R. Gregor - Academia.edu (original) (raw)
Papers by R. Gregor
ABSTRACT INTRODUCTION During the paw-shake (PS) in the cat a differential activation of ankle ext... more ABSTRACT INTRODUCTION During the paw-shake (PS) in the cat a differential activation of ankle extensor synergists, the two-joint gastrocnemius (GA) and the one-joint soleus (SO), occurs: the GA demonstrates very high activation, whereas SO is either inactive or its activation is substantially reduced [1,5]. The two muscles are activated during the lengthening phase of the muscle-tendon complex (MTC) [1,4], in which substantial activation of SO and GA Ia-and Ib-afferents has been reported [4]. Thus, both velocity-dependent (Ia) and force-dependent (Ib) feedback might be used to regulate the differential activation of the two muscles. The velocity-dependent feedback is related among other factors to muscle fascicle velocity rather than to MTC velocity. Therefore, the role of MTC and fascicle velocity in the regulation of muscle activity in the PS remains unclear. High shortening velocity in muscle fascicles during PS can also be a limiting factor in muscle force production. The aim of this study was to determine fascicle and MTC velocities of the cat medial gastrocnemius (MG) and SO during the PS. METHODS Four cats were surgically instrumented with EMG electrodes in SO and MG [2]. Selected cats were also instrumented with sonomicrometry crystals to measure fascicle length [3]. After recovery, the PS was elicited by attaching a sticking tape to the paw and allowing the animal to walk on a walkway. Reflective markers on the animals were video-filmed using high-speed (120 Hz) motion capture system (Vicon, UK) with simultaneous recordings of EMG or sonomicrometry signals. The recorded kinematics and a geometric model of the hindlimb were used to calculate the origin-to-insertion (MTC) lengths of MG and SO. Joint velocities, moments and powers were also calculated for the major hindlimb joints.
Medicine & Science in Sports & Exercise, 2008
Journal of Neuroscience Methods, 1986
Journal of Neurophysiology, 2005
Recent progress in the understanding of motor cortex function has been achieved primarily by simu... more Recent progress in the understanding of motor cortex function has been achieved primarily by simultaneously recording motor cortex neuron activity and the movement kinematics of the corresponding limb. We have expanded this approach by combining high-quality cortical single-unit activity recordings with synchronized recordings of full-body kinematics and kinetics in the freely behaving cat. The method is illustrated by selected results obtained from two cats tested while walking on a flat surface. Using this method, the activity of 43 pyramidal tract neurons (PTNs) was recorded, averaged over 10 bins of a locomotion cycle, and compared with full-body mechanics by means of principal component and multivariate linear regression analyses. Patterns of 24 PTNs (56%) and 219 biomechanical variables (73%) were classified into just four groups of inter-correlated variables that accounted for 91% of the total variance, indicating that many of the recorded variables had similar patterns. The ...
Journal of Biomechanics, 2012
Journal of Applied Physiology, 2009
On the basis of differences in physiology, e.g., histochemical properties and spindle density, an... more On the basis of differences in physiology, e.g., histochemical properties and spindle density, and the structural design of the cat soleus (SO) and medial gastrocnemius (MG) muscles, we hypothesized that 1) fascicle length changes during overground walking would be both muscle and slope dependent, which would have implications for the muscles' force output as well as sensory function, and that 2) muscle-tendon unit (MTU) and fascicle length changes would be different, in which case MTU length could not be used as an indicator of muscle spindle strain. To test these hypotheses, we quantified muscle fascicle length changes and compared them with length changes of the whole MTU in the SO and MG during overground walking at various slopes (0, ± 25, ± 50, +75, and +100%). The SO and MG were surgically instrumented with sonomicrometry crystals and fine-wire electromyogram electrodes to measure changes in muscle fascicle length and muscle activity, respectively. MTU lengths were calcul...
Experimental Brain Research, 2010
The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle ext... more The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle extensor during walking shortly after paralysis of its synergists is not fully understood. It is possible that due to greater ankle Xexion in stance in this situation, muscle spindles are stretched to a greater extent and, thus, contribute to the EMG enhancement. However, also changes in force feedback and central drive may play a role. The aim of the present study was to investigate the short-term (1-to 2-week post-op) eVects of lateral gastrocnemius (LG) and soleus (SO) denervation on muscle fascicle and muscle-tendon unit (MTU) length changes, as well as EMG activity of the intact medial gastrocnemius (MG) muscle in stance during overground walking on level (0%), downslope (¡50%, presumably enhancing stretch of ankle extensors in stance) and upslope (+50%, enhancing load on ankle extensors) surfaces. Fascicle length was measured directly using sonomicrometry, and MTU length was calculated from joint kinematics. For each slope condition, LG-SO denervation resulted in an increase in MTU stretch and peak stretch velocity of the intact MG in early stance. MG muscle fascicle stretch and peak stretch velocity were also higher than before denervation in downslope walking. Denervation sig-niWcantly decreased the magnitude of MG fascicle shortening and peak shortening velocity during early stance in level and upslope walking. MG EMG magnitude in the swing and stance phases was substantially greater after denervation, with a relatively greater increase during stance of level and upslope walking. These results suggest that the fascicle length patterns of MG muscle are signiWcantly altered when two of its synergists are in a state of paralysis. Further, the compensatory increase in MG EMG is likely mediated by enhanced MG length feedback during downslope walking, enhanced feedback from load-sensitive receptors during upslope walking and enhanced central drive in all walking conditions.
Experimental Brain Research, 2007
The aim of this study was to investigate the effects of self-reinnervation of the medial (MG) and... more The aim of this study was to investigate the effects of self-reinnervation of the medial (MG) and lateral gastrocnemius (LG) muscles on joint kinematics of the whole hindlimb during overground walking on surfaces of varying slope in the cat. Hindlimb kinematics were assessed (1) with little or no activity in MG and LG (short-term effects of self-reinnervation), and (2) after motor function of these muscles was presumably recovered but their proprioceptive feedback permanently disrupted (long-term effects of self-reinnervation). The stance phase was examined in three walking conditions: downslope (−50%, i.e. −26.6°), level (0%) and upslope (+50%, +26.6°). Measurements were performed prior to and at consecutive time points (between 1 and 57 weeks) after transecting and immediately suturing MG and LG nerves. It was found that MG-LG self-reinnervation did not significantly change hip height and hindlimb orientation in any of the three walking conditions. Substantial short-term effects were observed in the ankle joint (e.g., increased flexion in early stance) as well as in metatarsophalangeal and knee joints, leading to altered interjoint coordination. Hindlimb kinematics in level and upslope walking progressed back towards baseline within 14-19 weeks. Thus in these two conditions the cats were walking without any detectable kinematic deficits, despite the absence of length feedback from two major ankle extensors. This was verified in a decerebrate preparation for four of the five cats. In contrast, ankle joint kinematics as well as interjoint coordination in downslope walking gradually progressed towards, but never reached their baseline patterns. The short-term effects can be explained by both mechanical and neural factors that are affected by the functional elimination of MG and LG. Permanent changes in kinematics during
Journal of Experimental Biology, 2012
Summary Understanding the functional significance of morphological diversity of mammalian skeleta... more Summary Understanding the functional significance of morphological diversity of mammalian skeletal muscles is limited by technical difficulties of estimating the contribution of motor units with different properties to unconstrained motor behaviours. Recently developed wavelet and principal components analysis of intramuscular myoelectric signals has linked signals with lower and higher frequency contents to use of slower and faster motor unit populations. In this study we estimated the relative contributions of lower- and higher-frequency signals of cat ankle extensors (soleus, medial and lateral gastrocnemii; plantaris) during level, downslope and upslope walking and the paw-shake response. This was done using the first two myoelectric-signal principal components (PCI, PCII), explaining over 90% of signal, and an angle theta, a function of PCI/PCII, indicating the relative contribution of slower and faster motor unit populations. Mean myoelectric frequencies in all walking conditi...
Journal of Applied Physiology, 2009
Experimental Brain Research, 2010
The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle ext... more The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle extensor during walking shortly after paralysis of its synergists is not fully understood. It is possible that due to greater ankle flexion in stance in this situation, muscle spindles are stretched to a greater extent and, thus, contribute to the EMG enhancement. However, also changes in force feedback and central drive may play a role. The aim of the present study was to investigate the short-term (1- to 2-week post-op) effects of lateral gastrocnemius (LG) and soleus (SO) denervation on muscle fascicle and muscle–tendon unit (MTU) length changes, as well as EMG activity of the intact medial gastrocnemius (MG) muscle in stance during overground walking on level (0%), downslope (−50%, presumably enhancing stretch of ankle extensors in stance) and upslope (+50%, enhancing load on ankle extensors) surfaces. Fascicle length was measured directly using sonomicrometry, and MTU length was calcul...
Understanding the functional significance of the morphological diversity of mammalian skeletal mu... more Understanding the functional significance of the morphological diversity of mammalian skeletal muscles is limited by technical difficulties of estimating the contribution of motor units with different properties to unconstrained motor behaviours. Recently developed wavelet and principal components analysis of intramuscular myoelectric signals has linked signals with lower and higher frequency contents to the use of slower and faster motor unit populations. In this study we estimated the relative contributions of lower and higher frequency signals of cat ankle extensors (soleus, medial and lateral gastrocnemii, plantaris) during level, downslope and upslope walking and the paw-shake response. This was done using the first two myoelectric signal principal components (PCI, PCII), explaining over 90% of the signal, and an angle , a function of PCI/PCII, indicating the relative contribution of slower and faster motor unit populations. Mean myoelectric frequencies in all walking conditions were lowest for slow soleus (234Hz) and highest for fast gastrocnemii (307 and 330Hz) muscles. Motor unit populations within and across the studied muscles that demonstrated lower myoelectric frequency (suggesting slower populations) were recruited during tasks and movement phases with lower mechanical demands on the ankle extensors -during downslope and level walking and in early walking stance and paw-shake phases. With increasing mechanical demands (upslope walking, mid-phase of paw-shake cycles), motor unit populations generating higher frequency signals (suggesting faster populations) contributed progressively more. We conclude that the myoelectric frequency contents within and between feline ankle extensors vary across studied motor behaviours, with patterns that are generally consistent with muscle fibre-type composition.
Journal of Neuroscience Methods, 1986
The dynamic properties of skeletal muscle have been studied under well defined, artificial condit... more The dynamic properties of skeletal muscle have been studied under well defined, artificial conditions and provide some insight as to how the musculoskeletal system might respond to maximal neural input.
ABSTRACT INTRODUCTION During the paw-shake (PS) in the cat a differential activation of ankle ext... more ABSTRACT INTRODUCTION During the paw-shake (PS) in the cat a differential activation of ankle extensor synergists, the two-joint gastrocnemius (GA) and the one-joint soleus (SO), occurs: the GA demonstrates very high activation, whereas SO is either inactive or its activation is substantially reduced [1,5]. The two muscles are activated during the lengthening phase of the muscle-tendon complex (MTC) [1,4], in which substantial activation of SO and GA Ia-and Ib-afferents has been reported [4]. Thus, both velocity-dependent (Ia) and force-dependent (Ib) feedback might be used to regulate the differential activation of the two muscles. The velocity-dependent feedback is related among other factors to muscle fascicle velocity rather than to MTC velocity. Therefore, the role of MTC and fascicle velocity in the regulation of muscle activity in the PS remains unclear. High shortening velocity in muscle fascicles during PS can also be a limiting factor in muscle force production. The aim of this study was to determine fascicle and MTC velocities of the cat medial gastrocnemius (MG) and SO during the PS. METHODS Four cats were surgically instrumented with EMG electrodes in SO and MG [2]. Selected cats were also instrumented with sonomicrometry crystals to measure fascicle length [3]. After recovery, the PS was elicited by attaching a sticking tape to the paw and allowing the animal to walk on a walkway. Reflective markers on the animals were video-filmed using high-speed (120 Hz) motion capture system (Vicon, UK) with simultaneous recordings of EMG or sonomicrometry signals. The recorded kinematics and a geometric model of the hindlimb were used to calculate the origin-to-insertion (MTC) lengths of MG and SO. Joint velocities, moments and powers were also calculated for the major hindlimb joints.
Medicine & Science in Sports & Exercise, 2008
Journal of Neuroscience Methods, 1986
Journal of Neurophysiology, 2005
Recent progress in the understanding of motor cortex function has been achieved primarily by simu... more Recent progress in the understanding of motor cortex function has been achieved primarily by simultaneously recording motor cortex neuron activity and the movement kinematics of the corresponding limb. We have expanded this approach by combining high-quality cortical single-unit activity recordings with synchronized recordings of full-body kinematics and kinetics in the freely behaving cat. The method is illustrated by selected results obtained from two cats tested while walking on a flat surface. Using this method, the activity of 43 pyramidal tract neurons (PTNs) was recorded, averaged over 10 bins of a locomotion cycle, and compared with full-body mechanics by means of principal component and multivariate linear regression analyses. Patterns of 24 PTNs (56%) and 219 biomechanical variables (73%) were classified into just four groups of inter-correlated variables that accounted for 91% of the total variance, indicating that many of the recorded variables had similar patterns. The ...
Journal of Biomechanics, 2012
Journal of Applied Physiology, 2009
On the basis of differences in physiology, e.g., histochemical properties and spindle density, an... more On the basis of differences in physiology, e.g., histochemical properties and spindle density, and the structural design of the cat soleus (SO) and medial gastrocnemius (MG) muscles, we hypothesized that 1) fascicle length changes during overground walking would be both muscle and slope dependent, which would have implications for the muscles' force output as well as sensory function, and that 2) muscle-tendon unit (MTU) and fascicle length changes would be different, in which case MTU length could not be used as an indicator of muscle spindle strain. To test these hypotheses, we quantified muscle fascicle length changes and compared them with length changes of the whole MTU in the SO and MG during overground walking at various slopes (0, ± 25, ± 50, +75, and +100%). The SO and MG were surgically instrumented with sonomicrometry crystals and fine-wire electromyogram electrodes to measure changes in muscle fascicle length and muscle activity, respectively. MTU lengths were calcul...
Experimental Brain Research, 2010
The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle ext... more The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle extensor during walking shortly after paralysis of its synergists is not fully understood. It is possible that due to greater ankle Xexion in stance in this situation, muscle spindles are stretched to a greater extent and, thus, contribute to the EMG enhancement. However, also changes in force feedback and central drive may play a role. The aim of the present study was to investigate the short-term (1-to 2-week post-op) eVects of lateral gastrocnemius (LG) and soleus (SO) denervation on muscle fascicle and muscle-tendon unit (MTU) length changes, as well as EMG activity of the intact medial gastrocnemius (MG) muscle in stance during overground walking on level (0%), downslope (¡50%, presumably enhancing stretch of ankle extensors in stance) and upslope (+50%, enhancing load on ankle extensors) surfaces. Fascicle length was measured directly using sonomicrometry, and MTU length was calculated from joint kinematics. For each slope condition, LG-SO denervation resulted in an increase in MTU stretch and peak stretch velocity of the intact MG in early stance. MG muscle fascicle stretch and peak stretch velocity were also higher than before denervation in downslope walking. Denervation sig-niWcantly decreased the magnitude of MG fascicle shortening and peak shortening velocity during early stance in level and upslope walking. MG EMG magnitude in the swing and stance phases was substantially greater after denervation, with a relatively greater increase during stance of level and upslope walking. These results suggest that the fascicle length patterns of MG muscle are signiWcantly altered when two of its synergists are in a state of paralysis. Further, the compensatory increase in MG EMG is likely mediated by enhanced MG length feedback during downslope walking, enhanced feedback from load-sensitive receptors during upslope walking and enhanced central drive in all walking conditions.
Experimental Brain Research, 2007
The aim of this study was to investigate the effects of self-reinnervation of the medial (MG) and... more The aim of this study was to investigate the effects of self-reinnervation of the medial (MG) and lateral gastrocnemius (LG) muscles on joint kinematics of the whole hindlimb during overground walking on surfaces of varying slope in the cat. Hindlimb kinematics were assessed (1) with little or no activity in MG and LG (short-term effects of self-reinnervation), and (2) after motor function of these muscles was presumably recovered but their proprioceptive feedback permanently disrupted (long-term effects of self-reinnervation). The stance phase was examined in three walking conditions: downslope (−50%, i.e. −26.6°), level (0%) and upslope (+50%, +26.6°). Measurements were performed prior to and at consecutive time points (between 1 and 57 weeks) after transecting and immediately suturing MG and LG nerves. It was found that MG-LG self-reinnervation did not significantly change hip height and hindlimb orientation in any of the three walking conditions. Substantial short-term effects were observed in the ankle joint (e.g., increased flexion in early stance) as well as in metatarsophalangeal and knee joints, leading to altered interjoint coordination. Hindlimb kinematics in level and upslope walking progressed back towards baseline within 14-19 weeks. Thus in these two conditions the cats were walking without any detectable kinematic deficits, despite the absence of length feedback from two major ankle extensors. This was verified in a decerebrate preparation for four of the five cats. In contrast, ankle joint kinematics as well as interjoint coordination in downslope walking gradually progressed towards, but never reached their baseline patterns. The short-term effects can be explained by both mechanical and neural factors that are affected by the functional elimination of MG and LG. Permanent changes in kinematics during
Journal of Experimental Biology, 2012
Summary Understanding the functional significance of morphological diversity of mammalian skeleta... more Summary Understanding the functional significance of morphological diversity of mammalian skeletal muscles is limited by technical difficulties of estimating the contribution of motor units with different properties to unconstrained motor behaviours. Recently developed wavelet and principal components analysis of intramuscular myoelectric signals has linked signals with lower and higher frequency contents to use of slower and faster motor unit populations. In this study we estimated the relative contributions of lower- and higher-frequency signals of cat ankle extensors (soleus, medial and lateral gastrocnemii; plantaris) during level, downslope and upslope walking and the paw-shake response. This was done using the first two myoelectric-signal principal components (PCI, PCII), explaining over 90% of signal, and an angle theta, a function of PCI/PCII, indicating the relative contribution of slower and faster motor unit populations. Mean myoelectric frequencies in all walking conditi...
Journal of Applied Physiology, 2009
Experimental Brain Research, 2010
The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle ext... more The mechanism of the compensatory increase in electromyographic activity (EMG) of a cat ankle extensor during walking shortly after paralysis of its synergists is not fully understood. It is possible that due to greater ankle flexion in stance in this situation, muscle spindles are stretched to a greater extent and, thus, contribute to the EMG enhancement. However, also changes in force feedback and central drive may play a role. The aim of the present study was to investigate the short-term (1- to 2-week post-op) effects of lateral gastrocnemius (LG) and soleus (SO) denervation on muscle fascicle and muscle–tendon unit (MTU) length changes, as well as EMG activity of the intact medial gastrocnemius (MG) muscle in stance during overground walking on level (0%), downslope (−50%, presumably enhancing stretch of ankle extensors in stance) and upslope (+50%, enhancing load on ankle extensors) surfaces. Fascicle length was measured directly using sonomicrometry, and MTU length was calcul...
Understanding the functional significance of the morphological diversity of mammalian skeletal mu... more Understanding the functional significance of the morphological diversity of mammalian skeletal muscles is limited by technical difficulties of estimating the contribution of motor units with different properties to unconstrained motor behaviours. Recently developed wavelet and principal components analysis of intramuscular myoelectric signals has linked signals with lower and higher frequency contents to the use of slower and faster motor unit populations. In this study we estimated the relative contributions of lower and higher frequency signals of cat ankle extensors (soleus, medial and lateral gastrocnemii, plantaris) during level, downslope and upslope walking and the paw-shake response. This was done using the first two myoelectric signal principal components (PCI, PCII), explaining over 90% of the signal, and an angle , a function of PCI/PCII, indicating the relative contribution of slower and faster motor unit populations. Mean myoelectric frequencies in all walking conditions were lowest for slow soleus (234Hz) and highest for fast gastrocnemii (307 and 330Hz) muscles. Motor unit populations within and across the studied muscles that demonstrated lower myoelectric frequency (suggesting slower populations) were recruited during tasks and movement phases with lower mechanical demands on the ankle extensors -during downslope and level walking and in early walking stance and paw-shake phases. With increasing mechanical demands (upslope walking, mid-phase of paw-shake cycles), motor unit populations generating higher frequency signals (suggesting faster populations) contributed progressively more. We conclude that the myoelectric frequency contents within and between feline ankle extensors vary across studied motor behaviours, with patterns that are generally consistent with muscle fibre-type composition.
Journal of Neuroscience Methods, 1986
The dynamic properties of skeletal muscle have been studied under well defined, artificial condit... more The dynamic properties of skeletal muscle have been studied under well defined, artificial conditions and provide some insight as to how the musculoskeletal system might respond to maximal neural input.