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PubMed1999

Physiological determinants of best performances in human locomotion.

In human locomotion, the metabolic power required (E) to cover a given distance d, in the time t is set by the product of the energy cost of the locomotion (C), i.e. the amount of metabolic energy spent to move over one unit of distance, and the speed (v = d t(-1)): E = Cv = Cdt(-1). Since, for any given d, v is a decreasing function of t and C is either constant or increases with v, it necessarily follows that E is larger the smaller the value of t. Thus, for any given distance and subject, the shortest time will be achieved when E is equal to the individual maximal metabolic power (Emax). In turn, Emax is a decreasing function of t: it depends upon the subject's maximal aerobic power (MAP) and on the maximal amount of energy derived from the full utilisation of anaerobic energy stores (AnS). So, if the relationship between C and (v) in the locomotion at stake and the subject's MAP and AnS are known, his best performance time (BPT) over any given distance can be obtained by solving the equality Emax(t) = E(t). This approach has been applied to estimate individual BPTs in running and cycling. In this paper, the above approach will be used to quantify the role of C, MAP, and AnS in determining BPTs for running, track cycling and swimming. This has been achieved by calculating the changes in BPT obtained when each variable, or a combination thereof, is changed by a given percentage. The results show that in all the three types of locomotion, regardless of the speed, the changes in BPT brought about by changes of C alone account for 45-55% of the changes obtained when all three variables (C, MAP and AnS) are changed by the same amount.

Adult↗
PubMed1998

A mathematical model of adaptive behavior in quadruped locomotion.

Locomotion involves repetitive movements and is often executed unconsciously and automatically. In order to achieve smooth locomotion, the coordination of the rhythms of all physical parts is important. Neurophysiological studies have related that basic rhythms are produced in the spinal network called, the central pattern generator (CPG), where some neural oscillators interact to self-organize coordinated rhythms. We present a model of the adaptation of locomotion patterns to a variable environment, and attempt to elucidate how the dynamics of locomotion pattern generation are adjusted by the environmental changes. Recent experimental results indicate that decerebrate cats have the ability to learn new gait patterns in a changed environment. In those experiments, a decerebrate cat was set on a treadmill consisting of three moving belts. This treadmill provides a periodic perturbation to each limb through variation of the speed of each belt. When the belt for the left forelimb is quickened, the decerebrate cat initially loses interlimb coordination and stability, but gradually recovers them and finally walks with a new gait. Based on the above biological facts, we propose a CPG model whose rhythmic pattern adapts to periodic perturbation from the variable environment. First, we design the oscillator interactions to generate a desired rhythmic pattern. In our model, oscillator interactions are regarded as the forces that generate the desired motion pattern. If the desired pattern has already been realized, then the interactions are equal to zero. However, this rhythmic pattern is not reproducible when there is an environmental change. Also, if we do not adjust the rhythmic dynamics, the oscillator interactions will not be zero. Therefore, in our adaptation rule, we adjust the memorized rhythmic pattern so as to minimize the oscillator interactions. This rule can describe the adaptive behavior of decerebrate cats well. Finally, we propose a mathematical framework of an adaptation in rhythmic motion. Our framework consists of three types of dynamics: environmental, rhythmic motion, and adaptation dynamics. We conclude that the time scale of adaptation dynamics should be much larger than that of rhythmic motion dynamics, and the repetition of rhythmic motions in a stable environment is important for the convergence of adaptation.

Adaptation, Physiological↗
PubMed1979

Motorneuronal control of locomotion in Aplysia.

We have carried out a combined behavioral and cellular analysis of escape locomotion in Aplysia. Using videotape recording we obtained a detailed description of the coordinated movements of the different regions of the foot and body during locomotion. Alternating waves of extension and longitudinal contraction begin at the head and propagate caudally through each pedal segment at a constant rate. Cobalt backfill of pedal nerves indicated that certain regions of the pedal ganglia were likely to contain motor neurons for the foot and body wall musculature. We examined these areas using intracellular techniques and identified three unique cells and three regional classes of neurons having clear motor effects on the foot and body wall. We also found that locomotion is driven by a central program. The basic locomotor pattern of the identified motor neurons and regional classes of motor neurons persists even after the circumesophageal ganglia have been isolated from the periphery. The motor neurons are not synaptically interconnected; patterned bursting during locomotor activity is produced by cyclic synaptic input. Because the locomotor system has large neurons favorable for cellular analysis and because locomotion is characterized by features of both stereotypy and flexibility, Aplysia promises to be useful for investigating the mechanisms underlying both the generation and modulation of a central program.

Animals↗
PubMed1987

Locomotion elicited by lateral hypothalamic stimulation in the anesthetized rat does not require the dorsal midbrain.

Locomotor stepping elicited by lateral hypothalamic stimulation in the anesthetized rat is blocked by lesions in the anterior ventromedial midbrain. This study determined in acute experiments whether the dorsal midbrain regions implicated in locomotion were also part of the necessary pathway. Rats were anesthetized with Nembutal and held in a stereotaxic apparatus so that stepping responses rotated a wheel. Stepping was elicited by stimulation of the lateral hypothalamus (up to 100 microA, 0.5 ms cathodal pulses, 50 Hz, 10-s train length). Nine rats received unilateral lesions ipsilateral to the locomotor electrode and 3 rats received bilateral lesions. None of the dorsal midbrain lesions reduced locomotion elicited by ipsilateral lateral hypothalamic stimulation. Therefore the following regions are unnecessary for this type of locomotion: the dorsal and lateral central gray, the tegmentum lateral to the central gray, and in particular the area cuneiformis and the dorsal aspect of the pedunculopontine region. The neural systems required for lateral hypothalamic locomotion are located ventral to the superior cerebellar peduncle.

Animals↗
PubMed1988

Functional regeneration of descending brainstem command pathways for locomotion demonstrated in the in vitro lamprey CNS.

Lower vertebrates can recover locomotor function after spinal transections, and several classes of neurons in these animals can regenerate. However, no studies have directly tested for functional regeneration of descending command pathways for the initiation of locomotion in the absence of complications from sensory feedback. In the present study, the contribution of regeneration of descending command pathways to the reacquisition of locomotion was examined in behaviorally recovered, spinal-transected larval lampreys using in vitro brain/spinal cord preparations, in which mechanosensory feedback was eliminated. Activation of brainstem command centers produced locomotor activity below a healed transection site and this burst activity was coupled 1:1 with locomotor activity above the transection site. Furthermore, the parameters characterizing locomotor patterns in in vitro preparations were similar to those recorded during locomotion in normal, whole-animals. Additional experiments indicated that descending pathways from the brainstem had regenerated across the healed transection site and could directly activate spinal locomotor networks below the lesion area. These data appear to be the first direct demonstration in a vertebrate of functional regeneration of descending command pathways for the initiation of locomotion.

Action Potentials↗
PubMed1989

Electromyographic activity of cat hindlimb flexors and extensors during locomotion at varying speeds and inclines.

Electromyographic activity (EMG) was used to determine how hindlimb muscle activation patterns are modified as speed and incline of locomotion are varied in treadmill-trained cats. EMG was recorded using chronically implanted i.m. electrodes from the soleus, medial gastrocnemius, gluteus medius, and tibialis anterior muscles of adult cats during treadmill locomotion at a range of speeds and inclines. The patterns of changes in EMG activity at varying speeds and inclines were similar in all cats. Across speeds, the integrated EMG per step decreased for the soleus but remained constant for the other muscles. The integrated EMG per step was elevated in all muscles at higher inclines. Generally, with increased speed or incline the mean EMG per step was elevated in the medial gastrocnemius, gluteus medius, and tibialis anterior, the largest increase seen in the medial gastrocnemius. Soleus mean EMG per step remained unchanged with increased speed, but showed an absolute increase at the higher inclines. The integrated EMG per minute was always highest for the soleus followed by the medial gastrocnemius, and always lowest for the tibialis anterior. At the faster speeds, the 'on-time' increased in the tibialis anterior and decreased in the other muscles. These data suggest that the number of motor units activated and/or their firing frequencies increased in the medial gastrocnemius and the gluteus medius during locomotion at faster speeds or larger inclines, while relatively little change occurred in the soleus and tibialis anterior. These data also suggest that while there is considerable modulation of the level and duration of excitation of the extensor motor pools there is relatively little modulation of the flexor motor pools to adjust for both the speed and the incline of locomotion.

Acceleration↗
PubMed1989

Modulation of reflex responses during fictive locomotion in the forelimb of the cat.

During cat forelimb fictive locomotion, short-latency reflex pathways were examined by recording nerve discharges and intracellularly from motoneurones. Stimulation of cutaneous afferents, superficial radial nerves, evoked trisynaptic excitation of the elbow flexors, biceps brachii and brachialis, and stimulation of muscle afferents, deep radial nerves, evoked oligosynaptic, i.e. monosynaptic and disynaptic excitation of the flexors. The short-latency excitatory postsynaptic potentials (EPSPs) evoked from both nerves were rhythmically modulated; they were facilitated during the flexion phase and suppressed during the extension phase. Stimulation of high threshold muscle afferents evoked EPSPs with a central delay of ca. 4.2 ms, which were depressed throughout episodes of fictive locomotion. Since the short-latency EPSPs and longer-latency EPSPs in the same motoneurone were differently influenced during fictive locomotion, the effects observed could not be explained by changes occurring at only the motoneuronal level but they probably occurred at the premotoneuronal level. In addition, short-latency cutaneous excitation of the distal muscles, innervated by the median and ulnar nerves, was little modulated during fictive locomotion.

Action Potentials↗
PubMed1990

Effects of bicuculline and strychnine on synaptic inputs to edge cells during fictive locomotion.

Edge cells are mechanoreceptive neurones located in the lateral tracts of the lamprey spinal cord. Phasic activation of these cells by lateral bending can entrain the activity of the locomotor central pattern generator. During fictive locomotion induced by bath-applied NMDLA (N-methyl-D,L-aspartate) or sensory stimulation, edge cells receive synaptic input. In this paper we provide evidence that the tonic inhibition received during sensory-induced fictive locomotion is glycinergic. We also show that during fictive locomotion induced by application of NMDLA to the spinal cord, bicuculline unveils phasic synaptic activity in edge cells. During sensory-evoked fictive locomotion, by contrast, only tonic synaptic activity is apparent in the presence of bicuculline.

Action Potentials↗
PubMed1990

Phase-dependent modulation of primary afferent depolarization in single cutaneous primary afferents evoked by peripheral stimulation during fictive locomotion in the cat.

Previous results from our laboratory have shown with intra-axonal recordings that hindfoot cutaneous primary afferents are subjected to rhythmic depolarizations during fictive locomotion (L-PAD) suggesting that cutaneous presynaptic mechanisms are activated by the central locomotor program. In this study, we examined the transmission in pathways responsible for primary afferent depolarizations (PAD) of cutaneous fibres during spontaneous fictive locomotion in decorticate cats and in spinal cats injected with nialamide and L-DOPA. PADs were evoked (E-PADs) by electrical stimulation of peripheral nerves and recorded intra-axonally with micropipettes in identified superficialis peroneal (SP; n = 7) and tibialis posterior (TP; n = 17) cutaneous primary afferents. Results showed that the amplitude of E-PADs, which were superimposed on the L-PAD, was deeply modulated throughout the locomotor cycle; decreasing to reach a minimum during the flexor phase and increasing to a maximum during the extensor phase. The results were not statistically different in fibres of the two nerves and in both types of preparation. The amplitude of E-PADs was always maximum during the extensor phase whether there was a large L-PAD or not during that phase. This suggests that the presynaptic mechanisms activated by central locomotor networks (L-PAD) and those activated by peripheral inputs (E-PAD) may in part be controlled differently. The results thus show that the transmission in PAD pathways activated by cutaneous inputs is phasically modulated by the central pattern generator for locomotion. This strongly suggests that the presynaptic inhibition in cutaneous fibres evoked by the movement-related feedback during real locomotion could be similarly modulated.

Animals↗
PubMed1992

Phasic modulation of transmission from vestibular inputs to reticulospinal neurons during fictive locomotion in lampreys.

The aim of this study was to determine whether the transmission from sensory inputs to reticulospinal neurons is modulated during fictive locomotion in lampreys. Reticulospinal neurons play a key role in the control of locomotion; modulation of sensory transmission to these neurons might be of importance for the adaptation of the control they exert during locomotion. In this series of experiments, intracellular synaptic responses of reticulospinal neurons of the posterior rhombencephalic reticular nucleus elicited by electrical stimulation of vestibular nerves on each side were studied during fictive locomotion induced by 50 microM N-methyl-D-aspartate (NMDA). Interestingly, shortly after NMDA had reached the bath and much before locomotor discharges were apparent in the recorded ventral roots, there was a significant depression of the synaptic transmission from vestibular nerves. The effect was reversed by washing out the NMDA and persisted in the isolated brainstem after spinal transection at the first segmental level. As locomotor discharges appeared in the ventral roots, synaptic responses elicited by vestibular nerve stimulation showed a clear phasic modulation of their amplitude during the locomotor cycle. Responses to stimulation of the ipsilateral vestibular nerve were smaller during the ipsilateral burst discharge than during the contralateral activity, whilst responses to stimulation of the contralateral vestibular nerve were minimal during contralateral activity and maximal during ipsilateral activity. This opposite pattern of modulation observed in the same reticulospinal neuron suggests that the phasic modulation of vestibular transmission is not due to changes in the membrane properties of the reticulospinal cell but is produced at a pre-reticular level.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Effects of selective spinal cord lesions on hind limb locomotion in birds.

In birds, a variety of subtotal thoracic spinal cord lesions were made to determine the spinal cord pathways essential for avian hind limb locomotion (bipedal walking). The various surgical disruptions included: section of the dorsal half of the cord, a hemisection, section of the dorsal cord and ventromedial funiculi, section of the dorsal cord ventrolateral funiculi, section of the entire thoracic cord except for one ventrolateral quadrant, section of the ventral half of the cord, and complete transection of the thoracic cord. The study compared the locomotion following these lesions in both chronic surviving and acutely decerebrated, brain stem-stimulated birds. Behavioral assessments and electromyographic recording techniques were used to evaluate locomotor activity. Our results showed that transectioning pathways within the dorsal cord did not hinder the activation and maintenance of self-supported walking in either preparation. However, sparing the spinal cord pathways within either the ventromedial or ventrolateral funiculi of the thoracic spinal cord was essential for the activation of self-supported walking in both preparations. When our findings are integrated with previous studies, medullary reticulospinal pathways (projecting through the ventral funiculi) are strongly implicated as a common descending projection for the activation of spinal cord locomotor networks and the initiation of locomotion. Similar findings have been found in quadrapedal mammals and, as a complement, birds may make an excellent model for the study of bipedal locomotion.

Animals↗
PubMed1982

Methysergide releases locomotion without support in lateral hypothalamic akinesia.

Rats made profoundly akinetic by large bilateral electrolytic partial transections of the lateral hypothalamus were released from their akinesia by methysergide maleate (45 mg/kg, IP). When tested as soon as 24 hr postoperatively, lateral hypothalamic rats treated with methysergide displayed vigorous forward locomotion without postural support for as long as an hour and a half. By postoperative day 5, the locomotion elicited by methysergide was integrated with postural support to produce a more normal form of walking. Although atropine sulfate (50 mg/kg, IP) releases excessive walking in akinetic rats treated with 6-hydroxydopamine [53] it did not release locomotion lateral hypothalamic rats. Similarly, apomorphine, clonidine and phentolamine did not do so. Assuming that methysergide in the dose used exerts its effects primarily via the blockade of serotonin systems, we suggest that, in addition to an inhibitory cholinergic system, an independent inhibitory serotonergic system may also exaggerate the akinesia seen following treatments that diminish the action of brain catecholamine systems. Furthermore, the type of locomotion released by methysergide is a fractional form not previously isolated.

Animals↗
PubMed1986

Tactile stimulation inhibits locomotion produced by stimulation of the lateral hypothalamus in the anesthetized rat.

Rats were anesthetized with Nembutal and suspended in a stereotaxic apparatus so that their limbs contacted the outer surface of a 30-cm diameter wheel. Stimulation in the lateral hypothalamus (0.5 msec cathodal pulses at 50 Hz, up to 150 microA) produced locomotor stepping which turned the wheel. During continuous locomotion maintained by electrical stimulation, tactile stimulation was applied manually for 5-sec periods to various body regions in six subjects. Profound inhibition of locomotor stepping was produced in all subjects by mild pressure applied to the nose or the vibrissae pad. Vibrissae pad stimulation either ipsilateral or contralateral to the stimulation site was effective. Stroking of the vibrissae inhibited locomotion in only 2 of 6 subjects and in these cases the effective stimulation was contralateral to the brain stimulation site. With pressure applied to more caudal body regions, including the dorsum, the abdomen and the tail, the inhibition was less pronounced and less consistent than that produced by pressure on the snout region. The findings indicate that the tactile system provides an important modulation of locomotion and that the anesthetized locomoting rat offers a useful preparation for its further study.

Anesthesia, General↗
PubMed1993

Human locomotion and workload for simulated lunar and Martian environments.

Human locomotion in simulated lunar and Martian environments is investigated. A unique human-rated underwater treadmill and an adjustable ballasting harness simulate partial gravity in order to better understand how gravity determines the biomechanics and energetics of human locomotion. This study has two research aspects, biomechanics and energetics. The fundamental biomechanics measurements are continuously recorded vertical forces as exerted by subjects of the treadmill which is instrumented with a force platform. Experimental results indicate that peak vertical force and stride frequency decrease as the gravity level is reduced. Foot contact time is independent of gravity level. Oxygen uptake measurements, VO2, constitute the energetics, or workload, data for this study. As theory predicts, locomotion energy requirements for lunar (1/6-g) and Martian (3/8-g) gravity levels are significantly less than at 1-g. The observed variation in workload with gravity level is nonmonotonic, however, in over half the subject population. The hypothesis is offered that energy expenditure increases for lunar, as compared with Martian, locomotion due to the subject "wasting energy" for stability and posture control in simulated lunar gravity. Biomechanics data could influence advanced spacesuit design and planetary habitat design, while workload data will help define oxygen requirements for planetary life support systems.

Adult↗
PubMed1985

An hypothesis for the role of the spine in human locomotion: a challenge to current thinking.

Locomotion was first achieved by the motion of the spine. The limbs came after, as an improvement, not as a substitute; and yet, analysis of bipedal gait concentrates almost exclusively on the motion of the limbs. The requirements for land locomotion are examined from a general point of view and the evolution of the vertebrate spine is presented as a mechanism designed to move the animal. The necessary spinal movements are also analysed; the role of the musculoskeletal system is discussed and it is shown that the lumbar spine is a key structure in land locomotion, the pelvis being driven by the spine. The optimum control of motion demands that the stress at all the intervertebral joints should be minimized and equalized. This theory of locomotion requires the central nervous system to control the torque at those intervertebral joints and suggests that a breakdown of the control system would result in torsional failure of the spine. The theory is supported by EMG, force and torque data collected from several sources.

Animals↗
PubMed1994

Stimulation of locomotion in neonate rats by TRH analogue CG3703.

Thyrotropin releasing hormone (TRH) and its analogues have been shown to depolarise motoneurons and stimulate cyclical motor activities such as respiration and locomotion. It has been suggested that one of its roles might be modulation of neuronal membrane excitability to release intrinsic rhythmicity. The present experiments were designed to determine whether it would initiate locomotion in the neonate rat prior to the development of spontaneous walking. It was found that the TRH analogue CG3703 did activate locomotion in 3-day-old rat pups. Quantification of various gait parameters and study of spatiotemporal footfall patterns showed the gait to be indistinguishable from the spontaneous locomotion of older pups. Possible loci of action are discussed.

Animals↗
PubMed1993

A new learning paradigm: adaptive changes in interlimb coordination during perturbed locomotion in decerebrate cats.

Adaptive interlimb coordination was studied during perturbed locomotion in experimental chronically decerebrate cats. Perturbations were applied to the stance phases of the left forelimb using a newly developed treadmill which consisted of three compartments, one each for the left forelimb, the left hindlimb and both right limbs. During the perturbed locomotion, the treadmill belt for the left forelimb was driven at about twice the speed for the other limbs. During the first 1-50 perturbed steps, the step cycles of both forelimbs showed marked fluctuations; thereafter, the animals achieved stable locomotion by slightly shortening step cycle durations, and also by adjusting durations of bisupport phases asymmetrically in the left and right forelimbs. The present method provides a new test paradigm for adaptive interlimb coordination in locomotion, which will be useful in studying neural mechanisms of motor learning involving cerebellar synaptic plasticity.

Adaptation, Psychological↗
PubMed1993

Preoptic and hypothalamic neurons and the initiation of locomotion in the anesthetized rat.

Despite its insensate condition and apparent motoric depression, the anesthetized rat can provide useful information about the systems involved in locomotor initiation. The preparation appears to be particularly appropriate for the study of the appetitive locomotor systems and may be more limited for the study of the circuits involved in exploratory and defensive locomotion. In the anesthetized rat, pharmacological evidence indicates that the preoptic basal forebrain contains neurons which initiate locomotor stepping. Mapping with low levels of electrical stimulation indicates, but does not prove, that a region centered in the lateral preoptic area might be the location of these neurons. Several lines of evidence indicate that locomotor stepping elicited by electrical stimulation of the hypothalamus is mediated by neurons in the perifornical and lateral hypothalamus. Locomotor effects of hypothalamic stimulation persist in the absence of descending fibers of passage from the ipsilateral preoptic locomotor regions but are severely impaired by kainic acid lesions in the area of stimulation. Injections of glutamate into the perifornical and lateral hypothalamus elicit locomotor stepping at short latencies. Anatomical evidence suggests that the two regions are components of a network for appetitive locomotion. The recognition that multiple systems initiate locomotion both clarifies and complicates the study of locomotion. It provides a framework that incorporates disparate findings but it also underscores the need for increased attention to behavioral issues in studies of locomotor circuitry.

Anesthesia, General↗