Disturbed motor control of rhythmic movement at 2 h and delayed after maximal eccentric actions

The aim of this study was to examine the influence of exercise-induced muscle damage on elbow rhythmic movement (RM) performance and neural activity pattern and to investigate whether this influence is joint angle specific. Ten males performed an exercise of 50 maximal eccentric elbow flexions in isokinetic machine with duty cycle of 1:15. Maximal dynamic and isometric force tests (90°, 110° and 130° elbow angle) and both active and passive stretch reflex tests of elbow flexors were applied to the elbow joint. The intentional RM was performed in the horizontal plane at elbow angles; 60–120° (SA-RM), 80–140° (MA-RM) and 100–160° (LA-RM). All measurements together with the determination of muscle soreness, swelling, passive stiffness, serum creatine kinase were conducted before, immediately and 2 h as well as 2 days, 4 days, 6 days and 8 days post-exercise. Repeated maximal eccentric actions modified the RM trajectory symmetry acutely (SA-RM) and delayed (SA/MA/LA-RM) until the entire follow up of 8 days. Acutely lowered MA-RM peak velocity together with reduced activity of biceps brachii (BB) at every RM range, reflected a poorer acceleration and deceleration capacity of elbow flexors. A large acute drop of BB EMG burst amplitude together with parallel decrease in BB active stretch reflex amplitude, especially 2 h post-exercise, suggested an inhibitory effect originating most likely from groups III/IV mechano-nociceptors.     

Helix neurons invovled in control of rhythmic movement in the pneumostome

Three neurons capable of generating coordinated bursting activity or synchronized slow-wave fluctuations in membrane potential (MP) were identified in the left parietal ganglion ofHelix pomatia. The function of these units contributes to regulating rhythmic opening and closing movements in the pneumostome. Both bursting activity and slow-wave neuronal MP synchronize with rhythmic movements of the pneumostome. Onset of bursting activity and fluctuations in MP on the one hand or suppression of these effects due to different influences on the cells on the other leads to initiation or extinction of pneumostome movements respectively. These neurons do not exhibit endogenous bursting activity but do produce a fairly high rate of firing activity without bursting pattern and without slow-waves in MP in isolation. Bursting activity occurs in these neurons in the intact central nervous system (CNS) as a result of gigantic synchronized IPSP in some cases and due to the aforementioned slow waves in MP and in others. No direct chemically- or electrically-operated synaptic connections exist between the three cells. Serotonin triggers both waves in MP and bursting activity in all three neurons in the intact CNS and exerts a pronounced hyperpolarizing action on each of these factors in isolation.N. K. Kol'tsov Institute of Developmental Biology, Academy of Sciences of the USSR. Moscow. Balaton Limnological Research Institute of the Hungarian Academy of Sciences, Tihany. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 509–517, July–August, 1988.     

Mechanomyographic and electromyographic responses during submaximal to maximal eccentric isokinetic muscle actions of the biceps brachii

The purpose of this investigation was to determine the mechanomyography (MMG) and electromyography (EMG) amplitude and mean power frequency (MPF) vs. eccentric isokinetic torque relationships for the biceps brachii muscle. Nine adults (mean +/- SD age = 23.1 +/- 2.9 years) performed submaximal to maximal eccentric isokinetic muscle actions of the dominant forearm flexors. After determination of isokinetic peak torque (PT), the subjects randomly performed submaximal step muscle actions in 10% increments from 10 to 90% PT. Polynomial regression analyses indicated that the MMG amplitude vs. eccentric isokinetic torque relationship was best fit with a quadratic model (R(2) = 0.951), where MMG amplitude increased from 10 to 60% PT and then plateaued from 60 to 100% PT. There were linear increases in MMG MPF (r(2) = 0.751) and EMG amplitude (r(2) = 0.988) with increases in eccentric isokinetic torque, but there was no significant change in EMG MPF from 10 to 100% PT. The results suggested that for the biceps brachii, eccentric isokinetic torque was increased to approximately 60% PT through concurrent modulation of the number of active motor units and their firing rates, whereas additional torque above 60% PT was produced only by increases in firing rates. These findings contribute to current knowledge of motor-control strategies during eccentric isokinetic muscle actions and could be useful in the design of training programs.     

Possible contributions of CPG activity to the control of rhythmic human arm movement

There is extensive modulation of cutaneous and H-reflexes during rhythmic leg movement in humans. Mechanisms controlling reflex modulation (e.g., phase- and task-dependent modulation, and reflex reversal) during leg movements have been ascribed to the activity of spinal central pattern generating (CPG) networks and peripheral feedback. Our working hypothesis has been that neural mechanisms (i.e., CPGs) controlling rhythmic movement are conserved between the human lumbar and cervical spinal cord. Thus reflex modulation during rhythmic arm movement should be similar to that for rhythmic leg movement. This hypothesis has been tested by studying the regulation of reflexes in arm muscles during rhythmic arm cycling and treadmill walking. This paper reviews recent studies that have revealed that reflexes in arm muscles show modulation within the movement cycle (e.g., phase-dependency and reflex reversal) and between static and rhythmic motor tasks (e.g., task-dependency). It is concluded that reflexes are modulated similarly during rhythmic movement of the upper and lower limbs, suggesting similar motor control mechanisms. One notable exception to this pattern is a failure of contralateral arm movement to modulate reflex amplitude, which contrasts directly with observations from the leg. Overall, the data support the hypothesis that CPG activity contributes to the neural control of rhythmic arm movement.     

Voltage-sensitive ion channels in rhythmic motor systems

Voltage-sensitive ionic currents shape both the firing properties of neurons and their synaptic integration within neural networks that drive rhythmic motor patterns. Persistent sodium currents underlie rhythmic bursting in respiratory neurons. H-type pacemaker currents can act as leak conductances in spinal motoneurons, and also control long-term modulation of synaptic release at the crayfish neuromuscular junction. Calcium currents travel in rostro-caudal waves with motoneuron activity in the spinal cord. Potassium currents control spike width and burst duration in many rhythmic motor systems. We are beginning to identify the genes that underlie these currents.     

Muscle function in men and women during maximal eccentric exercise

This study assessed muscle fatigue patterns of the elbow flexors in untrained men and women to determine if sex differences exist during acute maximal eccentric exercise. High-intensity eccentric exercise is often used by athletes to elicit gains in muscle strength and size gains. Development of fatigue during this type of exercise can increase risk of injury; therefore, it is important to understand fatigue patterns during eccentric exercise to minimize injury risk exposure while still promoting training effects. While many isometric exercise studies have demonstrated that women show less fatigue, the patterns of fatigue during purely eccentric exercise have not been assessed in men and women. Based on the lack of sex differences in overall strength loss immediately post-eccentric exercise, it was hypothesized that women and men would have similar relative fatigue pattern responses (i.e., change from baseline) during a single bout of maximal eccentric exercise. Forty-six subjects (24 women and 22 men) completed 5 sets of 10 maximal eccentric contractions on an isokinetic dynamometer. Maximal voluntary isometric contraction strength was assessed at baseline and immediately following each exercise set. Maximal eccentric torque and contractile properties (i.e., contraction time, work, half relaxation time, and maximal rate of torque development) were calculated for each contraction. Men and women demonstrated similar relative isometric (32% for men and 39% for women) and eccentric (32% for men and 39% for women) fatigue as well as similar deficits in work done and rates of torque development and relaxation during exercise (p > 0.05). Untrained men and women displayed similar relative responses in all measures of muscle function during a single bout of maximal eccentric exercise of the elbow flexors. Thus, there is no reason to suspect that women may be more vulnerable to fatigue-related injury.     

Insights from models of rhythmic motor systems

Computational models of rhythmic motor systems are valuable tools for the study of motor pattern generation and control. Recent modeling advances, together with experimental results, suggest that rhythmic behaviors, such as breathing or walking, are influenced by complex interactions among motor system components. Such interactions occur at all levels of organization, from the subcellular through to the cellular, synaptic, and network levels to the level of neuromuscular interactions and that of the whole organism. Simultaneously, safety mechanisms at all levels contribute to network stability and the generation of robust motor patterns.     

Deterministic and stochastic features of rhythmic human movement

The dynamics of rhythmic movement has both deterministic and stochastic features. We advocate a recently established analysis method that allows for an unbiased identification of both types of system components. The deterministic components are revealed in terms of drift coefficients and vector fields, while the stochastic components are assessed in terms of diffusion coefficients and ellipse fields. The general principles of the procedure and its application are explained and illustrated using simulated data from known dynamical systems. Subsequently, we exemplify the method’s merits in extracting deterministic and stochastic aspects of various instances of rhythmic movement, including tapping, wrist cycling and forearm oscillations. In particular, it is shown how the extracted numerical forms can be analysed to gain insight into the dependence of dynamical properties on experimental conditions.     

On rhythmic movement of the diatom Amphora ovalis

The vertical migration, motility and cell division rhythms of the diatom Amphora ovalis Kütz from Lake Kinneret, Israel, have been studied under laboratory conditions and results compared with comparable rhythms of other unicellular algae. The vertical migration rhythm exhibits two peaks during the light period, both when the cells are kept in continuous light or continuous dark. There is a single peak of motility occurring in the first half of the natural light period and a single peak of cell division in the latter half of the dark period. Rephasing of the rhythm by means of delayed start up time is illustrated and the possible interaction of phototactic and geotactic rhythms discussed.     

Effect of vanadate on rhythmic leaflet movement in albizzia julibrissin

Vanadate (Na₃VO₄) selectively and reversibly affects the rhythmic movement of Albizzia julibrissin leaflets. Leaflets floated on 1 millimolar vanadate open at the same rate or more rapidly than controls, but closure is inhibited. After 6 to 24 hours incubation, the inhibition can be reversed by a 24-to 48-hour period on water or control buffer. Recovery is complete in light-dark cycles, and it is almost complete under free-running conditions (prolonged darkness). Leaflets floated on 10 millimolar vanadate do not open in darkness, but they open at a reduced rate in light. Concentrations of 100 micromolar or less are ineffective.     

Coordinated cell-shape changes control epithelial movement in zebrafish and Drosophila

Epithelial morphogenesis depends on coordinated changes in cell shape, a process that is still poorly understood. During zebrafish epiboly and Drosophila dorsal closure, cell-shape changes at the epithelial margin are of critical importance. Here evidence is provided for a conserved mechanism of local actin and myosin 2 recruitment during theses events. It was found that during epiboly of the zebrafish embryo, the movement of the outer epithelium (enveloping layer) over the yolk cell surface involves the constriction of marginal cells. This process depends on the recruitment of actin and myosin 2 within the yolk cytoplasm along the margin of the enveloping layer. Actin and myosin 2 recruitment within the yolk cytoplasm requires the Ste20-like kinase Msn1, an orthologue of Drosophila Misshapen. Similarly, in Drosophila, actin and myosin 2 localization and cell constriction at the margin of the epidermis mediate dorsal closure and are controlled by Misshapen. Thus, this study has characterized a conserved mechanism underlying coordinated cell-shape changes during epithelial morphogenesis.     

Rapid muscle force reactions during regulation of rhythmic movement

It was shown by experiments with human forearm rhythmic movements that summary force, stiffness and viscosity of musculature quickly increased during the action of external unshocked disturbance. These effects limited the movement trajectory changes during latent interval preceding nervous reactions.     

Acute effects of static stretching on maximal eccentric torque production in women

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and the joint angle at PT during maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors at 60 and 180 degrees x s(-1) for the stretched and unstretched limbs in women. Thirteen women (mean age +/- SD = 20.8 +/- 0.8 yr; weight +/- SD = 63.3 +/- 9.5 kg; height +/- SD = 165.9 +/- 7.9 cm) volunteered to perform separate maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors with the dominant and nondominant limbs on a Cybex 6000 dynamometer at 60 and 180 degrees x s(-1). PT (Nm) and the joint angle at PT (degrees) were recorded by the dynamometer software. Following the initial isokinetic assessments, the dominant leg extensors were stretched (mean stretching time +/- SD = 21.2 +/- 2.0 minutes) using 1 unassisted and 3 assisted static stretching exercises. After the stretching (4.3 +/- 1.4 minutes), the isokinetic assessments were repeated. The statistical analyses indicated no changes (p > 0.05) from pre- to poststretching for PT or the joint angle at PT. These results indicated that static stretching did not affect PT or the joint angle at PT of the leg extensors during maximal, voluntary, eccentric isokinetic muscle actions at 60 and 180 degrees x s(-1) in the stretched or unstretched limbs in women. In conjunction with previous studies, these findings suggested that static stretching may affect torque production during concentric, but not eccentric, muscle actions.     

Ontogeny of rhythmic motor networks in the stomatogastric nervous system

We used the lobster Homarus gammarus to study the ontogeny of neural networks involved in rhythmic behaviours. Since in the adult the neural networks belonging to the stomatogastric nervous system and controlling the rhythmic movements of the foregut are well characterised, we have studied them during ontogeny. While this foregut develops slowly throughout embryonic and larval stages, the neuronal population of these motor networks is quantitatively established since the mid-embryonic period. Moreover, in the embryo, this neural population is organised into a single functional network that displays a unique motor output. By contrast, in the adult the same neuronal elements are organised into three neural networks that express independent motor programs. Our results indicate that the multiple adult networks are partitioned progressively from a single embryonic network during development. Accepted: 23 May 1999     

Adaptive motor behavior in insects

As insects move through tortuous, unpredictable terrain, their neural system allows them to exhibit striking adaptability and researchers must use every technique at their disposal to unravel the underlying mechanisms. Descending commands from brain centers that process tremendous amounts of information from head sensors work together with local motor control altering their operation to deal with barriers or move toward important targets. By analyzing movements in detail with high-speed video, recording from identified neurons in thoracic ganglia and examining activity in different brain regions, we are beginning to understand how these remarkable animals navigate their environment. Coupled with new and exciting neurogenetic tools, the near future promises an exciting time for studying the neural basis of insect movement.     

Adaptive changes of locomotion after central and peripheral lesions

This paper reviews findings on the adaptive changes of locomotion in cats after spinal cord or peripheral nerve lesions. From the results obtained after lesions of the ventral/ventrolateral pathways or the dorsal/dorsolateral pathways, we conclude that with extensive but partial spinal lesions, cats can regain voluntary quadrupedal locomotion on a treadmill. Although tract-specific deficits remain after such lesions, intact descending tracts can compensate for the lesioned tracts and access the spinal network to generate voluntary locomotion. Such neuroplasticity of locomotor control mechanisms is also demonstrated after peripheral nerve lesions in cats with intact or lesioned spinal cords. Some models have shown that recovery from such peripheral nerve lesions probably involves changes at the supra spinal and spinal levels. In the case of somesthesic denervation of the hindpaws, we demonstrated that cats with a complete spinal section need some cutaneous inputs to walk with a plantigrade locomotion, and that even in this spinal state, cats can adapt their locomotion to partial cutaneous denervation. Altogether, these results suggest that there is significant plasticity in spinal and supraspinal locomotor controls to justify the beneficial effects of early proactive and sustained locomotor training after central (Rossignol and Barbeau 1995; Barbeau et al. 1998) or peripheral lesions.     

Positive work as a function of eccentric load in maximal leg extension movements

Negative and positive work performed during leg extension movements of 53 well trained subjects was measured with the help of a special dynamometer. The subjects performed four maximal push off trials against five different loads (25-105 kg): two two-legged extensions from a squatting position (SM) with a knee angle of 70 degrees and two trials with a preliminary counter movement (CM) but with the same extension range as in the SM. Positive work differed only by about 4% between CM and SM in spite of large differences in initial forces at the onset of concentric contraction. Based on simulations, it is suggested that in CM the advantage of stored elastic energy can almost completely be nullified by the disadvantage of a limited shortening distance of the contractile elements. It is hypothesised that elastic energy in CM can only cause considerable extra work during concentric contraction compared to the maximal positive work done in SM if the total range of lengthening and shortening of the muscle(s) involved is larger in CM than in SM.     

Mathematical model of activity of spinal generators producing rhythmic movement

Different organizational arrangements of scratching and locomotor rhythm generators were simulated by a computer-aided mathematical model. A functional group of neurons (a hemicenter constructed on the basis of a stochastically arranged neuronal network) served as the basis for the generator. Several organizational arrangements of scratching and locomotor rhythm generators are considered: two hemicenters with reciprocal inhibitory connections and tonic excitatory influences on both; two hemicenters with inhibitory-excitatory connections and tonic excitatory influences on only one of these; circular structures consisting of more than two functional groups of neurons with excitatory and inhibitory connections between them. All these arrangements would allow for generation of rhythmic activity with a similar time course to that of scratching and locomotor rhythm. It was found that the transition from locomotor to scratching rhythm could be based on fairly simply organized effects on generator neurons. Principles possibly guiding the construction of spinal generators of scratching and locomotor movements are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 586–597, September–October, 1988.