Lower Limbs In Humans Research Articles

Dynamics of Changes in Muscle Architecture, Force, Strength-Velocity Properties of the Muscles of Lower Limbs in Humans under the Influence of a Three Week Unloading

The present study examined the hypothesis that significant alterations in antigravity muscle architecture would occur with dry water immersion (DI) and that some structural changes may be seen in postural muscles because of the overall decrease in physical activity. Ten men (age (mean ± SE) – 24.5 ± 3.9 years, height – 176.1 ± 1.2 m, mass – 71.1 ± 3.4 kg) volunteered for the study. The healthy men underwent of DI for 21 days. All subjects did not use physical training during the exposure. The contractile properties of the muscle ankle extensors and flexors (maximal voluntary contraction (MVC) and strength-velocity relationship) were evaluated using an isokinetic dynamometer. The internal architecture of the triceps surae muscle of its two heads (medial (MG) and lateral (LG) gastrocnemius muscles) was determined by in vivo ultrasound (US) at ankle angles of –15° (dorsiflexion), 0° (neutral anatomical position), and +30° (plantarflexion) with an angle in the knee joint of 0°. In each position, longitudinal US of MG and LG were obtained at the proximal levels 30% (MG and LG) of the distance between the popliteal crease and the center of the lateral malleolus. US images were detected at rest for each ankle position, and the fiber length (Lf) and pennation angle (Θf) relative to the aponeurosis were determined. After DI the MVC muscle ankle extensors decreased from 122.6 ± 43.1 to 99.5 ± 22.7 N (19%). Although there was a significant no change in dorsiflexion. After DI with the ankle angle increasing from –15° to +30°, Lf changes from 43 ± 1 to 32 ± 2 mm (25.6%, p 0.01) for MG and from 45 ± 2 to 34 ± 1 mm (24.4%, p 0.01) for LG, and Θf increased from 21° ± 1° to 26° ± 2° (23.8%) for MG and from 14° ± 1° to 18° ± 2° (28.6%) for LG. Collectively, the present data suggest that the architecture and contractile capacity of human pennate muscle are interrelated, in vivo. The finding that amongst the antigravity muscles, the MG deteriorated to a greater extent than the LG is possibly related to the differences in relative load that this muscle possibly experiences during daily loading. Different Lf and Θf, and their changes by after unloading, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses. Structural muscle changes can be considered as an adaptive process, in response to disuse.

Skeletal Structure and Training Adaptability of Athletes Based on Biomechanical Analysis.

According to the kinematics analysis of the human body, a set of exoskeleton mechanical structures is designed to imitate the physiological structure and movement characteristics of the lower limbs of humans. To study the biomechanical characteristics of the exoskeleton in two different phases during walking and to provide a research basis for the design and optimization of the exoskeleton. Doctors and engineers are actively committed to the basic understanding and improvement of the tissue characteristics, structure, and function of the human musculoskeletal system. Firstly, according to the gait analysis of the lower limbs, the exoskeleton mechanical structure is designed by using three-dimensional modeling software. After the solid model is generated, the assembly, meshing, and element attribute assignment are carried out by using finite element software. And the face-to-face contact relationship between each building is established, and the stress distribution of the exoskeleton is simulated and analyzed. The stress distribution of the exoskeleton under different working conditions is significantly different. Since the calculation does not take into account uncertainties such as shocks that may occur during walking, it is necessary to consider and multiply a certain safety factor when designing the optimized exoskeleton.

An ePIC Assessment of Quadriceps Motor Unit Firing Patterns During Isometric Knee Extension: A High Density Surface Electromyography Study

Motor neurons (MNs) are the ‘final common path’ through which all motor commands must converge to generate motor output. MN firing patterns are readily accessible in humans due to the one‐to‐one spike ratio between MNs and the muscle fibers that they innervate. MNs are, therefore, the only neurons in the body in which the firing patterns can be directly associated with functional behaviors. Observed firing patterns vary systematically across the muscles of the human body, reflecting the interplay between the synaptic organization of motor commands, structure of the musculoskeletal system, and diversity of motor tasks. The goal of our lab is to develop a “human motor output map”, using newly developed high‐density surface electromyography (EMG) array electrodes that discriminate motor unit firing patterns based on convolutive blind source separation. Two main advantages of these arrays are: 1) the relatively high motor unit yield, and 2) the fact that motor units can be recorded with minimally invasive methods. We estimate the level of neuromodulatory drive (estimated persistent inward current, i.e. ePIC) to MNs using the well‐established paired motor unit analysis technique, which compares the onset and offset of a high‐threshold motor unit with respect to a low‐threshold unit and quantifies discharge rate hysteresis (ΔF). Preliminary studies in our lab suggest a strong proximal to distal gradient along the arm for motor unit firing patterns. Proximal muscles (i.e. Anterior Deltoid, Triceps Brachii, and Biceps Brachii) generate motor unit firing patterns consistent with high neuromodulatory drive (i.e. ΔF = ~4–6 spikes/s), whereas distal muscles (i.e. finger flexors or extensors, and intrinsic hand muscles) show lower neuromodulatory drive (i.e. ΔF = ~2–3 spikes/s). In the legs, the ankle dorsi‐ and plantarflexors generate motor unit firing patterns with moderate neuromodulatory drive (i.e. ΔF = ~3–5 spikes/s). However, it is unknown whether the proximal to distal gradient found in the arm also occurs in the leg. In the present study, we used high‐density surface EMG arrays to decompose motor unit firing patterns of three of the four quadriceps muscles: vastus lateralis, rectus femoris, and vastus medialis oblique. Decomposition of the EMG yielded ~7 motor units per trial, which is fewer than the decomposed motor unit yield of the lower leg, though still considerably higher than more traditional in‐dwelling EMG electrodes used for motor unit discrimination. Our data indicate that activation of the quadriceps generates motor unit firing patterns consistent with moderate neuromodulatory drive (i.e. ΔF = ~3.5 spikes/s), similar to the more distal muscles. These findings suggest that the proximal to distal gradient in motor unit firing patterns observed in the upper limbs is not analogous in the lower limbs of humans, likely reflecting the differences in functional organization between the arms and legs in bipeds.

Contributions of Limb Joints to Energy Absorption during Landing in Cats.

There is a high risk of serious injury to the lower limbs in a human drop landing. However, cats are able to jump from the same heights without any sign of injury, which is attributed to the excellent performance of their limbs in attenuating the impact forces. The bionic study of the falling cat landing may therefore contribute to improve the landing-shock absorbing ability of lower limbs in humans. However, the contributions of cat limb joints to energy absorption remain unknown. Accordingly, a motion capture system and plantar pressure measurement platform were used to measure the joint angles and vertical ground reaction forces of jumping cats, respectively. Based on the inverse dynamics, the joint angular velocities, moments, powers, and work from different landing heights were calculated to expound the synergistic mechanism and the dominant muscle groups of cat limb joints. The results show that the buffering durations of the forelimbs exhibit no significant difference with increasing height while the hindlimbs play a greater role than the forelimbs in absorbing energy when jumping from a higher platform. Furthermore, the joint angles and angular velocities exhibit similar variations, indicating that a generalized motor program can be adopted to activate limb joints for different landing heights. Additionally, the elbow and hip are recognized as major contributors to energy absorption during landing. This experimental study can accordingly provide biological inspiration for new approaches to prevent human lower limb injuries.

Femoral vascular conductance and peroneal muscle sympathetic nerve activity responses to acute epidural spinal cord stimulation in humans.

What is the central question of this research? Does acute spinal cord stimulation increase vascular conductance and decrease muscle sympathetic nerve activity in the lower limbs of humans? What is the main finding and its importance? Acute spinal cord stimulation led to a rapid rise in femoral vascular conductance, and peroneal muscle sympathetic nerve activity demonstrated a delayed reduction that was not associated with the initial increase in femoral vascular conductance. These findings suggest that neural mechanisms in addition to attenuated muscle sympathetic nerve activity might be involved in the initial increase in femoral vascular conductance during acute spinal cord stimulation. Clinical cases have indicated an increase in peripheral blood flow after continuous epidural spinal cord stimulation (SCS) and that reduced muscle sympathetic nerve activity (MSNA) might be a potential mechanism. However, no studies in humans have directly examined the effects of acute SCS (<60min) on vascular conductance and MSNA. In study 1, we tested the hypothesis that acute SCS (<60min) of the thoracic spine would lead to increased common femoral vascular conductance, but not brachial vascular conductance, in 11 patients who previously underwent surgical SCS implantation for management of neuropathic pain. Throughout 60min of SCS, common femoral artery conductance was elevated and significantly different from brachial artery conductance [in millilitres per minute: 15min, change (Δ) 26±37 versus Δ-2±19%; 30min, Δ28±45 versus Δ0±26%; 45min, Δ48±43 versus Δ2±21%; 60min, Δ36±61 versus Δ1±24%; and 15min post-SCS, Δ51±64 versus Δ6±33%; P=0.013]. A similar examination in a patient with cervical SCS revealed minimal changes in vascular conductance. In study 2, we examined whether acute SCS reduces peroneal MSNA in a subset of SCS patients (n=5). The MSNA burst incidence in response to acute SCS gradually declined and was significantly reduced at 45 and 60min of SCS (in bursts per 100heart beats: 15min, Δ-1±12%; 30min, Δ-14±12%; 45min, Δ-19±16%; 60min, Δ-24±18%; and 15min post-SCS: Δ-11±7%; P=0.015). These data demonstrate that acute SCS rapidly increases femoral vascular conductance and reduces peroneal MSNA. The gradual reduction in peroneal MSNA observed during acute SCS suggests that neural mechanisms in addition to attenuated MSNA might be involved in the acute increase in femoral vascular conductance.

Laterality of Static and Dynamic Balance Abilities during One-leg Standing

Lower human limbs may not show laterality, differing from preferential use of upper limbs, because both legs are generally used at the same time. This study examined laterality of static and dynamic balance abilities during one-leg standing. The subjects were 100 healthy male university students (age 19.6 ± 2.4 years，height 172.3 ± 6.2 cm, weight 64.8 ± 8.5 kg). All subjects were judged right-leg dominant based on a previous survey. They underwent static and dynamic balance tests with each lower limb. A total path length during one-leg standing on a fixed stabilometer for the static balance test and an omnidirectional stability index during one-leg standing on an unstable platform (DYJOC Board) for the dynamic balance test was each used as an evaluation parameter. The mean of two trials was used as a representative value in each test. Intraclass correlation coefficients (ICCs) in both balance tests were very high (ICC = 0.75-0.91). A non-significant difference between means of dominant and non-dominant legs was found in both tests; their correlations were significant and high (0.93 and 0.75). In addition, a correlation between dynamic and static balance tests in both legs was found be significant but low (0.21-0.25). In conclusion, the laterality is not found in the static and dynamic balance abilities during one-leg standing evaluated by the tests selected in this study, and the relation between both abilities is negligible size.

Relationship between jumping abilities and skeletal muscle architecture of lower limbs in humans: Systematic review and meta-analysis

The aim of this study was to examine the influence of skeletal muscle architecture (SMA) features measured by 2-D ultrasonography on jumping performance in humans.A systematic review and meta-analysis was conducted, registry number: CRD42016043602.The scientific literature was systematically searched in eight databases, last run on March 14th, 2017. Cross-sectional studies focused on the association between SMA features and vertical jumping performance were selected. A random-effects model was used to analyze the influence of lower-limb SMA and maximal jump height. A total of 11 studies were included in the qualitative synthesis and 6 studies were selected for meta-analysis. 250 correlations were reviewed across studies. The vast majority were either not statistically significant (185; 74%), weak or very weak (169; 68%) for different jump modalities; counter-movement jump (CMJ), squat jump (SJ), and drop jump. There was insufficient data to perform meta-analysis on muscles other than vastus lateralis for CMJ and SJ. The meta-analyses did not yield any significant association between vastus lateralis SMA and SJ height. Only a significant overall association was shown between vastus lateralis thickness and CMJ height (summary-r = 0.28; 95% confidence interval (CI) = −0.05 to 0.48; p = .059) for a 90% CI level. No differences were found between summary-r coefficients for SMA parameters and jump height during both jumps (CMJ: χ2 = 2.43; df = 2; p = .30; SJ: χ2 = 0.45; df = 2; p = .80) with a low heterogeneity ratio. Current evidence does not suggest a great influence of lower-limb SMA on vertical jumping performance in humans.

Metrological Evaluation of a Novel Medical Robot and Its Kinematic Calibration

The vessels are twisted in a longitudinal 3D space in the lower limbs of humans. Thus, it is difficult to perform an ultrasound scanning examination in this area. In this paper, a new medical parallel robot is introduced to effectively diagnose vessel disease in the lower limbs. The robot's position repeatability and accuracy are evaluated. Furthermore, the robot's accuracy is improved through a calibration process in which the kinematic parameters are identified through a simple identification approach.

Neck proprioceptors contribute to the modulation of muscle sympathetic nerve activity to the lower limbs of humans

Several different strategies have now been used to demonstrate that the vestibular system can modulate muscle sympathetic nerve activity (MSNA) in humans and thereby contribute to the regulation of blood pressure during changes in posture. However, it remains to be determined how the brain differentiates between head-only movements that do not require changes in vasomotor tone in the lower limbs from body movements that do require vasomotor changes. We tested the hypothesis that neck movements modulate MSNA in the lower limbs of humans. MSNA was recorded in 10 supine young adult subjects, at rest, during sinusoidal stretching of neck muscles (100 cycles, 35° peak to peak at 0.37 ± 0.02 Hz) and during a ramp-and-hold (17.5° for 54 ± 9 s) static neck muscle stretch, while their heads were held fixed in space. Cross-correlation analysis revealed cyclical modulation of MSNA during sinusoidal neck muscle stretch (modulation index 45.4 ± 5.3 %), which was significantly less than the cardiac modulation of MSNA at rest (78.7 ± 4.2 %). Interestingly, cardiac modulation decreased significantly during sinusoidal neck displacement (63.0 ± 9.3 %). By contrast, there was no significant difference in MSNA activity during static ramp-and-hold displacements of the neck to the right or left compared with that with the head and neck aligned. These data suggest that dynamic, but not static, neck movements can modulate MSNA, presumably via projections of muscle spindle afferents to the vestibular nuclei, and may thus contribute to the regulation of blood pressure during orthostatic challenges.

Expression of genes involved in fatty acid transport and insulin signaling is altered by physical inactivity and exercise training in human skeletal muscle

Physical deconditioning is associated with the development of chronic diseases, including type 2 diabetes and cardiovascular disease. Exercise training effectively counteracts these developments, but the underlying mechanisms are largely unknown. To gain more insight into these mechanisms, muscular gene expression levels were assessed after physical deconditioning and after exercise training of the lower limbs in humans by use of gene expression microarrays. To exclude systemic effects, we used human models for local physical inactivity (3 wk of unilateral limb suspension) and for local exercise training (6 wk of functional electrical stimulation exercise of the extremely deconditioned legs of individuals with a spinal cord injury). The most interesting subset of genes, those downregulated after deconditioning as well as upregulated after exercise training, contained 18 genes related to both the "insulin action" and "adipocytokine signaling" pathway. Of these genes, the three with strongest up/downregulation were the muscular fatty acid-binding protein-3 (FABP3), the fatty acid oxidizing enzyme hydroxyacyl-CoA dehydrogenase (HADH), and the mitochondrial fatty acid transporter solute carrier 25 family member A20 (SLC25A20). The expression levels of these genes were confirmed using RT-qPCR. The results of the present study indicate an important role for a decreased transport and metabolism of fatty acids, which provides a link between physical activity levels and insulin signaling.

Impact of wall thickness on conduit artery function in humans: Is there a “Folkow” effect?

Regional heterogeneity in wall architecture and thickness may be present between conduit arteries in the upper and lower limbs in humans. These differences in wall architecture may, in turn, influence vascular responsiveness. Folkow proposed in the 1950s that heterogeneity in wall-to-lumen ratio (W:L) could contribute to differences in vascular responsiveness, but this hypothesis has never been directly confirmed in vivo. Our first aim was to examine wall thickness and W:L across arteries in the lower (common and superficial femoral) and upper limbs (brachial and radial) of healthy men ( n = 35) using high resolution ultrasound. In a subgroup ( n = 20) we examined the relationship between W:L of these arteries, physiological (flow-mediated dilation, FMD) and pharmacological vasodilation (glyceryl trinitrate, GTN). Diameter and wall thickness differed significantly across all arteries (ANOVA P < 0.001), with smaller arteries having a relatively larger wall thickness. Moreover, we found a significant correlation between W:L and the FMD-response ( r = 0.55, P < 0.001), which remained significant after correcting for the eliciting shear stress ( r = 0.47, P < 0.001), indicating that W:L/FMD relationship was not primarily related to the impact of diameter on the shear rate stimulus to FMD. W:L also correlated strongly with the GTN-response ( r = 0.56, P < 0.001) across all arteries studied. These results indicate that regional heterogeneity exists in W:L within, but also between, limbs. More importantly, differences in W:L contribute to differences in vascular functional responses, reinforcing the conceptual proposal of Folkow, who suggested that arteries with larger W:L exhibit exaggerated responses to vasoactive stimuli.

Impact of age, sex and exercise on brachial and popliteal artery remodelling in humans

ObjectiveTo examine the impact of age, sex and exercise on wall thickness and remodelling in the popliteal and brachial arteries. MethodsWe compared wall thickness, lumen diameter and wall:lumen ratios in the brachial and popliteal arteries of 15 young (Y, 25.4±0.8yr; 7M 8W) and 16 older sedentary (OS, 58.8±1.1yr; 8M 8W) subjects, with 12 of the OS group also studied following 12 and 24 weeks exercise training. ResultsWall thickness and lumen diameter were higher in the popliteal than the brachial artery for both groups (P<0.05); wall:lumen ratio was similar between arteries. Comparison of the Y and OS groups revealed no impact on wall thickness, whereas diameter values were higher in OS subjects (P<0.05). Whilst there were no significant differences in wall thickness between men and women in the Y or OS groups, diameter was larger in men than in women for both arteries (P<0.05). After 24 weeks of training the wall thickness of both arteries decreased (P<0.01) and the wall:lumen ratio of the brachial (P<0.01) and the popliteal (P<0.05) decreased. ConclusionThe cross-sectional results suggest that ageing was associated with increased lumen diameter, although wall:lumen ratio remained unchanged. Wall:lumen ratio was higher in women than men, irrespective of subject age or the artery studied. This related primarily to differences in lumen diameter between the sexes, as wall thickness did not significantly differ between men and women. Our longitudinal data strongly suggest that exercise training is associated with beneficial effects on conduit artery wall thickness and wall:lumen ratio in both upper and lower limbs in humans.

Upper and Lower Limb Muscle Activation Is Bidirectionally and Ipsilaterally Coupled

There are neural connections between the upper and lower limbs of humans that enable muscle activation in one limb pair (upper or lower) to modulate muscle activation in the other limb pair (lower or upper, respectively). The aims of this study were to extend previous findings regarding submaximal exercise to maximal effort exercise and determine whether there is an ipsilateral or contralateral bias to the neural coupling during a rhythmic locomotor-like task. We measured upper and lower limb muscle activity, joint kinematics, and limb forces in neurologically intact subjects (n = 16) as they performed recumbent stepping using different combinations of upper and lower limb efforts. We found increased muscle activation in passive lower limbs during active upper limb effort compared with passive upper limb effort. Likewise, increased muscle activation in passive upper limbs occurred during active lower limb effort compared with passive lower limb effort, suggesting a bidirectional effect. Maximal muscle activation in the active lower limbs was not different between conditions with active upper limb effort and conditions with passive upper limb movement. Similarly, maximal muscle activation in the active upper limbs was not different between conditions with active lower limb effort and conditions with passive lower limb movement. Further comparisons revealed that neural coupling was primarily from active upper limb muscles to passive ipsilateral lower limb muscles. These findings indicate that interlimb neural coupling affects muscle recruitment during maximal effort upper and lower limb rhythmic exercise and provides insight into the architecture of the neural coupling.

Neural coupling between the upper and lower limbs in humans

The aim of this study was to establish the effects of active sinusoidal ipsilateral and contralateral upper limb flexion, extension, abduction, and adduction with elbows extended on the right soleus H-reflex with subjects seated and standing. Reflex effects were also established when both arms moved synchronously in a reciprocal pattern with elbows flexed in seated and standing subjects. Sinusoidal arm movements were timed to a metronome and performed at 0.2 Hz. Soleus H-reflexes were elicited only once (every 4 s) in every movement cycle of the upper limbs. Position of arms, and activity of shoulder muscles were recorded through twin-axis goniometers and surface electromyography (EMG), respectively. We found that in seated subjects, regardless the direction of the active movement or the upper limb being moved, the soleus H-reflex was depressed. In standing subjects, a reflex depression was observed during extension, abduction, and adduction of the ipsilateral and contralateral upper limbs. Muscles were active during arm flexion and abduction in all directions of arm movement with subjects either seated or standing. It is suggested that arm movement might be incorporated in the rehabilitation training of people with a supraspinal or spinal cord lesion, since it can benefit motor recovery by decreasing spinal reflex excitability of the legs in these patients.

Muscle Blood-Flow Dynamics at Exercise Onset

Common approaches to understanding control of muscle blood flow in exercise focus on the contributions of various putative vasoregulatory mechanisms to the magnitude of the steady-state response. The application of systems-control principles offers a unique approach to characterizing and quantifying the non-steady-state adaptation of muscle blood flow with exercise onset. Information gained from this approach provides novel insight into the nature of control mechanisms governing physiological responses to exercise. This review is intended to provide the reader with an understanding of 1) exercise models, methodology for measuring muscle blood flow, and analysis approaches for quantifying muscle blood-flow dynamics; 2) what is currently known about the dynamic response of muscle blood-flow control mechanisms in humans; and 3) the similarities and differences in exercising muscle blood-flow control in the upper versus the lower limbs in humans.

Forearm vascular responses to combined muscle metaboreceptor activation in the upper and lower limbs in humans

Our previous studies showed that venous occlusion or passive stretch of the lower limb, assuming a mechanical stimulus, attenuates the vasoconstriction in the non-exercised forearm during postexercise muscle ischaemia (PEMI) of the upper limb. In this study, we investigated whether a metabolic stimulus to the lower limb induces a similar response. Eight subjects performed a 2 min static handgrip exercise at 30% maximal voluntary contraction (MVC) followed by 3 min PEMI of the upper limb, concomitant with or without 2 min static ankle dorsiflexion at 30% MVC followed by 2 min PEMI of the lower limb. During PEMI of the upper limb alone, forearm blood flow (FBF) and forearm vascular conductance (FVC) in the non-exercised arm decreased significantly, whereas during combined PEMI of the upper and lower limbs, the decreases in FBF and FVC produced by PEMI of the upper limb was attenuated. Forearm blood flow and FVC were significantly greater during combined PEMI of the upper and lower limbs than during PEMI of the upper limb alone. When PEMI of the lower limb was released after combined PEMI of the upper and lower limbs (only PEMI of the upper limb was maintained continuously), the attenuated decreases in FBF and FVC observed during combined PEMI of the upper and lower limbs was not observed. Thus, forearm vascular responses differ when muscle metaboreceptors are activated in the upper limb and when there is combined activation of muscle metaboreceptors in both the upper and lower limbs.

Estimation of the interplay between groups of fast and slow muscle fibers of the tibialis anterior and gastrocnemius muscle while running

Electromyograms recorded from the lower limbs of humans while running were submitted to a time/frequency analysis using wavelets. The results of the wavelet analysis yielded intensity spectra at every time point during the swing and the stance phase. It was previously shown that more or less high frequency components get activated during different periods of the movement. The purpose of this study was to test to what extent the spectra can be reconstructed by a linear superposition of two generating spectra that were associated to groups of fast and slow muscle fibers. The terms fast and slow do not only refer to the conduction velocity but also to the shape of the motor unit action potential and are used to characterize the groups in a broader sense. The principal component analysis of the spectra confirmed that a two dimensional spectral space was appropriate. A parametric spectral decomposition was used to extract the generating spectra within the two dimensional spectral space. The generating spectra were in turn used to compute the power with which the groups of muscle fibers contribute to the measured spectra and thus to the overall muscular activity. The power that was obtained for the different time points during the movement reflects the biomechanically important interplay between the groups of muscle fibers while running.

Middle cerebral artery stroke that includes the premotor cortex reduces mobility outcome.

The premotor cortex (PMC) (Brodmann 6) contributes uniquely to proximal upper and lower limb power and plays a role in the organization of motor behaviors. We assessed the degree to which PMC damage affected functional outcome. We prospectively compared the functional outcome of patients with a first stroke in the middle cerebral artery distribution that either left the PMC intact (PMC-; n=19) or damaged the PMC (PMC+; n=12). The Functional Independence Measure for disability and the motor score of the Stroke Impairment Assessment Set for impairment assessed outcome. Demographic and clinical features and lesion volume were comparable for the PMC+ and PMC- groups. However, the PMC- group demonstrated significant gain in mobility and in proximal leg movement. This focal improvement contributed to the trend in the PMC- group toward greater independent ambulation. Decreased motor recovery of proximal lower limbs in humans with PMC damage supports the idea that it is the origin of corticoreticulospinal pathways that subserve proximal lower extremity function. Furthermore, persistent proximal weakness after PMC damage may amplify other motor impairments, which include defects in planning, initiating, and sequencing. Neurorehabilitation outcomes may contribute to a more detailed functional anatomy after stroke and partial recovery.

Decreased capacitance response with age in lower limbs of humans – a potential error in the study of cardiovascular reflexes in ageing

The cardiovascular regulation in humans depends to a major extent on sympathetic reflexes originating from volume receptors in the arterial as well as the cardiopulmonary region. With experimental approaches, such as lower body negative pressure (LBNP) and tilting, signs of reduced efficiency with ageing have been shown. However, a confounding factor may be an age-related decline in venous capacitance response of the lower limbs, reducing the decrease in central blood volume and thus the deactivation of baro/cardiopulmonary receptors. This potential error was addressed in the present study. Central hypovolaemic stress was produced by LBNP 60 cmH2O in 10 young (mean age 23, range 20-25 years) and 10 old males (mean age 65, range 61-70 years). Changes in tissue volume of the calf were studied by strain gauge volumetric technique. Transmission of negative pressure to the calf muscle was studied in two young and two old volunteers. The haemodynamic response to hypovolaemic circulatory stress was attenuated in the old as compared with the young subjects, with a less marked increase in heart rate and peripheral resistance. Further, in the old subjects, the decrease in systolic blood pressure, pulse pressure and forearm blood flow was attenuated. Transmission of negative pressure to the calf was equal in both groups. The capacitance response was reduced with age from 2.27 +/- 0.14 to 1.64 +/- 0.13 mL 100 mL-1 (P < 0.005). However, the net capillary fluid filtration was unchanged. The reduced capacitance function might partly explain the declining reflex responses with age in humans, and thus seems to be of considerable importance when studying cardiovascular sympathetic reflex responses in ageing.

An autosomal dominant triphalangeal thumb: Polysyndactyly syndrome with variable expression in a large Indian family maps to 7q36

Hereditary developmental abnormalities of the upper or lower limbs in humans are easily recognizable phenotypes that can be used in the mapping and cloning of genes involved in normal human development. We studied a large Indian pedigree (UR002) with an autosomal dominant triphalangeal thumb (TPT) and polysyndactyly (PSD). The abnormalities were present only in the upper limbs, and the phenotype was fully penetrant. The expression of the phenotype was variable and ranged from unilateral TPT to bilateral TPT, preaxial du-, tri-, or quadruplication of the thumb, or syndactyly of multiple thumbs. There were 112 affected individuals in the pedigree. Previous linkage analyses on apparently similar phenotypes have identified a locus at 7q36 [Heutink et al., 1994, Nature Genet 6:287–291; Tsukurov et al., 1994]. To map the gene responsible for the TPT-PSD in family UR002, we performed linkage analysis in DNA from 47 affected and 7 normal individuals. Marker D7S550, located at 7q36, yielded a maximum LOD score of 11.31 at θ = 0.00. Additional markers in the region also showed no recombination. These data indicate that the gene responsible for the hand abnormality in pedigree UR002 maps to the same region as that in previous pedigrees with similar phenotype. Further analyses of recombinants among all the linked families by using new polymorphic markers will narrow the critical genomic region and facilitate positional cloning of the elusive gene. © 1996 Wiley-Liss, Inc.