Prediction of leg muscle activities from arm muscle activities in arm and leg cycling

Functional electrical stimulation (FES) driven leg cycling is usually controlled by previously established stimulation patterns. We investigated the potential utilization of a particular computational method for controlling electrical stimulation of lower limb muscles by real-time electromyography (EMG) signals of arm muscles during hybrid arm and leg cycling. In hybrid arm and leg cycling, arm cranking is performed voluntarily, while leg cycling is driven by FES. In this study, we investigate arm and leg cycling movements of able-bodied persons when both arm and leg cycling is performed voluntarily without FES. We present a neural network-based model in which the input of the neural network is given by a time series of upper limb muscle activities (EMG), and the output provides potential lower limb muscle activities. The particular neural network was a nonlinear autoregressive exogen (NARX) neural network. The measured EMG signals of the lower limb muscles were compared to the signals that were predicted by the neural network. The neural network was trained with data recorded from four participants. Our preliminary results show notable differences between the predicted and the experimentally measured lower limb muscle activities. The prediction was good only for 60% of the movement time. We conclude that-while including arm cycling in the movement-simpler control modalities or further consideration of applying machine-learning techniques has to be taken into account to improve voluntary upper limb-controlled FES assisted leg cycling.

Effect of FES controlled cycling training on cardiovascular and pulmonary systems in a spinal cord injured patient

Introduction: The results of two spiroergometric measurements are presented that were taken from a spinal cord injured patient who participated in FES cycling training sessions for 11 months. Methods: The two measurements were taken 4 and 11 months after starting the training program. We investigated the respiratory exchange ratio (RER) and ventilation (VE/VO2, VE’/VCO2) ratios and the cycling cadence in the two investigated training sessions. Results: In the first assessment, the RER was below 1, which is the anaerobic training limit. Seven months later, in the second assessment, the RER value exceeded the anaerobic limit a few times and remained above it at the end of the session. The VE /VO2 and VE/VCO2 curves did not intersect during the first assessment. In the second one, the VE/VO2 and VE/VCO2 curves intersected several times and the oxygen quotient curve exceeded the carbon dioxide quotient curve. The patient achieved a low but similar cycling speed during the two assessments. Conclusion: Through the activation of paralyzed muscles with FES cycling we are able to train the paraplegic patient in aerobic and anaerobic training zones. This is shown by the value of RER, which reached the anaerobic training limit during the second assessment and remained in the anaerobic range for longer time.

Effects of gravity and kinematic constraints on muscle synergies in arm cycling

Arm cycling is a bimanual motor task used in medical rehabilitation and in sports training. Understanding how muscle coordination changes across different biomechanical constraints in arm cycling is a step toward improved rehabilitation approaches. This exploratory study aims to get new insights on motor control during arm cycling. To achieve our main goal, we used the muscle synergies analysis to test three hypotheses: 1) body position with respect to gravity (sitting and supine) has an effect on muscle synergies; 2) the movement size (crank length) has an effect on the synergistic behavior; 3) the bimanual cranking mode (asynchronous and synchronous) requires different synergistic control. Thirteen able-bodied volunteers performed arm cranking on a custom-made device with unconnected cranks, which allowed testing three different conditions: body position (sitting vs. supine), crank length (10 cm vs. 15 cm), and cranking mode (synchronous vs. asynchronous). For each of the eight possible combinations, subjects cycled for 30 s while electromyography of eight muscles (four from each arm) were recorded: biceps brachii, triceps brachii, anterior deltoid, and posterior deltoid. Muscle synergies in this eight-dimensional muscle space were extracted by nonnegative matrix factorization. Four synergies accounted for over 90% of muscle activation variances in all conditions. Results showed that synergies were affected by body position and cranking mode but practically unaffected by movement size. These results suggest that the central nervous system may employ different motor control strategies in response to external constraints such as cranking mode and body position during arm cycling.NEW & NOTEWORTHY Recent studies analyzed muscle synergies in lower limb cycling. Here, we examine upper limb cycling and specifically the effect of body position with respect to gravity, movement size, and cranking mode on muscle coordination during arm cranking tasks. We show that altered body position and cranking mode affects modular organization of muscle activities. To our knowledge, this is the first study assessing motor control through muscle synergies framework during upper limb cycling with different constraints.

The Effect of Crank Resistance on Arm Configuration and Muscle Activation Variances in Arm Cycling Movements

Arm cycling on an ergometer is common in sports training and rehabilitation protocols. The hand movement is constrained along a circular path, and the user is working against a resistance, maintaining a cadence. Even if the desired hand trajectory is given, there is the flexibility to choose patterns of joint coordination and muscle activation, given the kinematic redundancy of the upper limb. With changing external load, motor noise and changing joint stiffness may affect the pose of the arm even though the endpoint trajectory is unchanged. The objective of this study was to examine how the crank resistance influences the variances of joint configuration and muscle activation. Fifteen healthy participants performed arm cranking on an arm-cycle ergometer both unimanually and bimanually with a cadence of 60 rpm against three crank resistances. Joint configuration was represented in a 3-dimensional joint space defined by inter-segmental joint angles, while muscle activation in a 4-dimensional "muscle activation space" defined by EMGs of 4 arm muscles. Joint configuration variance in the course of arm cranking was not affected by crank resistance, whereas muscle activation variance was proportional to the square of muscle activation. The shape of the variance time profiles for both joint configuration and muscle activation was not affected by crank resistance. Contrary to the prevailing assumption that an increased motor noise would affect the variance of auxiliary movements, the influence of noise doesn't appear at the joint configuration level even when the system is redundant. Our results suggest the separation of kinematic- and force-control, via mechanisms that are compensating for dynamic nonlinearities. Arm cranking may be suitable when the aim is to perform training under different load conditions, preserving stable and secure control of joint movements and muscle activations.

Jerk Decomposition during Bimanual Independent Arm Cranking

The relationship between the smoothness of the upper limb endpoint movement and multi joint angular motion is a function of the individual joint angular velocities, accelerations, and jerks as well as the instantaneous arm configuration and its rate of change during movement execution. We compared the contribution of jerk components to the total endpoint jerk in able bodied participants who performed arm cranking movements on an arm cranking device where the two arms could crank independently. The results of this investigation suggest that the most dominant components of the end effector jerk are related to both the angular jerks and to the change of arm configuration pose. This jerk partitioning is much stronger as it was found previously for both reaching arm movements and single hand cranking. This shows the task specificity of the decomposition of endpoint jerk and the effect that bi-manual tasks can have on the smoothness of movements. The proposed decomposition may give useful information in why certain bi-manual rehabilitation processes are more useful than others.

Control of Cycling Limb Movements: Aspects for Rehabilitation

Walking, swimming, cycling, and running are cyclic movements that are often performed in training programs or rehabilitation protocols by athletes or people with neuromotor disorders. The muscular and kinematic activities that are acquired during cyclic movements reveal control principles, especially for the optimization and stabilization of motor performance, for a given criterion in rehabilitation processes. The influence of external loads and resistive forces on limb movements should be considered in rehabilitation protocols and when assessing physical activity levels or defining activity patterns for the artificial control of limb movements. This chapter focuses on special cyclic limb movements: lower and upper limb cycling. Two aspects of this research and applications are discussed. First, variances of movement patterns are examined at different levels of the motor system (endpoint, joint configuration, muscle) during unimanual right and left arm cycling and bimanual cycling movements. Second, it is shown that the muscle activity patterns that are acquired during lower and upper limb cycling in able-bodied people may be used to define and improve stimulation patterns for functional electrical stimulation-driven cycling movements in spinal cord-injured individuals. This report also discusses the advantages of the application and control of these types of movements for the rehabilitation of people with paralyzed limbs.

Submovements during reaching movements after stroke

Neurological deficits after cerebrovascular accidents very frequently disrupt the kinematics of voluntary movements with the consequent impact in daily life activities. Robotic methodologies enable the quantitative characterization of specific control deficits needed to understand the basis of functional impairments and to design effective rehabilitation therapies. In a group of right handed chronic stroke survivors (SS) with right side hemiparesis, intact proprioception, and differing levels of motor impairment, we used a robotic manipulandum to study right arm function during discrete point-to-point reaching movements and reciprocal out-and-back movements to visual targets. We compared these movements with those of neurologically intact individuals (NI). We analyzed the presence of secondary submovements in the initial (i.e. outward) trajectory portion of the two tasks and found that the SS with severe impairment (FM < 30) presented arm submovements that differed notably not only from NI but also from those of SS with moderate arm impairment (FM 30-50). Therefore the results of this pilot study suggest that in SS arm kinematics vary significantly across differing levels of motor impairment. Our results support the development of rehabilitation therapies carefully tailored to each individual stroke survivor.

The effect of load on torques in point-to-point arm movements: a 3D model

A dynamic, 3-dimensional model was developed to simulate slightly restricted (pronation-supination was not allowed) point-to-point movements of the upper limb under different external loads, which were modeled using 3 objects of distinct masses held in the hand. The model considered structural and biomechanical properties of the arm and measured coordinates of joint positions. The model predicted muscle torques generated by muscles and needed to produce the measured rotations in the shoulder and elbow joints. The effect of different object masses on torque profiles, magnitudes, and directions were studied. Correlation analysis has shown that torque profiles in the shoulder and elbow joints are load invariant. The shape of the torque magnitude-time curve is load invariant but it is scaled with the mass of the load. Objects with larger masses are associated with a lower deflection of the elbow torque with respect to the sagittal plane. Torque direction-time curve is load invariant scaled with the mass of the load. The authors propose that the load invariance of the torque magnitude-time curve and torque direction-time curve holds for object transporting arm movements not restricted to a plane.

The time course of the return of upper limb bradykinesia after cessation of subthalamic stimulation in Parkinson's disease

To investigate the time span within which bradykinesia re-occurs, we registered movement parameters immediately after the termination of deep brain stimulation of the subthalamic nucleus (STN) in nine Parkinson patients with chronically implanted bilateral STN electrodes. Two repetitive movements were investigated: finger-tapping and forearm pronation-supination. When stimulation was switched off, the amplitude and velocity of the investigated movements significantly declined, but the frequency did not. The time course of this decline was modeled by an exponential function that yielded time constants between 15 and 30s. The effect of stimulation had completely disappeared within 1 min. These results suggest that it is necessary to wait at least for 1 min after the end of stimulation before performing further assessments.

Joint angle variability in 3D bimanual pointing: uncontrolled manifold analysis

The structure of joint angle variability and its changes with practice were investigated using the uncontrolled manifold (UCM) computational approach. Subjects performed fast and accurate bimanual pointing movements in 3D space, trying to match the tip of a pointer, held in the right hand, with the tip of one of three different targets, held in the left hand during a pre-test, several practice sessions and a post-test. The prediction of the UCM approach about the structuring of joint angle variance for selective stabilization of important task variables was tested with respect to selective stabilization of time series of the vectorial distance between the pointer and aimed target tips (bimanual control hypothesis) and with respect to selective stabilization of the endpoint trajectory of each arm (unimanual control hypothesis). The components of the total joint angle variance not affecting (V(COMP)) and affecting (V(UN)) the value of a selected task variable were computed for each 10% of the normalized movement time. The ratio of these two components R(V)=V(COMP)/V(UN) served as a quantitative index of selective stabilization. Both the bimanual and unimanual control hypotheses were supported, however the R(V) values for the bimanual hypothesis were significantly higher than those for the unimanual hypothesis applied to the left and right arm both prior to and after practice. This suggests that the CNS stabilizes the relative trajectory of one endpoint with respect to the other more than it stabilizes the trajectories of each of the endpoints in the external space. Practice-associated improvement in both movement speed and accuracy was accompanied by counter-intuitive lack of changes in R(V). Both V(COMP) and V(UN) variance components decreased such that their ratio remained constant prior to and after practice. We conclude that the UCM approach offers a unique and under-explored opportunity to track changes in the organization of multi-effector systems with practice and allows quantitative assessment of the degree of stabilization of selected performance variables.

Structure of joint variability in bimanual pointing tasks

Changes in the structure of motor variability during practicing a bimanual pointing task were investigated using the framework of the uncontrolled manifold (UCM) hypothesis. The subjects performed fast and accurate planar movements with both arms, one moving the pointer and the other moving the target. The UCM hypothesis predicts that joint kinematic variability will be structured to selectively stabilize important task variables. This prediction was tested with respect to selective stabilization of the trajectory of the endpoint of each arm (unimanual control hypotheses) and with respect to selective stabilization of the timecourse of the vectorial distance between the target and the pointer tip (bimanual control hypothesis). Components of joint position variance not affecting and affecting a mean value of a selected variable were computed at each 10% of normalized movement time. The ratio of these two components ( R(V)) served as a quantitative index of selective stabilization. Both unimanual control hypotheses and the bimanual control hypothesis were supported both prior to and after practice. However, the R(V) values for the bimanual control hypothesis were significantly higher than for either of the unimanual control hypothesis, suggesting that the bimanual synergy was not simply a simultaneous execution of two unimanual synergies. After practice, an improvement in both movement speed and accuracy was accompanied by counterintuitive changes in the structure of kinematic variability. Components of joint position variance affecting and not affecting a mean value of a selected variable decreased, but there was a significantly larger drop in the latter when applied on each of the three selected task variables corresponding to the three control hypotheses. We conclude that the UCM hypothesis allows quantitative assessment of the degree of stabilization of selected performance variables and provides information on changes in the structure of a multijoint synergy that may not be reflected in its overall performance.

Secretion of phospholipase A2 induced by interactions of human platelets with monocytes

Phospholipase A2 (PLA2) activity was found and measured in the cell-free supernatants of human mononuclear cells (monocytes and lymphocytes) cultured with platelets for 48 h at 37 degrees C. The relative molecular mass of purified, calcium-dependent PLA2 was 14 kD. The amount of PLA2 in the supernatants correlated positively with the number of monocytes and platelets in the cultures. Electron microscopically, direct cell-to-cell interactions of monocytes and platelets were observed. Cultivation of suspensions of human mononuclear cells with platelets in serum-free medium was found to be an efficient way to produce and purify human secretable PLA2. In the release of secretable PLA2 in peripheral blood, the interactions between platelets and monocytes may play a considerable role.

The presence of a covalently cross-linked matrix in human platelets

Exhaustive extraction of human platelets with 6 M guanidine-HCl, and 5% beta-mercaptoethanol, followed by 5% SDS resulted in a sedimentable material which showed fibrous structure by transmission electron microscopy. When platelets treated with 8 M urea, 50 mM DTT and 2% SDS were applied on a 3% solubilizable acrylamide gel a high molecular weight material could be also isolated which was highly crosslinked by epsilon(gamma-glutamyl)lysine bonds. Its amino acid composition was Asp 110, Glu 119, Ser 55, Gly 70, Arg 33, Thr 41, Ala 112, Pro 93, Tyr 35, Val 18, Met 55, Cys 46, IIe 47, Leu 71, Phe 27, Lys 76 expressed as residue per 1000. The quantity of platelet polymer material as well as the amount of epsilon(gamma-glutamyl)lysine bond was slightly higher in thrombin activated platelets. The insoluble matrix of resting platelets reacts with antibodies against spectrin, alpha-actinin, actin, myosin, tropomyosin. The matrix from activated platelets has shown reaction with additional antibodies including ones against blood coagulation factor XIIIa, fibrinogen, von Willebrand factor, thrombospondin, tubulin and filamin. The presence of an epsilon(gamma-glutamyl)lysine cross-linked cell matrix in platelets is consistent with the observation of a similar structure in other cells.

Immunocytochemical characterization of amniotic fluid macrophages in cases of fetal neural tube defects

Amniotic fluid cells from 31 pregnancies with fetuses having open neural tube defects (NTDs) and from 43 pregnancies with fetuses free of NTDs were studied with the use of the immunoperoxidase method for alpha-fetoprotein (AFP) and glial fibrillary acidic protein (GFAP). The authors also used cytochemical stains for endogenous peroxidase and nonspecific esterase activity. In cases of NTDs, macrophages were present in the amniotic fluid, and in the authors' system they showed intense immunoreactivity for both AFP and GFAP and showed very strong activity for peroxidase and nonspecific esterase, whereas the epithelial cells and red blood cells showed no activity. In six cases of anencephaly, sections from the margin of the cranial end of defective spinal cords at the aperture of the open lesion were also studied for AFP and GFAP. In these cases, AFP- and GFAP-positive cells were found, indicating the possible neural (glial) origin of a part of amniotic fluid macrophages. Although the determination of AFP levels in maternal blood and amniotic fluid is widely used in the prenatal diagnosis of NTDs, demonstration of AFP in amniotic fluid cells by means of immunocytochemistry has not been described.