Search results for " muscle contraction."
showing 10 items of 33 documents
Strength training in old age: adaptation of antagonist muscles at the ankle joint.
2005
The purpose of this study was to determine whether strength training could reduce the deficit in plantarflexion (PF) maximal voluntary contraction (MVC) torque observed in previous studies in older subjects relative to young adults. Accordingly, the effects of a 6-month strength training program on the muscle and neural properties of the major muscle groups around the ankle were examined. PF and dorsiflexion (DF) isometric MVC torques were measured and surface electromyographic activity of the triceps surae and tibialis anterior muscles was recorded. The strength training program was very effective in improving strength in PF (+24.5%), and it thus reduced the DF-to-PF MVC torque ratio; in a…
The Inactivation Principle: Mathematical Solutions Minimizing the Absolute Work and Biological Implications for the Planning of Arm Movements
2008
An important question in the literature focusing on motor control is to determine which laws drive biological limb movements. This question has prompted numerous investigations analyzing arm movements in both humans and monkeys. Many theories assume that among all possible movements the one actually performed satisfies an optimality criterion. In the framework of optimal control theory, a first approach is to choose a cost function and test whether the proposed model fits with experimental data. A second approach (generally considered as the more difficult) is to infer the cost function from behavioral data. The cost proposed here includes a term called the absolute work of forces, reflecti…
Long-term effects on motor cortical excitability induced by repeated muscle vibration during contraction in healthy subjects
2008
article i nfo Objective: The effects of a novel repeated muscle vibration intervention (rMV; 100 Hz, 90 min over 3 consecutive days) on corticomotor excitability were studied in healthy subjects. Methods: rMV was applied over the flexor carpi radialis (FCR) during voluntary contraction (experiment 1), during relaxation and during contraction without vibration (experiment 2). Focal transcranial magnetic stimulation (TMS) was applied before rMV and one hour, and one, two and three weeks after the last muscle vibration intervention. At each of these time points, we assessed the motor map area and volume in the FCR, extensor digitorum communis (EDC) and abductor digiti minimi (ADM). Short-inter…
Effects of 5-HT4 receptor stimulation on basal and electrically evoked release of acetylcholine from guinea-pig myenteric plexus
1992
The effects of 5-methoxytryptamine and 5-hydroxytryptamine (5-HT) on both basal and electrically evoked outflow of tritium were studied in guinea-pig myenteric plexus preparations preincubated with [3H]-choline. Basal outflow. 5-Methoxytryptamine caused a transient and calcium-dependent increase in basal outflow of [3H]acetylcholine that was abolished by tetrodotoxin. Ondansetron (1 μmol/1) did not affect the stimulatory response of 5-methoxytryptamine but ICS 205-930 (1 and 3 μmol/1) produced parallel rightward displacements of the concentration-response curve to 5-methoxytryptamine. The PKB value for ICS 205-930 was 6.6 suggesting an involvement of 5-HT4 receptors. 5-HT caused an increase…
The effects of racemic bethanechol and its (R)- and (S)-enantiomers on pre- and postjunctional muscarine receptors in the guinea-pig ileum
1985
The effect of racemic bethanechol and its (R)- and (S)-enantiomers on smooth muscle contraction and outflow of [3H]-acetylcholine were studied in the guinea-pig myenteric plexus-longitudinal muscle preparation that had been preincubated with [3H]-choline. (S)-, racemic, and (R)-bethanechol caused concentration-dependent contractions of the longitudinal muscle. The potency ratio of the strong isomer (S) to the weak one (R) was 915. Racemic and (S)-bethanechol concentration-dependently inhibited the evoked outflow of [3H]-acetylcholine. Racemic bethanechol was more potent than (S)-bethanechol. (R)-bethanechol up to a concentration of 1 mM did no affect the evoked outflow of [3H]-acetylcholine…
Distribution of origin of nitric oxide synthase-immunoreactive nerve fibers in the rat epididymis.
1996
Abstract Distribution of neuronal nitric oxide synthase-immunoreactive (nNOS-IR) nerve fibers and somata in the rat epididymis and major pelvic ganglia was studied by immunohistochemical methods. In the epididymis, the supply of nNOS-IR fibers was highest in the cauda and became progressively fewer toward the caput. In the cauda and corpus, nNOS-IR fibers were distributed throughout the subepithelial tissues and around the epithelium. The pattern of distribution of vasoactive intestinal polypeptide (VIP)- and tyrosine hydroxylase (TH)-immunoreactive fibers in the epididymis was similar but the latter was generally more numerous in a given region as compared to that of nNOS-IR fibers. A popu…
Plantar flexor activation capacity and H reflex in older adults: adaptations to strength training.
2002
The purpose of this study was to investigate whether the voluntary neural drive and the excitability of the reflex arc could be modulated by training, even in old age. To this aim, the effects of a 16-wk strengthening program on plantar flexor voluntary activation (VA) and on the maximum Hoffman reflex (Hmax)-to-maximum M wave (Mmax) ratio were investigated in 14 elderly men (65–80 yr). After training, isometric maximum voluntary contraction (MVC) increased by 18% ( P < 0.05) and weight-lifting ability by 24% ( P < 0.001). Twitch contraction time decreased by 8% ( P < 0.01), but no changes in half relaxation time and in peak twitch torque were observed. The VA, assessed by twitch …
Interplay between PACAP and NO in mouse ileum
2003
Abstract We investigated the possibility that pituitary adenylate cyclase activating peptide (PACAP) has a role in the control of contractility in the mouse ileum. PACAP-(1-27) produced tetrodotoxin (TTX)-insensitive, concentration-dependent reduction of the amplitude of the spontaneous contractions of longitudinal muscle up to their complete disappearance. This effect was inhibited by PACAP-(6-38), PACAP receptor antagonist, and by apamin, blocker of small-conductance Ca2+-activated K+-channels. Nω-nitro- l -arginine methyl ester (L-NAME), nitric oxide (NO) synthase inhibitor, reduced the PACAP-inhibitory response, and the joint application of apamin plus L-NAME produced additive effects. …
Angiotensin II contractile effects in mouse colon: role for pre- and post-junctional AT1A receptors
2013
Aim This study investigates whether a local renin–angiotensin system (RAS) exists in mouse colon and whether angiotensin II (Ang II) may play a role in the regulation of the contractile activity. Methods Isometric recordings were performed in vitro on the longitudinal muscle of mouse proximal and distal colon. Transcripts encoding for RAS components were investigated by RT-PCR. Results Ang II caused, in both preparations, a concentration-dependent contractile effect, antagonized by losartan, AT1 receptor antagonist, but not by PD123319, AT2 receptor antagonist. The combination of losartan plus PD123319 caused no change on the Ang II-induced contraction than losartan alone. Tetrodotoxin, neu…
Muscarinic inhibition of acetylcholine release from a novel in vitro preparation of the guinea-pig trachea
1990
An isolated preparation of the guinea-pig trachea is described which allows the simultaneous measurement of acetylcholine release and smooth muscle contraction. Incubation of the epithelium-free preparation with [3H]choline resulted in the formation of [3H]acetylcholine. Electrical stimulation caused the release of [3H]acetylcholine and a contractile response. Tetrodotoxin and omission of calcium from the medium abolished both the evoked release and contractions. The muscarinic agonists oxotremorine, carbachol and pilocarpine concentration-dependently inhibited the electrically evoked acetylcholine release and contracted the tracheal smooth muscle. Pre- and postsynaptic EC50 values for a gi…