Search results for "Muscle Contraction"
showing 10 items of 569 documents
Universal spectral profile and dynamic evolution of muscle activation: A hallmark of muscle type and physiological state
2020
The skeletal muscle is an integrated multicomponent system with complex dynamics of continuous myoelectrical activation of various muscle types across time scales to facilitate muscle coordination among units and adaptation to physiological states. To understand the multiscale dynamics of neuromuscular activity, we investigated spectral characteristics of different muscle types across time scales and their evolution with physiological states. We hypothesized that each muscle type is characterized by a specific spectral profile, reflecting muscle composition and function, that remains invariant over time scales and is universal across subjects. Furthermore, we hypothesized that the myoelectr…
Coimpairments as Predictors of Severe Walking Disability in Older Women
2001
OBJECTIVE: Severe disabilities are common among older people who have impairments in a range of physiologic systems. It is not known, however, whether the presence of multiple impairments, or coimpairments, is associated with increased risk of developing new disability. The aim of this study was to determine the combined effects of two impairments, decreased knee-extension strength and poor standing balance, on the risk of developing severe walking disability among older, moderately-to-severely disabled women who did not have severe walking disability at baseline. DESIGN: The Women's Health and Aging Study is a 3-year prospective study with 6 semi-annual follow-up data-collection rounds fol…
Serum basal hormone concentrations and muscle mass in aging women: Effects of strength training and diet
2006
This study examined the effects of strength training and diet on serum basal hormone concentrations and muscle mass in aging women. Fifty-one women age 49 to 74 y were divided into two groups: strength training and nutritional counseling (n = 25), and strength training (n = 26). Both groups performed strength training twice a week for 21 wk. Nutritional counseling was given to attain sufficient energy and protein intake and recommended intake of fat and fiber. We found that the cross-sectional area of the quadriceps femoris increased by 9.5 ± 4.1% in the nutritional counseling group versus 6.8 ± 3.5% in the strength training only group after training (P < 0.052). Nutritional counseling e…
Relaxation of human isolated mesenteric arteries by vasopressin and desmopressin.
1994
1. The effects of vasopressin and deamino-8-D-arginine vasopressin (DDAVP, desmopressin) were studied in artery rings (0.8-1 mm in external diameter) obtained from portions of human omentum during the course of abdominal operations (27 patients). 2. In arterial rings under resting tension, vasopressin produced concentration-dependent, endothelium-independent contractions with an EC50 of 0.59 +/- 0.12 nM. The V1 antagonist d(CH2)5Tyr(Me)AVP (1 microM) and the mixed V1-V2 antagonist desGly-d(CH2)5D-Tyr(Et)ValAVP (0.01 microM) displaced the control curve to vasopressin to the right in a parallel manner without differences in the maximal responses. In the presence of indomethacin (1 microM) the…
Velocity-specific training in elbow flexors.
1999
The purpose of this study was to show that velocity-specific training may be implicated in modifications in the level of coactivation of agonist and antagonist muscles. Healthy males (n = 20) were randomly placed in to two groups: one group trained using concentric contractions (n = 12), the other was an untrained control group (n = 8). The training group underwent unilateral resistance training at a level of 35 (5)% of a one-repetition maximal contraction of the elbow flexors, executed at maximal angular velocity. Training sessions consisted of six sets of eight consecutive elbow flexions, three times per weak for a total of seven weeks. The velocity of the ballistic movements executed dur…
Changes in agonist-antagonist EMG, muscle CSA, and force during strength training in middle-aged and older people
1998
Effects of 6 mo of heavy-resistance training combined with explosive exercises on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris, as well as maximal and explosive strength were examined in 10 middle-aged men (M40; 42 ± 2 yr), 11 middle-aged women (W40; 39 ± 3 yr), 11 elderly men (M70; 72 ± 3 yr) and 10 elderly women (W70; 67 ± 3 yr). Maximal and explosive strength remained unaltered during a 1-mo control period with no strength training. After the 6 mo of training, maximal isometric and dynamic leg-extension strength increased by 36 ± 4 and 22 ± 2% ( P < 0.001) in M40, by 36 ± 3 and 21 ± 3% ( P < 0.001) in M7…
Antagonist mechanical contribution to resultant maximal torque at the ankle joint in young and older men.
2007
Abstract A recorded muscular torque at one joint is a resultant torque corresponding to the participation of both agonist and antagonist muscles. This study aimed to examine the effect of aging on the mechanical contributions of both plantar- and dorsi-flexors to the resultant maximal voluntary contraction (MVC) torques exerted at the ankle joint, in dorsi-flexion (DF) and plantar-flexion (PF). The estimation of isometric agonist and antagonist torques by means of an EMG biofeedback technique was made with nine young (mean age 24 years) and nine older (mean age 80 years) men. While there was a non-significant age-related decline in the measured resultant DF MVC torque (−15%; p =0.06), there…
Inhibition of human detrusor contraction by a urothelium derived factor.
2003
Stimulating muscarinic receptors in pig bladder urothelium causes the release of a diffusable factor that inhibits contractions of the underlying detrusor muscle. We investigated whether the contractions of human detrusor strips elicited by the muscarinic agonist carbachol, electrical field stimulation, KCl or the neurokinin receptor agonist neurokinin A are affected by the urothelium.Paired intact and urothelium denuded muscle strips were placed in modified gassed Tyrode's solution at 37C. Cumulative concentration-response curves to carbachol or KCl were constructed. In other tissues the strips were stimulated electrically (1 to 40 Hz) with trains of square wave pulses 20 seconds in durati…
Histaprodifens: synthesis, pharmacological in vitro evaluation, and molecular modeling of a new class of highly active and selective histamine H(1)-r…
2000
A new class of histamine analogues characterized by a 3, 3-diphenylpropyl substituent at the 2-position of the imidazole nucleus has been prepared outgoing from 4,4-diphenylbutyronitrile (4b) via cyclization of the corresponding methyl imidate 5b with 2-oxo-4-phthalimido-1-butyl acetate or 2-oxo-1,4-butandiol in liquid ammonia, followed by standard reactions. The title compounds displayed partial agonism on contractile H(1) receptors of the guinea-pig ileum and endothelium-denuded aorta, respectively, except 10 (histaprodifen; 2-[2-(3, 3-diphenylpropyl)-1H-imidazol-4-yl]ethanamine) which was a full agonist in the ileum assay. While 10 was equipotent with histamine (1), methylhistaprodifen (…
Effects of dantrolene on the responses to methylxanthines in the isolated guinea-pig trachea.
1991
The effect of dantrolene on the responses to methylxanthines (caffeine and theophylline) and a beta-adrenoceptor agonist (salbutamol) was studied in isolated guinea-pig trachea. Caffeine and theophylline (1 microM-10 mM) and salbutamol (1 nM-10 microM) produced concentration-dependent relaxation of spontaneous and stimulated (acetylcholine 1 mM) tone. Responses to high concentrations (10 mM) of caffeine and theophylline added to tracheal strips either unstimulated (spontaneous tone) or indomethacin (2.8 microM)-treated were reversed to contractions in the presence of dantrolene (3 microM-0.3 mM). This effect was not observed for salbutamol or when relaxant responses to the agonists were gen…