Current research in biology and physiology has unequivocally demonstrated the significance of variability for the optimal functioning of healthy and adaptable systems. Different pathologies are characterized by reductions in complexity of organization, often signified by loss of variability and adaptability. It is argued that the traditional perspective on biology in general and movement science in particular that tended to associate noise and variability with performance decrements and pathology is no longer tenable. Tools and methodologies that have emerged from the dynamical systems perspective to coordination and control are discussed in the context of postural control and transitions in interlimb coordination and locomotion. First, it is shown that variability can play a functional role in the detection and exploration of stability boundaries during balance control. Second, pattern transitions are characterized by increased variability in movement coordination dynamics. Under conditions of movement pathologies, such as in Parkinson’s disease, reductions in variability in coordination dynamics clearly identify movement coordination and transition problems so characteristic for these patients. It is concluded that the relation between variability and stability is complex and that variability cannot be equated with instability without knowledge of the underlying movement dynamics.
Search Results
On Variability and Stability in Human Movement
Richard E.A. van Emmerik and Erwin E.H. van Wegen
A Work-Loop Method for Characterizing Leg Function During Sagittal Plane Movements
Daniel Maykranz, Sten Grimmer, and Andre Seyfarth
The work-loop method is frequently used to determine the mechanical work performed by a system, for instance, when analyzing muscles or describing the work balance at the joint level. While for these examples usually only one-dimensional movements are investigated, for two- or three-dimensional movements, such as leg function during walking and running, the work-loop has to be adapted. In this paper, we present an analytical derivation that extends the work-loop method to two-dimensional sagittal plane movements. Three effects contribute to the mechanical work of the leg: (1) forces directed along the leg axis, (2) forces acting perpendicular to the leg axis, and (3) a shift of the center of pressure (COP) during stance. These three contributors to the mechanical work performed can be interpreted as three general tasks of the leg. To demonstrate the new work-loop method, we analyzed experimental data on hopping, running and walking. The results indicate that the proposed new generalized work-loop concept is suitable for describing the overall mechanical work performed on the COM during stance with energy consistent net work balances. Depending on the type of gait, specific contributions of each work term were found that characterize leg function during locomotion.
The Relative Roles of Feedforward and Feedback in the Control of Rhythmic Movements
Arthur D. Kuo
A simple pendulum model is used to study how feedforward and feedback can be combined to control rhythmic limb movements. I show that a purely feedforward central pattern generator (CPG) is highly sensitive to unexpected disturbances. Pure feedback control analogous to reflex pathways can compensate for disturbances but is sensitive to imperfect sensors. I demonstrate that for systems subject to both unexpected disturbances and sensor noise, a combination of feedforward and feedback can improve performance. This combination is achieved by using a state estimation interpretation, in which a neural oscillator acts as an internal model of limb motion that predicts the state of the limb, and by using alpha-gamma coactivation or its equivalent to generate a sensory error signal that is fed back to entrain the neural oscillator. Such a hybrid feedforward/feedback system can optimally compensate for both disturbances and sensor noise, yet it can also produce fictive locomotion when sensory output is removed, as is observed biologically. CPG behavior arises due to the interaction of the internal model and a feedback control that uses the predicted state. I propose an interpretation of the neural oscillator as a filter for processing sensory information rather than as a generator of commands.
Bipedal Locomotion of Bonnet Macaques after Spinal Cord Injury
Rangasamy Suresh Babu, P. Anand, Mathew Jeraud, P. Periasamy, and A. Namasivayam
Experimental studies concerning the analysis of locomotor behavior in spinal cord injury research are widely performed in rodent models. The purpose of this study was to quantitatively evaluate the degree of functional recovery in reflex components and bipedal locomotor behavior of bonnet macaques (Macaca radiata) after spinal contusive injury. Six monkeys were tested for various reflex components (grasping, righting, hopping, extension withdrawal) and were trained preoperatively to walk in bipedal fashion on the simple and complex locomotor runways (narrow beam, grid, inclined plane, treadmill) of this investigation. The overall performance of the animals’ motor behavior and the functional status of limb movements during bipedal locomotion were graded by the Combined Behavioral Score (CBS) system. Using the simple Allen weight-drop technique, a contusive injury was produced by dropping a 13-g weight from a height of 30 cm to the exposed spinal cord at the T12-L1 vertebral level of the trained monkeys. All the monkeys showed significant impairments in every reflex activity and in walking behavior during the early part of the postoperative period. In subsequent periods, the animals displayed mild alterations in certain reflex responses, such as grasping, extension withdrawal, and placing reflexes, which persisted through a 1-year follow-up. The contused animals traversed locomotor runways—narrow beam, incline plane, and grid runways—with more steps and few errors, as evaluated with the CBS system. Eventually, the behavioral performance of all spinal-contused monkeys recovered to near-preoperative level by the fifth postoperative month. The findings of this study reveal the recovery time course of various reflex components and bipedal locomotor behavior of spinal-contused macaques on runways for a postoperative period of up to 1 year. Our spinal cord research in primates is advantageous in understanding the characteristics of hind limb functions only, which possibly mimic the human motor behavior. This study may be also useful in detecting the beneficial effect of various donor tissue–neuroprotective drugs on the repair of impaired functions in a bipedal primate model of spinal injury.
Target Constraints Influence Locomotion Pattern to the First Hurdle
Athanasia Smirniotou, Flora Panteli, and Apostolos Theodorou
assess whether observable differences existed in the locomotion pattern and movement kinematics when approaching the first hurdle by modifying the task constraint of hurdle height. More specifically, the study examined to what extent the manipulation of task constraint (hurdle height) would affect visual
Effectiveness of a Variable-Speed Control Based on Auditory Feedback: Is It Possible?
Leonardo Lagos-Hausheer, Renata L. Bona, and Carlo M. Biancardi
Humans in general move with variable speeds; despite this, the literature is extensive in studies of locomotion at constant and controlled speed. The experimental designs at constant speed on a treadmill have been more applied mainly because they are easily replicable in a controlled environment
Load Carriage During Walking Increases Dynamic Stiffness at Distal Lower Limb Joints
Thiago R.T. Santos, Sergio T. Fonseca, Vanessa L. Araújo, Sangjun Lee, Fabricio Saucedo, Stephen Allen, Christopher Siviy, Thales R. Souza, Conor Walsh, and Kenneth G. Holt
angular displacement as a function of the joint moment and used to investigate joint level mechanics during locomotion. 13 – 15 Thus, dynamic stiffness might inform about the changes needed in joint angle coupled to its moment to deal with the greater external moment due to load carriage. Since the lower
Variability of Spatiotemporal Gait Kinematics During Treadmill Walking: Is There a Hawthorne Effect?
Saaniya Farhan, Marco A. Avalos, and Noah J. Rosenblatt
global control of locomotion, as reflected by variability, appears to be altered in response to observation, with potentially stronger effects on processes and/or networks that control lateral foot placement on a step-to-step basis, that is, SWV. Whereas variability in gait generally reflects underlying
One or Many? A Brief History of Culture and Cultures in the Evolution of “Physical Culture”
Mark Dyreson
, built not only by anthropologists and historians but also by exercise physiologists and biomechanists, provides me with a biocultural launching pad that I need to meet these demands. 37 The new paradigm about the crucial role that locomotion played in both the natural and the cultural histories of the
The Relationship between Joint Kinetic Factors and the Walk–Run Gait Transition Speed during Human Locomotion
Alan Hreljac, Rodney T. Imamura, Rafael F. Escamilla, W. Brent Edwards, and Toran MacLeod
The primary purpose of this project was to examine whether lower extremity joint kinetic factors are related to the walk–run gait transition during human locomotion. Following determination of the preferred transition speed (PTS), each of the 16 subjects walked down a 25-m runway, and over a floor-mounted force platform at five speeds (70, 80, 90, 100, and 110% of the PTS), and ran over the force platform at three speeds (80, 100, and 120% of the PTS) while being videotaped (240 Hz) from the right sagittal plane. Two-dimensional kinematic data were synchronized with ground reaction force data (960 Hz). After smoothing, ankle and knee joint moments and powers were calculated using standard inverse dynamics calculations. The maximum dorsiflexor moment was the only variable tested that increased as walking speed increased and then decreased when gait changed to a run at the PTS, meeting the criteria set to indicate that this variable influences the walk–run gait transition during human locomotion. This supports previous research suggesting that an important factor in changing gaits at the PTS is the prevention of undue stress in the dorsiflexor muscles.
