Activation of the human diaphragm during a repetitive postural task.
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The co-ordination between respiratory and postural functions of the diaphragm was investigated during repetitive upper limb movement. It was hypothesised that diaphragm activity would occur either tonically or phasically in association with the forces from each movement and that this activity would combine with phasic respiratory activity. Movements of the upper limb and ribcage were measured while standing subjects performed repetitive upper limb movements 'as fast as possible'. Electromyographic (EMG) recordings of the costal diaphragm were made using intramuscular electrodes in four subjects. Surface electrodes were placed over the deltoid and erector spinae muscles. In contrast to standing at rest, diaphragm activity was present throughout expiration at 78 +/- 17% (mean +/- s.d.) of its peak inspiratory magnitude during repeated upper limb movement. Bursts of deltoid and erector spinae EMG activity occurred at the limb movement frequency (approximately 2.9 Hz). Although the majority of diaphragm EMG power was at the respiratory frequency (approximately 0.4 Hz), a peak was also present at the movement frequency. This finding was corroborated by averaged EMG activity triggered from upper limb movement. In addition, diaphragm EMG activity was coherent with ribcage motion at the respiratory frequency and with upper limb movement at the movement frequency. The diaphragm response was similar when movement was performed while sitting. In addition, when subjects moved with increasing frequency the peak upper limb acceleration correlated with diaphragm EMG amplitude. These findings support the argument that diaphragm contraction is related to trunk control. The results indicate that activity of human phrenic motoneurones is organised such that it contributes to both posture and respiration during a task which repetitively challenges trunk posture. (+info)
The Southampton examination schedule for the diagnosis of musculoskeletal disorders of the upper limb.
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OBJECTIVES: Following a consensus statement from a multidisciplinary UK workshop, a structured examination schedule was developed for the diagnosis and classification of musculoskeletal disorders of the upper limb. The aim of this study was to test the repeatability and the validity of the newly developed schedule in a hospital setting. METHOD: 43 consecutive referrals to a soft tissue rheumatism clinic (group 1) and 45 subjects with one of a list of specific upper limb disorders (including shoulder capsulitis, rotator cuff tendinitis, lateral epicondylitis and tenosynovitis) (group 2), were recruited from hospital rheumatology and orthopaedic outpatient clinics. All 88 subjects were examined by a research nurse (blinded to diagnosis), and everyone from group 1 was independently examined by a rheumatologist. Between observer agreement was assessed among subjects from group 1 by calculating Cohen's kappa for dichotomous physical signs, and mean differences with limits of agreement for measured ranges of joint movement. To assess the validity of the examination, a pre-defined algorithm was applied to the nurse's examination findings in patients from both groups, and the sensitivity and specificity of the derived diagnoses were determined in comparison with the clinic's independent diagnosis as the reference standard. RESULTS: The between observer repeatability of physical signs varied from good to excellent, with kappa coefficients of 0.66 to 1.00 for most categorical observations, and mean absolute differences of 1.4 degrees -11.9 degrees for measurements of shoulder movement. The sensitivity of the schedule in comparison with the reference standard varied between diagnoses from 58%-100%, while the specificities ranged from 84%-100%. The nurse and the clinic physician generally agreed in their diagnoses, but in the presence of shoulder capsulitis the nurse usually also diagnosed shoulder tendinitis, whereas the clinic physician did not. CONCLUSION: The new examination protocol is repeatable and gives acceptable diagnostic accuracy in a hospital setting. Examination can feasibly be delegated to a trained nurse, and the protocol has the benefit of face and construct validity as well as consensus backing. Its performance in the community, where disease is less clear cut, merits separate evaluation, and further refinement is needed to discriminate between discrete pathologies at the shoulder. (+info)
How likely is it that Stockholm stage 1 of the hand arm vibration syndrome will progress to stages 2 and 3?
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The progression of symptoms in the hand arm vibration syndrome (HAVS) is dependent on the interaction of individual and workplace factors. Workplace factors include type, magnitude and intermittency of exposure to hand transmitted vibration (HTV), anti-vibration tool design and workpiece characteristics. Individual susceptibility and constitutional factors are poorly understood and the reliance on anamnesis for diagnosis can lead to recall bias, inaccurate classification and an unreliable assessment of the stage of deterioration. This may be overcome by the adoption of multiple standardized testing. The introduction of a policy covering identification, risk assessment, health surveillance and reasonably practicable control measures will have the most significant impact on the incidence of new cases and deterioration in established cases. (+info)
Exclusion of chromosome 9 helps to identify mild variants of acromesomelic dysplasia Maroteaux type.
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Acromesomelic dysplasia Maroteaux type (AMDM) is an autosomal recessive disorder belonging to the group of acromesomelic dysplasias. AMDM is characterised by severe dwarfism with shortening of the middle and distal segments of the limbs. An AMDM gene has recently been mapped to human chromosome 9p13-q12 by homozygosity mapping in four consanguineous families. Here, we show linkage of the disease gene to chromosome 9p13-q12 in four of five consanguineous AMDM families and its exclusion in a fifth family with two children affected with a mild form of the disease. This study suggests that genetic heterogeneity accounts for the variable clinical and radiological severity of AMDM. (+info)
The fat-free mass compartment influences serum leptin in men.
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OBJECTIVE: Recent experimental work in mice has demonstrated that leptin is synthesized by muscle cells. As this latter tissue is the main target for insulin-estimulated glucose disposal, we hypothesized that the muscular and fat-free mass (FFM) compartments might influence serum leptin levels in humans through increased insulin resistance. DESIGN AND METHODS: We evaluated body composition (through bioelectric impedance and anthropometrical parameters), insulin resistance (using the fasting insulin resistance index (FIRI) and insulin sensitivity (S(I)) from the minimal model analysis) and leptin levels in 140 men and 114 women. RESULTS: Serum insulin, FIRI and leptin levels were significantly increased in men in the highest quintile of FFM. Leptin levels positively correlated with FFM in men (r=0.24, P=0004) but not in women (r=0.02, P=not significant). With weight gain, however, approximately 25% of the additional weight is lean mass, so that obese people have higher fat-free mass than lean people. Hence, we performed a multiple linear regression analysis in a stepwise manner to predict leptin levels, in which fat mass (FM), FFM, and FIRI, but not age or waist-to-hip ratio (WHR) independently contributed to 32%, 6% and 3% of the variance in serum leptin levels in men. In women, FM (49%), FIRI (3.6%) and WHR (2.4%), but not FFM or age explained this variance. In a sample of 40 subjects, S(I) and leptin correlated with mid-arm muscle circumference (r=-0.51, P=0.03 and r=0.53, P=0.02) and mid-arm muscle area (r=-0.52, P=0.03 and r=0.53, P=0.02) in men (n=17) but not in women (n=23). CONCLUSIONS: The fat-free mass compartment contributes to the variability of serum leptin levels in men. Whether insulin resistance at this level mediates an increased production of leptin merits further research. (+info)
Control strategies for the transition from multijoint to single-joint arm movements studied using a simple mechanical constraint.
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Changes were studied in neuromotor control that were evoked by constraining the motion of the elbow joint during planar, supported movements of the dominant arm in eight normal human subjects. Electromyograph (EMG) recordings from shoulder and arm muscles were used to determine whether the normal multijoint muscle activity patterns associated with reaching to a visual target were modified when the movement was reduced to a single-joint task, by pinning the elbow to a particular location in the planar work space. Three blocks of 150 movements each were used in the experiments. Subjects were presented with the unconstrained task in the first and third blocks with an intervening block of constrained trials. Kinematic, dynamic, and EMG measures of performance were compared across blocks. The imposition of the pin constraint caused predictable changes in kinematic performance, in that near-linear motions of the hand became curved. This was followed by changes in limb dynamic performance at the elbow. However, changes in EMG activity at the shoulder lagged the kinematic changes substantially (by about 15 trials). The gradual character of the changes in EMG timing does not support a primary role for segmental reflex action in mediating the transition between multijoint and single-joint control strategies. Furthermore, the scope and magnitude of these changes argues against the notion that human motor performance is driven by the optimization of muscle- or joint-related criteria alone. The findings are best described as reflecting the actions of a feedforward adaptive controller that has properties that are modified progressively according to the environmental state. (+info)
Correlations between corticomotoneuronal (CM) cell postspike effects and cell-target muscle covariation.
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The presence of postspike facilitation (PSpF) in spike-triggered averages of electromyographic (EMG) activity provides a useful means of identifying cortical neurons with excitatory synaptic linkages to motoneurons. Similarly the presence of postspike suppression (PSpS) suggests the presence of underlying inhibitory synaptic linkages. The question we have addressed in this study concerns the extent to which the presence and strength of PSpF and PSpS from corticomotoneuronal (CM) cells correlates with the magnitude of covariation in activity of the CM cell and its target muscles. For this purpose, we have isolated cells during a reach and prehension task during which the activity of 24 individual proximal and distal forelimb muscles was recorded. These muscles show broad coactivation but with a highly fractionated and muscle specific fine structure of peaks and valleys. Covariation was assessed by computing long-term (2 s) cross-correlations between CM cells and forelimb muscles. The magnitude of cross-correlations was greater for muscles with facilitation effects than muscles lacking effects in spike-triggered averages. The results also demonstrate a significant relationship between the sign of the postspike effect (facilitation or suppression) and the presence of a peak or trough in the cross-correlation. Of all the target muscles with facilitation effects in spike-triggered averages (PSpF, PSpF with synchrony, or synchrony facilitation alone), 89.5% were associated with significant cross-correlation peaks, indicating positively covarying muscle and CM cell activity. Seven percent of facilitation effects were not associated with a significant effect in the cross-correlation, whereas only 3.4% of effects were associated with correlation troughs. In contrast, of all the muscles with suppression effects in spike-triggered averages, 38.9% were associated with significant troughs in the cross-correlation, indicating an inverse relation between CM cell and muscle activity consistent with the presence of suppression. Fifty-five percent of suppression effects was associated with correlation peaks, whereas 5.6% was not associated with a significant effect in the cross-correlation. Limiting the analysis to moderate and strong facilitation effects, the magnitude of PSpF was correlated weakly with the magnitude of the cell-muscle cross-correlation peak. Nevertheless, the results show that although many CM cell-target muscle pairs covary during the reach and prehension task in a way consistent with the sign and strength of the CM cell's synaptic effects on target motoneurons, many exceptions exist. The results are compatible with a model in which control of particular motoneuron pools reflects not only the summation of signals from many CM cells but also signals from additional descending, sensory afferent, and intrinsic spinal cord neurons. Any one neuron will make only a small contribution to the overall activity of the motoneuron pool. In view of this, it is not surprising that relationships between postspike effects and CM cell-target muscle covariation are relatively weak with many apparent incongruities. (+info)
Dissociation between neural and vascular responses to sympathetic stimulation : contribution of local adrenergic receptor function.
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Sympathetic activation produced by various stimuli, eg, mental stress or handgrip, evokes regional vascular responses that are often nonhomogeneous. This phenomenon is believed to be the consequence of the recruitment of differential central neural pathways or of a sympathetically mediated vasodilation. The purpose of this study was to determine whether a similar heterogeneous response occurs with cold pressor stimulation and to test the hypothesis that local differences in adrenergic receptor function could be in part responsible for this diversity. In 8 healthy subjects, local norepinephrine spillover and blood flow were measured in arms and legs at baseline and during sympathetic stimulation induced by baroreflex mechanisms (nitroprusside infusion) or cold pressor stimulation. At baseline, legs had higher vascular resistance (27+/-5 versus 17+/-2 U, P=0.05) despite lower norepinephrine spillover (0.28+/-0.04 versus 0.4+/-0.05 mg. min(-1). dL(-1), P=0.03). Norepinephrine spillover increased similarly in both arms and legs during nitroprusside infusion and cold pressor stimulation. On the other hand, during cold stimulation, vascular resistance increased in arms but not in legs (20+/-9% versus -7+/-4%, P=0.03). Increasing doses of isoproterenol and phenylephrine were infused intra-arterially in arms and legs to estimate beta-mediated vasodilation and alpha-induced vasoconstriction, respectively. beta-Mediated vasodilation was significantly lower in legs compared with arms. Thus, we report a dissociation between norepinephrine spillover and vascular responses to cold stress in lower limbs characterized by a paradoxical decrease in local resistance despite increases in sympathetic activity. The differences observed in adrenergic receptor responses cannot explain this phenomenon. (+info)