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PubMed1990

Regulation of murine lymphokine production in vivo. III. The lymphoid tissue microenvironment exerts regulatory influences over T helper cell function.

We investigated the capacity of murine T lymphocytes, isolated from various lymphoid organs of normal or antigen-primed donors, to produce IL-2 or IL-4 after activation with anti-CD3 or specific antigen. Our results established that T cells resident within lymphoid organs being drained by nonmucosal tissue sites (e.g., axillary, inguinal, brachial lymph nodes, or spleen) produced IL-2 as the predominant T cell growth factor (TCGF) after activation. Conversely, activated T cells from lymphoid organs being drained by mucosal tissues (Peyer's patches, and cervical, periaortic, and parathymic lymph nodes) produced IL-4 as the major species of TCGF. Analysis of the lymphoid tissues obtained from adoptive recipients of antigen-primed lymphocytes provided by syngeneic donors provided evidence that direct influences were being exerted on T cells during their residence within defined lymphoid compartments. These lymphoid tissue influences appeared to be responsible for altering the potential of resident T cells to produce distinct species of TCGF. Steroid hormones, known transcriptional enhancers and repressors of specific cellular genes, were implicated in the controlling mechanisms over TCGF production. Glucocorticoids (GCs) were found to exert a systemic effect on all recirculating T cells, evidenced by a marked dominance in IL-4 production by T cells obtained from all lymphoid organs of GC-treated mice, or after a direct exposure of normal lymphoid cells to GCs in vitro before cellular activation with T cell mitogens. Further, the androgen steroid DHEA appeared to be responsible for providing an epigenetic influence to T cells trafficking through peripheral lymphoid organs. This steroid influence resulted in an enhanced potential for IL-2 secretion after activation. Anatomic compartmentalization of the DHEA-facilitated influence appears to be mediated by differential levels of DHEA-sulfatase in lymphoid tissues. DHEA-sulfatase is an enzyme capable of converting DHEA-sulfate (inactive) to the active hormone DHEA. We find very high activities of this enzyme isolated in murine macrophages. The implications of our findings to immunobiology are very great, and indicate that T cells, while clonally restricted for antigen peptide recognition, also appear to exhibit an extreme flexibility with regards to the species of lymphokines they produce after activation. Regulation of this highly conservative mechanism appears to be partially, if not exclusively, controlled by cellular influences being exerted by distinct species of steroid hormones, supplied in an endocrine or a paracrine manner where they mediate either systemic or tissue-localized influences, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

A1 receptor mediated myocardial infarct size reduction by endogenous adenosine is exerted primarily during ischaemia.

OBJECTIVE: The aim was to test the hypothesis that A1 receptor mediated cardioprotection by endogenous adenosine is exerted during ischaemia rather than reperfusion. METHODS: Anaesthetised open chest rabbits were subjected to 30 min regional ischaemia and 120 min reperfusion, and randomised to one of six groups: group I--saline vehicle (VEH) (n = 12) to allow A1 and A2 adenosine receptor interactions during ischaemia and reperfusion; group II--both A1 and A2 receptors were antagonised during ischaemia and reperfusion with 8-p-sulphophenyltheophylline (SPT) (10 mg.kg-1) (SPTIR, n = 14); groups III and IV--the selective A1 adenosine receptor antagonist 8-(3-noradamantyl)-1,3-dipropylxanthine (KW-3902) was given during ischaemia-reperfusion in low dose (1 mg.kg-1, LA1-IR, n = 11) and higher dose (2 mg.kg-1, HA1-IR, n = 6); group V--KW-3902 (1 mg.kg-1) was given only during reperfusion (A1-R, n = 12); group VI--SPT was given only at reperfusion (SPTR, n = 11). RESULTS: In in vitro studies, (1) KW-3902 completely inhibited negative inotropic effects of the A1 agonist R(-)N6-(2-phenylisopropyl) adenosine (R-PIA) in catecholamine stimulated papillary muscles, and (2) had no effect on concentration dependent vasorelaxation to adenosine or R-PIA. In in vivo studies, transmural myocardial blood flow in the area at risk (determined using 15 microns radiolabelled microspheres) was reduced by 98% in all groups from 139(SEM 15.8) to 2.7(1.1) ml.min-1 x 100 g-1 (p < 0.001). At 120 min of reperfusion, blood flow in the area of necrosis was significantly less in groups LA1-IR [48.6(6.2)], HA1-IR [36.1(7.1)], SPTIR [35.9(6.4)], and SPTR [25.1(5.4)] compared to groups VEH [69.1(15.8)] and A1-R [77.2(11.8)]. The area at risk (Ar) was equivalent among groups. SPT treatment during ischaemia-reperfusion in the SPTIR group increased the area of necrosis (An, assessed by triphenyltetrazolium chloride) relative to Ar (An/Ar) to 51(1.9)% v 26.0(1.7)% in VEH group. KW-3902 in LA1-IR and HA1-IR during both ischaemia and reperfusion increased An/Ar to 35.2(2.5)% and 35.2(2.1)% of area at risk, respectively, both of which were significantly less than the SPTIR group. With A1 blockade at reperfusion (A1-R), An/Ar was equivalent to that in VEH [27.0(1.9)%], while an infarct size of 46.7(2.1)% was still observed in SPTR. CONCLUSIONS: While adenosine exerts its predominant modulation of infarct size during reperfusion, the cardioprotection mediated by A1 receptor mechanisms is modest and exerted principally during the ischaemic time period.

Adenosine↗
PubMed2006

Contemporary mortality due to acute myocardial infarction, unstable angina and exertional angina in a population in South East London.

BACKGROUND: Data on the contemporary mortality of coronary heart disease (CHD) are surprisingly sparse. AIM: To describe the contemporary mortality of all manifestations of CHD. DESIGN: Prospective follow-up of patients with a first presentation of CHD in a defined population. METHODS: We studied 537 patients with a first presentation of acute myocardial infarction, unstable angina or new exertional angina in Bromley Health Authority, London (population 295,000). Patients were prospectively monitored for cardiac and non-cardiac mortality for a median of 6 years. RESULTS: During a median 6 years follow-up, there were 88 (16%) deaths. Survival free from cardiac death was not significantly different between unstable angina (92%) and new exertional angina (94%), but was lower for acute myocardial infarction (84%). DISCUSSION: Mortality from CHD appears to be falling. However, efforts to prevent myocardial infarction should continue to be a priority, because on-going early mortality remains high. New exertional angina should be diagnosed and managed promptly, as its mortality is similar to that of unstable angina.

Adult↗
PubMed2003

Reduced neural drive in bilateral exertions: a performance-limiting factor?

PURPOSE: Activity of the motor cortex in one hemisphere reduces the maximum motor outflow of homologous parts of the opposite hemisphere, causing a reduction in the maximum force a muscle can exert when the contralateral homologous muscle is activated concurrently. The purpose of this study was to establish whether this bilateral deficit is large enough to explain limitations in performance in bilateral exertions. METHODS: Voluntary force production and neural drive during unilateral and bilateral exertions were compared in three experiments, consisting of unilateral maximum contractions, synchronous bilateral contractions, and asynchronous bilateral contractions of finger flexors and knee extensors. RESULTS: Maximum voluntary force was overall about 7% lower in bilateral knee extension as compared with unilateral knee extension (P < 0.001). In finger flexion, a bilateral voluntary force deficit of as much as 20% was found ( P= 0.001). Corresponding deficits in agonist EMG activity were also significant and on average found to be of similar size, though the magnitude of the bilateral deficit in EMG was not consistently related to the magnitude of the bilateral force deficit. In knee extension, a deficit in voluntary activation of 4% (P = 0.003) was demonstrated by means of superimposed tetanic stimulation. The magnitude of this deficit was correlated to the magnitude of the voluntary force deficit (r = 0.80, P= 0.002). The maximum rate of force development in bilateral knee extensions was 13% lower than in a unilateral knee extension (P = 0.002). CONCLUSION: These results suggest that deficits in bilateral force production are large enough to constitute an important performance-limiting factor. Furthermore, the data suggest that a reduced neural drive underlies this bilateral deficit.

Adolescent↗
PubMed1999

Wavelet analysis of electromyography for back muscle fatigue detection during isokinetic constant-torque exertions.

STUDY DESIGN: An investigation of the effects of human trunk extensor muscle fatigue on the temporal change in frequency content of the electromyogram as quantified using the Fourier and wavelet transforms during the performance of repetitive dynamic trunk extension. OBJECTIVE: To evaluate whether alterations in the Fourier and wavelet transform measures were consistent with a shift of the signal power to lower frequencies, and to determine which measures were more highly correlated with the decline in maximal trunk extension torque. SUMMARY OF BACKGROUND DATA: Objective assessment of trunk muscle fatigue is likely to play a more important role in the rehabilitation and prevention of low back injuries, given the association between lack of trunk muscle endurance and acquisition of low back pain. Validation of new methods designed to quantify the level of fatigue using the surface electromyogram is necessary before these techniques can be used in industrial rehabilitation settings. The wavelet transform is a recent development in the signal processing of electromyograms that shows promise as a method for assessment of fatigue. METHODS: Trunk muscle electromyograms obtained from study participants performing repetitive isokinetic trunk extension endurance tests were analyzed using the wavelet and the traditional Fourier methods. Trunk extension torque was controlled at 35% and 70% of the participants' maximal voluntary contraction while they exerted at 5 and 10 repetitions per minute. The decline in maximal trunk extension torque was measured once per minute. Linear regression quantified the rate of change in Fourier and wavelet measures caused by fatigue, whereas Pearson's correlation coefficient determined their association with the decline in maximum torque. RESULTS: Changes in the characteristics of the electromyogram were consistent with a shift to lower frequencies: The signal power at higher frequencies was reduced, whereas the power at lower frequencies was elevated. The amount of change was dependent on the task conditions (exertion level and repetition rate). The wavelet-based measures demonstrated as strong an association with the decline in maximal torque output as the Fourier-based measures. CONCLUSIONS: This study demonstrates that assessment of trunk muscle fatigue during isokinetic movementis possible using both Fourier and wavelet measurements. However, the methods were not as likely to change significantly during lower rates of exertion. These methods, when implemented in a controlled setting, may be used to document the rehabilitation process and guide preventive exercise training.

Adult↗
PubMed1986

Force exerted by epidural catheters.

In a study of epidural catheters, it was found that catheter material and catheter diameter both influenced in force exerted. Catheters made of nylon exert less force than those made of polyethylene. Diameter is proportional to the logarithm of force exerted.

Catheterization↗
PubMed1989

Angiographically demonstrated arterial spasm in a case of benign sexual headache and benign exertional headache.

Benign headaches related to sexual activity and exertion are being recognised with increasing frequency. We wish to report a case of benign sexual headache (Type 2) and benign exertional headache, occurring sequentially in the same patient. Multiple areas of cerebral arterial spasm were demonstrable on angiography. This observation would support the concept that benign sexual headache (Type 2) and benign exertional headache may have a similar pathophysiology.

Adult↗
PubMed2005

Enhancement of glutamate uptake mediates the neuroprotection exerted by activating group II or III metabotropic glutamate receptors on astrocytes.

We investigated whether the activation of astroglial group II and III metabotropic glutamate receptors (mGluRs) could exert neuroprotective effects and whether the neuroprotection was related to glutamate uptake. Our results showed that the activation of astroglial group II or III mGluRs exerted neuroprotection against 1-methyl-4-phenylpyridinium (MPP+) astroglial conditioned medium-induced neurotoxicity in midbrain neuron cultures. Furthermore, MPP+ decreased glutamate uptake of primary astrocytes and C6 glioma cells, which was recovered by activating group II or III mGluRs. Specific group II or III mGluRs antagonists completely abolished the neuroprotective effects and the enhancement of glutamate uptake of their respective agonists. Our results showed that the primary cultured rat astrocytes and C6 glioma cells expressed receptor proteins for group II mGluR2/3, group III mGluR4, mGluR6 and mGluR7. C6 glioma cells expressed mRNA for group II mGluR3, group III mGluR4, mGluR6, mGluR7 and mGluR8. In conclusion, we confirmed that the activation of astroglial mGluRs exerted neuroprotection, and demonstrated that the mechanism underlying this protective role was at least partially related to the enhancement of glutamate uptake.

1-Methyl-4-phenylpyridinium↗
PubMed2006

Exertional headache and coronary ischemia despite normal electrocardiographic stress testing.

Exertional headaches may under certain conditions reflect coronary ischemia. We report the case of a patient seen in a neurology referral practice whose exertional headaches, even in the face of two normal electrocardiographic stress tests and in the absence of underlying chest pain were the sole symptoms of coronary ischemia as detected by Tc-99m Sestamibi testing SPECT stress testing. Stent placement resulted in complete resolution of headaches. Exertional headache in the absence of chest pain may reflect underlying symptomatic coronary artery disease (CAD) even when conventional electrocardiographic stress testing does not indicate ischemia.

Electrocardiography↗
PubMed1980

Prolonged exercise in adolescent boys with juvenile diabetes mellitus. Circulatory and metabolic responses in relation to perceived exertion.

Seven well-trained adolescent boys with juvenile diabetes mellitus were studied. They were non-ketotic and performed a 60 min exercise in the afternoon at an average intensity of 58% of maximal working capacity. Blood glucose, blood lactate, plasma levels of insulin, C-peptide and 3-hydroxybutyrate, oxygen uptake and respiratory quotient were determined. The perception of exertion was scored as rate of perceived exertion. Healthy athletes of the same age were controls. Blood glucose, monitored continuously, decreased successively after 10-15 min of exercise with a significant correlation to the pre-exercise glucose value. Blood glucose decreased during exercise to the same level or below that of controls. Despite hypoglycemia with values of 2-3 mmol/l, the exercise continued. Plasma insulin was unchanged. The 3-hydroxybutyrate level was significantly higher in the diabetics, increased somewhat during exercise and still more during the recovery period. The diabetic subjects had significantly higher systolic blood pressure and heart rate during exercise despite a relatively equal work intensity and lower absolute workload. The rate of perceived exertion increased normally during exercise without interference of decreasing blood glucose.

Adolescent↗
PubMed1999

Frusemide and weight carriage alter the acid:base responses of horses to incremental and to brief intense exertion.

We speculated that frusemide would attenuate the acidosis associated with intense exertion, and that weight carriage would mitigate this effect. Therefore, in each of 2 experiments we measured pulmonary artery and systemic arterial blood pH, PCO2, PO2 and pulmonary artery temperature in 9 horses during exertion on a treadmill after each of 3 treatments. The treatments were: 1) injection of saline solution (C), 2) injection of frusemide (1 mg/kg bwt, i.v. 4 h before running) (FU) and 3) injection of frusemide (F) as for FU and the horses carried weight equal to that lost in the 4 h after frusemide administration (FL). In Experiment 1 the horses performed an incremental exercise test of 90 s at each of 4, 7 and 9 m/s (4 degrees incline). In Experiment 2, the horses ran on a treadmill inclined at 4 degrees for 3 min at 3 m/s, at approximately 120% VO2max for 2 min, and 3 m/s for 5 min. Blood samples for measurement of blood pH, PCO2 and PO2 were collected into heparinised glass syringes. Values were adjusted for changes in pulmonary artery blood temperature. Data were analysed using a 2 way repeated measures ANOVA. There was a consistent pattern in both experiments characterised by a mild alkalosis or mitigated acidosis, compared to C, at rest and during exercise and recovery after FU (P < 0.05). Weight carriage blunted or inhibited the effect of frusemide during exercise and recovery. In experiment 2, at the end of the sprint, FU treatment resulted in a less severe acidosis than did C or FI: mixed venous pH for C, FU, and FL at the end of the sprint were 6.93, 6.98 and 6.93, respectively (P interaction = 0.038), mixed venous base excess was -12.4, -9.91, and -11.8 mmol/l, respectively, and arterial base excess of -1.44, -12.7 and -14.1 mmol/l (P interaction = 0.006) respectively. These effects persisted into recovery. A similar pattern of responses occurred during the incremental exercise test, with weight carriage offsetting the alkalinizing effect of frusemide. We conclude that frusemide attenuates the acidosis of intense exertion and that carriage of weight prevents this effect.

Acid-Base Equilibrium↗
PubMed1990

The carboxy-terminal domains of erbB-2 and epidermal growth factor receptor exert different regulatory effects on intrinsic receptor tyrosine kinase function and transforming activity.

The erbB-2 gene product, gp185erbB-2, displays a potent transforming effect when overexpressed in NIH 3T3 cells. In addition, it possesses constitutively high levels of tyrosine kinase activity in the absence of exogenously added ligand. In this study, we demonstrate that its carboxy-terminal domain exerts an enhancing effect on erbB-2 kinase and transforming activities. A premature termination mutant of the erbB-2 protein, lacking the entire carboxy-terminal domain (erbB-2 delta 1050), showed a 40-fold reduction in transforming ability and a lowered in vivo kinase activity for intracellular substrates. When the carboxy-terminal domain of erbB-2 was substituted for its analogous region in the epidermal growth factor receptor (EGFR) (EGFR/erbB-2COOH chimera), it conferred erbB-2-like properties to the EGFR, including transforming ability in the absence of epidermal growth factor, elevated constitutive autokinase activity in vivo and in vitro, and constitutive ability to phosphorylate phospholipase C-gamma. Conversely, a chimeric erbB-2 molecule bearing an EGFR carboxy-terminal domain (erbB-2/EGFRCOOH chimera) showed reduced transforming and kinase activity with respect to the wild-type erbB-2 and was only slightly more efficient than the erbB-2 delta 1050 mutant. Thus, we conclude that the carboxy-terminal domains of erbB-2 and EGFR exert different regulatory effects on receptor kinase function and biological activity. The up regulation of gp185erbB-2 enzymatic activity exerted by its carboxy-terminal domain can explain, at least in part, its constitutive level of kinase activity.

Animals↗
PubMed2002

Lactobacillus acidophilus (strain LB) from the resident adult human gastrointestinal microflora exerts activity against brush border damage promoted by a diarrhoeagenic Escherichia coli in human enterocyte-like cells.

BACKGROUND AND AIMS: The normal gastrointestinal microflora exerts a barrier effect against enteropathogens. The aim of this study was to examine whether lactobacilli, a minor genus of the resident gut microflora, exerts a protective effect against the cellular injuries promoted by the diarrhoeagenic Afa/Dr diffusely adhering Escherichia coli (Afa/Dr DAEC) C1845 strain in human intestinal cells. METHODS: Cultured human intestinal fully differentiated enterocyte-like Caco-2/TC7 cells were used. Antibacterial activity was examined by measuring the viability of the adhering C1845 bacteria. The distribution of brush border associated cytoskeleton and functional proteins was examined by immunofluorescence labelling coupled to confocal laser scanning microscopy analysis. RESULTS: The activity of Lactobacillus acidophilus strain LB isolated from the resident human gastrointestinal microflora was examined. A dose dependent decrease in viability of C1845 bacteria was observed after both direct contact in vitro between the spent culture supernatant (LB-SCS) and the bacteria, and when the bacteria were adherent on Caco-2/TC7 cells. Protection against the C1845 induced alterations in expression of F-actin, sucrase-isomaltase, dipeptidylpeptidase IV, alkaline phosphatase, and fructose transporter alterations was observed when the cells were exposed to LB-SCS. CONCLUSION: L acidophilus strain isolated from the resident adult human gastrointestinal microflora, together with its antimicrobial activity, exerts a protective effect against the brush border lesions promoted by the diarrhoeagenic Afa/Dr DAEC strain C1845.

Actins↗
PubMed1998

Omeprazole may exert both a bacteriostatic and a bacteriocidal effect on the growth of Helicobacter pylori (NCTC 11637) in vitro by inhibiting bacterial urease activity.

AIMS: To assess the potential antibacterial effect of omeprazole, a benzimidazole proton pump inhibitor, on the growth of Helicobacter pylori in vitro and to evaluate the effect of this compound on bacterial urease activity. METHODS: The growth of H pylori was observed in liquid culture in the presence and absence of omeprazole (0.8 mg/ml). Urease activity was evaluated in aliquots removed from two hour cultures by monitoring the initial change in absorbency at 560 nm in the presence of 0.02% phenol red. RESULTS: The minimum inhibitory concentration of omeprazole against H pylori was 0.8 mg/ml. The concentration of omeprazole required to inhibit growth was dependent on inoculum density: omeprazole (0.8 mg/ml) prevented growth from a 1 x 10(6) cfu/ml inoculum, but not from the higher inocula of 10(7) or 10(8) cfu/ml. This is the first study to demonstrate that omeprazole exerts a bacteriocidal effect against low bacterial densities and a bacteriostatic effect when bacterial density is high. When used at the onset of growth, this concentration of omeprazole has a bacteriocidal effect after four hours, although it exerts a bacteriostatic effect when added to cultures after the exponential phase. Bacterial urease activity is competitively inhibited by omeprazole in a dose dependent manner. CONCLUSION: The results suggest that omeprazole exerts both a bacteriocidal and a bacteriostatic effect against H pylori and competitively inhibits bacterial extracellular urease activity.

Anti-Ulcer Agents↗
PubMed1998

Chronic exertional compartment syndrome: MR imaging at 0.1 T compared with tissue pressure measurement.

PURPOSE: To compare low-field-strength magnetic resonance (MR) imaging with intracompartmental tissue pressure measurement for the diagnosis of chronic exertional compartment syndrome. MATERIALS AND METHODS: Thirteen patients suspected clinically of having chronic exertional compartment syndrome in the anterior tibial compartment were studied. MR imaging at 0.1-T and intracompartmental tissue pressure measurements of the anterior tibial compartment were performed before and immediately after standard treadmill exercise. The MR measurements were also obtained in eight anterior tibial compartments of four control subjects without the syndrome. Intracompartmental signal intensity was normalized with the signal intensity from lower leg tissues not affected by the compartment syndrome (subcutaneous fat, tibial bone marrow, or superficial posterior compartment). RESULTS: In the patient group, the relative change from rest to the postexercise state in the normalized MR signal intensity parameter correlated significantly (P < .001) with the respective change in intracompartmental pressure and with the absolute postexercise pressure. In the patients with elevated postexercise intracompartmental pressure, the increase in normalized MR signal intensity from rest to the postexercise state was significantly greater (P < .01) than that in the control subjects or the patients with normal or borderline postexercise intracompartmental pressure. In the latter two groups, the MR results were comparable. CONCLUSION: MR imaging performed at rest and immediately after muscular exercise is a promising method for diagnosing chronic exertional compartment syndrome and assessing its severity.

Adult↗
PubMed2005

Uncertainty of knee joint muscle activity during knee joint torque exertion: the significance of controlling adjacent joint torque.

In the single-joint torque exertion task, which has been widely used to control muscle activity, only the relevant joint torque is specified. However, the neglect of the neighboring joint could make the procedure unreliable, considering our previous result that even monoarticular muscle activity level is indefinite without specifying the adjacent joint torque. Here we examined the amount of hip joint torque generated with knee joint torque and its influence on the activity of the knee joint muscles. Twelve healthy subjects were requested to exert various levels of isometric knee joint torque. The knee and hip joint torques were obtained by using a custom-made device. Because no information about hip joint torque was provided to the subjects, the hip joint torque measured here was a secondary one associated with the task. The amount of hip joint torque varied among subjects, indicating that they adopted various strategies to achieve the task. In some subjects, there was a considerable internal variability in the hip joint torque. Such variability was not negligible, because the knee joint muscle activity level with respect to the knee joint torque, as quantified by surface electromyography (EMG), changed significantly when the subjects were requested to change the strategy. This change occurred in a very systematic manner: in the case of the knee extension, as the hip flexion torque was larger, the activity of mono- and biarticular knee extensors decreased and increased, respectively. These results indicate that the conventional single knee joint torque exertion has the drawback that the intersubject and/or intertrial variability is inevitable in the relative contribution among mono- and biarticular muscles because of the uncertainty of the hip joint torque. We discuss that the viewpoint that both joint torques need to be considered will bring insights into various controversial problems such as the shape of the EMG-force relationship, neural factors that help determine the effect of muscle strength training, and so on.

Adult↗
PubMed2004

Changes in the inhibitory control exerted by the antagonist Ia afferents on human wrist extensor motor units during an attention-demanding motor task.

The aim of this study was to determine the extent to which an attention-demanding visuomotor task affects the strength of the inhibitory control exerted by the wrist flexor group Ia afferents on the wrist extensor motoneurons. Effects of median nerve stimulation on the tonic activity of wrist extensor single motor units were analyzed in terms of the interspike interval (ISI) lengthening. Results show that the inhibitory effects exerted by the antagonistic group Ia afferents were significantly enhanced when the wrist extensor motoneurons were involved in an attention-demanding task. Enhanced inhibition from antagonist afferents may reflect task-related changes in the excitability of the di- and/or polysynaptic pathways mediating reciprocal inhibition due to either the action of descending inputs and/or an increase in the efficiency of the Ia inputs to the premotoneuronal inhibitory interneurons. Modulation of the inhibition exerted by proprioceptive antagonist afferents may be one of the processes which contribute to the fine adjustment of the wrist muscle force output required in fine handling tasks.

Action Potentials↗
PubMed1999

Coordinated ground forces exerted by buttocks and feet are adequately programmed for weight transfer during sit-to-stand.

The purpose of this study was to test the hypothesis whether weight transfer during sit-to-stand (STS) is the result of coordinated ground forces exerted by buttocks and feet before seat-off. Whole-body kinematics and three-dimensional ground forces from left and right buttock as well as from left and right foot were recorded for seven adults during STS. We defined a preparatory phase from onset of the first detectable anterior/posterior (A/P) force to seat-off (buttock forces fell to 0) and a rising phase from seat-off to the decrease of center of mass (CoM) vertical velocity to zero. STS was induced by an increase of vertical and backward directed ground forces exerted by the buttocks that significantly preceded the onset of any trunk movement. All ground forces peaked before or around the moment of seat-off, whereas all kinematic variables, except trunk forward rotation and hip flexion, peaked after seat-off, during or after the rising phase. The present study suggests that the weight transfer from sit to stand is induced by ground forces exerted by buttocks and feet before seat-off, i.e., during the preparatory phase. The buttocks generate the isometric "rising forces," e.g., the propulsive impulse for the forward acceleration of the body, while the feet apply adequate damping control before seat-off. This indicates that the rising movement is a result of these coordinated forces, targeted to match the subject's weight and support base distance between buttocks and feet. The single peaked, bell-shaped profiles peaking before seat-off, were seen beneath buttocks for the "rising drive," i.e., between the time of peak backward directed force and seat-off, as well as beneath the feet for the "damping drive," i.e., from onset to the peak of forward-directed force and for CoM A/P velocity. This suggests that both beginning and end of the weight transfer process are programmed before seat-off. The peak deceleration of A/P CoM took place shortly ( approximately 100 ms) after CoM peak velocity, resulting in a well controlled CoM deceleration before seat-off. In contrast to the view of other authors, this suggests that body equilibrium is controlled during weight transfer.

Adult↗