			Home About us Contact

Leg Muscles (leg + muscle)

Distribution by Scientific Domains

Life Sciences	69%
Medical Sciences	30%

Distribution within Life Sciences

Anatomy & Physiology	62%
Neuroscience	11%

Selected Abstracts

Effects of Ischaemia on Subsequent Exercise-Induced Oxygen Uptake Kinetics in Healthy Adult Humans

EXPERIMENTAL PHYSIOLOGY, Issue 2 2002
Michael L. Walsh
Leg muscles were occluded (33 kPa) prior to exercise to determine whether the induced metabolic changes, and reactive hyperaemia upon occlusion release just prior to the exercise, would accelerate the subsequent oxygen consumption (V,O2) response. Eight subjects performed double bouts (6 min duration, 6 min rest in-between) of square wave leg cycle ergometry both below and above their lactate threshold (LT). Prior to exercise, large blood pressure cuffs were put around the upper thighs. Occlusion durations were 0 min (control), 5 min and 10 min. Ischaemia was terminated within 5 s prior to exercise onset. Heart rate, V,O2, ventilatory rate (V,E), electromyogram (EMG) and haemoglobin/myoglobin (Hb/Mb) saturation were recorded continuously. Single exponential modelling demonstrated that, compared to control (time constant = 53.9 ± 13.9 s), ischaemia quickened the V,O2 response (P < 0.05) for the first bout of exercise above LT (time constant = 48.3 ± 14.5 s) but not to any other exercise bout below or above LT. The 3-6 min integrated EMG (iEMG) slope was correlated to the 3-6 min V,O2 slope (r = 0.73). Hb/Mb saturation verified the ischaemia but did not show a consistent relation to the V,O2 time course. Reactive hyperaemia induced a faster V,O2 response for work rates above LT. The effect, while significant, was not large considering the expected favourable metabolic and circulatory changes induced by ischaemia. [source]

Arm and leg substrate utilization and muscle adaptation after prolonged low-intensity training

ACTA PHYSIOLOGICA, Issue 4 2010
J. W. Helge
Abstract This review will focus on current data where substrate metabolism in arm and leg muscle is investigated and discuss the presence of higher carbohydrate oxidation and lactate release observed during arm compared with leg exercise. Furthermore, a basis for a possible difference in substrate partitioning between endogenous and exogenous substrate during arm and leg exercise will be debated. Moreover the review will probe if differences between arm and leg muscle are merely a result of different training status rather than a qualitative difference in limb substrate regulation. Along this line the review will address the available studies on low-intensity training performed separately with arm or legs or as whole-body training to evaluate if this leads to different adaptations in arm and leg muscle resulting in different substrate utilization patterns during separate arm or leg exercise at comparable workloads. Finally, the influence and capacity of low-intensity training to influence metabolic fitness in the face of a limited effect on aerobic fitness will be challenged. [source]

Proton and sodium MRI assessment of fluid level in calf tissue

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006
Chun S. Zuo PhD
Abstract Purpose To investigate the feasibility of using 1H and 23Na MRI to detect fluid levels in the lower leg muscle. Materials and Methods Proton and sodium MRI was applied to detect body fluid levels in the lower leg muscles of 18 healthy young male subjects at 3T and 4T. The paradigms under investigation were a postural change from sitting upright to lying supine, and saline infusion. Results We found that the average proton MR signal in gastrocnemius and soleus muscles were reduced following the postural change by 3.5% ± 1.4% (P < 0.05) and rose following saline infusion by 3.7% ± 0.9% (P < 0.01). More dramatically, the sodium MR signal decreased by 7.1% ± 1.2% (P < 0.01) following the postural change and increased following saline infusion by 12% ± 3.8% (P < 0.05). The ratio of intra- to extracellular fluid levels was 1.6 ± 0.5 for the subjects based on the acquired proton and sodium data. Conclusion Our results indicate that proton and sodium MRI can be used to assess fluid levels in the lower extremities, and this technique may be applied to evaluate fluid retention. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source]

Sodium MRI using a density-adapted 3D radial acquisition technique

MAGNETIC RESONANCE IN MEDICINE, Issue 6 2009
Armin M. Nagel
Abstract A density-adapted three-dimensional radial projection reconstruction pulse sequence is presented which provides a more efficient k -space sampling than conventional three-dimensional projection reconstruction sequences. The gradients of the density-adapted three-dimensional radial projection reconstruction pulse sequence are designed such that the averaged sampling density in each spherical shell of k -space is constant. Due to hardware restrictions, an inner sphere of k -space is sampled without density adaption. This approach benefits from both the straightforward handling of conventional three-dimensional projection reconstruction sequence trajectories and an enhanced signal-to-noise ratio (SNR) efficiency akin to the commonly used three-dimensional twisted projection imaging trajectories. Benefits for low SNR applications, when compared to conventional three-dimensional projection reconstruction sequences, are demonstrated with the example of sodium imaging. In simulations of the point-spread function, the SNR of small objects is increased by a factor 1.66 for the density-adapted three-dimensional radial projection reconstruction pulse sequence sequence. Using analytical and experimental phantoms, it is shown that the density-adapted three-dimensional radial projection reconstruction pulse sequence allows higher resolutions and is more robust in the presence of field inhomogeneities. High-quality in vivo images of the healthy human leg muscle and the healthy human brain are acquired. For equivalent scan times, the SNR is up to a factor of 1.8 higher and anatomic details are better resolved using density-adapted three-dimensional radial projection reconstruction pulse sequence. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source]

Glucose clearance is higher in arm than leg muscle in type 2 diabetes

THE JOURNAL OF PHYSIOLOGY, Issue 2 2005
David B. Olsen
Insulin-mediated glucose clearance (GC) is diminished in type 2 diabetes. Skeletal muscle has been estimated to account for essentially all of the impairment. Such estimations were based on leg muscle and extrapolated to whole body muscle mass. However, skeletal muscle is not a uniform tissue and insulin resistance may not be evenly distributed. We measured basal and insulin-mediated (1 pmol min,1 kg,1) GC simultaneously in the arm and leg in type 2 diabetes patients (TYPE 2) and controls (CON) (n= 6 for both). During the clamp arterio-venous glucose extraction was higher in CON versus TYPE 2 in the arm (6.9 ± 1.0 versus 4.7 ± 0.8%; mean ±s.e.m.; P= 0.029), but not in the leg (4.2 ± 0.8 versus 3.1 ± 0.6%). Blood flow was not different between CON and TYPE 2 but was higher (P < 0.05) in arm versus leg (CON: 74 ± 8 versus 56 ± 5; TYPE 2: 87 ± 9 versus 43 ± 6 ml min,1 kg,1 muscle, respectively). At basal, CON had 84% higher arm GC (P= 0.012) and 87% higher leg GC (P= 0.016) compared with TYPE 2. During clamp, the difference between CON and TYPE 2 in arm GC was diminished to 54% but maintained at 80% in the leg. In conclusion, this study shows that glucose clearance is higher in arm than leg muscles, regardless of insulin resistance, which may indicate better preserved insulin sensitivity in arm than leg muscle in type 2 diabetes. [source]

A new class of neurotoxin from wasp venom slows inactivation of sodium current

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2000
Yoshinori Sahara
Abstract The effects of ,-pompilidotoxin (,-PMTX), a new neurotoxin isolated from the venom of a solitary wasp, were studied on the neuromuscular synapses in lobster walking leg and the rat trigeminal ganglion (TG) neurons. Paired intracellular recordings from the presynaptic axon terminals and the innervating lobster leg muscles revealed that ,-PMTX induced long bursts of action potentials in the presynaptic axon, which resulted in facilitated excitatory and inhibitory synaptic transmission. The action of ,-PMTX was distinct from that of other known facilitatory presynaptic toxins, including sea anemone toxins and ,-scorpion toxins, which modify the fast inactivation of Na+ current. We further characterized the action of ,-PMTX on Na+ channels by whole-cell recordings from rat trigeminal neurons. We found that ,-PMTX slowed the Na+ channels inactivation process without changing the peak current,voltage relationship or the activation time course of tetrodotoxin (TTX)-sensitive Na+ currents, and that ,-PMTX had voltage-dependent effects on the rate of recovery from Na+ current inactivation and deactivating tail currents. The results suggest that ,-PMTX slows or blocks conformational changes required for fast inactivation of the Na+ channels on the extracellular surface. The simple structure of ,-PMTX, consisting of 13 amino acids, would be advantageous for understanding the functional architecture of Na+ channel protein. [source]

Leptin receptor 170 kDa (OB-R170) protein expression is reduced in obese human skeletal muscle: a potential mechanism of leptin resistance

EXPERIMENTAL PHYSIOLOGY, Issue 1 2010
T. Fuentes
To examine whether obesity-associated leptin resistance could be due to down-regulation of leptin receptors (OB-Rs) and/or up-regulation of suppressor of cytokine signalling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) in skeletal muscle, which blunt janus kinase 2-dependent leptin signalling and signal transducer and activator of transcription 3 (STAT3) phosphorylation and reduce AMP-activated protein kinase (AMPK) and acetyl-coenzyme A carboxylase (ACC) phosphorylation. Deltoid and vastus lateralis muscle biopsies were obtained from 20 men: 10 non-obese control subjects (mean ±s.d. age, 31 ± 5 years; height, 184 ± 9 cm; weight, 91 ± 13 kg; and percentage body fat, 24.8 ± 5.8%) and 10 obese (age, 30 ± 7 years; height, 184 ± 8 cm; weight, 115 ± 8 kg; and percentage body fat, 34.9 ± 5.1%). Skeletal muscle OB-R170 (OB-R long isoform) protein expression was 28 and 25% lower (both P < 0.05) in arm and leg muscles, respectively, of obese men compared with control subjects. In normal-weight subjects, SOCS3 protein expression, and STAT3, AMPK, and ACC, phosphorylation, were similar in the deltoid and vastus lateralis muscles. In obese subjects, the deltoid muscle had a greater amount of leptin receptors than the vastus lateralis, whilst SOCS3 protein expression was increased and basal STAT3, AMPK, and ACC, phosphorylation levels were reduced in the vastus lateralis compared with the deltoid muscle (all P < 0.05). In summary, skeletal muscle leptin receptors and leptin signalling are reduced in obesity, particularly in the leg muscles. [source]

The training stimulus experienced by the leg muscles during cycling in humans

EXPERIMENTAL PHYSIOLOGY, Issue 6 2009
Jamie S. McPhee
Considerable variability exists between people in their health- and performance-related adaptations to conventional endurance training. We hypothesized that some of this variability might be due to differences in the training stimulus received by the working muscles. In 71 young sedentary women we observed large variations in the ratio of one-leg cycling muscle aerobic capacity to two-leg cycling whole-body maximal oxygen uptake (; Ratio1:2; range 0.58,0.96). The variability in Ratio1:2 was primarily due to differences between people in one-leg (r= 0.71, P < 0.0005) and was not related to two-leg (r= 0.15, P= 0.209). Magnetic resonance imaging (n= 30) and muscle biopsy sampling (n= 20) revealed that one-leg was mainly determined by muscle volume (r= 0.73, P < 0.0005) rather than muscle fibre type or oxidative capacity. A high one-leg was associated with favourable lipoprotein profiles (P= 0.033, n= 24) but this was not the case for two-leg . Calculations based on these data suggest that conventional two-leg exercise at 70% requires subjects with the lowest Ratio1:2 to work their legs at 60% of single-leg , whilst those with the highest Ratio1:2 work their legs at only 36% of maximum. It was concluded that endurance training carried out according to current guidelines will result in highly variable training stimuli for the leg muscles and variable magnitudes of adaptation. These conclusions have implications for the prescription of exercise to improve health and for investigations into the genetic basis of muscle adaptations. [source]

Changes in body mass and organ size during wing moult in non-breeding greylag geese Anser anser

JOURNAL OF AVIAN BIOLOGY, Issue 6 2005
Anthony D. Fox
The "cost-benefit" hypothesis states that specific body organs show mass changes consistent with a trade-off between the importance of their function and cost of their maintenance. We tested four predictions from this hypothesis using data on non-breeding greylag geese Anser anser during the course of remigial moult: namely that (i) pectoral muscles and heart would atrophy followed by hypertrophy, (ii) leg muscles would hypertrophy followed by atrophy, (iii) that digestive organs and liver would atrophy followed by hypertrophy and (iv) fat depots be depleted. Dissection of geese captured on three different dates during wing moult on the Danish island of Saltholm provided data on locomotory muscles and digestive organ size that confirmed these predictions. Locomotory organs associated with flight showed initial atrophy (a maximum loss of 23% of the initial pectoral muscle mass and 37% heart tissue) followed by hypertrophy as birds regained the powers of flight. Locomotory organs associated with running (leg muscles, since geese habitually run to the safety of water from predator-type stimuli) showed initial hypertrophy (a maximum gain of 37% over initial mass) followed by atrophy. The intestines and liver showed initial atrophy (41% and 37% respectively), consistent with observed reductions in daily time spent feeding during moult, followed by hypertrophy. The majority of the 22% loss in overall body mass (mean 760 g) during the flightless period involved fat utilisation, apparently consumed to meet shortfalls between daily energetic needs and observed rates of exogenous intake. The results support the hypothesis that such phenotypic plasticity in size of fat stores, locomotor and digestive organs can be interpreted as an evolutionary adaptation to meet the conflicting needs of the wing moult. [source]

Proton and sodium MRI assessment of fluid level in calf tissue

Lower leg muscle atrophy in ankle osteoarthritis

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 12 2006
Victor Valderrabano
Abstract The aim of this study was to determine changes in the lower leg muscles associated with ankle osteoarthritis. Fifteen unilateral ankle osteoarthritis patients and fifteen age-gender-matched normal subjects were assessed with clinical [osteoarthritis latency time, pain, alignment, AOFAS ankle score, ankle range of motion (ROM), calf circumference], radiological (ankle osteoarthritis grading), and muscular-physiological parameters [isometric maximal voluntary ankle torque, surface electromyography of the anterior tibial (AT), medial gastrocnemius (MG), soleus (SO), and peroneus longus (PL) muscle]. The osteoarthritis patients had increased pain (6.8 points) and reduced AOFAS score (33.7 points) compared to the control group. Compared to the contralateral healthy leg, the arthritic leg showed reduced mean dorsi-/plantar flexion ROM (16.0°), reduced mean calf circumference (2.1 cm), smaller mean dorsiflexion (16.4 Nm) and plantar flexion (15.8 Nm) torques, lower mean electromyography frequency for all muscles (AT ,22.6 Hz; MG ,27.3 Hz; SO ,25.9 Hz; PL ,28.5 Hz), and lower mean electromyography intensity in the AT [,28.0,×,103 (µv)2], MG [,13.3,×,103 (µv)2], and PL [,12.8,×,103 (µv)2]. SO mean electromyography intensity was not significantly changed [+2.0,×,103 (µv)2]. Unilateral ankle osteoarthritis is associated with atrophic changes of the lower leg muscles. This study supports previous observations on muscle dysfunction in knee osteoarthritis. © 2006 Orthopaedic Research Society. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source]

The role of M. popliteus in unpredictable and in self-initiated balance provocations

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2006
Ann-Katrin Stensdotter
Abstract The purpose of this study was to determine whether m. popliteus (POP) activity would contribute to the control of knee joint position in unpredictable and in self-initiated provocations of standing balance. Ten healthy women (age 25.2,±,4.5 years, means and SD) without known knee pathology were tested for postural reactions (1) to unpredictable support surface translations in anterior and posterior directions, and (2) in self-initiated balance provocations in a reaction time (RT) forward reach-and-grip task. Electromyographic activity was recorded from POP and other leg muscles plus the deltoid muscle. Three-dimensional kinematics were captured for the knee joint and the body centre of mass was calculated. POP was active first of all the muscles recorded, regardless of translation direction, and knee joint movements elicited were either knee extension or external rotation of the tibia. In the RT task, the POP was active after initiation of reaching movement, and there was little consistency in the kinematic response. POP activity was not direction specific in response to support surface translation, but appeared triggered from reactive knee joint movement. The response to the support-surface translation suggests that POP served to control knee joint position rather than posture. In the RT task, we could not deduce whether POP activity was attributed to knee joint control or to postural control. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:524,530, 2006 [source]

Congenital hypomyelination neuropathy in a newborn infant: unusual cause of diaphragmatic and vocal cord paralyses

JOURNAL OF THE PERIPHERAL NERVOUS SYSTEM, Issue 2 2002
JS Hahn
We report a case of congenital hypomyelination neuropathy presenting at birth. The infant had generalized hypotonia and weakness. There was decreased respiratory effort along with a right phrenic nerve and left vocal cord paralyses. Tongue fasciculations were present. Deep tendon reflexes were absent in the upper extremities and hypoactive (1+) in the lower extremities. Magnetic resonance imaging of the head revealed no intracranial abnormalities, including normal cerebral myelination. Nerve conduction study showed absence of motor and sensory action potentials in the hands when the nerves in the upper limbs were stimulated. A motor response could be elicited only in the proximal leg muscles. Needle electromyography study was normal in the proximal limb muscles, but showed active denervation in the distal muscles of the arm and leg. These findings were thought to be consistent with a length-dependent sensorimotor peripheral polyneuropathy of axonal type with greater denervation of the distal muscles. A biopsy of the quadriceps muscle showed mild variability in fiber diameter, but no group typing or group atrophy. The muscle fibers showed no intrinsic abnormalities. Biopsy of the sural nerve showed scattered axons with very thin myelin sheaths. There was also a nearly complete loss of large diameter myelinated fibers. No onion bulb formations were noted. These findings were thought to be consistent with congenital hypomyelination neuropathy with a component of axonopathy. DNA analysis for identification of previously characterized mutations in the genes MPZ, PMP22, and EGR2 was negative. Several attempts at extubation failed and the infant became increasingly ventilator-dependent with increasing episodes of desaturation and hypercapnea. He also developed increasing weakness and decreased movement of all extremities. He underwent surgery at 2 months of age for placement of a gastrostomy tube and a tracheostomy. He was discharged from the hospital on a ventilator at 6 months of age. The infant was 13 months old at the time of submission of this report. Although he appears cognitively normal, he remains profoundly hypotonic and is on a home ventilator. There was no evidence of progressive weakness. Congenital hypomyelination neuropathy is a rare form of neonatal neuropathy that should be considered in the differential diagnosis of a newborn with profound hypotonia and weakness. It appears to be a heterogeneous disorder with some of the cases being caused by specific genetic mutations. [source]

Gabapentin can improve postural stability and quality of life in primary orthostatic tremor

MOVEMENT DISORDERS, Issue 7 2005
Julian P. Rodrigues MD
Abstract Primary orthostatic tremor (OT) is characterized by leg tremor and instability on standing. High frequency (13,18 Hz) tremor bursting is present in leg muscles during stance, and posturography has shown greater than normal sway. We report on an open-label add-on study of gabapentin in 6 patients with OT. Six patients were studied with surface electromyography, force platform posturography, and a modified Parkinson's disease questionnaire (PDQ-39) quality of life (QOL) scale before and during treatment with gabapentin 300 mg t.d.s. If on other medications for OT, these were continued unchanged. Of the 6 patients, 4 reported a subjective benefit of 50 to 75% with gabapentin, 3 of whom showed reduced tremor amplitude and postural sway of up to 70%. Dynamic balance improved in all 3 patients who completed the protocol. QOL data from 5 patients showed improvement in all cases. No adverse effects were noted. Gabapentin may improve tremor, stability, and QOL in patients with OT, and symptomatic response correlated with a reduction in tremor amplitude and postural sway. The findings confirm previous reports of symptomatic benefit with gabapentin and provide justification for larger controlled clinical trials. Further work is required to establish the optimal dosage and to validate the methods used to quantify the response to treatment. © 2005 Movement Disorder Society [source]

Comparison of oxidative capacity among leg muscles in humans using gated 31P 2-D chemical shift imaging

NMR IN BIOMEDICINE, Issue 10 2009
Sean C. Forbes
Abstract In many small animals there are distinct differences in fiber-type composition among limb muscles, and these differences typically correspond to marked disparities in the oxidative capacities. However, whether there are similar differences in the oxidative capacity among leg muscles in humans is less clear. The purpose of this study was to compare the rate of phosphocreatine (PCr) recovery, a functional in vivo marker of oxidative capacity, in the lateral and medial gastrocnemius, soleus, and the anterior compartment of the leg (primarily the tibialis anterior) of humans. Subjects performed plantar flexion and dorsiflexion gated exercise protocols consisting of 70 sets of three rapid dynamic contractions (<2.86,s) at 20,s intervals (total: 23.3,min). Starting after the sixth set of contractions, 31P 2-D CSI (8,×,8 matrix, 14,16,cm FOV, 3,cm slice, TR 2.86,s) were acquired via a linear transmit/receive surface coil using a GE 3T Excite System. The CSI data were zero-filled (32,×,32) and a single FID was produced for each time point in the lateral and medial gastrocnemius, soleus, and anterior compartment. The time constant for PCr recovery was calculated from ,,=,-,t/ln[D/(D,+,Q)], where Q is the percentage change in PCr due to contraction during the steady-state portion of the protocol, D the additional drop in PCr from rest, and ,t is the interval between contractions. The , of PCr recovery was longer (p,<,0.05) in the anterior compartment (32,±,3,s) than in the lateral (23,±,2,s) and medial gastrocnemius muscles (24,±,3,s) and the soleus (22,±,3,s) muscles. These findings suggest that the oxidative capacity is lower in the anterior compartment than in the triceps surae muscles and is consistent with the notion that fiber-type phenotypes vary among the leg muscles of humans. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Actions of motor neurons and leg muscles in jumping by planthopper insects (hemiptera, issidae)

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 8 2010
Malcolm Burrows
Abstract To understand the catapult mechanism that propels jumping in a planthopper insect, the innervation and action of key muscles were analyzed. The large trochanteral depressor muscle, M133b,c, is innervated by two motor neurons and by two dorsal unpaired median (DUM) neurons, all with axons in N3C. A smaller depressor muscle, M133a, is innervated by two neurons, one with a large-diameter cell body, a large, blind-ending dendrite, and a giant ovoid, axon measuring 50 ,m by 30 ,m in nerve N5A. The trochanteral levator muscles (M132) and (M131) are innervated by N4 and N3B, respectively. The actions of these muscles in a restrained jump were divisible into a three-phase pattern. First, both hind legs were moved into a cocked position by high-frequency bursts of spikes in the levator muscles lasting about 0.5 seconds. Second, and once both legs were cocked, M133b,c received a long continuous sequence of motor spikes, but the two levators spiked only sporadically. The spikes in the two motor neurons to M133b,c on one side were closely coupled to each other and to the spikes on the other side. If one hind leg was cocked then the spikes only occurred in motor neurons to that side. The final phase was the jump movement itself, which occurred when the depressor spikes ceased and which lasted 1 ms. Muscles 133b,c activated synchronously on both sides, are responsible for generating the power, and M133a and its giant neuron may play a role in triggering the release of a jump. J. Comp. Neurol. 518:1349,1369, 2010. © 2009 Wiley-Liss, Inc. [source]

The effects of experimental muscle and skin pain on the static stretch sensitivity of human muscle spindles in relaxed leg muscles

THE JOURNAL OF PHYSIOLOGY, Issue 11 2008
Ingvars Birznieks
Animal studies have shown that noxious inputs onto ,-motoneurons can cause an increase in the activity of muscle spindles, and it has been proposed that this causes a fusimotor-driven increase in muscle stiffness that is believed to underlie many chronic pain syndromes. To test whether experimental pain also acts on the fusimotor system in humans, unitary recordings were made from 19 spindle afferents (12 Ia, 7 II) located in the ankle and toe extensors or peronei muscles of awake human subjects. Muscle pain was induced by bolus intramuscular injection of 0.5 ml 5% hypertonic saline into tibialis anterior (TA); skin pain was induced by 0.2 ml injection into the overlying skin. Changes in fusimotor drive to the muscle spindles were inferred from changes in the mean discharge frequency and discharge variability of spindle endings in relaxed muscle. During muscle pain no afferents increased their discharge activity: seven afferents (5 Ia, 2 II) showed a decrease and six (4 Ia, 2 II) afferents were not affected. During skin pain of 13 afferents discharge rate increased in one (Ia) and decreased in two (1 Ia, 1 II). On average, the overall discharge rate decreased during muscle pain by 6.1% (P < 0.05; Wilcoxon), but remained essentially the same during skin pain. There was no detectable correlation between subjective pain level and the small change in discharge rate of muscle spindles. Irrespective of the type of pain, discharge variability parameters were not influenced (P > 0.05; Wilcoxon). We conclude that, contrary to the ,vicious cycle' hypothesis, acute activation of muscle or skin nociceptors does not cause a reflex increase in fusimotor drive in humans. Rather, our results are more aligned with the pain adaptation model, based on clinical studies predicting pain-induced reductions of agonist muscle activity. [source]

Glucose clearance is higher in arm than leg muscle in type 2 diabetes

Phase-dependent and task-dependent modulation of stretch reflexes during rhythmical hand tasks in humans

THE JOURNAL OF PHYSIOLOGY, Issue 3 2005
Ruiping Xia
Phase-dependent and task-dependent modulation of reflexes has been extensively demonstrated in leg muscles during locomotory activity. In contrast, the modulation of reflex responses of hand muscles during rhythmic movement is poorly documented. The objective of this study was to determine whether comparable reflex modulation occurs in muscles controlling finger motions during rhythmic, fine-motor tasks akin to handwriting. Twelve healthy subjects performed two rhythmic tasks while reflexes were evoked by mechanical perturbations applied at various phases of each task. Electromyograms (EMGs) were recorded from four hand muscles, and reflexes were averaged during each task relative to the movement phase. Stretch reflexes in all four muscles were found to be modulated in amplitude with respect to the phase of the rhythmic tasks, and also to vary distinctly with the tasks being conducted. The extent and pattern of reflex modulation differed between muscles in the same task, and between tasks for the same muscle. Muscles with a primary role in each task showed a higher correlation between reflex response and background EMG than other muscles. The results suggest that the modulation patterns observed may reflect optimal strategies of central,peripheral interactions in controlling the performance of fine-motor tasks. As with comparable studies on locomotion, the phase-dependency of the stretch reflexes implies a dynamically fluctuating role of proprioceptive feedback in the control of the hand muscles. The clear task-dependency is also consistent with a dynamic interaction of sensory feedback and central programming, presumably adapted to facilitate the successful performance of the different fine-motor tasks. [source]

Visual and non-visual control of landing movements in humans

THE JOURNAL OF PHYSIOLOGY, Issue 1 2001
Marco Santello
1The role of vision in controlling leg muscle activation in landing from a drop was investigated. Subjects (n= 8) performed 10 drops from four heights (0.2, 0.4, 0.6 and 0.8 m) with and without vision. Drop height was maintained constant throughout each block of trials to allow adaptation. The aim of the study was to assess the extent to which proprioceptive and vestibular information could substitute for the lack of vision in adapting landing movements to different heights. 2At the final stages of the movement, subjects experienced similar peak centre of body mass (CM) displacements and joint rotations, regardless of the availability of vision. This implies that subjects were able to adapt the control of landing to different heights. The amplitude and timing of electromyographic signals from the leg muscles scaled to drop height in a similar fashion with and without vision. 3However, variables measured throughout the execution of the movement indicated important differences. Without vision, landings were characterised by 10 % larger ground reaction forces, 10 % smaller knee joint rotations, different time lags between peak joint rotations, and more variable ground reaction forces and times to peak CM displacement. 4We conclude that non-visual sensory information (a) could not fully compensate for the lack of continuous visual feedback and (b) this non-visual information was used to reorganise the motor output. These results suggest that vision is important for the very accurate timing of muscle activity onset and the kinematics of landing. [source]