Walking In Man Research Articles

EMG burst pattern in quadrupedal and bipedal walking in man and the rat bipedal walking model (RBWM) on the treadmill

EMG burst pattern in quadrupedal and bipedal walking in man and the rat bipedal walking model (RBWM) on the treadmill

Seeking functions for spinal recurrent inhibition

In this issue of The Journal of Physiology, Lamy et al. (2008) describe a rhythmic modulation of recurrent inhibition during walking in man. This provides some insight into the function of recurrent inhibition, first described by Renshaw (1941) as an inhibition of cat motoneurones produced by antidromic stimulation of the axons of neighbouring motoneurones (homonymous action). Subsequent work, also in cats, showed that motor axon collaterals activate interneurones (the eponymous Renshaw cells) that in turn inhibit motoneurones. Actions extend to more distant muscle groups (heteronymous) and parallel the pattern of heteronymous monosynaptic excitation from muscle spindle Ia afferents. Renshaw cells receive peripheral sensory and descending inputs and have output connections to other spinal interneurones and to other Renshaw cells. So recurrent inhibition is more than just negative feedback from and to motoneurones and may have several functions depending upon motor context. Lamy et al. have focused on heteronymous actions (which are more widespread in man than in cats or monkeys) in the context of our unique bipedal form of walking. The knee extensor quadriceps is a source of recurrent inhibition to the ankle extensor and the flexor muscles soleus and tibialis anterior. But given that these ankle muscles are antagonists, how is differential activation achieved? The authors found that around heel strike and early in stance, when quadriceps is active and soleus activity is increasing, recurrent inhibition of soleus is weak. Conversely, later in stance, when quadriceps is active and soleus activity is declining, recurrent inhibition of soleus is strong. Recurrent inhibition of tibialis anterior motoneurones was neither task nor phase dependent. The reduction in soleus recurrent inhibition would assist the transition from swing to stance and enhanced inhibition later in stance would favour the transition from stance to swing by reducing reciprocal inhibition of tibialis anterior. The origin of these changes in recurrent inhibition remains uncertain but activity of peripheral sensory or descending motor pathways could be involved. Two interesting possibilities are the corticospinal pathway, known to depress homonymous recurrent inhibition of soleus in sitting subjects (Mazzocchio et al. 1994) and the vestibulospinal pathway that depresses recurrent inhibition of soleus in standing stance (Iles & Pisini, 1992). It might be possible to extend such studies to heteronymous actions in walking stance. More meticulous experiments built upon the framework of human research protocols pioneered by the Paris group will likely increase our understanding of recurrent inhibition even further.

11.9 Modulation of the activity of a propriospinal reflexpathway during walking in man

Antidromic stimulation and intra-axonal injections of horseradish peroxidase have been used to investigate axonal branching and termination of single C3 C4 propriospinal neurones (PNs) that project to the forelimb segments (C6 Th1). Branching at several spinal cord levels and terminations were found in laminae VI VIII and IX. With respect to terminations in laminae VII and IX, 3 patterns were observed: (i) termination only in lamina IX. (ii) only in lamina VII in the region of Ia inhibitory interneurones and (iii) in both laminae VII and IX. These findings are consistent with previous results showing monosynaptic projections of C3 C4 PNs to forelimb motoneurones and la inhibitory interneurones. Terminations in laminae VI, VIII and other parts of lamina VII suggest that C3 C4 PNs also project to other neurones in the forelimb segments.

Strengthening of Partially Denervated Knee Extensors Using Percutaneous Electric Stimulation in a Young Man With Spinal Cord Injury

Johnston TE, Smith BT, Betz RR. Strengthening of partially denervated knee extensors using percutaneous electric stimulation in a young man with spinal cord injury. Objective To evaluate the effects of percutaneous electric stimulation on knee extensor strength and muscle hypertrophy, gait, and energy cost of walking in a young man with partial denervation of the knee extensors. Design One-way repeated measures. Setting Pediatric orthopedic hospital. Participant A man in his early twenties, who had an L2 American Spinal Injury Association class D spinal cord injury, presented with strength deficits in his left knee extensors and reported falling frequently. When walking, his left knee remained locked in extension throughout stance. Electromyographic testing revealed chronic denervation and reinnervation changes. Intervention Because of sensory difficulties with surface stimulation, a percutaneous electrode was surgically implanted near the femoral nerve. The subject exercised isometrically with a research grade stimulator for 1 hour a day until his strength plateaued. Main outcome measures Quadriceps femoris strength and hypertrophy, gait, and energy cost of walking were recorded preintervention, every 2 months during the strengthening phase, and 2 months after withdrawal. Results Voluntary isometric torque improved from 7 to 14.8Nm (112%) and decreased to 8.5Nm after stimulation was withdrawn. Mean circumferential measures of the thigh improved from 12.3 to 13.5cm (9.8%) and then decreased to 13.1cm. Gait kinematics and kinetics were unchanged, although the subject reported greater stability in his left knee and fewer falls. Conclusions The study indicates that percutaneous electric stimulation could be used to strengthen partially denervated muscle and to affect function. However, gains in strength may not be maintained once treatment is withdrawn.

Phase-dependent modulation of short latency cutaneous reflexes during walking in man

In reduced animal preparation (cat fictive locomotion) most of our knowledge on the phase-dependent modulation of cutaneous reflexes concerns early- (P1 responses) rather than medium-latency (P2) responses. In contrast, in humans, virtually only P2 responses have been studied because P1 responses are relatively rare in adults. In this work, human P1 and P2 responses following sural nerve stimulation were compared in BF (biceps femoris). Some 14% of all subjects showed P1 responses, which could be either suppressive or facilitatory. The suppressive responses were most common, and they occurred primarily at end swing. When a subject showed both suppressive P1 and P2 responses, the P2 suppressions were stronger than the P1 suppressions (as measured in the same phase at end swing). However, the P2 suppressions were less consistent across subjects than the P1 suppressions. In some subjects, there were also facilitatory P1 responses, mostly throughout stance (when facilitatory P2 responses occur as well). These facilitatory P1 responses were consistent across experimental conditions in these subjects. Similar to the cat, the facilitatory P1 responses were much smaller than the facilitatory P2 responses. It is concluded that P1 and P2 reflexes can appear independently from each other, but that their modulation in the step cycle is mostly quite similar in some phases of the step cycle (end swing).

Major role for sensory feedback in soleus EMG activity in the stance phase of walking in man.

1. Sensory feedback plays a major role in the regulation of the spinal neural locomotor circuitry in cats. The present study investigated whether sensory feedback also plays an important role during walking in 20 healthy human subjects, by arresting or unloading the ankle extensors 6 deg for 210 ms in the stance phase of gait. 2. During the stance phase of walking, unloading of the ankle extensors significantly (P < 0.05) reduced the soleus activity by 50 % in early and mid-stance at an average onset latency of 64 ms. 3. The onset and amplitude of the decrease in soleus activity produced by the unloading were unchanged when the common peroneal nerve, which innervates the ankle dorsiflexors, was reversibly blocked by local injection of lidocaine (n = 3). This demonstrated that the effect could not be caused by a peripherally mediated reciprocal inhibition from afferents in the antagonist nerves. 4. The onset and amplitude of the decrease in soleus activity produced by the unloading were also unchanged when ischaemia was induced in the leg by inflating a cuff placed around the thigh. At the same time, the group Ia-mediated short latency stretch reflex was completely abolished. This demonstrated that group Ia afferents were probably not responsible for the decrease of soleus activity produced by the unloading. 5. The findings demonstrate that afferent feedback from ankle extensors is of significant importance for the activation of these muscles in the stance phase of human walking. Group II and/or group Ib afferents are suggested to constitute an important part of this sensory feedback.

Modulation of reciprocal inhibition between ankle extensors and flexors during walking in man.

1. The modulation of disynaptic reciprocal inhibition between antagonistic ankle muscles during walking was investigated in 17 healthy human subjects. Inhibition from ankle dorsiflexors to ankle plantar flexors was evoked by stimulation of the common peroneal nerve (CPN) and evaluated as the stimulus-induced depression of rectified soleus EMG activity (latency approx. 40 ms) or the short-latency depression of the soleus H-reflex (conditioning-test intervals around 2-3 ms). In some experiments the inhibition from ankle plantar flexors to ankle dorsiflexors was investigated. In these experiments the tibial nerve was stimulated and the amount of inhibition was evaluated from the short-latency depression of the voluntary rectified tibialis anterior (TA) EMG. 2. The short-latency inhibition of the soleus H-reflex following the CPN stimulation (1.1 x motor threshold; MT) was strongly modulated during walking, being large in the swing phase and absent in the stance phase. 3. A smaller amount of EMG depression following the CPN stimulation (1. 1-1.2 x MT) was observed in the stance phase of walking as compared to tonic or dynamic plantar flexion at a similar background EMG activity level in standing or sitting subjects. 4. In four subjects a depression of the TA EMG activity was produced by stimulation of the tibial nerve (1.1-1.2 x MT). In all subjects a smaller amount of inhibition was observed in the swing phase of walking as compared to tonic dorsiflexion at a comparable EMG activity level. 5. It is concluded that the transmission in the disynaptic Ia reciprocal pathway between ankle plantar flexors and dorsiflexors is modulated during walking. Inhibition from dorsiflexors to plantar flexors seems to be large in swing and small in stance, whereas inhibition from plantar flexors to dorsiflexors seems to be small in swing.

Evidence suggesting that a transcortical reflex pathway contributes to cutaneous reflexes in the tibialis anterior muscle during walking in man.

Stimulation of cutaneous foot afferents has been shown to evoke a facilitation of the tibialis anterior (TA) EMG-activity at a latency of 70-95 ms in the early and middle swing phase of human walking. The present study investigated the underlying mechanism for this facilitation. In those subjects in whom it was possible to elicit a reflex during tonic dorsiflexion while seated (6 out of 17 tested), the facilitation in the TA EMG evoked by stimulation of the sural nerve (3 shocks, 3-ms interval, 2.0-2.5x perception threshold) was found to have the same latency in the swing phase of walking. The facilitation observed during tonic dorsiflexion has been suggested to be -- at least partly -- mediated by a transcortical pathway. To investigate whether a similar mechanism contributes to the facilitation observed during walking, magnetic stimulation of the motor cortex (1.2x motor threshold) was applied in the early swing phase at different intervals in relation to the cutaneous stimulation in 17 subjects. In 13 of the subjects, the motor potentials evoked by the magnetic stimulation (MEPs) were more facilitated by prior sural-nerve stimulation (conditioning-test intervals of 50-80 ms) than the algebraic sum of the control MEP and the cutaneous facilitation in the EMG when evoked separately. In four of these subjects, a tibialis anterior H-reflex could also be evoked during walking. In none of the subjects was an increase of the H-reflex similar to that for the MEP observed. In five experiments on four subjects, MEPs evoked by magnetic and electrical cortical stimulation were compared. In four of these experiments, only the magnetically induced MEPs were facilitated by prior stimulation of the sural nerve. We suggest that a transcortical pathway may also contribute to late cutaneous reflexes during walking.

The influence of cold stress and a 36- h fast on the physiological responses to prolonged intermittent walking in man.

In a previous study, rectal temperature (Tre) was found to be lower, and oxygen consumption (VO2) and the respiratory exchange ratio (R) were higher in a cold (+5 degrees C), wet and windy environment (COLD), compared with a thermoneutral environment during intermittent walking at approximately 30% of peak VO2 (Weller AS, Millard CE, Stroud MA et al. Am J Physiol 272:R226-R233, 1997). The aim of the present study was to establish whether these cold-induced responses are influenced by prior fasting, as impaired thermoregulation has been demonstrated in cold-exposed, resting men following a 48-h fast. To address this question, eight men attempted a 360-min intermittent (15 min rest, 45 min exercise) walking protocol under COLD conditions on two occasions. In one condition, the subjects started the exercise protocol approximately 120 min after a standard meal (FED/ COLD), whereas in the other the subjects had fasted for 36 h (FASTED/COLD). The first two exercise periods were conducted at a higher intensity (HIGHER, 6 km x h[-1] and 10% incline), than the four subsequent exercise periods (LOW, 5 km x h[-1] and 0% incline). There was no difference in the time endured in FED/ COLD and FASTED/COLD. In FASTED/COLD compared with FED/COLD, R was lower during HIGHER and LOW, and Tre was lower during LOW, whereas there was no difference in VO2, mean skin temperature and heart rate. Therefore, although the 36-h fast impaired temperature regulation during intermittent low-intensity exercise in the cold, wet and windy environment, it was unlikely to have been the principal factor limiting exercise performance under these experimental conditions.

Modulations of the optical flow did not induce locomotor pattern fluctuations in treadmill walking in man.

We report an analysis of gait during human treadmill walking when visual information from the self-displacement velocity was modulated. Removing or sinusoidally modulating the frequency edge information in the optical flow did not induce significant changes in the walking velocity as analyzed using Fast Fourier Transform or in the spatiotemporal gait parameters. While low-frequency fluctuations in displacement speed increased, there was no significant change in locomotor cycle stability, When a constant frequency edge was provided, i.e., when a backward optical flow was added, stride length decreased as compared to the no-optical-flow condition and instantaneous fluctuations in stride amplitude increased. Temporal gait parameters did not change. These partial effects might be better explained by modifications in trunk balance. In humans, modulation of velocity information on self-motion cannot induce unintentional modulation of walking velocity and did not enhance fluctuations in the locomotor pattern. These results argue against the proprioceptive role of sagittal visual-motion information in control of stability of rhythmic leg movement, at least when other proprioceptive feedback sources are available.

Feedback control system for walking in man

A computer control stimulation system is described which has been successfully tested by allowing a paraplegic subject to stand and walk through closed loop control. This system is a Z80 microprocessor system with eight channels of analog to digital and 16 channels of digital to analog control. Programming is written in CPM and works quite successfully for maintaining lower body postural control in paraplegics. Further expansion of this system would enable a feedback control system for multidirectional walking in man.

Role of reflex responses of knee musculature during the swing phase of walking in man.

Muscle activation patterns of the quadriceps and hamstrings were studied in normal human subjects walking at comfortable speed on a treadmill. In addition knee angular velocity patterns and swing and stance phases of the step cycle were recorded. Data were collected from normal paces and from paces in which a momentary unexpected resistance was applied to the leg during swing. The application of the resistance caused an advance in the onset of both quadriceps and hamstrings activity. The latency of the onset of activity following the resistance in the quadriceps was 78.2 +/- 26.4 ms and this was considered to indicate a long latency stretch reflex. There was a close association between the onset of quadriceps and hamstrings activity both in the normal and resistance paces. The changes observed in knee angular velocity upon application of the resistance indicate tight control of angular velocity patterns. The results have important implications regarding neural control of muscle during purposive movement and the regulation of sensitivity of muscle receptors during such movements, especially during the periods when the muscle is normally inactive.

Modification, by tractive loading, of the energy cost of walking in sheep, cattle and man.

1. A study was made in sheep and cattle walking on a treadmill, of the alteration to the energy expenditure that was caused by voluntarily exerted tension in the tether between animal and treadmill. 2. An additional experiment was carried out to investigate in human subjects walking on a treadmill, the alteration to the energy expenditure as a result of positive and negative tractive loads applied at waist level through a rope parallel to the plane of the treadmill. 3. Alterations to the net energy expenditure when walking were generally similar in the three species and varied with speed and gradient up to a maximum value of approximately 0.04 J per metre walked per gram of tension or negative load.

Energetic cost of grade walking in man and burro, Equus asinus: desert and mountain.

Energetic cost of grade walking in man and burro, Equus asinus: desert and mountain.