Distribution by Scientific Domains

Kinds of Extensors

  • knee extensor
  • leg extensor

  • Terms modified by Extensors

  • extensor digitorum longu
  • extensor digitorum longu muscle
  • extensor muscle
  • extensor strength
  • extensor surface
  • extensor tendon

  • Selected Abstracts

    Vibration signals from the FT joint can induce phase transitions in both directions in motoneuron pools of the stick insect walking system

    Ulrich Bässler
    Abstract The influence of vibratory signals from the femoral chordotonal organ fCO on the activities of muscles and motoneurons in the three main leg joints of the stick insect leg, i.e., the thoraco,coxal (TC) joint, the coxa,trochanteral (CT) joint, and the femur,tibia (FT) joint, was investigated when the animal was in the active behavioral state. Vibration stimuli induced a switch in motor activity (phase transition), for example, in the FT joint motor activity switched from flexor tibiae to extensor tibiae or vice versa. Similarly, fCO vibration induced phase transitions in both directions between the motoneuron pools of the TC joint and the CT joint. There was no correlation between the directions of phase transition in different joints. Vibration stimuli presented during simultaneous fCO elongation terminated the reflex reversal motor pattern in the FT joint prematurely by activating extensor and inactivating flexor tibiae motoneurons. In legs with freely moving tibia, fCO vibration promoted phase transitions in tibial movement. Furthermore, ground vibration promoted stance,swing transitions as long as the leg was not close to its anterior extreme position during stepping. Our results provide evidence that, in the active behavioral state of the stick insect, vibration signals can access the rhythm generating or bistable networks of the three main leg joints and can promote phase transitions in motor activity in both directions. The results substantiate earlier findings on the modular structure of the single-leg walking pattern generator and indicate a new mechanism of how sensory influence can contribute to the synchronization of phase transitions in adjacent leg joints independent of the walking direction. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 125,138, 2003 [source]

    The pathophysiology of spasticity

    G. Sheean
    Spasticity is only one of several components of the upper motor neurone (UMN) syndrome, known collectively as the `positive' phenomena, that are characterized by muscle overactivity. Other components include tendon hyper-reflexia, clonus, the clasp-knife phenomenon, flexor and extensor spasms, a Babinski sign, and spastic dystonia. Spasticity is a form of hypertonia due to hyperexcitable tonic stretch reflexes. It is distinguished from rigidity by its dependence upon the speed of the muscle stretch and by the presence of other positive UMN signs. Hyperactive spinal reflexes mediate most of these positive phenomena, while others are due to disordered control of voluntary movement or abnormal efferent drive. An UMN lesion disturbs the balance of supraspinal inhibitory and excitatory inputs, producing a state of net disinhibition of the spinal reflexes. These include proprioceptive (stretch) and nociceptive (flexor withdrawal and extensor) reflexes. The clinical syndrome resulting from an UMN lesion depends more upon its location and extent, and the time since it occurred, than on the pathology of the lesion. However, the change in spinal reflex excitability cannot simply be due to an imbalance in supraspinal control. The delayed onset after the lesion and the frequent reduction in reflex excitability over time, suggests plasticity in the central nervous system. Knowledge of the electrophysiology and neurochemistry of spinal reflexes, together with the action of antispasticity drugs, helps us to understand the pathophysiology of spasticity. [source]

    Cortical and subcortical correlates of functional electrical stimulation of wrist extensor and flexor muscles revealed by fMRI

    HUMAN BRAIN MAPPING, Issue 3 2009
    Armin Blickenstorfer
    Abstract The main scope of this study was to test the feasibility and reliability of FES in a MR-environment. Functional Electrical Stimulation (FES) is used in the rehabilitation therapy of patients after stroke or spinal cord injury to improve their motor abilities. Its principle lies in applying repeated electrical stimulation to the relevant nerves or muscles for eliciting either isometric or concentric contractions of the treated muscles. In this study we report cerebral activation patterns in healthy subjects undergoing fMRI during FES stimulation. We stimulated the wrist extensor and flexor muscles in an alternating pattern while BOLD-fMRI was recorded. We used both block and event-related designs to demonstrate their feasibility for recording FES activation in the same cortical and subcortical areas. Six out of fifteen subjects repeated the experiment three times within the same session to control intraindividual variance. In both block and event-related design, the analysis revealed an activation pattern comprising the contralateral primary motor cortex, primary somatosensory cortex and premotor cortex; the ipsilateral cerebellum; bilateral secondary somatosensory cortex, the supplementary motor area and anterior cingulate cortex. Within the same subjects we observed a consistent replication of the activation pattern shown in overlapping regions centered on the peak of activation. Similar time course within these regions were demonstrated in the event-related design. Thus, both techniques demonstrate reliable activation of the sensorimotor network and eventually can be used for assessing plastic changes associated with FES rehabilitation treatment. Hum Brain Mapp, 2009. © 2008 Wiley-Liss, Inc. [source]

    Clinical Characteristics of Flexed Posture in Elderly Women

    Lara Balzini PT
    Objectives: To investigate the relationships between the severity of flexed posture (FP), skeletal fragility, and functional status level in elderly women. Design: Cross-sectional study. Setting: Geriatric rehabilitation research hospital. Participants: Sixty elderly women (aged 70,93) with FP referred to a geriatric rehabilitation department for chronic back pain without apparent comorbid conditions. Measurements: Multidimensional clinical assessment included the severity of FP (standing occiput-to-wall distance) demographic (age) and anthropometric (height, weight) data, clinical profile (number of falls, pain assessment, Mini-Mental State Examination, Comorbidity Severity Index, Geriatric Depression Scale, Multidimensional Fatigue Inventory), measures of skeletal fragility (number of vertebral fractures by spine radiograph, bone mineral density (BMD), and T-score of lumbar spine and proximal femur), muscular impairment assessment (muscle strength and length), motor performance (Short Physical Performance Battery, Performance Oriented Mobility Assessment, instrumented gait analysis), and evaluation of disability (Barthel Index, Nottingham Extended Activities of Daily Living Index). Results: The severity of FP was classified as mild in 11, moderate in 28, and severe in 21 patients. Although there were no differences between FP groups on the skeletal fragility measurements, the moderate and severe FP groups were significantly different from the mild FP group for greater pain at the level of the cervical and lumbar spine. The severe FP group was also significantly different from the mild but not the moderate FP group in the following categories: clinical profile (greater depression, reduced motivation), muscle impairment (weaker spine extensor, ankle plantarflexor, and dorsiflexor muscles; shorter pectoralis and hip flexor muscles), the motor function performance-based tests (lower scores in the balance and gait subsets of the Performance Oriented Mobility Assessment), the instrumented gait analysis (slower and wider base of support), and disability (lower score on the Nottingham Extended Activities of Daily Living Index). The total number of vertebral fractures was not associated with differences in severity of FP, demographic and anthropometric characteristics, clinical profile, muscular function, performance-based and instrumental measures of motor function, and disability, but it was associated with reduced proximal femur and lumbar spine BMD. Conclusion: The severity of FP in elderly female patients (without apparent comorbid conditions) is related to the severity of vertebral pain, emotional status, muscular impairments, and motor function but not to osteoporosis, and FP has a measurable effect on disability. In contrast, the presence of vertebral fractures in patients with FP is associated with lower BMD but not patients' clinical and functional status. Therefore, FP, back pain, and mobility problems can occur without osteoporosis. Older women with FP and vertebral pain may be candidates for rehabilitation interventions that address muscular impairments, posture, and behavior modification. Randomized controlled trials are needed to support these conclusions. [source]

    Low Serum Vitamin D Does Not Predict New Disability or Loss of Muscle Strength in Older Women

    René Verreault MD
    OBJECTIVES: To determine whether serum levels of 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) predict accelerated decline in muscular strength or onset of new disability in mobility and upper extremity functioning over a 3-year follow-up. DESIGN: A community-based prospective cohort study. PARTICIPANTS: Six hundred twenty-eight moderately to severely disabled women aged 65 and older living in the community. MEASUREMENTS: Subjects were divided into three groups of baseline 25(OH)D serum levels (deficiency: <25 nmol/L; low normal: 25,52 nmol/L; high normal: ,53 nmol/L) and into tertiles of PTH levels. Objective performance measures (hip flexor, knee extensor, and grip strengths; walking speed; and time for repeated chair stands) and disability in activities involving mobility and upper extremity function were assessed at baseline and every 6 months for 3 years. Decline in performance measures and onset of new disability were compared between 25(OH)D and PTH groups using random effects models and proportional hazards models, respectively, while adjusting for age, race, education, body mass index, baseline performance, and chronic conditions. RESULTS: The annual rate of decline over 3 years in muscular strength, walking speed, and time to perform repeated chair stands was similar across 25(OH)D groups. We observed a nonsignificantly faster decline in proximal muscle strength and walking speed with increasing PTH levels. There was no association for either measure between serum levels and the risk of incident disability in activities relating to mobility and upper extremity function. CONCLUSION: This study does not support the hypothesis that vitamin D deficiency is associated with loss in muscular strength and decline in mobility and upper extremity functioning over time in older women who were moderately to severely disabled at baseline. [source]

    Comparative anatomy of the cheek muscles within the Centromochlinae subfamily (Ostariophysi, Siluriformes, Auchenipteridae)

    Luisa Maria Sarmento-Soares
    Abstract Glanidium melanopterum Miranda Ribeiro, a typical representative of the subfamily Centromochlinae (Siluriformes: Auchenipteridae), is herein described myologically and compared to other representative species within the group, Glanidium ribeiroi, G. leopardum, Tatia neivai, T. intermedia, T. creutzbergi, Centromochlus heckelii, and C. existimatus. The structure of seven pairs of striated cephalic muscles was compared anatomically: adductor mandibulae, levator arcus palatini, dilatator operculi, adductor arcus palatini, extensor tentaculi, retractor tentaculi, and levator operculi. We observed broad adductor mandibulae muscles in both Glanidium and Tatia, catfishes with depressed heads and smaller eyes. Similarities between muscles were observed: the presence of a large aponeurotic insertion for the levator arcus palatini muscle; an adductor arcus palatini muscle whose origin spread over the orbitosphenoid, pterosphenoid, and parasphenoid; and the extensor tentaculi muscle broadly attached to the autopalatine. There is no retractor tentaculi muscle in either the Glanidium or Tatia species. On the other hand, in Centromochlus, with forms having large eyes and the tallest head, the adductor mandibulae muscles are slim; there is a thin aponeurotic or muscular insertion for the levator arcus palatini muscle; the adductor arcus palatini muscle originates from a single osseous process, forming a keel on the parasphenoid; the extensor tentaculi muscle is loosely attached to the autopalatine, permitting exclusive rotating and sliding movements between this bone and the maxillary. The retractor tentaculi muscle is connected to the maxilla through a single tendon, so that both extensor and retractor tentaculi muscles contribute to a wide array of movements of the maxillary barbels. A discussion on the differences in autopalatine-maxillary movements among the analyzed groups is given. J. Morphol. © 2005 Wiley-Liss, Inc. [source]

    Repeatability of joint proprioception and muscle torque assessment in healthy children and in children diagnosed with hypermobility syndrome

    Francis A. Fatoye MSc
    Abstract Background:,Impairment of joint proprioception in patients with hypermobility syndrome (HMS) has been well documented. Both joint proprioception and muscle torque are commonly assessed in patients with musculoskeletal complaints. It is unknown, however, if these measures change significantly on repeated application in healthy children and in children with HMS. Aim:,To investigate the between-days repeatability of joint proprioception and muscle torque in these groups. Methods:,Twenty children (10 healthy and 10 with HMS), aged eight to 15 years, were assessed on two separate occasions (one week apart) for joint kinaesthesia (JK), joint position sense (JPS), and the extensor and knee flexor muscle torque of the knee. JK was measured using threshold to detection of passive movement. JPS was measured using the absolute angular error (AAE; the absolute difference between the target and perceived angles). Knee extensor and flexor muscle torque was normalized to body weight. Results:,Intra-class correlation coefficients (ICC) for JK, extensor and flexor muscle torque were excellent in both groups (range 0.83 to 0.98). However, ICC values for JPS tests were poor to moderate in the two groups (range 0.18 to 0.56). 95% limits of agreement (LOA) were narrow in both cohorts for JK and muscle torque (indicating low systematic error) but wide for the JPS tests. 95% LOA also demonstrated that the measuring instruments used in this study had low between-days systematic error. Conclusions:,Based on ICC and 95% LOA, the repeatability of JK and muscle torque measurements was excellent in both healthy children and those with HMS. The JPS test can only be assessed with poor to moderate repeatability. The use of the JPS test in these children should be undertaken with caution. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    Clinical analyses of atopic dermatitis in the aged

    Ryoji TANEI
    ABSTRACT The aim of the present study was to analyze the characteristics of atopic dermatitis (AD) in the senile phase. Subjects were comprised of 16 patients investigated for clinical features, serum immunoglobulin (Ig)E levels and skin manifestations. Mean age was 76.9 ± 6.2 years (range, 68,87), with a man : woman ratio of 3:1. Mean age at onset was 67.7 ± 15.7 years. Eight patients (50%) had personal histories of chronic eczema until the young adult phase and three patients (18.8%) showed the classic course of child AD. Eczematous erythroderma in 10 patients (62.5%) and unclassified chronic eczema in five patients (31.3%) were the predominant clinical presentations. Mean total IgE level in sera of the 16 patients was 8810 ± 13 511 IU/mL (range, 5,53 605). Fourteen patients showed positive results for antigen-specific IgE antibodies, and the mean total IgE level for these patients was 10 056 ± 14 044 IU/mL. Specific IgE to the main antigen, Dermatophagoides farinae, was observed in 12 patients (85.7%), representing the principal antibody in eight patients (57.1%). Eczematous dermatitis manifested predominantly in the face and neck, trunk and extensor and flexure sites of extremities, and less commonly in the antecubital and popliteal areas. Other stigmata of AD were observed as follows: red face in 10 patients (62.5%); Hertoghe's sign in six (37.5%); goose-skin in four (25%); facial pallor in three (18.8%); and dirty neck in one (6.3%). These results indicate that senile-type AD represents a characteristic subgroup of AD that appears in the last stage of life in AD patients. [source]

    Intraspinally mediated state-dependent enhancement of motoneurone excitability during fictive scratch in the adult decerebrate cat

    Kevin E. Power
    This is the first study to report on the increase in motoneurone excitability during fictive scratch in adult decerebrate cats. Intracellular recordings from antidromically identified motoneurones revealed a decrease in the voltage threshold for spike initiation (Vth), a suppression of motoneurone afterhyperpolarization and activation of voltage-dependent excitation at the onset of scratch. These state-dependent changes recovered within 10,20 s after scratch and could be evoked after acute transection of the spinal cord at C1. Thus, there is a powerful intraspinal system that can quickly and reversibly re-configure neuronal excitability during spinal network activation. Fictive scratch was evoked in spinal intact and transected decerebrate preparations by stroking the pinnae following topical curare application to the dorsal cervical spinal cord and neuromuscular block. Hyperpolarization of Vth occurred (mean ,5.8 mV) in about 80% of ipsilateral flexor, extensor or bifunctional motoneurones during fictive scratch. The decrease in Vth began before any scratch-evoked motoneurone activity as well as during the initial phase in which extensors are tonically hyperpolarized. The Vth of contralateral extensors depolarized by a mean of +3.7 mV during the tonic contralateral extensor activity accompanying ipsilateral scratch. There was a consistent and substantial reduction of afterhyperpolarization amplitude without large increases in motoneurone conductance in both spinal intact and transected preparations. Depolarizing current injection increased, and hyperpolarization decreased the amplitude of rhythmic scratch drive potentials in acute spinal preparations indicating that the spinal scratch-generating network can activate voltage-dependent conductances in motoneurones. The enhanced excitability in spinal preparations associated with fictive scratch indicates the existence of previously unrecognized, intraspinal mechanisms increasing motoneurone excitability. [source]

    Reliability of knee extension and flexion measurements using the Con-Trex isokinetic dynamometer

    Nicola A. Maffiuletti
    Summary The aim of this study was to evaluate the reliability of isokinetic and isometric assessments of the knee extensor and the flexor muscle function using the Con-Trex isokinetic dynamometer. Thirty healthy subjects (15 males, 15 females) were tested and retested 7 days later for maximal strength (isokinetic peak torque, work, power and angle of peak torque as well as isometric maximal voluntary contraction torque and rate of torque development) and fatigue (per cent loss and linear slope of torque and work across a series of 20 contractions). For both the knee extensor and the flexor muscle groups, all strength data , except angle of peak torque , demonstrated moderate-to-high reliability, with intraclass correlation coefficients (ICC) higher than 0·86. The highest reliability was observed for concentric peak torque of the knee extensor muscles (ICC = 0·99). Test,retest reliability of fatigue variables was moderate for the knee extensor (ICC range 0·84,0·89) and insufficient-to-moderate for the knee flexor muscles (ICC range 0·78,0·81). The more reliable index of muscle fatigue was the linear slope of the decline in work output. These findings establish the reliability of isokinetic and isometric measurements using the Con-Trex machine. [source]

    Differential age-related changes in motor unit properties between elbow flexors and extensors

    ACTA PHYSIOLOGICA, Issue 1 2010
    B. H. Dalton
    Abstract Aim:, Healthy adult ageing of the human neuromuscular system is comprised of changes that include atrophy, weakness and slowed movements with reduced spinal motor neurone output expressed by lower motor unit discharge rates (MUDRs). The latter observation has been obtained mostly from hand and lower limb muscles. The purpose was to determine the extent to which elbow flexor and extensor contractile properties, and MUDRs in six old (83 ± 4 years) and six young (24 ± 1 years) men were affected by age, and whether any adaptations were similar for both muscle groups. Methods:, Maximal isometric voluntary contraction (MVC), voluntary activation, twitch contractile properties, force,frequency relationship and MUDRs from sub-maximal to maximal intensities were assessed in the elbow flexors and extensors. Results:, Both flexor and extensor MVCs were significantly (P < 0.05) less (,42% and ,46% respectively) in the old than in the young. Contractile speeds and the force,frequency relationship did not show any age-related differences (P > 0.05). For the elbow flexors contraction duration was ,139 ms and for the extensors it was ,127 ms for both age groups (P > 0.05). The mean MUDRs from 25% MVC to maximum were lower (,10% to ,36%) in the old than in the young (P < 0.01). These age-related differences were larger for biceps (Cohen's d = 8.25) than triceps (Cohen's d = 4.79) brachii. Conclusion:, Thus, at least for proximal upper limb muscles, mean maximal MUDR reductions with healthy adult ageing are muscle specific and not strongly related to contractile speed. [source]

    Myotonic dystrophy: muscle involvement in relation to disease type and size of expanded CTG-repeat sequence

    Anna-Karin Kroksmark PT Msc
    This study aimed to: classify a cohort of children and adolescents with myotonic dystrophy (dystrophia myotonica: DM) into congenital and childhood onset forms; estimate CTG expansion size; and quantify muscle strength, contractures, and motor function in children with DM and compare results with those of controls. Participants were clinically examined, medical records were reviewed, and isometric muscle strength, contractures, and motor function were measured. Participants were: 42 children with DM (18 females, 24 males; mean age 8y 9mo [SD 4y 7mo], range 10mo to 17y) and 42 age- and sex-matched, healthy controls. Children with DM were divided into three groups: severe congenital (n=13), mild congenital (n=15), and childhood (n=14). Children with childhood DM were significantly weaker than controls (wrist and ankle dorsiflexors [p=0.0044, p=0.0044 respectively]; hip abductors and flexors [p=0.0464, p=0.0217]; and knee flexors and extensors: [p=0.0382, p=0.0033]). Children with mild congenital DM were significantly weaker than controls in all assessed muscle groups Contractures and skeletal deformities were more frequent at time of investigation than at birth, suggesting that foot and spine deformities in particular increase over time. Motor function score was significantly lower for children with DM than for controls. Children with severe congenital DM had the lowest motor function, with correlation between motor function and size of CTG repeat (p=-0.743). Children found jumping, heel standing, and head lifting the most difficult items to perform but few had difficulty walking, running, or stair climbing. DM in children is a heterogeneous disorder with a wide spectrum of muscle involvement, and owing to increased risk of contractures and skeletal deformities, regular follow-ups are recommended. [source]

    Adults with cerebral palsy: walking ability after progressive strength training

    C Andersson MSc PT
    The purpose of this study was to evaluate effects of a progressive strength training programme on walking ability in adults with cerebral palsy. Ten individuals with spastic diplegia (seven males, three females; mean age 31, range 23,44 years) participated twice a week over 10 weeks. Seven individuals with spastic diplegia (four males, three females; mean age 33, range 25,47 years) who did not receive strength training served as controls. All individuals were ambulatory but motor ability ranged from functional walkers to individuals who always required walking aids and used a wheelchair regularly. Significant improvements were seen in isometric strength (hip extensorsp=0.006, hip abductors p=0.01), and in isokinetic concentric work at 30/s (knee extensors p=0.02) but not in eccentric work. Results also showed significant improvements in Gross Motor Function Measure (GMFM) dimensions D and E (p=0.005), walking velocity (p=0.005), and Timed Up and Go (p=0.01). There was no increase in spasticity for those who underwent strength training. Individuals in the control group did not show any significant improvement in any measured variable. The groups were small, however, and there was no significant difference between the groups in any measured variable. These findings suggest that a 10-week progressive strength training programme improves muscle strength and walking ability without increasing spasticity. [source]

    Computerized Tremor Analysis of Valproate-induced Tremor: A Comparative Study of Controlled-release versus Conventional Valproate

    EPILEPSIA, Issue 2 2005
    Martina Rinnerthaler
    Summary:,Purpose: Valproate (VPA) induces postural tremor in 6,45% of patients. The characteristics of VPA-induced tremor have not yet been quantitatively assessed, and it is not known whether tremor prevalence or severity is affected by VPA formulation (controlled-release CR-VPA vs. conventional VPA). The aim of this study was quantitatively to assess tremor in epilepsy patients receiving VPA and to compare the effects of two VPA formulations (CR-VPA vs. VPA) on tremor severity. Methods: In a prospective study, 18 consecutive patients with newly diagnosed focal or generalized epilepsy were assigned to receive alternately either VPA (n = 10) or CR-VPA (n = 8) monotherapy. Computerized tremor analysis was performed at baseline 1 day before initiating VPA treatment and repeated after a seizure-free period of ,8 weeks, during which VPA doses had remained stable. Rest and postural tremor were recorded by accelerometry, and surface electromyograms (EMGs) were recorded from the wrist flexors and extensors. Results: At baseline, the two groups had similar postural tremor amplitudes. At follow-up, the CR-VPA group had remained at the same level, whereas VPA subjects exhibited a significant increase in tremor amplitudes (p < 0.05) despite comparable VPA doses and comparable plasma VPA concentrations at the time of tremor testing. Conclusions: This is the first study to assess quantitatively VPA-induced tremor by standardized tremor analysis. These results suggest that CR-VPA may cause less tremorigenic activity as compared with standard VPA. The mechanisms underlying this difference are unclear but may include greater peak,trough variation with VPA than with CR-VPA. [source]

    A unique case of limb-girdle muscular dystrophy type 2A carrying novel compound heterozygous mutations in the human CAPN3 gene

    E. Matsubara
    A unique sib pair afflicted by limb girdle muscular dystrophy type 2A (LGMD2A) is described showing a slowly progressive autosomal recessive type of muscular dystrophy with onset in the third and fourth decades. The patients had early asymmetric muscle involvement characterized by prominent biceps brachii atrophy with sparing of the knee extensors. Additional findings included elevation of serum creatine kinase level, myopathic EMG changes and dystrophic type of pathology on muscle biopsy. Asymmetrical wasting of muscles in the extremities exhibited uniform and highly selective CT imaging patterns. RNA and DNA analyses confirmed novel compound heterozygous mutations (R147X/L212F) in the human CAPN3 gene. [source]

    Corticospinal control of antagonistic muscles in the cat

    Christian Ethier
    Abstract We recently suggested that movement-related inter-joint muscle synergies are recruited by selected excitation and selected release from inhibition of cortical points. Here we asked whether a similar cortical mechanism operates in the functional linking of antagonistic muscles. To this end experiments were done on ketamine-anesthetized cats. Intracortical microstimulation (ICMS) and intramuscular electromyographic recordings were used to find and characterize wrist, elbow and shoulder antagonistic motor cortical points. Simultaneous ICMS applied at two cortical points, each evoking activity in one of a pair of antagonistic muscles, produced co-contraction of antagonistic muscle pairs. However, we found an obvious asymmetry in the strength of reciprocal inhibition; it was always significantly stronger on physiological extensors than flexors. Following intravenous injection of a single bolus of strychnine, a cortical point at which only a physiological flexor was previously activated also elicited simultaneous activation of its antagonist. This demonstrates that antagonistic corticospinal neurons are closely grouped, or intermingled. To test whether releasing a cortical point from inhibition allows it to be functionally linked with an antagonistic cortical point, one of three GABAA receptor antagonists, bicuculline, gabazine or picrotoxin, was injected iontophoretically at one cortical point while stimulation was applied to an antagonistic cortical point. This coupling always resulted in co-contraction of the represented antagonistic muscles. Thus, antagonistic motor cortical points are linked by excitatory intracortical connections held in check by local GABAergic inhibition, with reciprocal inhibition occurring at the spinal level. Importantly, the asymmetry of cortically mediated reciprocal inhibition would appear significantly to bias muscle maps obtained by ICMS in favor of physiological flexors. [source]

    Differential maturation of motoneurons innervating ankle flexor and extensor muscles in the neonatal rat

    L Vinay
    Abstract The first postnatal week is a critical period for the development of posture in the rat. The use of ankle extensor muscles in postural reactions increases during this period. Changes in excitability of motoneurons are probably an important factor underlying this maturation. The aim of this study was to identify whether variations in the maturation exist between motor pools innervating antagonistic muscles. Intracellular recordings in the in vitro brain stem,spinal cord preparation of neonatal rats (from postnatal day 0,5) were used to examine the developmental changes in excitability of motoneurons innervating the ankle flexors (F-MNs) and the antigravity ankle extensors (E-MNs). No significant difference in resting potential, action potential threshold, input resistance or rheobase was observed at birth. The age-related increase in rheobase was more pronounced for F-MNs than for E-MNs. The development of discharge properties of E-MNs lagged behind that of F-MNs. More F-MNs than E-MNs were able to fire repetitively in response to current injection at birth. F-MNs discharged at a higher frequency than E-MNs at all ages. Differences in the duration of action potential afterhyperpolarization accounted, at least partly, for the differences in discharge frequency between E-MNs and F-MNs at birth, and for the age-related increase in firing rate. These results suggest that E-MNs are more immature at birth than F-MNs and that there is a differential development of motoneurons innervating antagonistic muscles. This may be a critical factor in the development of posture and locomotion. [source]

    Exercise Heat Stress does not Reduce Central Activation to non-exercised Human Skeletal Muscle

    Julian Saboisky
    In this study we measured the central activation ratio (CAR) of the leg extensors and the elbow flexor muscles before and after exhaustive exercise in the heat to determine whether exercise-induced hyperthermia affects the CNS drive to exercised (leg extensors) and/or non-exercised (forearm flexors) muscle groups. Thirteen subjects exercised at fixed intensities representative of a percentage of peak power output (PPO) for 10 min periods (50%, 40%, 60%, 50%) and then at 75% PPO until exhaustion in ambient conditions of 39.3 ± 0.8 °C and 60.0 ± 0.8% relative humidity. Before and immediately following exercise subjects performed a series of maximal voluntary contractions (MVCs) with the leg extensors (exercised muscles) and forearm flexors (non-exercised muscles). The degree of voluntary activation during the sustained MVCs was assessed by superimposing electrical stimulation to the femoral nerve and the biceps brachii. Exercise to exhaustion increased the rectal temperature from 37.2 ± 0.2 to 38.8 ± 0.2 °C (P < 0.0001). The mean heart rate at the end of exercise to exhaustion was 192 ± 3 beats min,1. Leg extensor voluntary force was significantly reduced from 595 ± 143 to 509 ± 105 N following exercise-induced hyperthermia but forearm flexor force was similar before and after exercise. The CAR of the leg extensors decreased from 94.2 ± 1.3% before exercise to 91.7 ± 1.5% (P < 0.02) following exercise-induced hyperthermia. However, the CAR for the forearm flexors remained at similar levels before and after exercise. The data suggest that the central nervous system selectively reduces central activation to specific skeletal muscles as a consequence of exercise-induced hyperthermia. [source]

    Isokinetic Leg Muscle Strength in Older Americans and Its Relationship to a Standardized Walk Test: Data from the National Health and Nutrition Examination Survey 1999,2000

    Yechiam Ostchega PhD
    Objectives: To describe isokinetic knee extensor muscle strength in older U.S. men and women by age and race/ethnicity and to ascertain its relationship to a standard, timed walking-speed test. Setting: The U.S. National Health and Nutrition Examination Survey (NHANES) 1999,2000. Design: A cross-sectional nationally representative health examination survey. Participants: All surveyed persons aged 50 and older (N=1,499) who performed muscle strength and timed walk examinations in the NHANES mobile examination center. Measurements: Concentric peak torque (strength) of the knee extensors at 1.05 rads/ s,1 velocity and a 6-m walk timed in seconds. Results: Knee extensor strength was inversely associated with age (P<.01), and women had less knee extensor muscle strength than men (P<.01). After adjustment for standing height, no significant difference in muscle strength was found across the three race/ethnicity groups (Mexican Americans, non-Hispanic blacks, and non-Hispanic whites) for men or women. After adjustment for age, race/ethnicity, weight, and height, increasing knee extensor strength was associated with significant increases in meters walked per second (P<.01). Conclusion: Knee extensor muscle strength is affected by age and sex but not by race/ethnicity and it is significantly associated with timed walk. [source]

    Muscle Strength After Resistance Training Is Inversely Correlated with Baseline Levels of Soluble Tumor Necrosis Factor Receptors in the Oldest Old

    Helle Bruunsgaard MD
    Objectives:, To test the hypothesis that physical exercise induces an antiinflammatory response that is associated with reduced chronic activation of the tumor necrosis factor (TNF)-alpha system in frail elders and that the increase in muscle strength after resistance training is limited by systemic low-grade inflammation. Design:, A 12-week controlled resistance-training study. Setting:, Nursing homes in Copenhagen, Denmark. Participants:, Twenty-one frail nursing home residents aged 86 to 95 completed the study. Intervention:, Ten participants were randomized to a program of resistance training of knee extensors and flexors three times a week for 12 weeks; the remaining 11 participants served as a control group who joined social activities supervised by an occupation therapist. Measurements:, Muscle strength, plasma levels of TNF-,, soluble TNF receptor (sTNFR)-1, and interleukin (IL)-6 were measured before and at the end of the intervention period. Results:, The training program improved muscle strength but did not affect plasma levels of TNF-, and sTNFR-I or IL-6. However, plasma levels of sTNFR-I at baseline were inversely correlated with the increase in muscle strength. Conclusion:, Low-grade activation of the TNF system could limit the increase in muscle strength after resistance training in the oldest old. Furthermore, data suggest that theantiinflammatory response induced by 12 weeks of resistance training is not sufficient to reduce chronic activation of the TNF system, but the small sample size limited this interpretation. [source]

    The Relationship Between Lower Body Strength and Obstructed Gait in Community-Dwelling Older Adults

    Ecosse L. Lamoureux PhD
    OBJECTIVES: To determine the relationship between lower body strength of community-dwelling older adults and the time to negotiate obstructed gait tasks. DESIGN: A correlational study. SETTING: The Biomechanics Laboratory, Deakin University, Australia. PARTICIPANTS: Twenty-nine women and 16 men aged 62 to 88 were recruited using advertisements placed in local newspapers. The participants were independent community dwellers, healthy and functionally mobile. MEASUREMENTS: Maximal isometric strength of the knee extensors and dynamic strength of the hip extensors, hip flexors, hip adductors, hip abductors, knee extensors, knee flexors, and ankle plantar flexors were assessed. The times to negotiate four obstructed gait tasks at three progressively challenging levels on an obstacle course and to complete the course were recorded. The relationship between strength and the crossing times was explored using linear regression models. RESULTS: Significant associations between the seven strength measures and the times to negotiate each gait task and to walk the entire course at each level were obtained (r = ,0.38 to ,0.55; P < .05). In addition, the percentage of the variance explained by strength (R2), consistently increased as a function of the progressively challenging level. This increase was particularly marked for the stepping over task (R2 = 19.3%, 25.0%, and 27.2%, for levels 1, 2, and 3, respectively) and the raised surface condition (R2 = 17.1%, 21.1%, and 30.8%, for levels 1, 2, and 3, respectively). CONCLUSION: The findings of the study showed that strength is a critical requirement for obstructed locomotion. That the magnitude of the association increased as a function of the challenging levels suggests that intervention programs aimed at improving strength would potentially be effective in helping community-dwelling older adults negotiate environmental gait challenges. J Am Geriatr Soc 50:468,473, 2002. [source]

    Muscle moment arms of the gibbon hind limb: implications for hylobatid locomotion

    JOURNAL OF ANATOMY, Issue 4 2010
    Anthony J. Channon
    Abstract Muscles facilitate skeletal movement via the production of a torque or moment about a joint. The magnitude of the moment produced depends on both the force of muscular contraction and the size of the moment arm used to rotate the joint. Hence, larger muscle moment arms generate larger joint torques and forces at the point of application. The moment arms of a number of gibbon hind limb muscles were measured on four cadaveric specimens (one Hylobates lar, one H. moloch and two H. syndactylus). The tendon travel technique was used, utilizing an electro-goniometer and a linear voltage displacement transducer. The data were analysed using a technique based on a differentiated cubic spline and normalized to remove the effect of body size. The data demonstrated a functional differentiation between voluminous muscles with short fascicles having small muscle moment arms and muscles with longer fascicles and comparatively smaller physiological cross-sectional area having longer muscle moment arms. The functional implications of these particular configurations were simulated using a simple geometric fascicle strain model that predicts that the rectus femoris and gastrocnemius muscles are more likely to act primarily at their distal joints (knee and ankle, respectively) because they have short fascicles. The data also show that the main hip and knee extensors maintain a very small moment arm throughout the range of joint angles seen in the locomotion of gibbons, which (coupled to voluminous, short-fascicled muscles) might help facilitate rapid joint rotation during powerful movements. [source]

    Mechanical constraints on the functional morphology of the gibbon hind limb

    JOURNAL OF ANATOMY, Issue 4 2009
    Anthony J. Channon
    Abstract Gibbons utilize a number of locomotor modes in the wild, including bipedalism, leaping and, most of all, brachiation. Each locomotor mode puts specific constraints on the morphology of the animal; in some cases these may be complementary, whereas in others they may conflict. Despite several studies of the locomotor biomechanics of gibbons, very little is known about the musculoskeletal architecture of the limbs. In this study, we present quantitative anatomical data of the hind limb for four species of gibbon (Hylobates lar, H. moloch, H. pileatus and Symphalangus syndactylus). Muscle mass and fascicle lengths were obtained from all of the major hind limb muscles and the physiological cross-sectional area was calculated and scaled to remove the effect of body size. The results clearly indicate that, for all of the species studied, the major hip, knee and ankle extensors are short-fascicled and pennate. The major hip and knee flexors, however, are long-fascicled, parallel muscles with relatively small physiological cross-sectional areas. We hypothesize that the short-fascicled muscles could be coupled with a power-amplifying mechanism and are predominantly useful in leaping. The long-fascicled knee and hip flexors are adapted for a wide range of joint postures and can play a role in flexing the legs during brachiation. [source]

    Musculoskeletal Rehabilitation in Osteoporosis: A Review,

    Michael Pfeifer
    Abstract Measures of musculoskeletal rehabilitation play an integral part in the management of patients with increased fracture risk because of osteoporosis or extraskeletal risk factors. This article delineates current scientific evidence concerning nonpharmacologic approaches that are used in conjunction with pharmacotherapy for prevention and management of osteoporosis. Fractures caused by osteoporotic fragility may be prevented with multidisciplinary intervention programs, including education, environmental modifications, aids, and implementation of individually tailored exercise programs, which are proved to reduce falls and fall-related injuries. In addition, strengthening of the paraspinal muscles may not only maintain BMD but also reduce the risk of vertebral fractures. Given the strong interaction between osteoporosis and falls, selection of patients for prevention of fracture should be based on bone-related factors and on risk factors for falls. Rehabilitation after vertebral fracture includes proprioceptive dynamic posture training, which decreases kyphotic posturing through recruitment of back extensors and thus reduces pain, improves mobility, and leads to a better quality of life. A newly developed orthosis increases back extensor strength and decreases body sway as a risk factor for falls and fall-related fractures. Hip fractures may be prevented by hip protectors, and exercise programs can improve strength and mobility in patients with hip fracture. So far, there is no conclusive evidence that coordinated multidisciplinary inpatient rehabilitation is more effective than conventional hospital care with no rehabilitation professionals involved for older patients with hip fracture. Further studies are needed to evaluate the effect of combined bone- and fall-directed strategies in patients with osteoporosis and an increased propensity to falls. [source]

    Effect of 6-Month Whole Body Vibration Training on Hip Density, Muscle Strength, and Postural Control in Postmenopausal Women: A Randomized Controlled Pilot Study,

    Sabine MP Verschueren
    Abstract High-frequency mechanical strain seems to stimulate bone strength in animals. In this randomized controlled trial, hip BMD was measured in postmenopausal women after a 24-week whole body vibration (WBV) training program. Vibration training significantly increased BMD of the hip. These findings suggest that WBV training might be useful in the prevention of osteoporosis. Introduction: High-frequency mechanical strain has been shown to stimulate bone strength in different animal models. However, the effects of vibration exercise on the human skeleton have rarely been studied. Particularly in postmenopausal women,who are most at risk of developing osteoporosis,randomized controlled data on the safety and efficacy of vibration loading are lacking. The aim of this randomized controlled trial was to assess the musculoskeletal effects of high-frequency loading by means of whole body vibration (WBV) in postmenopausal women. Materials and Methods: Seventy volunteers (age, 58,74 years) were randomly assigned to a whole body vibration training group (WBV, n = 25), a resistance training group (RES, n = 22), or a control group (CON, n = 23). The WBV group and the RES group trained three times weekly for 24 weeks. The WBV group performed static and dynamic knee-extensor exercises on a vibration platform (35,40 Hz, 2.28,5.09g), which mechanically loaded the bone and evoked reflexive muscle contractions. The RES group trained knee extensors by dynamic leg press and leg extension exercises, increasing from low (20 RM) to high (8 RM) resistance. The CON group did not participate in any training. Hip bone density was measured using DXA at baseline and after the 6-month intervention. Isometric and dynamic strength were measured by means of a motor-driven dynamometer. Data were analyzed by means of repeated measures ANOVA. Results: No vibration-related side effects were observed. Vibration training improved isometric and dynamic muscle strength (+15% and + 16%, respectively; p < 0.01) and also significantly increased BMD of the hip (+0.93%, p < 0.05). No changes in hip BMD were observed in women participating in resistance training or age-matched controls (,0.60% and ,0.62%, respectively; not significant). Serum markers of bone turnover did not change in any of the groups. Conclusion: These findings suggest that WBV training may be a feasible and effective way to modify well-recognized risk factors for falls and fractures in older women and support the need for further human studies. [source]

    Impaired heteronymous somatosensory motor cortical inhibition in dystonia

    MOVEMENT DISORDERS, Issue 11 2003
    Laura Bertolasi MD
    Abstract A typical pathophysiological abnormality in dystonia is cocontraction of antagonist muscles, with impaired reciprocal inhibitory mechanisms in the spinal cord. Recent experimental data have shown that inhibitory interactions between antagonist muscles have also a parallel control at the level of the sensorimotor cortex. The aim of this work was to study heteronymous effects of a median nerve stimulus on the corticospinal projections to forearm muscles in dystonia. We used the technique of antagonist cortical inhibition, which assesses the conditioning effect of median nerve afferent input on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in ipsilateral forearm extensor muscles at rest. Nine healthy subjects and 10 patients with torsion dystonia participated in the study. MEPs and somatosensory evoked potentials were normal in patients. In healthy subjects, median nerve stimulation at 15- to 18-msec intervals inhibited the test MEPs in forearm extensors. In dystonic patients, median nerve stimulation delivered at the same conditioning,test intervals elicited significantly less inhibition of the test MEP. On the whole, these data suggest an impaired sensory,motor integration in dystonia and, more specifically, the decreased antagonistic cortical inhibition could suggest that functional interactions between antagonist muscles are primarily impaired at the cortical level. © 2003 Movement Disorder Society [source]

    Linearity and reliability of the mechanomyographic amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles

    MUSCLE AND NERVE, Issue 3 2010
    Matthew S. Stock MS
    Abstract The purpose of this investigation was to examine the linearity and reliability of the mechanomyographic (MMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Nine healthy men and 11 healthy women performed submaximal to maximal, concentric, isokinetic muscle actions of the leg extensors at 30° s,1 on two occasions. Surface MMG signals were detected from the VL, RF, and VM of the dominant thigh during both trials. The ranges of the coefficients of determination for the MMG amplitude versus dynamic torque relationships were 0.01,0.94 for the VL, 0.01,0.84 for the RF, and 0.19,0.96 for the VM. The intraclass correlation coefficients for the linear MMG amplitude versus torque slope coefficients were 0.823 (VL), 0.792 (RF), and 0.927 (VM). These results indicate that, when analyzed for individual subjects, the MMG amplitude versus dynamic torque relationships demonstrated inconsistent linearity. When using MMG in the clinical setting, dynamic muscle actions of the superficial quadriceps femoris muscles do not appear to be appropriate for assessing changes in muscle function during strength training. Muscle Nerve, 2009 [source]

    Development and Experimental Identification of a Biomechanical Model of the Trunk for Functional Electrical Stimulation Control in Paraplegia

    NEUROMODULATION, Issue 4 2008
    Ingenieur Michele Vanoncini
    ABSTRACT Objectives., Theoretic modeling and experimental studies suggest that functional electrical stimulation (FES) can improve trunk balance in spinal cord injured subjects. This can have a positive impact on daily life, increasing the volume of bimanual workspace, improving sitting posture, and wheelchair propulsion. A closed loop controller for the stimulation is desirable, as it can potentially decrease muscle fatigue and offer better rejection to disturbances. This paper proposes a biomechanical model of the human trunk, and a procedure for its identification, to be used for the future development of FES controllers. The advantage over previous models resides in the simplicity of the solution proposed, which makes it possible to identify the model just before a stimulation session (taking into account the variability of the muscle response to the FES). Materials and Methods., The structure of the model is based on previous research on FES and muscle physiology. Some details could not be inferred from previous studies, and were determined from experimental data. Experiments with a paraplegic volunteer were conducted in order to measure the moments exerted by the trunk-passive tissues and artificially stimulated muscles. Data for model identification and validation also were collected. Results., Using the proposed structure and identification procedure, the model could adequately reproduce the moments exerted during the experiments. The study reveals that the stimulated trunk extensors can exert maximal moment when the trunk is in the upright position. In contrast, previous studies show that able-bodied subjects can exert maximal trunk extension when flexed forward. Conclusions., The proposed model and identification procedure are a successful first step toward the development of a model-based controller for trunk FES. The model also gives information on the trunk in unique conditions, normally not observable in able-bodied subjects (ie, subject only to extensor muscles contraction). [source]

    Upper limb musculoskeletal stress markers among middle Holocene foragers of Siberia's Cis-Baikal region

    Angela R. Lieverse
    Abstract This evaluation of musculoskeletal stress markers (MSMs) in the Cis-Baikal focuses on upper limb activity reconstruction among the region's middle Holocene foragers, particularly as it pertains to adaptation and cultural change. The five cemetery populations investigated represent two discrete groups separated by an 800,1,000 year hiatus: the Early Neolithic (8000,7000/6800 cal. BP) Kitoi culture and the Late Neolithic/Bronze Age (6000/5800,4000 cal. BP) Isakovo-Serovo-Glaskovo (ISG) cultural complex. Twenty-four upper limb MSMs are investigated not only to gain a better understanding of activity throughout the middle Holocene, but also to independently assess the relative distinctiveness of Kitoi and ISG adaptive regimes. Results reveal higher heterogeneity in overall activity levels among Early Neolithic populations,with Kitoi males exhibiting more pronounced upper limb MSMs than both contemporary females and ISG males,but relative constancy during the Late Neolithic/Bronze Age, regardless of sex or possible status. On the other hand, activity patterns seem to have varied more during the latter period, with the supinator being ranked high among the ISG, but not the Kitoi, and forearm flexors and extensors being ranked generally low only among ISG females. Upper limb rank patterning does not distinguish Early Neolithic males, suggesting that their higher MSM scores reflect differences in the degree (intensity and/or duration), rather than the type, of activity employed. Finally, for both Kitoi and ISG peoples, activity patterns,especially the consistently high-ranked costoclavicular ligament and deltoid and pectoralis major muscles,appear to be consistent with watercraft use. Am J Phys Anthropol, 2009. © 2008 Wiley-Liss, Inc. [source]

    Intraspinally mediated state-dependent enhancement of motoneurone excitability during fictive scratch in the adult decerebrate cat

    Kevin E. Power
    This is the first study to report on the increase in motoneurone excitability during fictive scratch in adult decerebrate cats. Intracellular recordings from antidromically identified motoneurones revealed a decrease in the voltage threshold for spike initiation (Vth), a suppression of motoneurone afterhyperpolarization and activation of voltage-dependent excitation at the onset of scratch. These state-dependent changes recovered within 10,20 s after scratch and could be evoked after acute transection of the spinal cord at C1. Thus, there is a powerful intraspinal system that can quickly and reversibly re-configure neuronal excitability during spinal network activation. Fictive scratch was evoked in spinal intact and transected decerebrate preparations by stroking the pinnae following topical curare application to the dorsal cervical spinal cord and neuromuscular block. Hyperpolarization of Vth occurred (mean ,5.8 mV) in about 80% of ipsilateral flexor, extensor or bifunctional motoneurones during fictive scratch. The decrease in Vth began before any scratch-evoked motoneurone activity as well as during the initial phase in which extensors are tonically hyperpolarized. The Vth of contralateral extensors depolarized by a mean of +3.7 mV during the tonic contralateral extensor activity accompanying ipsilateral scratch. There was a consistent and substantial reduction of afterhyperpolarization amplitude without large increases in motoneurone conductance in both spinal intact and transected preparations. Depolarizing current injection increased, and hyperpolarization decreased the amplitude of rhythmic scratch drive potentials in acute spinal preparations indicating that the spinal scratch-generating network can activate voltage-dependent conductances in motoneurones. The enhanced excitability in spinal preparations associated with fictive scratch indicates the existence of previously unrecognized, intraspinal mechanisms increasing motoneurone excitability. [source]