Vision can improve bipedal upright stability during standing and locomotion. However, during loco... more Vision can improve bipedal upright stability during standing and locomotion. However, during locomotion, vision supports additional behaviors such as gait cycle modulation, navigation, and obstacle avoidance. Here, we investigate how the multiple roles of vision are reflected in the dynamics of trunk control as the neural control problem changes from a fixed to a moving base of support. Subjects were presented with either low- or high-amplitude broadband visual stimuli during standing posture or while walking on a treadmill at 1 km/h and 5 km/h. Frequency response functions between visual scene motion (input) and trunk kinematics (output) revealed little or no change in the gain of trunk orientation in the standing posture and walking conditions. However, a dramatic increase in gain was observed in trunk (hip and shoulder) horizontal displacement from posture to locomotion. Such increases in gain may be interpreted as an increased coupling to visual scene motion. However, we believe that the increased gain reflects a decrease in stability due to a change of the control problem from standing to locomotion. Indeed, keeping the body upright with the use of vision during walking is complicated by the additional locomotor processes at work. Unlike during standing, vision plays many roles during locomotion, providing information for upright stability as well as body position relative to the external environment.
Previous studies mainly evaluated the neuromuscular pattern generation in cerebral palsy (CP) dur... more Previous studies mainly evaluated the neuromuscular pattern generation in cerebral palsy (CP) during unobstructed gait. Here we characterized impairments in the obstacle task performance associated with a limited adaptation of the task-relevant muscle module timed to the foot lift during obstacle crossing. Impaired task performance in children with CP may reflect basic developmental deficits in the adaptable control of gait when the locomotor task is superimposed with the voluntary movement.
The accomplishment of mature locomotor movements relies upon the integrated coordination of the l... more The accomplishment of mature locomotor movements relies upon the integrated coordination of the lower and upper limbs and the trunk. Human adults normally swing their arms and a quadrupedal limb coordination persists during bipedal walking despite a strong corticospinal control of the upper extremities that allows to uncouple this connection during voluntary activities. Here we investigated arm-leg coordination during stepping responses on a surface in human neonates. In eight neonates, we found the overt presence of alternating arm-leg oscillations, the arms moving up and down in alternation with ipsilateral lower limb movements. These neonates moved the diagonal limbs together, and the peak of the arm-to-trunk angle (i.e., maximum vertical excursion of the arm) occurred around the end of the ipsilateral stance phase, as it occurs during typical adult walking. Although episodes of arm-leg coordination were sporadic in our sample of neonates, their presence provides significant evid...
Background: On Earth only a few legged species, such as water strider insects, some aquatic birds... more Background: On Earth only a few legged species, such as water strider insects, some aquatic birds and lizards, can run on water. For most other species, including humans, this is precluded by body size and proportions, lack of appropriate appendages, and limited muscle power. However, if gravity is reduced to less than Earth's gravity, running on water should require less muscle power. Here we use a hydrodynamic model to predict the gravity levels at which humans should be able to run on water. We test these predictions in the laboratory using a reduced gravity simulator. Methodology/Principal Findings: We adapted a model equation, previously used by Glasheen and McMahon to explain the dynamics of Basilisk lizard, to predict the body mass, stride frequency and gravity necessary for a person to run on water. Progressive bodyweight unloading of a person running in place on a wading pool confirmed the theoretical predictions that a person could run on water, at lunar (or lower) gravity levels using relatively small rigid fins. Three-dimensional motion capture of reflective markers on major joint centers showed that humans, similarly to the Basilisk Lizard and to the Western Grebe, keep the head-trunk segment at a nearly constant height, despite the high stride frequency and the intensive locomotor effort. Trunk stabilization at a nearly constant height differentiates running on water from other, more usual human gaits. Conclusions/Significance: The results showed that a hydrodynamic model of lizards running on water can also be applied to humans, despite the enormous difference in body size and morphology.
Motion of the upper limbs is often coupled to that of the lower limbs in human bipedal locomotion... more Motion of the upper limbs is often coupled to that of the lower limbs in human bipedal locomotion. It is unclear, however, whether the functional coupling between upper and lower limbs is bi-directional, i.e. whether arm movements can affect the lumbosacral locomotor circuitry. Here we tested the effects of voluntary rhythmic arm movements on the lower limbs. Participants lay horizontally on their side with each leg suspended in an unloading exoskeleton. They moved their arms on an overhead treadmill as if they walked on their hands. Hand-walking in the antero-posterior direction resulted in significant locomotor-like movements of the legs in 58% of the participants. We further investigated quantitatively the responses in a subset of the responsive subjects. We found that the electromyographic (EMG) activity of proximal leg muscles was modulated over each cycle with a timing similar to that of normal locomotion. The frequency of kinematic and EMG oscillations in the legs typically differed from that of arm oscillations. The effect of hand-walking was direction specific since medio-lateral arm movements did not evoke appreciably leg air-stepping. Using externally imposed trunk movements and biomechanical modelling, we ruled out that the leg movements associated with hand-walking were mainly due to the mechanical transmission of trunk oscillations. EMG activity in hamstring muscles associated with hand-walking often continued when the leg movements were transiently blocked by the experimenter or following the termination of arm movements. The present results reinforce the idea that there exists a functional neural coupling between arm and legs.
During the evolution of bipedal modes of locomotion, a sequential rostrocaudal activation of trun... more During the evolution of bipedal modes of locomotion, a sequential rostrocaudal activation of trunk muscles due to the undulatory body movements was replaced by more complex and discrete bursts of activity. Nevertheless, the capacity for segmental rhythmogenesis and the rostrocaudal propagation of spinal cord activity has been conserved. In humans, motoneurons of different muscles are arranged in columns, with a specific grouping of muscles at any given segmental level. The muscle patterns of locomotor activity and the biomechanics of the body center of mass have been studied extensively, but their interrelationship remains poorly understood. Here we mapped the electromyographic activity recorded from 30 bilateral leg muscles onto the spinal cord in approximate rostrocaudal locations of the motoneuron pools during walking and running in humans. We found that the rostrocaudal displacements of the center of bilateral motoneuron activity mirrored the changes in the energy due to the cen...
During gradual speed changes, humans exhibit a sudden discontinuous switch from walking to runnin... more During gradual speed changes, humans exhibit a sudden discontinuous switch from walking to running at a specific speed, and it has been suggested that different gaits may be associated with different functioning of neuronal networks. In this study we recorded the EMG activity of leg muscles at slow increments and decrements in treadmill belt speed and at different levels of body weight unloading. In contrast to normal walking at 1 g, at lower levels of simulated gravity (<0.4 g) the transition between walking and running was generally gradual, without systematic abrupt changes in either intensity or timing of EMG patterns. This phenomenon depended to a limited extent on the gravity simulation technique, although the exact level of the appearance of smooth transitions (0.4–0.6 g) tended to be lower for the vertical than for the tilted body weight support system. Furthermore, simulations performed with a half-center oscillator neuromechanical model showed that the abruptness of mot...
In human and animal locomotion, sensory input is thought to be processed in a phase-dependent man... more In human and animal locomotion, sensory input is thought to be processed in a phase-dependent manner. Here we use full-field transient visual scene motion toward or away from subjects walking on a treadmill. Perturbations were presented at three phases of walking to test 1) whether phase dependence is observed for visual input and 2) whether the nature of phase dependence differs across body segments. Results demonstrated that trunk responses to approaching perturbations were only weakly phase dependent and instead depended primarily on the delay from the perturbation. Recording of kinematic and muscle responses from both right and left lower limb allowed the analysis of six distinct phases of perturbation effects. In contrast to the trunk, leg responses were strongly phase dependent. Leg responses during the same gait cycle as the perturbation exhibited gating, occurring only when perturbations were applied in midstance. In contrast, during the postperturbation gait cycle, leg resp...
When a toddler starts to walk without support, gait kinematics and electromyographic (EMG) activi... more When a toddler starts to walk without support, gait kinematics and electromyographic (EMG) activity differ from those of older children and the body displays considerable oscillations due to poor equilibrium. Postural instability clearly affects motor patterns in adults, but does instability explain why toddlers walk with a different gait? Here we addressed this question by comparing kinematics and EMGs in toddlers performing their first independent steps with or without hand or trunk support. Hand support significantly improved postural stability and some general gait parameters, reducing percent of falls, step width, lateral hip deviations and trunk oscillations. However, the kinematic and EMG patterns were unaffected by increased postural stability. In particular, the co-variance of the angular motion of the lower limb segments, the pattern of bilateral coordination of the vertical movement of the two hip joints, high variability of the foot path, the elliptic or single peak traj...
The concept of body schema has been introduced and widely discussed in the literature to explain ... more The concept of body schema has been introduced and widely discussed in the literature to explain various clinical observations and distortions in the body and space representation. Here we address the role of body schema related information in multi-joint limb motion. The processing of proprioceptive information may differ significantly in static and dynamic conditions since in the latter case the control system may employ specific dynamic rules and constraints. Accordingly, the perception of movement, e.g., estimation of step length and walking distance, may rely on a priori knowledge about intrinsic dynamics of limb segment motion and inherent relationships between gait parameters and body proportions. The findings are discussed in the general framework of space and body movement representation and suggest the existence of a dynamic locomotor body schema used for controlling step length and path estimation.
Chapter 12. Descending tracts' and spinal disorders Methods: We asked healthy subjects to produce... more Chapter 12. Descending tracts' and spinal disorders Methods: We asked healthy subjects to produce various voluntary movements during over-ground locomotion: kick a ball, step over an obstacle, or reach down and grasp an object on the floor. We applied a factor analysis to the EMG waveforms of the 32 ipsilateral limb and trunk muscles recorded during each task to determine the underlying activation components. Results: Five basic activation factors were invariantly present in each of the voluntary movement tasks, though the number of muscles activated by a particular factor, the factor loadings, could differ. In addition, we found a separate 6 th activation factor timed to the voluntary task and associated with specific muscle loadings (for instance, similar to those when the movement was performed during quite standing). The separate factor tended to be extensively weighted across muscles, including many of the muscles activated during normal walking. Discussion and Conclusion: The results suggest that the coordination of an invariant locomotion program with a voluntary movement is accomplished by combining factors that are separately associated with each task. Compound movements may thus be produced through a superposition of motor programs.
Despite distinct differences between walking and running, the two types of human locomotion are l... more Despite distinct differences between walking and running, the two types of human locomotion are likely to be controlled by shared pattern-generating networks. However, the differences between their kinematics and kinetics imply that corresponding muscle activations may also be quite different. We examined the differences between walking and running by recording kinematics and electromyographic (EMG) activity in 32 ipsilateral limb and trunk muscles during human locomotion, and compared the effects of speed (3–12 km/h) and gait. We found that the timing of muscle activation was accounted for by five basic temporal activation components during running as we previously found for walking. Each component was loaded on similar sets of leg muscles in both gaits but generally on different sets of upper trunk and shoulder muscles. The major difference between walking and running was that one temporal component, occurring during stance, was shifted to an earlier phase in the step cycle during...
The concept of body schema has been introduced and widely discussed in the literature to explain ... more The concept of body schema has been introduced and widely discussed in the literature to explain various clinical observations and distortions in the body and space representation. Here we address the role of body schema related information in multi-joint limb motion. The processing of proprioceptive information may differ significantly in static and dynamic conditions since in the latter case the control system may employ specific dynamic rules and constraints. Accordingly, the perception of movement, e.g., estimation of step length and walking distance, may rely on a priori knowledge about intrinsic dynamics of limb segment motion and inherent relationships between gait parameters and body proportions. The findings are discussed in the general framework of space and body movement representation and suggest the existence of a dynamic locomotor body schema used for controlling step length and path estimation.
Vision can improve bipedal upright stability during standing and locomotion. However, during loco... more Vision can improve bipedal upright stability during standing and locomotion. However, during locomotion, vision supports additional behaviors such as gait cycle modulation, navigation, and obstacle avoidance. Here, we investigate how the multiple roles of vision are reflected in the dynamics of trunk control as the neural control problem changes from a fixed to a moving base of support. Subjects were presented with either low- or high-amplitude broadband visual stimuli during standing posture or while walking on a treadmill at 1 km/h and 5 km/h. Frequency response functions between visual scene motion (input) and trunk kinematics (output) revealed little or no change in the gain of trunk orientation in the standing posture and walking conditions. However, a dramatic increase in gain was observed in trunk (hip and shoulder) horizontal displacement from posture to locomotion. Such increases in gain may be interpreted as an increased coupling to visual scene motion. However, we believe that the increased gain reflects a decrease in stability due to a change of the control problem from standing to locomotion. Indeed, keeping the body upright with the use of vision during walking is complicated by the additional locomotor processes at work. Unlike during standing, vision plays many roles during locomotion, providing information for upright stability as well as body position relative to the external environment.
Previous studies mainly evaluated the neuromuscular pattern generation in cerebral palsy (CP) dur... more Previous studies mainly evaluated the neuromuscular pattern generation in cerebral palsy (CP) during unobstructed gait. Here we characterized impairments in the obstacle task performance associated with a limited adaptation of the task-relevant muscle module timed to the foot lift during obstacle crossing. Impaired task performance in children with CP may reflect basic developmental deficits in the adaptable control of gait when the locomotor task is superimposed with the voluntary movement.
The accomplishment of mature locomotor movements relies upon the integrated coordination of the l... more The accomplishment of mature locomotor movements relies upon the integrated coordination of the lower and upper limbs and the trunk. Human adults normally swing their arms and a quadrupedal limb coordination persists during bipedal walking despite a strong corticospinal control of the upper extremities that allows to uncouple this connection during voluntary activities. Here we investigated arm-leg coordination during stepping responses on a surface in human neonates. In eight neonates, we found the overt presence of alternating arm-leg oscillations, the arms moving up and down in alternation with ipsilateral lower limb movements. These neonates moved the diagonal limbs together, and the peak of the arm-to-trunk angle (i.e., maximum vertical excursion of the arm) occurred around the end of the ipsilateral stance phase, as it occurs during typical adult walking. Although episodes of arm-leg coordination were sporadic in our sample of neonates, their presence provides significant evid...
Background: On Earth only a few legged species, such as water strider insects, some aquatic birds... more Background: On Earth only a few legged species, such as water strider insects, some aquatic birds and lizards, can run on water. For most other species, including humans, this is precluded by body size and proportions, lack of appropriate appendages, and limited muscle power. However, if gravity is reduced to less than Earth's gravity, running on water should require less muscle power. Here we use a hydrodynamic model to predict the gravity levels at which humans should be able to run on water. We test these predictions in the laboratory using a reduced gravity simulator. Methodology/Principal Findings: We adapted a model equation, previously used by Glasheen and McMahon to explain the dynamics of Basilisk lizard, to predict the body mass, stride frequency and gravity necessary for a person to run on water. Progressive bodyweight unloading of a person running in place on a wading pool confirmed the theoretical predictions that a person could run on water, at lunar (or lower) gravity levels using relatively small rigid fins. Three-dimensional motion capture of reflective markers on major joint centers showed that humans, similarly to the Basilisk Lizard and to the Western Grebe, keep the head-trunk segment at a nearly constant height, despite the high stride frequency and the intensive locomotor effort. Trunk stabilization at a nearly constant height differentiates running on water from other, more usual human gaits. Conclusions/Significance: The results showed that a hydrodynamic model of lizards running on water can also be applied to humans, despite the enormous difference in body size and morphology.
Motion of the upper limbs is often coupled to that of the lower limbs in human bipedal locomotion... more Motion of the upper limbs is often coupled to that of the lower limbs in human bipedal locomotion. It is unclear, however, whether the functional coupling between upper and lower limbs is bi-directional, i.e. whether arm movements can affect the lumbosacral locomotor circuitry. Here we tested the effects of voluntary rhythmic arm movements on the lower limbs. Participants lay horizontally on their side with each leg suspended in an unloading exoskeleton. They moved their arms on an overhead treadmill as if they walked on their hands. Hand-walking in the antero-posterior direction resulted in significant locomotor-like movements of the legs in 58% of the participants. We further investigated quantitatively the responses in a subset of the responsive subjects. We found that the electromyographic (EMG) activity of proximal leg muscles was modulated over each cycle with a timing similar to that of normal locomotion. The frequency of kinematic and EMG oscillations in the legs typically differed from that of arm oscillations. The effect of hand-walking was direction specific since medio-lateral arm movements did not evoke appreciably leg air-stepping. Using externally imposed trunk movements and biomechanical modelling, we ruled out that the leg movements associated with hand-walking were mainly due to the mechanical transmission of trunk oscillations. EMG activity in hamstring muscles associated with hand-walking often continued when the leg movements were transiently blocked by the experimenter or following the termination of arm movements. The present results reinforce the idea that there exists a functional neural coupling between arm and legs.
During the evolution of bipedal modes of locomotion, a sequential rostrocaudal activation of trun... more During the evolution of bipedal modes of locomotion, a sequential rostrocaudal activation of trunk muscles due to the undulatory body movements was replaced by more complex and discrete bursts of activity. Nevertheless, the capacity for segmental rhythmogenesis and the rostrocaudal propagation of spinal cord activity has been conserved. In humans, motoneurons of different muscles are arranged in columns, with a specific grouping of muscles at any given segmental level. The muscle patterns of locomotor activity and the biomechanics of the body center of mass have been studied extensively, but their interrelationship remains poorly understood. Here we mapped the electromyographic activity recorded from 30 bilateral leg muscles onto the spinal cord in approximate rostrocaudal locations of the motoneuron pools during walking and running in humans. We found that the rostrocaudal displacements of the center of bilateral motoneuron activity mirrored the changes in the energy due to the cen...
During gradual speed changes, humans exhibit a sudden discontinuous switch from walking to runnin... more During gradual speed changes, humans exhibit a sudden discontinuous switch from walking to running at a specific speed, and it has been suggested that different gaits may be associated with different functioning of neuronal networks. In this study we recorded the EMG activity of leg muscles at slow increments and decrements in treadmill belt speed and at different levels of body weight unloading. In contrast to normal walking at 1 g, at lower levels of simulated gravity (<0.4 g) the transition between walking and running was generally gradual, without systematic abrupt changes in either intensity or timing of EMG patterns. This phenomenon depended to a limited extent on the gravity simulation technique, although the exact level of the appearance of smooth transitions (0.4–0.6 g) tended to be lower for the vertical than for the tilted body weight support system. Furthermore, simulations performed with a half-center oscillator neuromechanical model showed that the abruptness of mot...
In human and animal locomotion, sensory input is thought to be processed in a phase-dependent man... more In human and animal locomotion, sensory input is thought to be processed in a phase-dependent manner. Here we use full-field transient visual scene motion toward or away from subjects walking on a treadmill. Perturbations were presented at three phases of walking to test 1) whether phase dependence is observed for visual input and 2) whether the nature of phase dependence differs across body segments. Results demonstrated that trunk responses to approaching perturbations were only weakly phase dependent and instead depended primarily on the delay from the perturbation. Recording of kinematic and muscle responses from both right and left lower limb allowed the analysis of six distinct phases of perturbation effects. In contrast to the trunk, leg responses were strongly phase dependent. Leg responses during the same gait cycle as the perturbation exhibited gating, occurring only when perturbations were applied in midstance. In contrast, during the postperturbation gait cycle, leg resp...
When a toddler starts to walk without support, gait kinematics and electromyographic (EMG) activi... more When a toddler starts to walk without support, gait kinematics and electromyographic (EMG) activity differ from those of older children and the body displays considerable oscillations due to poor equilibrium. Postural instability clearly affects motor patterns in adults, but does instability explain why toddlers walk with a different gait? Here we addressed this question by comparing kinematics and EMGs in toddlers performing their first independent steps with or without hand or trunk support. Hand support significantly improved postural stability and some general gait parameters, reducing percent of falls, step width, lateral hip deviations and trunk oscillations. However, the kinematic and EMG patterns were unaffected by increased postural stability. In particular, the co-variance of the angular motion of the lower limb segments, the pattern of bilateral coordination of the vertical movement of the two hip joints, high variability of the foot path, the elliptic or single peak traj...
The concept of body schema has been introduced and widely discussed in the literature to explain ... more The concept of body schema has been introduced and widely discussed in the literature to explain various clinical observations and distortions in the body and space representation. Here we address the role of body schema related information in multi-joint limb motion. The processing of proprioceptive information may differ significantly in static and dynamic conditions since in the latter case the control system may employ specific dynamic rules and constraints. Accordingly, the perception of movement, e.g., estimation of step length and walking distance, may rely on a priori knowledge about intrinsic dynamics of limb segment motion and inherent relationships between gait parameters and body proportions. The findings are discussed in the general framework of space and body movement representation and suggest the existence of a dynamic locomotor body schema used for controlling step length and path estimation.
Chapter 12. Descending tracts' and spinal disorders Methods: We asked healthy subjects to produce... more Chapter 12. Descending tracts' and spinal disorders Methods: We asked healthy subjects to produce various voluntary movements during over-ground locomotion: kick a ball, step over an obstacle, or reach down and grasp an object on the floor. We applied a factor analysis to the EMG waveforms of the 32 ipsilateral limb and trunk muscles recorded during each task to determine the underlying activation components. Results: Five basic activation factors were invariantly present in each of the voluntary movement tasks, though the number of muscles activated by a particular factor, the factor loadings, could differ. In addition, we found a separate 6 th activation factor timed to the voluntary task and associated with specific muscle loadings (for instance, similar to those when the movement was performed during quite standing). The separate factor tended to be extensively weighted across muscles, including many of the muscles activated during normal walking. Discussion and Conclusion: The results suggest that the coordination of an invariant locomotion program with a voluntary movement is accomplished by combining factors that are separately associated with each task. Compound movements may thus be produced through a superposition of motor programs.
Despite distinct differences between walking and running, the two types of human locomotion are l... more Despite distinct differences between walking and running, the two types of human locomotion are likely to be controlled by shared pattern-generating networks. However, the differences between their kinematics and kinetics imply that corresponding muscle activations may also be quite different. We examined the differences between walking and running by recording kinematics and electromyographic (EMG) activity in 32 ipsilateral limb and trunk muscles during human locomotion, and compared the effects of speed (3–12 km/h) and gait. We found that the timing of muscle activation was accounted for by five basic temporal activation components during running as we previously found for walking. Each component was loaded on similar sets of leg muscles in both gaits but generally on different sets of upper trunk and shoulder muscles. The major difference between walking and running was that one temporal component, occurring during stance, was shifted to an earlier phase in the step cycle during...
The concept of body schema has been introduced and widely discussed in the literature to explain ... more The concept of body schema has been introduced and widely discussed in the literature to explain various clinical observations and distortions in the body and space representation. Here we address the role of body schema related information in multi-joint limb motion. The processing of proprioceptive information may differ significantly in static and dynamic conditions since in the latter case the control system may employ specific dynamic rules and constraints. Accordingly, the perception of movement, e.g., estimation of step length and walking distance, may rely on a priori knowledge about intrinsic dynamics of limb segment motion and inherent relationships between gait parameters and body proportions. The findings are discussed in the general framework of space and body movement representation and suggest the existence of a dynamic locomotor body schema used for controlling step length and path estimation.
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Papers by G. Cappellini