their coordinated performance by relying on weightlessness as a particularly enlightening experimental condition. Indeed, quantitative monitoring of sensorimotor adaptation of subjects exposed to weightlessness outlines the functional role of gravity in motor and postural organization. The recent accessibility of the MIR Space Station has allowed for the first time experimental quantitative kinematic analysis of long-term sensorimotor and postural adaptation to the weightless environment though opto-electronic techniques. In the frame of the EUROMIR'95 Mission, two protocols of voluntary posture perturbation (erect posture, EP; forward trunk bending, FTB) were carried out during four months of microgravity exposure. Results show that postural strategies for quasistatic body orientation in weightlessness are based on the alignment of geometrical body axes (head and trunk) along external references. A proper whole body positioning appears to be recovered only after months of microgravity exposure. By contrast, typically terrestrial strategies of co-ordination between movement and posture are promptly restored and used when performing motor activities in the weightless environment. This result is explained under the assumption that there may be different sensorimotor integration processes for static and dynamic postural function and that the organisation of coordinated movement might rely stably on egocentric references and kinematic synergies for motor control.

Quantitative analysis of motion control in long term μ-gravity

In the frame of the 179-days EUROMIR '95 space mission, two in-flight experiments have foreseen quantitative thres-dimensional human movement analysis in μgravity. For this aim, a space qualified opto-electronic motion analyser based on passive markers has been installed onboard the Russian Space Station MIR and 8 in flight sessions have been performed. Technology and method for the collection of kinematics data are described, evaluating the accuracy in three-dimensional marker localisation. Results confirm the suitability of opto-electronic technology for quantitative human motion analysis on orbital modules and raise a set of “lessons learned”, leading to the improvement of motion analyser performance with a contemporary swiftness of the on-board operations. Among the experimental program of T4, results of three voluntary posture perturbation protocols are described. The analysis suggests that a short term reinterpretation of proprioceptive information and re-calibration of sensorimotor mechanisms seem to end within the first weeks of flight, while a continues long term adaptation process allows the refinement of motor performance, in the frame of never abandoned terrestrial strategies.

K. Wасhhоldor. Willkürliche Haltunng und Bewegung insbesondere im Lichte elektrophysiologischer Untersuchungen. с 55 рис. в тексте. стр. 218. München, J. E. Bergmann. ц. M. 18.1928 год

The book is devoted to the study of voluntary posture and movement, especially from the point of view of electro-physiological research. In the introduction, the author gives a definition of voluntary movement and methods of study, consisting in recording the flow of movement, establishing the forces that cause movement, and establishing the uniformity of innervation.