Speed-related spinal excitation from ankle dorsiflexors to knee extensors during human walking (original) (raw)
Related papers
2009
Objective: To find out pattern of modulation of heteronymous reflex linking the pretibial muscles to quadriceps motoneurones in normal subjects during treadmill walking. Methodology: A non-randomized quasi-experimental study was performed in ten cases in Shahid Beheshti University (MC) Tehran, Iran, from September 2006 to August 2007. The reflex was elicited by applying stimuli of three time’s motor threshold in tibialis anterior to common peroneal nerve at several instants of gait cycle. Surface EMGs from tibialis anterior, vastus medialis and rectus femoris of the right leg was used to measure the intensity of the muscular activity and the magnitude of the reflex. The data were analysed by Pearson test for the strength of their correlation. Results: The reflex showed a significant correlation with the intensity of contraction in quadriceps especially during the early stance phase. The correlation was poor during transition period from stance to swing where rectus femoris showed a ...
Experimental Brain Research, 2009
The soleus H-reXex modulation pattern was investigated in ten spinal cord intact subjects during treadmill walking at varying levels of body weight support (BWS), and nine spinal cord injured (SCI) subjects at a BWS level that promoted the best stepping pattern. The soleus H-reXex was elicited by tibial nerve stimulation with a single 1-ms pulse at an intensity that the M-waves ranged from 4 to 8% of the maximal M-wave (M max ). During treadmill walking, the H-reXex was elicited every four steps, and stimuli were randomly dispersed across the gait cycle which was divided into 16 equal bins. EMGs were recorded with surface electrodes from major left and right hip, knee, and ankle muscles. M-waves and H-reXexes at each bin were normalized to the M max elicited at 60-100 ms after the test reXex stimulus. For every subject, the inte-grated EMG area of each muscle was established and plotted as a function of the step cycle phase. The H-reXex gain was determined as the slope of the relationship between H-reXex and soleus EMG amplitudes at 60 ms before H-reXex elicitation for each bin. In spinal cord intact subjects, the phase-dependent H-reXex modulation, reXex gain, and EMG modulation pattern were constant across all BWS (0, 25, and 50) levels, while tibialis anterior muscle activity increased with less body loading. In three out of nine SCI subjects, a phase-dependent H-reXex modulation pattern was evident during treadmill walking at BWS that ranged from 35 to 60%. In the remaining SCI subjects, the most striking diVerence was an absent H-reXex depression during the swing phase. The reXex gain was similar for both subject groups, but the y-intercept was increased in SCI subjects. We conclude that the mechanisms underlying cyclic H-reXex modulation during walking are preserved in some individuals after SCI.
Experimental Brain Research, 2005
Previously the modulation of the quadriceps H-reflex has only been investigated in the initial part of the gait cycle, and it was suggested that the quadriceps H-reflex modulates with relative high reflex gain at heel contact and decreases during the subsequent part of stance (Dietz et al. 1990b). The objectives of the present study was to elaborate on the previous results by increasing the measurement resolution around heel contact and include additional measures in order to relate the H-reflex modulation to the mechanical function of the knee extensors throughout the gait cycle. EMG profiles were measured in quadriceps and the antagonistic hamstring muscles simultaneously with the knee joint kinematics in ten subjects during treadmill walking at preferred speed. H-reflex excitability was measured in vastus lateralis (VL) and rectus femoris (RF) at 11 selected positions during the gait cycle. The resulting excitability curves showed a significant modulation of the quadriceps H-reflex during the gait cycle. The H-reflex amplitude increases shortly after heel contact and reflex inhibition is present in the remaining part of stance and most of the swing phase. The modulation of the quadriceps H-reflex during walking does not follow the classical pattern of reciprocal inhibition between antagonistic muscles. It is suggested that at least during the stance phase the modulation of the quadriceps H-reflex is controlled by presynaptic inhibition. The present results confirm the idea that the excitability of the quadriceps H-reflex is controlled to comply with the different mechanical demands on the muscle during the gait cycle in humans.
Journal of neurophysiology, 2000
Recently, Brooke and colleagues have suggested "that the strong inhibition arising from passive movement about the knee and hip joints, lays down the base for the soleus H-reflex gain modulation seen during human gait." In particular stretch-evoked afferent activity from the quadriceps muscle was emphasized as the most important source of movement-induced inhibition of the H-reflex. To test this hypothesis we examined the kinematics and electromyographic (EMG) activity of the leg during human walking and correlated these with the modulation pattern of the soleus H-reflex. To further test the possible contribution of stretch-evoked quadriceps afferent activity to the soleus H-reflex modulation pattern during walking different walking gaits were studied. In one condition subjects were asked to walk with their knee locked in full extension by a rigid knee brace. In a second condition subjects were asked to walk backwards. During normal walking, the soleus H-reflex modulation ...
Adaptive behaviour of the spinal cord in the transition from quiet stance to walking
BMC Neuroscience, 2012
Background: Modulation of nociceptive withdrawal reflex (NWR) excitability was evaluated during gait initiation in 10 healthy subjects to investigate how load-and movement-related joint inputs activate lower spinal centres in the transition from quiet stance to walking. A motion analysis system integrated with a surface EMG device was used to acquire kinematic, kinetic and EMG variables. Starting from a quiet stance, subjects were asked to walk forward, at their natural speed. The sural nerve was stimulated and EMG responses were recorded from major hip, knee and ankle muscles. Gait initiation was divided into four subphases based on centre of pressure and centre of mass behaviours, while joint displacements were used to categorise joint motion as flexion or extension. The reflex parameters were measured and compared between subphases and in relation to the joint kinematics. Results: The NWR was found to be subphase-dependent. NWR excitability was increased in the hip and knee flexor muscles of the starting leg, just prior to the occurrence of any movement, and in the knee flexor muscles of the same leg as soon as it was unloaded. The NWR was hip joint kinematics-dependent in a crossed manner. The excitability of the reflex was enhanced in the extensor muscles of the standing leg during the hip flexion of the starting leg, and in the hip flexors of the standing leg during the hip extension of the starting leg. No notable reflex modulation was observed in the ankle muscles. Conclusions: Our findings show that the NWR is modulated during the gait initiation phase. Leg unloading and hip joint motion are the main sources of the observed modulation and work in concert to prepare and assist the starting leg in the first step while supporting the contralateral leg, thereby possibly predisposing the lower limbs to the cyclical pattern of walking.
Modulation of recurrent inhibition from knee extensors to ankle motoneurones during human walking
Journal of Physiology-london, 2008
The neural control for muscle coordination during human locomotion involves spinal and supraspinal networks, but little is known about the exact mechanisms implicated. The present study focused on modulation of heteronymous recurrent inhibition from knee extensors to ankle motoneurones at different times in the gait cycle, when quadriceps (Quad) muscle activity overlaps that in tibialis anterior (TA) and soleus (Sol). The effects of femoral nerve stimulation on ankle motoneurones were investigated during treadmill walking and during tonic co-contraction of Quad and TA/Sol while standing. Recurrent inhibition of TA motoneurones depended on the level of background EMG, and was similar during walking and standing for matched background EMG levels. On the other hand, recurrent inhibition in Sol was reduced in early stance, with respect to standing, and enhanced in late stance. Reduced inhibition in Sol was also observed when Quad was coactivated with TA around the time of heel contact, compared to standing at matched background EMG levels in the two muscles. The modulation of recurrent inhibition of Sol during walking might reflect central and/or peripheral control of the Renshaw cells. These modulations could be implicated in the transition phases, from swing to stance to assist Sol activation during the stance phase, and from stance to swing, for its deactivation.
The effect of crossed reflex responses on dynamic stability during locomotion
Journal of neurophysiology, 2015
In recent studies, we demonstrated that a neural pathway within the human spinal cord allows direct communication between muscles located in opposing limb. Short-latency crossed responses (SLCRs) are elicited in the contralateral triceps surae at an onset of 40 to 69 ms following electrical stimulation of the ipsilateral tibial nerve (iTN). The SLCRs are significantly affected by lesions of the central nervous system where the patients are unable to attain normal walking symmetry. The aim of this study was to elucidate the functionality of SLCRs by investigating their effects on the center of pressure (CoP) and pressure distribution. SLCRs were elicited by iTN stimulation at the end of the ipsilateral swing phase, while the participants (n=8) walked on a treadmill. CoP location and pressure distribution on the sole of the contralateral foot were recorded using instrumented insoles inserted bilaterally in the participant's shoes. The SLCR induced a significant displacement of the...