Adaptive behaviour of the spinal cord in the transition from quiet stance to walking (original) (raw)
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.
Sign up for access to the world's latest research.
checkGet notified about relevant papers
checkSave papers to use in your research
checkJoin the discussion with peers
checkTrack your impact
Related papers
Speed-related spinal excitation from ankle dorsiflexors to knee extensors during human walking
Experimental Brain Research, 2008
Automatic adjustments of muscle activity throughout the body are required for the maintenance of balance during human walking. One mechanism that is likely to contribute to this control is the heteronymous spinal excitation between human ankle dorsiflexors and knee extensors (CPQ-reflex). Here, we investigated the CPQ-reflex at different walking speeds (1–6 km/h) and stride frequencies (0.6–1.3 Hz) in healthy human subjects to provide further evidence of its modulation, and its role in ensuring postural stability during walking. The CPQ-reflex was small or absent at walking speeds below 2–3 km/h, then increased with walking speeds about 3–4 km/h, and reached a plateau without any further change at walking speeds from 4 to 6 km/h. The reflex showed no modulation when the stride cycle was varied at constant speed (4 km/h; short steps versus long steps). These changes were unlikely to be only caused by changes in the background EMG activity and modifications in peripheral input, and likely reflected central modulation of transmission in the involved reflex pathways as well. It is suggested that the purpose of the reflex is to ensure knee stability at moderate-to-high walking speeds.
Interlimb communication to the knee flexors during walking in humans
The Journal of Physiology, 2013
• Following unexpected ipsilateral knee extension joint rotations applied during the late stance phase of the gait cycle in humans, a crossed reflex response was observed in the contralateral biceps femoris (cBF) muscle with a mean onset latency of 76 ms. • Transcranial magnetic and electrical stimulation applied to the primary motor cortex revealed that a transcortical pathway probably contributes to the cBF response. • We hypothesize that the cBF response signifies a preparation of the contralateral leg for early load bearing, helping the body to maintain dynamic stability during walking. • This is the first study to show that a transcortical pathway contributes to an interlimb reflex in upper leg muscles. The transcortical nature of the response may allow for more adaptable responses than purely spinally mediated reflexes due to integration with other sensory information.
Does postural instability affect the initiation of human gait
Neuroscience Letters, 2002
During gait initiation (GI), decoupling of the center of mass and center of pressure allows the center of mass to fall forwards. Subjects initiated gait rapidly before and after tibial nerve block of the tibial nerve. Static single limb stability, stance limb ground reaction forces, electromyogram and temporal data were measured. It was hypothesized that postural stability would decrease post-block and that this would affect the kinetic and temporal properties of GI. Subjects had significantly decreased postural stability post-block and changes in normal gait kinetics, however, no changes were noted in ground reaction forces or relative temporal data of the GI task. The finding that GI was unaffected by diminished single leg postural instability suggests that GI is a pre-programmed task. q
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 ...
Alternate Leg Movement Amplifies Locomotor-Like Muscle Activity in Spinal Cord Injured Persons
Journal of Neurophysiology, 2004
It is now well recognized that muscle activity can be induced even in the paralyzed lower limb muscles of persons with spinal cord injury (SCI) by imposing locomotion-like movements on both of their legs. Although the significant role of the afferent input related to hip joint movement and body load has been emphasized considerably in previous studies, the contribution of the "alternate" leg movement pattern has not been fully investigated.
Progress in Neurobiology, 1997
Studies are reviewed, predominantly involving healthy humans, on gain changes in spinal reflexes and supraspinal ascending paths during passive and active leg movement. The passive movement research shows that the pathways of H reflexes of the leg and foot are down-regulated as a consequence of movement-elicited discharge from somatosensory receptors, likely muscle spindle primary endings, both ipsi- and contralaterally. Discharge from the conditioning receptors in extensor muscles of the knee and hip appears to lead to presynaptic inhibition evoked over a spinal path, and to long-lasting attenuation when movement stops. The ipsilateral modulation is similar in phase to that seen with active movement. The contralateral conditioning does not phase modulate with passive movement and modulates to the phase of active ipsilateral movement. There are also centrifugal effects onto these pathways during movement. The pathways of the cutaneous reflexes of the human leg also are gain-modulated during active movement. The review summarizes the effects across muscles, across nociceptive and non-nociceptive stimuli and over time elapsed after the stimulus. Some of the gain changes in such reflexes have been associated with central pattern generators. However, the centripetal effect of movement-induced proprioceptive drive awaits exploration in these pathways. Scalp-recorded evoked potentials from rapidly conducting pathways that ascend to the human somatosensory cortex from stimulation sites in the leg also are gain-attenuated in relation to passive movement-elicited discharge of the extensor muscle spindle primary endings. Centrifugal influences due to a requirement for accurate active movement can partially lift the attenuation on the ascending path, both during and before movement. We suggest that a significant role for muscle spindle discharge is to control the gain in Ia pathways from the legs, consequent or prior to their movement. This control can reduce the strength of synaptic input onto target neurons from these kinesthetic receptors, which are powerfully activated by the movement, perhaps to retain the opportunity for target neuron modulation from other control sources. © 1997 Elsevier Science Ltd. All Rights Reserved.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.