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Journal of Applied Physiology... Sep 2002This study was undertaken to quantitatively account for the metabolic disposal of lactate in skeletal muscle exposed to an elevated lactate concentration during rest and...
This study was undertaken to quantitatively account for the metabolic disposal of lactate in skeletal muscle exposed to an elevated lactate concentration during rest and mild-intensity contractions. The gastrocnemius plantaris muscle group (GP) was isolated in situ in seven anesthetized dogs. In two experiments, the muscles were perfused with an artificial perfusate with a blood lactate concentration of ~9 mM while normal blood gas/pH status was maintained with [U-(14)C]lactate included to follow lactate metabolism. Lactate uptake and metabolic disposal were measured during two consecutive 40-min periods, during which the muscles rested or contracted at 1.25 Hz. Oxygen consumption averaged 10.1 +/- 2.0 micromol. 100 g(-1). min(-1) (2.26 +/- 0.45 ml. kg(-1). min(-1)) at rest and 143.3 +/- 16.2 micromol. 100 g(-1). min(-1) (32.1 +/- 3.63 ml. kg(-1). min(-1)) during contractions. Lactate uptake was positive during both conditions, increasing from 10.5 micromol. 100 g(-1). min(-1) at rest to 25.0 micromol. 100 g(-1). min(-1) during contractions. Oxidation and glycogen synthesis represented minor pathways for lactate disposal during rest at only 6 and 15%, respectively, of the [(14)C]lactate removed by the muscle. The majority of the [(14)C]lactate removed by the muscle at rest was recovered in the muscle extracts, suggesting that quiescent muscle serves as a site of passive storage for lactate carbon during high-lactate conditions. During contractions, oxidation was the dominant means for lactate disposal at >80% of the [(14)C]lactate removed by the muscle. These results suggest that oxidation is a limited means for lactate disposal in resting canine GP exposed to elevated lactate concentrations due to the muscle's low resting metabolic rate.
Topics: Animals; Dogs; Glycogen; Lactates; Muscle Contraction; Muscle, Skeletal; Osmolar Concentration; Oxidation-Reduction; Oxygen Consumption; Rest
PubMed: 12183479
DOI: 10.1152/japplphysiol.01119.2001 -
Journal of Neurology, Neurosurgery, and... Apr 1972The experiments reported in this paper tested the hypothesis that the afferent potential elicited by a tendon tap in an isometrically recorded phasic stretch reflex can...
The experiments reported in this paper tested the hypothesis that the afferent potential elicited by a tendon tap in an isometrically recorded phasic stretch reflex can be detected in the surface EMG of normal humans when appropriate techniques are used. These techniques involved (1) training the subjects to relax mentally and physically so that the EMG was silent before and immediately after the diphasic MAP which reflects a highly synchronous discharge of afferent impulses from low threshold muscle stretch receptors after a tendon tap, and (2) using a data retrieval computer to summate stimulus-locked potentials in the EMG over a series of 16 samples using taps of uniform peak force and duration on the Achilles tendon to elicit the tendon jerk in the calf muscles. A discrete, diphasic potential (`A-wave') was recorded from EMG electrodes placed on the surface of the skin over the medial gastrocnemius muscle. The `A-wave' afferent potential had the opposite polarity to the corresponding efferent MAP. Under control conditions of relaxation the `A-wave' had a latency after the onset of the tap of 2 msec, the peak to peak amplitude was of the order of 5 μV and the duration was in the range of 6 to 10 msec. Further experiments were conducted to show that the `A-wave' (1) was not an artefact of the instrumentation used, (2) had a threshold at low intensities of stimulation, and (3) could be reliably augmented by using a Jendrassik manoeuvre compared with the potential observed during control (relaxation) conditions. The results support the conclusion that the `A-wave' emanates from the pool of muscle spindles which discharges impulses along group Ia nerve fibres in response to the phasic stretch stimulus because the primary ending of the spindles is known to initiate the stretch reflex and the spindles can be sensitized by fusimotor impulses so that their threshold is lowered as a result of a Jendrassik manoeuvre. The finding has important implications for the investigation of the fusimotor system in intact man.
Topics: Achilles Tendon; Action Potentials; Adult; Computers; Electrodes; Electromyography; Female; Humans; Male; Mechanoreceptors; Middle Aged; Muscle Contraction; Muscle Spindles; Muscles; Neural Conduction; Neurons; Reflex, Stretch; Relaxation
PubMed: 4260958
DOI: 10.1136/jnnp.35.2.221 -
The Journal of Physiology Jun 2008Animal studies have shown that noxious inputs onto gamma-motoneurons can cause an increase in the activity of muscle spindles, and it has been proposed that this causes...
Animal studies have shown that noxious inputs onto gamma-motoneurons can cause an increase in the activity of muscle spindles, and it has been proposed that this causes a fusimotor-driven increase in muscle stiffness that is believed to underlie many chronic pain syndromes. To test whether experimental pain also acts on the fusimotor system in humans, unitary recordings were made from 19 spindle afferents (12 Ia, 7 II) located in the ankle and toe extensors or peronei muscles of awake human subjects. Muscle pain was induced by bolus intramuscular injection of 0.5 ml 5% hypertonic saline into tibialis anterior (TA); skin pain was induced by 0.2 ml injection into the overlying skin. Changes in fusimotor drive to the muscle spindles were inferred from changes in the mean discharge frequency and discharge variability of spindle endings in relaxed muscle. During muscle pain no afferents increased their discharge activity: seven afferents (5 Ia, 2 II) showed a decrease and six (4 Ia, 2 II) afferents were not affected. During skin pain of 13 afferents discharge rate increased in one (Ia) and decreased in two (1 Ia, 1 II). On average, the overall discharge rate decreased during muscle pain by 6.1% (P < 0.05; Wilcoxon), but remained essentially the same during skin pain. There was no detectable correlation between subjective pain level and the small change in discharge rate of muscle spindles. Irrespective of the type of pain, discharge variability parameters were not influenced (P > 0.05; Wilcoxon). We conclude that, contrary to the 'vicious cycle' hypothesis, acute activation of muscle or skin nociceptors does not cause a reflex increase in fusimotor drive in humans. Rather, our results are more aligned with the pain adaptation model, based on clinical studies predicting pain-induced reductions of agonist muscle activity.
Topics: Adolescent; Adult; Female; Humans; Leg; Male; Muscle Spindles; Muscle, Skeletal; Myofascial Pain Syndromes; Reflex, Stretch; Rest; Sensory Thresholds; Skin
PubMed: 18403422
DOI: 10.1113/jphysiol.2008.151746 -
Proceedings of the Royal Society of... Oct 1949
Topics: Humans; Muscles; Rest
PubMed: 18143369
DOI: 10.1098/rspb.1949.0033 -
British Journal of Pharmacology Aug 19951. Isolated preparations of rabbit anococcygeus muscle were exposed to electrical field stimulation (EFS; 50V, 0.3 ms duration, 0.08-40 Hz) for periods of 1-60 s...
1. Isolated preparations of rabbit anococcygeus muscle were exposed to electrical field stimulation (EFS; 50V, 0.3 ms duration, 0.08-40 Hz) for periods of 1-60 s (short-term EFS) or 10 min-2 h (long-term EFS). 2. Both short- and long-term EFS caused a contractile response which was enhanced by the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine (L-NOARG), showing that it is modulated by endogenous NO. 3. In preparations treated with scopolamine and guanethidine and in which a constrictor tone was induced by histamine, both short- and long-term EFS resulted in relaxation of the tissue. 4. Such relaxations were reversed by tetrodotoxin (TTX), omega-conotoxin, inhibitors of NO synthase and the NO scavenger, oxyhaemoglobin, indicating that they are neuronal in origin and nitrergic in nature. 5. The relaxations to long-term EFS persisted for the duration of the stimulation and were associated with sustained release of oxidation products of NO (NOx). The EFS-induced release of NOx was decreased by N-iminoethyl-L-ornithine (L-NIO), an inhibitor of NO synthase, and by TTX. 6. Inhibitors of NO synthase, in addition, increased the basal tone of the tissue and reduced the basal output of NOx. The basal output of NOx was also reduced by TTX. 7. Long-term EFS which induces approximately 50% of the maximum relaxation could be enhanced by addition of L-, but not D-, arginine to the perfusion medium. 8. These data show that there is a continuous basal release of NO from nitrergic nerve terminals which maintains a relaxant tone in the rabbit anococcygeus muscle. 9. In addition, NO is released during short- and long-term EFS which further relaxes the preparation and modulates sympathetic transmission. Activation of the L-argimne: NO pathway for periods up to2 h does not exhaust nitrergic transmission in any appreciable way.
Topics: Adenosine Triphosphate; Animals; Arginine; Electric Stimulation; Guanethidine; Histamine; Male; Muscle Relaxation; Muscles; Neurotoxins; Nitric Oxide; Nitroprusside; Rabbits; Scopolamine; Synaptic Transmission; Vasoactive Intestinal Peptide
PubMed: 7582537
DOI: 10.1111/j.1476-5381.1995.tb15017.x -
Acta Medica Scandinavica. Supplementum 1982beta-Adrenoceptor antagonists influence the metabolic responses in man at rest and during exercise. Impaired working capacity and muscular fatigue have been reported in...
beta-Adrenoceptor antagonists influence the metabolic responses in man at rest and during exercise. Impaired working capacity and muscular fatigue have been reported in patients on beta-blockers and this could be due to an altered substrate supply to the muscles. The results from several studies show that the main effect of beta-blockade on metabolism is decreased lipolysis, with less fat available to the muscles. This results in an increased carbohydrate demand to maintain an unchanged aerobic metabolism, and liver and muscle glycogen stores are more rapidly depleted. beta-blockade also results in decreased lactate release from the muscles, probably due to a membrane effect and/or changed perfusion. It is concluded that beta-blockade a) decreases fat metabolism in the muscle, which secondarily increases the use of carbohydrates during exercise, resulting in earlier hypoglycaemia and/or depletion of muscle glycogen with reduction of the working capacity, b) impairs lactate transport from the muscle but does not cause lactate accumulation within the muscle which could be responsible for muscular fatigue.
Topics: Adrenergic beta-Antagonists; Animals; Glycogen; Humans; Lactates; Lactic Acid; Lipid Metabolism; Muscles; Physical Exertion; Regional Blood Flow; Rest
PubMed: 6130673
DOI: 10.1111/j.0954-6820.1982.tb00418.x -
Proceedings of the Royal Society of... Oct 1949
Topics: Humans; Muscles; Relaxation
PubMed: 18143370
DOI: 10.1098/rspb.1949.0034 -
Journal of Orthopaedic Research :... May 1993The extent of immobilisation-induced adaptations of muscle length and muscle weight is known to be profoundly influenced by the position (or length) at which the muscle...
The extent of immobilisation-induced adaptations of muscle length and muscle weight is known to be profoundly influenced by the position (or length) at which the muscle is immobilised. However, the effect of the full range of positions of immobilisation on subsequent adaptations of muscle length and weight has not yet been investigated. To examine further the effect of position of immobilisation, we used cast-immobilisation of the hind limbs of 23 rabbits, in various positions between full plantar flexion and full dorsiflexion. Six muscles from non-immobilised rabbits were used as the controls. After 10 days of immobilisation, the wet weight of the soleus muscle and the resting length and resting stiffness of the soleus muscle-tendon unit were determined. Immobilisation in a shortened position was associated with a significantly greater decrease in length and weight than was immobilisation in a lengthened position. In addition, immobilisation produced significant increases in the resting stiffness of muscle-tendon units, although there was no evidence of a position-dependent increase in stiffness. Muscle weight was influenced by the position of immobilisation in a nonlinear way. The data support the views that the pre-immobilisation resting length of the muscle represents a threshold length and that immobilisation at lengths longer than this retards immobilisation-induced atrophy.
Topics: Animals; Elasticity; Female; Immobilization; Muscle Contraction; Muscles; Organ Size; Posture; Rabbits; Rest; Tarsus, Animal; Tendons
PubMed: 8326442
DOI: 10.1002/jor.1100110307 -
Journal of Acupuncture and Meridian... Feb 2018The purpose of this study was to analyze and compare intra and intergroup the immediate effect of the auricular and LR8 systemic acupuncture on the electromyographic... (Randomized Controlled Trial)
Randomized Controlled Trial
The purpose of this study was to analyze and compare intra and intergroup the immediate effect of the auricular and LR8 systemic acupuncture on the electromyographic activity of the trapezius with the trigger points. This is an experimental clinical trial; 40 people were split in 4 distinct groups (n = 10): GI mustard seed application in the auricular acupoint; GII bilateral needle application in the LR8 acupoint; GIII combination of the techniques; GIV/Control Group mustard seed application in an acupoint not linked to the muscle tension. The EMG was used to assess the muscle contraction for 5 seconds during the resting time and during the isometric contraction time. The EMG signal was first collect without the acupuncture intervention; then both techniques were applied for 5 minutes; and the EMG was collected again right after these applications. The Shapiro-Wilk test was used, the t test was paired with the Wilcoxon test to the intragroup comparison; One-way analysis of variance test for intergroup comparison. There was no statistical difference in the intragroup comparison for the groups. The same happened to the intergroup comparison before and after application. Systemic and auricular acupuncture did not promote immediate changes in the EMG activity of the trapezius muscle in individuals with MTrPs.
Topics: Acupuncture Points; Acupuncture, Ear; Adult; Electromyography; Female; Humans; Male; Muscle Contraction; Muscle, Skeletal; Needles; Pilot Projects; Rest; Superficial Back Muscles; Trigger Points; Young Adult
PubMed: 29482797
DOI: 10.1016/j.jams.2017.11.003 -
Brain : a Journal of Neurology 1970
Topics: Biopsy; Histocytochemistry; Humans; Male; Microscopy, Electron; Middle Aged; Muscles; Muscular Diseases; Myofibrils; Pain; Physical Exertion; Rest
PubMed: 5490280
DOI: 10.1093/brain/93.4.873