Age-related differences in adaptation during childhood: The influences of muscular power production and segmental energy flow caused by muscles

Acquisition of skillfulness is not only characterized by a task-appropriate application of muscular forces but also by the ability to adapt performance to changing task demands. Previous research suggests that there is a different developmental schedule for adaptation at the kinematic compared to the neuro-muscular level. The purpose of this study was to determine how age-related differences in neuro-muscular organization affect the mechanical construction of pedaling at different levels of the task. By quantifying the flow of segmental energy caused by muscles, we determined the muscular synergies that construct the movement outcome across movement speeds. Younger children (5-7 years; n = 11), older children (8-10 years; n = 8), and adults (22-31 years; n = 8) rode a stationary ergometer at five discrete cadences (60, 75, 90, 105, and 120 rpm) at 10% of their individually predicted peak power output. Using a forward dynamics simulation, we determined the muscular contributions to crank power, as well as muscular power delivered to the crank directly and indirectly (through energy absorption and transfer) during the downstroke and the upstroke of the crank cycle. We found significant age × cadence interactions for (1) peak muscular power at the hip joint [Wilks' Lambda = 0.441, F(8,42) = 2.65, p = 0.019] indicating that at high movement speeds children produced less peak power at the hip than adults, (2) muscular power delivered to the crank during the downstroke and the upstroke of the crank cycle [Wilks' Lambda = 0.399, F(8,42) = 3.07, p = 0.009] indicating that children delivered a greater proportion of the power to the crank during the upstroke when compared to adults, (3) hip power contribution to limb power [Wilks' Lambda = 0.454, F(8,42) = 2.54, p = 0.023] indicating a cadence-dependence of age-related differences in the muscular synergy between hip extensors and plantarflexors. The results demonstrate that in spite of a successful performance, children construct the task of pedaling differently when compared to adults, especially when they are pushed to their performance limits. The weaker synergy between hip extensors and plantarflexors suggests that a lack of inter-muscular coordination, rather than muscular power production per se, is a factor that limits children's performance ranges

Control of posture with FES systems

One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints

PRINCIPAL COMPONENT ANALYSIS OF NEURAL AND KINEMATIC PARAMETERS OF FORWARD AND BACKWARD WALKING ACROSS DIFFERENT INCLINES

The purpose of this study was to identify whether the motor pattern of forward walking (FW) and backward walking (BW) affects the neural control and kinematics of lower limbs. A 21-camera 3D motion analysis system was used for the examination of locomotion. The activation of seven muscles of the right leg was recorded. The motion analysis was performed during FW and BW on a treadmill with the subjects (n=15) walking at four different inclines. The primary analysis of the complexity of variability of the kinematics and neural data was assessed using Principal Component Analysis (PCA). The complexity of gait pattern during FW appears more varied than during BW across all inclines. The associated muscles with each component were different during FW and BW

Neuromechanics of Dynamic Balance Tasks in the Presence of Perturbations

Understanding the neuromechanical responses to perturbations in humans may help to explain the reported improvements in stability performance and muscle strength after perturbation-based training. In this study, we investigated the effects of perturbations, induced by unstable surfaces, on the mechanical loading and the modular organization of motor control in the lower limb muscles during lunging forward and backward. Fifteen healthy adults performed 50 forward and 50 backward lunges on stable and unstable ground. Ground reaction forces, joint kinematics, and the electromyogram (EMG) of 13 lower limb muscles were recorded. We calculated the resultant joint moments and extracted muscle synergies from the stepping limb. We found sparse alterations in the resultant joint moments and EMG activity, indicating a little if any effect of perturbations on muscle mechanical loading. The time-dependent structure of the muscle synergy responsible for the stabilization of the body was modified in the perturbed lunges by a shift in the center of activity (later in the forward and earlier in the backward lunge) and a widening (in the backward lunge). Moreover, in the perturbed backward lunge, the synergy related to the body weight acceptance was not present. The found modulation of the modular organization of motor control in the unstable condition and related minor alteration in joint kinetics indicates increased control robustness that allowed the participants to maintain functionality in postural challenging settings. Triggering specific modulations in motor control to regulate robustness in the presence of perturbations may be associated with the reported benefits of perturbation-based training.Peer Reviewe

Neuromuscular Control Strategy during Object Transport while Walking: Adaptive Integration of Upper and Lower Limb Movements

When carrying an object while walking, a significant challenge for the central nervous system (CNS) is to preserve the object’s stability against the inter-segmental interaction torques and ground reaction forces. Studies documented several strategies used by the CNS: modulation of grip force (GF), alterations in upper limb kinematics, and gait adaptations. However, the question of how the CNS organizes the multi-segmental joint and muscle coordination patterns to deal with gait-induced perturbations remains poorly understood. This dissertation aimed to explore the neuromuscular control strategy utilized by the CNS to transport an object during walking successfully. Study 1 examined the inter-limb coordination patterns of the upper limbs when carrying a cylinder-shaped object while walking on a treadmill. It was predicted that transporting an object in one hand would affect the movement pattern of the contralateral arm to maintain the overall angular momentum. The results showed that transporting an object caused a decreased anti-phase coordination, but it did not induce significant kinematic and muscle activation changes in the unconstrained arm. Study 2 examined muscle synergy patterns for upper limb damping behavior by using non-negative matrix factorization (NNMF) method. Four synergies were identified, showing a proximal-to-distal pattern of activation preceding heel contacts. Study 3 examined the effect of different precision demands (carrying a cup with or without a ball) and altered visual information (looking forward vs. looking at an object) on the upper limb damping behavior and muscle synergies. Increasing precision demand induced stronger damping behavior and increased the electromyography (EMG) activation of wrist/hand flexors and extensors. The NNMF results replicated Study 2 in that the stabilization of proximal joints occurred before the distal joints. The results indicated that the damping incorporates tonic and phasic muscle activation to ensure object stabilization. Overall, three experiments showed that the CNS adopts a similar synergy pattern regardless of task constraint or altered gaze direction while modulating the amount of muscle activation for object stabilization. Kinematic changes can differ depending on the different levels of constraint, as shown in the smaller movement amplitude of the shoulder joint in the transverse plane during the task with higher precision demand

TOTAL BODY KINETICS: OUR DIAGNOSTIC KEY TO HUMAN MOVEMENT

INTRODUCTION In all forms of human movement (normal daily activity, athletic movements and even pathological movement) the entire body is usually involved. As such a large number of segments and muscles must be controlled. If we wish to "diagnose" the detailed cause of any particular movement it is only through a kinetic analyses of the total body or the total limb. Here we see how the movement is being coordinated, and in many cases how adaptations are being organized by the CNS. In fact, without such analyses it is impossible to identify multiple syner- gies by several muscle groups and si- multaneous goals being accomplished by the same muscle group. Several inherent characteristics of the neuromusculosketal system must be recognized in order that our interpretations make sense. The structure of the neural system is converging in nature. Every a motoneuran is the final common pathway of scores of inhibitory and excitatory inputs, both central and peripheral, both proactive and reactive. All motor units converge to produce a single museie tension and each muscIe converges at each joint to produce a net moment of force. Then at the total limb level interlimb coupling allows for more collaboration towards a common goal. The byproduct of these many levels of integration is considerable variability and adaptability. In athletic movements this has distinct advantages in reducing fatigue and in enabling the athlete in being highly flexible. Three examples are presented here in order to demonstrate the need for kinetics at the joint or at the muscle level in order to "diagnose" how the CNS is accomplishing its goals. The first is a power analysis of the totallower Jimb during running in order to identify the energy sources and lasses and flows between segments. The second is a muscle/skeletal biomeehanics analysis, also of running, to see how the lower limb can damage the structure and also decrease the stress on certain structures. The third example is taken from walking (but is equally applicable in all forms of running) where the role of one muscle group (hip extensors/flexors) is examined and is found to accomplish 2 or 3 simultaneous goals during weight bearing. ENERGY GENERATION, ABSORPTION AND TRANSFERS DURING RUNNING Energy can only be generated by muscles; the net generation is given by Mj . roj where Mj is the joint moment and roj is the joint angular velocity. If Mj and roj have the same polarity (Le. both are flexor) then this product is positive and energy generation is taking place. If they have opposite polarities then Mj roj is negative indicating the muscles are absorbing energy. However, muscles can also transfer energy between adjacent segments and passive transfers between adjacent segments occurs at the joint centres (Robertson and Winter, 1980). Thus, in running it is desired to achieve efficiencies and through these transfers we can utilize energy from the decelerating swing limb to accelerate the trunk and accelerating limb. One gait cycle is analysed in order that we can identify all energy conservation mechanisms as weil as sites of generation and absorption CHRONIC RUNNING INJURIES A muscular-skeletal biomechanical analyses of the foot and leg during running is presented which predicts the compressive and shear forces at the ankle, knee and patello-femoral joints during weight bearing (Scott and Winter, 1990). A total lower limb kinetic analysis of the predicted muscle tension in the gastrocnemii, soleus and quadricips muscles. From the analyses the compressive and shear forces at the ankle and knee were estimated along with the bending moment in the tibia near the site of most stress of fractures. Not only did these analyses reveal very high compressive stresses on these joints but also a major stress reducing mechanism by the soleus during the intense push-off phase. The high force and angle of pull of the soleus served to cancel much of the potentially dangerous shear forces at the ankle and also created a bending moment in the tibia which cancelled much of the bending moment that causes stress fractures. MULTIPLE ROLES OF HIP EXTENSORS IFLEXORS DURING GAlT During the first half of stance the hip extensors are active and during the latter half of stance the flexors are active. There are three simultaneous roles of the hip extensors during the first half of stance: 1. To cancel the flexor couple created by the posterior acceleration of the hip joint, thereby balancing the HAT. segment; 2. To assist the quadriceps in controlling the vertical collapse of the lower limb; 3. To concentrically contract and generate forward propulsion energy During the latter half of stance there are two simultaneous roles of the hip flexors: 1. To cancel the extensor couple created by the anterior acceleration of the hip joint, thereby balancing the HAT. segment; 2. To concentrically contract and generate a "pull-off" of the lower limb. SUMMARY Many more examples of biomechanical analyses could be presented to demonstrate the need for full body or full limb kinetic analyses. However, it is hoped that these examples will be sufficient Extrapolating from these common gait analyses to complex athletic movements one would predict that biomechanical analyses will be extremely beneficial not only in understanding the movement but in improving them. REFERENCES Robertson, D.GE., Winter, DA (1980) Mechanical energy generation, absorption and transfer amongst segments during walking J. Biomeeh. 13: 845-854. Scott, S.H., Winter, DA (1990) Internal forces at chronic running injury sites. Med. Sci. Sports Exerc. 22: 357-369

Effects of personal and task constraints on limb coordination during walking: a systematic review and meta-analysis

Background In human behaviour, emergence of movement patterns is shaped by different, interacting constraints and consequently, individuals with motor disorders usually display distinctive lower limb coordination modes. Objectives To review existing evidence on the effects of motor disorders and different task constraints on emergent coordination patterns during walking, and to examine the clinical significance of task constraints on gait coordination in people with motor disorders. Methods The search included CINHAL Plus, MEDLINE, HSNAE, SPORTDiscus, Scopus, Pubmed and AMED. We included studies that compared intra-limb and inter-limb coordination during gait between individuals with a motor disorder and able-bodied individuals, and under different task constraints. Two reviewers independently examined the quality of studies by using the Newcastle Ottawa Scale-cohort study. Findings From the search results, we identified1416 articles that studied gait patterns and further analysis resulted in 33 articles for systematic review and 18 articles for meta-analysis-1, and 10 articles for meta-analysis-2. In total, the gait patterns of 539 patients and 358 able-bodied participants were analysed in the sampled studies. Results of the meta-analysis for group comparisons revealed a low effect size for group differences (ES = −0.24), and a moderate effect size for task interventions (ES = −0.53), on limb coordination during gait. Interpretation Findings demonstrated that motor disorders can be considered as an individual constraint, significantly altering gait patterns. These findings suggest that gait should be interpreted as functional adaptation to changing personal constraints, rather than as an abnormality. Results imply that designing gait interventions, through modifying locomotion tasks, can facilitate the emergent re-organisation of inter-limb coordination patterns during rehabilitation

Proactive Modulation in the Spatiotemporal Structure of Muscle Synergies Minimizes Reactive Responses in Perturbed Landings

Stability training in the presence of perturbations is an effective means of increasing muscle strength, improving reactive balance performance, and reducing fall risk. We investigated the effects of perturbations induced by an unstable surface during single-leg landings on the mechanical loading and modular organization of the leg muscles. We hypothesized a modulation of neuromotor control when landing on the unstable surface, resulting in an increase of leg muscle loading. Fourteen healthy adults performed 50 single-leg landings from a 30 cm height onto two ground configurations: stable solid ground (SG) and unstable foam pads (UG). Ground reaction force, joint kinematics, and electromyographic activity of 13 muscles of the landing leg were measured. Resultant joint moments were calculated using inverse dynamics and muscle synergies with their time-dependent (motor primitives) and time-independent (motor modules) components were extracted via non-negative matrix factorization. Three synergies related to the touchdown, weight acceptance, and stabilization phase of landing were found for both SG and UG. When compared with SG, the motor primitive of the touchdown synergy was wider in UG (p < 0.001). Furthermore, in UG the contribution of gluteus medius increased (p = 0.015) and of gastrocnemius lateralis decreased (p < 0.001) in the touchdown synergy. Weight acceptance and stabilization did not show any statistically significant differences between the two landing conditions. The maximum ankle and hip joint moment as well as the rate of ankle, knee, and hip joint moment development were significantly lower (p < 0.05) in the UG condition. The spatiotemporal modifications of the touchdown synergy in the UG condition highlight proactive adjustments in the neuromotor control of landings, which preserve reactive adjustments during the weight acceptance and stabilization synergies. Furthermore, the performed proactive control in combination with the viscoelastic properties of the soft surface resulted in a reduction of the mechanical loading in the lower leg muscles. We conclude that the use of unstable surfaces does not necessarily challenge reactive motor control nor increase muscle loading per se. Thus, the characteristics of the unstable surface and the dynamics of the target task must be considered when designing perturbation-based interventions.Peer Reviewe

Diagonals part seven. Stroke 5. Walking: what say the scientist and what is best practice

In this part we try to listen to the science, that has and still do over the whole world investigation by stroke patients over the walking aspect and the best way to get the best recovery or compensation. Recovery is only for a group possible, that had an “minor” stroke and there we see that the old system is not too much damaged and recovery is possible. But with greater damage of the brain individual after a stroke must go another way to get his independently and that is compensation. That compensation starts with the first movement in bed and will also affect the diagonal. The science has reported that the walking pattern on the EMG don’t change very much after a short period and they said that this pattern is fixed within in certain period. We have our doubt and have search to other forms of training and learning and see that changes is well possible but to be sure the science must have investigated that. Here is a problem because science gives another interpretation of the word intensity. For the scientist this is “more time” to do the exercises and in our view, it is the heaviness of the exercises and that can be done by an individual with a stroke a certain time before he is fatigue. In the treatment we start with the individual with a severe stroke that need all assistance to get him on his feet and will have need of a splint on his knee because the power in the knee muscle is to limited, to hold the knee. Regrettable an individual after a stroke that the scientist never investigates because this is too difficult. From this starting point we walk through all the steps, we must make to get independent walking individual when possible and what the problem were when that goal cannot fully be reached. And we discuss other forms, approach or new development to get walking possible with the use of the diagonals. Part 8 will discuss other cases with a severe stroke

In silico case studies of compliant robots: AMARSI deliverable 3.3

In the deliverable 3.2 we presented how the morphological computing ap- proach can significantly facilitate the control strategy in several scenarios, e.g. quadruped locomotion, bipedal locomotion and reaching. In particular, the Kitty experimental platform is an example of the use of morphological computation to allow quadruped locomotion. In this deliverable we continue with the simulation studies on the application of the different morphological computation strategies to control a robotic system