Interlimb transfer of grasp orientation is asymmetrical.

One the most fundamental aspects of the human motor system is the hemispheric asymmetry seen in behavioral specialization. Hemispheric dominance can be inferred by a contralateral hand preference in grasping. Few studies have considered grasp orientation in the context of manual lateralization and none has looked at grasp orientation with natural prehension. Thirty right-handed adults performed precision grasps of a cylinder using the thumb and index fingers, and the opposition axis (OA) was defined as the line connecting these two contact points on the cylinder. Subjects made ten consecutive grasps with one hand (primary hand movements) followed by ten grasps with the other hand (trailing movements). Differences between primary and trailing grasps revealed that each hemisphere is capable of programming the orientation of the OA and that primary movements with the right hand significantly influenced OA orientation of the trailing left hand. These results extend the hemispheric dominance of the left hemisphere to the final positions of fingers during prehension.

Quantification of level of effort at the plantarflexors and hip extensors and flexor muscles in healthy subjects walking at different cadences.

The plantarflexor, hip extensor and hip flexor muscle groups contribute by their concentric action to generate most of the energy during level gait in healthy subjects. The goal of the present study was to determine, during the main energy generation phases, the relative demand of these three groups in 14 healthy subjects walking at four cadences (self-selected, 60, 80 and 120 steps/min). The muscular utilization ratio (MUR), that compares the net joint moment obtained during gait to the maximal potential moment (MPM) at each percentage of the gait cycle, was used to estimate the mechanical relative demand. The MPM values were obtained by regression equations developed from torque data measured with a Biodex dynamometric system. The results showed that the peak MURs increased with gait cadence. The peak values were not significantly different between sides for all cadences despite mean absolute lateral differences ranging from 7% to 10%. The mean peak MURs of both sides ranged from 51.3% to 62.6%, from 20.7% to 49.9% and from 14.9% to 42.5%, for the plantarflexors, hip flexors and hip extensors, respectively. Highly significant associations were found between the MURs and net moments (numerator of the MUR ratio), with Pearson coefficients (r) superior to 0.80 for all muscles groups. The association between the MURs and the maximal potential moments (denominator of MUR ratio) was lower (0.01

Electrophysiological identification of a somaesthetic pathway to the red nucleus.

In awake chronically implanted cat, the cells in the red nucleus (RN) can be either activated or inhibited by natural stimulation on periphery. The effective stimuli are touching the fur, rotating the joints and tapping the muscles. A somaesthetic map has been constructed with the face area dorsally, the forelimb more ventrally and the hindlimb lateroventrally in the RN. In acute preparations, after ablation of the motor cortex and the cerebellum and section of the dorsal columns of the spinal cord at cervical level, the RN cells were still reacting to natural stimulation of the skin or electrical stimulation of peripheral nerves. The course of the somaesthetic pathway was systematically mapped by microstimulation of the spinal cord. It was shown that it follows the primary afferents which enter the dorsal columns, where they give off collaterals which relay at segment levels. After decussation the fibres ascend the ventromedial quadrant of the cord. A large portion of the fibres relay a second time in the medulla. The existence of such a pathway can account for the somaesthetic responses recorded in the RN in awake cats.

Interaction between forced grasping and a learned precision grip after ablation of the supplementary motor area.

Monkeys were trained to compress and release a force transducer held between the thumb and forefinger. Immediately following ablation of the contralateral supplementary motor area a grasp reflex produced a disturbance of the learned precision grip characterized by an increase in mean grasping force, an increase in the rate of prehensile force application and the inability to release the strain gauge. No change was observed in the same learned grip with the ipsilateral hand.

A new pathway from primary afferents to the red nucleus.

Evidence is provided that rubrospinal neurons receive feedback information from the periphery via pathways which bypass both the cerebellum and the cerebral cortex. It appears that the primary afferent fibers which ascend in the dorsal columns of the spinal cord give off collaterals via which they activate ascending tracts with axons in the ventral quandrants of the spinal cord. The existence of such pathways indicates that the red nucleus is part of a long feedback loop assisting the ongoing movement.

Interaction between motor commands and somatosensory afferents in the control of prehension.

In 1931, Hughlings Jackson made a distinction between voluntary and automatic movements. According to Jackson the former are varied and purposeful gestures, whereas the latter include stereotyped movements largely under immediate sensory control. In this regard it may be said that the motor function of the primate hand includes both voluntary as well as automatic responses. Phillips and Porter (1977) noted that injury to the nervous system may often disrupt tactile exploration and skilled manipulation, although the same lesion may fail to interfere with automatic prehension used in posture and locomotion. The effects of selective brain destruction as well as the results from single-cell recordings from moving animals have indicated some of the different contributions made by various parts of the cerebello-thalamo-cortical motor system. Prehension offers a unique opportunity in which the interactions between motor commands and somatosensory afferents may be studied.

A static dynamometer measuring multidirectional torques exerted simultaneously at the hip and knee.

The function of a static dynamometer measuring torques exerted simultaneously in the different anatomical planes of the hip (flexion-extension, abduction-adduction and internal-external rotation) and knee (flexion-extension) is described. Muscular torques were calculated in real time using a desktop computer from measurements of orthogonal forces applied at two locations and the lever arm values measured in each subject. The reliability of the force transducers was explored by examining their output, using calibrated weights, on three different days. The results were identical over this period of time, indicating that the transducers are highly reliable. A mechanical simulator of a lower limb was constructed to generate specific or combined torques of known values at the hip and knee. The torques measured by the dynamometer were found to be highly concordant with the known torques applied by the simulator, indicating that the torque measurements were valid. The usefulness of the dynamometer is demonstrated by evaluating the activity of the rectus femoris and biceps femoris muscles during static efforts exerted in various directions at the hip. In addition, the mechanical action of biarticular muscles at the hip was evaluated by quantification of hip torques during efforts exerted at the knee. From these results, it has been concluded that the present biarticular and multidirectional dynamometer is a valid, reliable and precise instrument that may prove to be useful in evaluating the muscular function of the lower limb.

The interrater reliability of force measurements using a modified sphygmomanometer in elderly subjects.

BACKGROUND AND PURPOSE: Physical therapists working with elderly people require an instrument that provides reliable force measurements and can be used in a clinical setting. The modified sphygmomanometer has been identified as potentially fulfilling these requirements, yet there is an absence of research on the reliability of measurements taken with this instrument on elderly patients. This study was undertaken to investigate the interrater reliability of force measurements, in a group of elderly subjects, using a modified sphygmomanometer. SUBJECTS: Thirty-six hospitalized subjects (mean age=75.28 years, SD=9.43, range=62-95) participated in the study. METHODS: With the modified sphygmomanometer, 3 examiners evaluated the isometric force of the elbow extensors and hip extensors using a break test and a make test, respectively. RESULTS: Intraclass correlation coefficients (2,1) reflecting reliability were .87 for the elbow extensors and .65 for the hip extensors. The estimation of the components of variance for hip extensors revealed that these results were due in part to the raters but that random error contributed to a much larger extent. CONCLUSION AND DISCUSSION: The modified sphygmomanometer appears to be practical to use, and the high correlations found in this study for the elbow extensors suggest that reliable measurements can be obtained with this instrument. Further research is needed, however, to specify the manner in which the modified sphygmomanometer can be used when assessing different muscle groups.

Topographical effects of transcutaneous electrical nerve stimulation on the H-reflex of the triceps surae muscles.

The present study was conducted on eight normal subjects in order to evaluate the effects of transcutaneous electrical nerve stimulation (TENS); 99 Hz, 250 µs pulse duration, applied over either the common peroneal (CPN) or sural nerve, on the H-reflex of the soleus (SO), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) muscles. Within each session, SO, GL and GM H-reflexes were recorded before (for 5 min), during (for 30 min) and after (for 10 min) TENS was applied at twice the sensory threshold for perception. It was found that, on average, while the stimulation was administered on the CPN: (a) the GL H-reflex amplitude increased by 40% (Friedman test: χ(2) = 11.71, P < 0.05); (b) the SO H-reflex decreased (≥ 10% H(ctrl)), although not in a statistically significant manner, in five of eight subjects; and (c) the GM H-reflex remained, overall, relatively stable. No significant effects of TENS over the sural nerve were found on any of the investigated muscles. The finding of increased H-reflex amplitudes in GL during TENS made it less likely that CPN stimulation had reciprocal inhibitory effects. However, such an increase could be attributed to a selective effect (such as a decrease in the recruitment threshold) on type II motoneurons of the GL. Furthermore, the topographical effects observed on the GL during TENS may reflect selective local effects due to stimulation of a sensory branch of the CPN, the lateral sural nerve, which mainly innervates the skin overlying the GL. The absence of effects noted on the GM during TENS further supports this hypothesis as the cutaneous afferents overlying that muscle were not stimulated. The repetitive cutaneous stimulation over the sural nerve, at the lateral malleolus, may have been too distal to stimulate the cutaneous receptors overlying the SO.

A method for quantification of directional patterns of muscle activation at the lower limb.

Several studies have examined muscle activation patterns during movements or static torques exerted in different directions in human subjects as well as in trained monkeys. However, no statistical approach has ever been proposed to characterize directional patterns of muscle activation in a given population. This report describes a method for the quantification and statistical analysis of directional patterns of muscle activation at the lower limb. This method was used with a group of 18 healthy subjects. Using a multidirectional dynamometer for the lower limb, subjects were asked to exert static torques (at approximately 5 and 15% of the maximal voluntary contraction) in eight directions covering a 360 degrees range at the hip. These were hip abduction, adduction, flexion, extension, and the intermediate directions (e.g., hip flexion and abduction). Electromyographic (EMG) activities of eight lower limb muscles were recorded during these efforts using surface electrodes. For each muscle, the mean rectified EMG activity obtained in each direction was considered a vector. Then, the overall directional pattern of activation for a given muscle was quantified for each subject by a vectorial summation of these vectors. The angle of the resultant vector was used along with the other subjects' angular values to calculate a mean vector representing the muscle's directional pattern of activation for the complete sample. This mean vector was used to perform the statistical analysis of the data. More specifically, the Rayleigh test for circular data was performed at both torque levels to determine, through the length of the mean vector, if a muscle showed a directional specificity in its activity, i.e., a tendency to be preferentially recruited toward a specific direction. In general, hip muscle activity demonstrated significant directional specificity during hip efforts in contrast to knee and ankle muscle activity. Moreover, the angle of the mean vector calculated for each hip muscle across the sample remained relatively stable at both torque levels. These results indicate that directional patterns of muscle activation are unaffected by the level of torque produced. It is concluded that the method used in the present study is effective in characterizing directional patterns of muscle activation in a given population. Also, this method provides new perspectives for further quantification of muscle activation patterns disturbances in populations presenting various neuromuscular disorders.

Directional patterns of muscle activation at the lower limb in subjects with hemiparesis and in healthy subjects: A comparative study.

This article reports the results of a comparative study on directional patterns of muscle activation at the lower limb in 15 subjects with hemiparesis and 18 healthy subjects. Subjects were required to exert static hip and knee torques using multidirectional and biarticular dynamometers designed for the lower limbs. Hip torques were performed in abduction, adduction, flexion, extension, and in combined directions (e.g., hip flexion and abduction) and knee torques were exerted in flexion and extension. The required torque levels corresponded to approximately 5% of the maximal voluntary contraction of healthy subjects. Electromyographic (EMG) activities of the rectus femoris, biceps femoris, gracilis, gluteus medius, gluteus maximus, vastus lateralis, tibialis anterior, and soleus were recorded during these torques. The descriptive analysis involved comparison between either the polar plots (for hip tasks) or the histograms (for knee tasks) representing the mean muscle activity obtained across subjects during torques exerted in each direction for the three groups of muscles analyzed (normal, paretic, and nonparetic muscles). Ciucular statistics were also used to characterize directional patterns of activation in each muscle during hip tasks while linear statistics permitted one to analyze these patterns during knee tasks. In general, the results of both the descriptive and inferential statistical analyses indicated that directional patterns of muscle activation during hip and knee torques are not altered in subjects with hemiparesis. These results are in contrast to the disturbances observed previously in a study of directional patterns of muscle activation at the upper extremity in this population. It is suggested that the contrast between the present results and those obtained at the upper limb in subjects with hemiparesis may reflect the difference in the motor recovery of upper and lower paretic limbs or in the severity of spasticity in the muscles involved at the studied joints. Results of this study also showed that the paretic muscles often demonstrate larger EMG signals than normal and nonparetic muscles, especially during knee flexion torques. These last observations, in addition to the fact that some subjects with hemiparesis could not complete all of the tasks with their paretic limb, under-score the muscle weakness inherent to this population.

Influence of gender on the EMG power spectrum during an increasing force level.

The aim of the present study was to contrast, between men and women, the behavior of EMG power spectrum statistics (median frequency (MF) and mean power frequency (MPF) obtained across increasing force levels. Thirteen men and sixteen women produced ramp (single contractions with the force increasing linearly) elbow flexions and extensions from 0 to 100% of the maximum voluntary contraction (MVC). Each ramp was produced in a 5-s period. Surface EMG signals from triceps brachii (TB), anconeus (AN), and biceps brachii (BB) were recorded with miniature surface electrodes placed 6 mm apart. These signals were sampled at 2,000 Hz. The MPF and MF of power spectra, obtained from single 256-ms windows, were computed for each muscle at 10, 20, 40, 60, and 80% MVC. Significant differences (two-way analyses of variance (ANOVAs); p < 0.05) in the behaviors of the MPF and MF across force levels were found between men and women. In general, the MPF and MF showed more pronounced increases across increasing force levels for men than for women. It is proposed that this gender effect could be explained by differences in skinfold thickness and fiber type characteristics between the two groups of subjects.

Correspondence between the directional patterns of hip muscle activation and their mechanical action in man.

The hypothesis that the pattern of muscle activation during a static voluntary effort exerted in different directions is oriented in the direction of the muscle's mechanical action was evaluated. The electromyographical (EMG) activation patterns of five hip muscles (gluteus medius, rectus femoris, tensor fasciae latae, gracilis and semitendinosus) and one knee muscle (vastus lateralis) were characterized in 11 normal subjects during static efforts at the hip joint. Subjects were asked to generate torques (10 and 20 Nm) in 24 directions covering 360 degrees at increments of 15 degrees in the transverse plane of the femur whereas torques at the knee were to be kept at zero. Using vector summation of the rectified EMGs, a mean angular value of muscle activation was calculated for each muscle across subjects. It was observed that the mean angular values of muscles acting at the hip were significantly oriented, whereas the activity of the vastus lateralis was not significantly oriented. In addition, the angular values of activation of the rectus femoris, tensor fasciae latae and semitendinosus muscles were not significantly different from the direction of mechanical action of these respective muscles as determined using a biomechanical model of the hip. However, the angular values of the gluteus medius and gracilis activations were found to be significantly different from their anatomical line of action. The angular values of activation of two muscles (rectus femoris and gluteus medius) were also compared to the mechanical pulling direction of these muscles as determined following electrical stimulation of the recorded muscle regions. The analysis revealed that the angular value of the gluteus medius and rectus femoris during voluntary static efforts at the hip was not significantly different from the direction of mechanical action of these muscles as determined by the electrical stimulation. In general, these results support the hypothesis that the degree of a muscle's activation in one direction is determined as a function of its mechanical action.

A motor reeducation program aimed to improve strength and coordination of the upper limb of a hemiparetic subject.

The objective of the study is to describe a new reeducation program based on a multi-directional and multi-articular dynamometer and to evaluate its applicability in one chronic right hemiparetic subject. The treatment sessions lasted 1 h and were conducted three times per week for a period of 8 weeks. During these sessions, the subject was asked to exert 10 repetitions of 16 torque combinations exerted at the shoulder, elbow and forearm or combined with handgrip exertion. The sequence of torques and force progressed from proximal to distal joints, and were realized in and out of the typical 'synergy patterns' described in this population. In addition, the levels of torque and force requested were increased progressively throughout the treatment period. The coordination of both upper extremities, tested using the finger to nose test, and the dexterity of the affected side, evaluated using the Box and Blocks assessment, tended to improve as treatments progressed. These results indicate the feasibility of this approach and suggest that it may be worthwhile examining the effectiveness of this approach on improving the functional performance of the upper extremity in a larger population of hemiparetic subjects.

Incoordination in patients with hemiparesis.

Incoordination is frequently observed in patients following a cerebrovascular accident. Clinical electromyographic studies which have furthered our understanding of this motor impairment are reviewed, and possible underlying mechanisms are discussed. It is suggested that the lack of coordinated voluntary movement observed in hemiparetic patients may be due, in part, to an impaired regulation of spinal neurones. In the rehabilitation sciences, the need to assess the effectiveness of treatment as well as develop new approaches for the treatment of hemiparetic subjects will require the combined efforts of many investigators. A two-fold research approach is supported which aims: 1) to quantify the motor deficit, and 2) to extend our knowledge of the physiological mechanisms underlying the deficit. Such a general research approach could be of value to the study of other sensorimotor deficits.

Static dynamometer for the measurement of multidirectional forces exerted by the thumb.

The functioning of a static dynamometer designed to measure simultaneous forces exerted by the thumb in the vertical and horizontal axes is described. The analysis of the output signals by a desktop computer program provides information regarding the forces generated in eight directions covering a plane transverse to the thumb by 45 degree increments. In 12 normal female subjects, the maximum voluntary torques exerted at the trapezo-metacarpal joint of the thumb were examined and the muscle activation patterns of the interosseus, flexor pollicis brevis and adductor pollicis brevis muscles were recorded in one subject. Torques and muscle activation patterns were depicted using polar plots. Dynamometric data indicate that strength varies with direction and that higher torques are obtained in directions that bring the thumb towards the palm, i.e. flexion, adduction, combined flexion-adduction and extension-adduction. Patterns of muscle activity vary according to the direction evaluated suggesting that strength depends on the number of activated muscles as well as the relative force contribution of each muscle.

Plantarflexor weakness as a limiting factor of gait speed in stroke subjects and the compensating role of hip flexors.

OBJECTIVE: To determine, using the Muscular Utilization Ratio (MUR) method, whether plantarflexor weakness is among the factors preventing stroke subjects from walking at faster speeds. Potential compensations by the hip flexors were also examined. DESIGN: A convenience sample of 17 chronic stroke subjects in a context of a descriptive study. BACKGROUND: Gait speed is correlated with the residual strength of the muscles involved in gait in stroke subjects. However, it has not been established if this residual strength limits gait speed. METHODS: Kinetic and kinematic data for comfortable and maximal gait speeds were collected on the paretic side, and were used to determine the moments in plantarflexion (mechanical demand: MUR numerator) during the push-off phase. The maximal potential moment (MUR denominator) of the plantarflexors during gait was predicted using an equation derived from dynamometric data collected with a Biodex system. The MURs of the plantarflexors were then calculated at every 1% interval of the push-off phase. The pull-off phase of gait and the hip flexor strength were also examined. RESULTS: Ten subjects of the sample had a MUR value between 80 and 150% at maximal gait speed. These subjects produced the lowest peak torques in plantarflexion. Each of the four fastest subjects of this group had a large hip flexion moment during the pull-off phase of gait and produced high hip flexion torque values on the dynamometer. Each of the seven remaining subjects had a MUR value under 70% when they walked at maximal speed. CONCLUSIONS: Weakness of the plantarflexors should be considered as one factor limiting gait speed in 10 hemiparetic subjects. Some subjects with weak plantarflexors could walk rapidly because they compensated with the hip flexors. For the remaining stroke subjects, factors other than weakness of the plantarflexors have to be considered in order to explain the reduction in their gait speed.

EMG power spectrum of elbow extensors: a reliability study.

In order to be considered a potential tool for the characterization of muscle activity, the reliability of EMG power spectral analysis should be demonstrated. In this study, the reliability of the mean power frequency (MPF) and of the median frequency (MF) of power spectra (triceps brachii (TB), anconeus (AN)) obtained at different force levels from both ramp and stepwise isometric contractions was tested across three similar sessions performed on three different days (N = 9). Two-way ANOVAs for repeated measures did not disclose any significant differences (p > 0.05) in the value of either the MF or the MPF across the different sessions for either type of contraction. In contrast, significant changes (p < 0.05) in both the MF and the MPF were found across force levels. No significant interactions (p > 0.05) were found between the session and the force factors, for any of the analyses performed. The present results indicate that the MPF and the MF of the EMG power spectrum, taken at a specific force level, are reliable measures across sessions performed on different days. Consequently, this supports the possible use of power spectral analysis of EMG signals as an evaluation technique that could monitor changes in the neuromuscular system that can occur over a given period.

Effects of transcutaneous electrical nerve stimulation on the H-reflex of muscles of different fibre type composition.

Differential effects of repetitive stimulation of low threshold afferents on both the recruitment threshold and motoneuronal excitability of type I and type II motor units have been demonstrated. The present study was aimed at further investigating the differential effects of 30 minutes of transcutaneous electrical nerve stimulation (TENS) on the H-reflex amplitude (Hmax/2) of the Soleus (SO), gastrocnemius lateralis (GL) and medialis (GM) muscles. Eleven healthy subjects were tested in order to evaluate the effects of TENS on either the common peroneal (CPN), saphenous or sural nerve. The experimental session consisted of three consecutive 45 min periods. Within each of these periods, H-reflexes were recorded before, during and after the TENS was applied. It was hypothesized that repetitive low threshold afferent stimulation would either have inhibitory or facilitatory effects on the H-reflex amplitude of the SO or gastrocnemii muscles respectively. Non-parametric Friedman ANOVAs revealed a significant tendency (p < 0.05) toward inhibition of the H-reflex amplitude of the SO and GL muscle during TENS applied over either the CPN or sural nerve, as well as that of the GM during repetitive stimulation of the saphenous nerve. Although the present study failed to reveal any differential effects of TENS on the H-reflex amplitude of muscle on different fibre type content, the significant decrease in H-reflex observed on the triceps surae muscles during TENS applied over the CPN might have promising clinical outcomes for hyperreflexive subjects.

Weakness in patients with hemiparesis.

Clinical and experimental results are reviewed concerning muscle weakness in patients with hemiparesis after a stroke. The discussion includes the important role that alterations in the physiology of motor units, notably changes in firing rates and muscle fiber atrophy, play in the manifestation of muscle weakness. This role is compared with the lesser role that spasticity (defined as hyperactive stretch reflexes) of the antagonist muscle group appears to play in determining the weakness of agonist muscles. The contribution of other factors that result in mechanical restraint of the agonist by the antagonist (e.g., passive mechanical properties and inappropriate cocontraction) is discussed relative to muscle weakness in patients with hemiparesis.