Joint-Angle Coordination Patterns Ensure Stabilization of a Body-Plus-Tool System in Point-to-Point Movements with a Rod

When performing a goal-directed action with a tool, it is generally assumed that the point of control of the action system is displaced from the hand to the tool, implying that body and tool function as one system. Studies of how actions with tools are performed have been limited to studying either end-effector kinematics or joint-angle coordination patterns. Because joint-angle coordination patterns affect end-effector kinematics, the current study examined them together, with the aim of revealing how body and tool function as one system. Seated participants made point-to-point movements with their index finger, and with rods of 10, 20, and 30 cm attached to their index finger. Start point and target were presented on a table in front of them, and in half of the conditions a participant displacement compensated for rod length. Results revealed that the kinematics of the rod’s tip showed higher peak velocity, longer deceleration time, and more curvature with longer rods. End-effector movements were more curved in the horizontal plane when participants were not displaced. Joint-angle trajectories were similar across rod lengths when participants were displaced, whereas more extreme joint-angles were used with longer rods when participants were not displaced. Furthermore, in every condition the end-effector was stabilized to a similar extent; both variability in joint-angle coordination patterns that affected end-effector position and variability that did not affect end-effector position increased in a similar way vis-à-vis rod length. Moreover, the increase was higher in those conditions, in which participants were not displaced. This suggests that during tool use, body and tool are united in a single system so as to stabilize the end-effector kinematics in a similar way that is independent of tool length. In addition, the properties of the actual trajectory of the end-effector, as well as the actual joint-angles used, depend on the length of the tool and the specifics of the task

Questionnaires to Assess Facilitators and Barriers of Early Mobilization in Critically Ill Patients; Which One to Choose? A Systematic Review

Implementing and performing early mobilization is a complex process requiring multidisciplinary input and cooperation. To gain insight in its facilitators and barriers, various surveys have been developed. A systematic review was conducted, to identify the psychometric properties, feasibility and suitability of questionnaires to assess facilitators and barriers of early mobilization in critically ill patients. Data were extracted regarding a.o. definition of early mobilization, development, psychometric properties, content and themes, question format. The search identified 537 publications of which 13 unique questionnaires were included. The questionnaires showed wide variation in extensiveness of development. Only six questionnaires actually assessed validity and reliability. Which questionnaire to choose depends on the aim of its use, required level of detail and specifics of the ICU, though three questionnaires were recommended as their definition of early mobilization covered a broad range of activities, including nursing related mobility activities. International consensus on what constitutes early mobilization is desirable

Active muscle mass affects endurance physiology: A review on single versus double-leg cycling

This review gives an overview of methods and outcomes of studies that compared circulatory, ventilatory, energetic or hormonal responses evoked by single-leg cycling and double-leg cycling at sub-maximal and maximal intensities. Through a systematic search, 18 studies were identified in the databases PubMed, Embase and Web of Science. Additionally, one study was added after a check of references. Critical analysis of each study showed that their quality was low to moderate. Between studies, widely divergent study procedures were present, such as different intensities, incremental or constant workloads, and different cycling frequencies. Moreover, a large variety of outcome variables was found and thereby comparison was hard. Nevertheless, results showed a tendency to higher hormonal levels of catecholamines as well as circulatory and ventilatory responses during double-leg cycling compared to one-leg cycling. Additionally, at similar normalized submaximal workloads, blood lactate levels tended to be lower during double-leg cycling, suggesting that more type II muscle fibers were recruited. From the reviewed studies the tentative conclusion is that active muscle mass seems a crucial factor in the regulation of endurance performance. Consequently, exercise regimens that recruit a larger active muscle mass, for example combined arm and leg exercise, would optimally stress the release of biochemicals and hence the modulation of central training adaptations, which may positively affect physical capacity in, for example, persons that have diminished leg muscle mass available. However, it also became clear that more information is needed to further understand the contributions of active muscle mass. The experimental possibilities of comparing one-legged and two-legged cycling is promising, but future studies should aim to provide complete quantitative data on the muscle mass recruited, as well as on the specific contribution of anaerobic/aerobic metabolism. They should also aim to include blood parameters such as PCO2, pH, myokines and physiological responses such as heart rate and ventilation

Synergies reciprocally relate end-effector and joint-angles in rhythmic pointing movements

During rhythmic pointing movements, degrees of freedom (DOF) in the human action system-such as joint-angles in the arm-are assumed to covary to stabilise end-effector movement, e.g. index finger. In this paper, it is suggested that the end-effector movement and the coordination of DOF are reciprocally related in synergies that link DOF so as to produce the end-effector movement. The coordination of DOF in synergies and the relation between end-effector movement and DOF coordination received little attention, though essential to understand the principles of synergy formation. Therefore, the current study assessed how the end-effector movement related to the coordination of joint-angles during rhythmic pointing across target widths and distances. Results demonstrated that joint-angles were linked in different synergies when end-effector movements differed across conditions. Furthermore, in every condition, three joint-angles (shoulder plane of elevation, shoulder inward-outward rotation, elbow flexion-extension) largely drove the end-effector, and all joint-angles contributed to covariation that stabilised the end-effector. Together, results demonstrated synergies that produced the end-effector movement, constrained joint-angles so that they covaried to stabilise the end-effector, and differed when end-effector movement differed. Hence, end-effector and joint-angles were reciprocally related in synergies-indicating that the action system was organised as a complex dynamical system

Magnetic Resonance-Compatible Arm-Crank Ergometry:A New Platform Linking Whole-Body Calorimetry to Upper-Extremity Biomechanics and Arm Muscle Metabolism

Introduction: Evaluation of the effect of human upper-body training regimens may benefit from knowledge of local energy expenditure in arm muscles. To that end, we developed a novel arm-crank ergometry platform for use in a clinical magnetic resonance (MR) scanner with 31P spectroscopy capability to study arm muscle energetics. Complementary datasets on heart-rate, whole-body oxygen consumption, proximal arm-muscle electrical activity and power output, were obtained in a mock-up scanner. The utility of the platform was tested by a preliminary study over 4 weeks of skill practice on the efficiency of execution of a dynamic arm-cranking task in healthy subjects. Results: The new platform successfully recorded the first ever in vivo 31P MR spectra from the human biceps brachii (BB) muscle during dynamic exercise in five healthy subjects. Changes in BB energy- and pH balance varied considerably between individuals. Surface electromyography and mechanical force recordings revealed that individuals employed different arm muscle recruitment strategies, using either predominantly elbow flexor muscles (pull strategy; two subjects), elbow extensor muscles (push strategy; one subject) or a combination of both (two subjects). The magnitude of observed changes in BB energy- and pH balance during ACT execution correlated closely with each strategy. Skill practice improved muscle coordination but did not alter individual strategies. Mechanical efficiency on group level seemed to increase as a result of practice, but the outcomes generated by the new platform showed the additional caution necessary for the interpretation that total energy cost was actually reduced at the same workload. Conclusion: The presented platform integrates dynamic in vivo 31P MRS recordings from proximal arm muscles with whole-body calorimetry, surface electromyography and biomechanical measurements. This new methodology enables evaluation of cyclic motor performance and outcomes of upper-body training regimens in healthy novices. It may be equally useful for investigations of exercise physiology in lower-limb impaired athletes and wheelchair users as well as frail patients including patients with debilitating muscle disease and the elderly

What the Dynamic Systems Approach Can Offer for Understanding Development:An Example of Mid-childhood Reaching

The Dynamic Systems Approach (DSA) to development has been shown to be a promising theory to understand developmental changes. In this perspective, we use the example of mid-childhood (6- to 10-years of age) reaching to show how using the DSA can advance the understanding of development. Mid-childhood is an important developmental period that has often been overshadowed by the focus on the acquisition of reaching during infancy. This underrepresentation of mid-childhood studies is unjustified, as earlier studies showed that important developmental changes in mid-childhood reaching occur that refine the skill of reaching. We review these studies here for the first time and show that different studies revealed different developmental trends, such as non-monotonic and linear trends, for variables such as movement time and accuracy at target. Unfortunately, proposed explanations for these developmental changes have been tailored to individual studies, limiting their scope. Also, explanations were focused on a single component or process in the system that supposedly causes developmental changes. Here, we propose that the DSA can offer an overarching explanation for developmental changes in this research field. According to the DSA, motor behavior emerges from interactions of multiple components entailed by the person, environment, and task. Changes in all these components can potentially contribute to the emerging behavior. We show how the principles of change of the DSA can be used as an overarching framework by applying these principles not only to development, but also the behavior itself. This underlines its applicability to other fields of development