PRESYNAPTIC AND POSTSYNAPTIC MECHANISMS INVOLVED IN TETANIC FADE INDUCED BY PANCURONIUM IN THE ISOLATED RAT MUSCLE

The mechanisms underlying the fade of the tetanic contraction induced by pancuronium were studied in vitro by means of myographical and electrophysiological techniques in the extensor digitorum longus muscle of the rat. Pancuronium (0.5 mu mol/l) induced a complete fade of the tetanic contraction while leaving the twitch unaffected. At the same concentration it decreased the amplitude and increased the tetanic rundown of trains of endplate potentials (e.p.ps) evoked in the frequency of 50 Hz. The electrophysiological changes induced by pancuronium were due to decreases in both quantal sizes and quantal contents of the e.p.ps. The former effect was the result of a postsynaptic competitive action and the latter of a presynaptic inhibitory action of that compound. The decrease in quantal. content affected the e.p.ps starting from the first in the train and became larger during the generation of the sequence of e.p.ps. This intensified their tetanic rundown. It is concluded that the fade of the tetanic contraction induced by pancuronium is due to a summation of pre- and postsynaptic actions and, therefore, not only to an increase in the tetanic rundown of e.p.ps. Possible explanations for the distinct abilities of neuromuscular blockers in affecting tetani and twitches in a differential manner are also discussed.

Morphometric and histochemical study of the human vocal muscle

The present study was conducted on vocal muscles removed at autopsy Rom adult individuals (10 men and 8 women, aes ranging from 48 to 78 years) with no laryngeal disease. Histologic analysis was performed with hematoxylin and eosin staining, and histochemical analysis was performed by nicotinamide-adenine-dinucleotide tetrazolium reductase, succinate dehydrogenase, and acid and alkaline myofibrillar adenosine triphosphatase reactions. The histochemical reactions showed that the muscle consists of slow-twitch oxidative (SO), fast-twitch glycolytic (FG), and fast-twitch glycolytic oxidative (FOG) fibers distributed in mosaic form. The frequencies of SO, FOG, and FG fibers were 40.50%, 54.75%, and 4.75%, respectively. The higher frequency of SO and FOG oxidative fibers characterizes the muscle as having aerobic metabolism, resistance to fatigue, and fast contraction. The mean minimum diameters were 31.37 mu m for SO fibers and 36.46 mu m for FOG and FG fibers.

INFLUENCE of HIP EXTERNAL ROTATION on HIP ADDUCTOR and RECTUS FEMORIS MYOELECTRIC ACTIVITY DURING A DYNAMIC PARALLEL SQUAT

Pereira, GR, Leporace, G, Chagas, DV, Furtado, LFL, Praxedes, J, and Batista, LA. Influence of hip external rotation on hip adductor and rectus femoris myoelectric activity during a dynamic parallel squat. J Strength Cond Res 24(10): 27492754, 2010-This study sought to compare the myoelectric activity of the hip adductors (HAs) and rectus femoris (RF) when the hip was in a neutral position or externally rotated by 30 degrees or 50 degrees (H0, H30, and H50, respectively) during a parallel squat. Ten healthy subjects performed 10 repetitions of squats in each of the 3 hip positions and the myoelectric activities of the HAs and RF were recorded. The signal was then divided into categories representing concentric (C) and eccentric (E) contractions in the following ranges of motion: 0-30 degrees (C1 and E1), 30-60 degrees (C2 and E2), and 60-90 degrees (C3 and E3) of knee flexion. From those signals, an root mean square (RMS) value for each range of motion in each hip position was obtained. All values were normalized to those obtained during maximum voluntary isometric contraction. We found that HAs showed a significant increase in myoelectric activity during C3 and E3 in the H30 and H50 positions, as compared with H0. Meanwhile, RF activity did not significantly differ between hip positions. Both muscles showed higher activation during 60-90 degrees (C3 and E3) of knee flexion, as compared with 0-30 degrees (C1 and E1) and 30-60 degrees (C2 and E2). The results suggest that if the aim is to increase HA activity despite the low percentage of muscle activation, squats should be performed with 30 degrees of external rotation and at least 90 degrees of knee flexion.

Muscle Activation During Four Pilates Core Stability Exercises in Quadruped Position

Queiroz BC, Cagliari MF, Amorim CF, Sacco IC. Muscle activation during four Pilates core stability exercises in quadruped position. Arch Phys Med Rehabil 2010;91: 86-92.Objective: To compare the activity of stabilizing trunk and hip muscles in 4 variations of Pilates stabilizing exercises in the quadruped position.Design: Repeated-measures descriptive study.Setting: A biomechanics laboratory at a university school of medicine.Participants: Healthy subjects (N=19; mean age +/- SD, 31 +/- 5y; mean weight +/- SD, 60 +/- 11 kg; mean height +/- SD, 166 +/- 9cm) experienced in Pilates routines.Interventions: Surface electromyographic signals of iliocostalis, multifidus, gluteus maximus, rectus abdominis, and external and internal oblique muscles were recorded in 4 knee stretch exercises: retroverted pelvis with flexed trunk; anteverted pelvis with extended trunk; neutral pelvis with inclined trunk; and neutral pelvis with trunk parallel to the ground.Main Outcome Measures: Root mean square values of each muscle and exercise in both phases of hip extension and flexion, normalized by the maximal voluntary isometric contraction.Results: The retroverted pelvis with flexed trunk position led to significantly increased external oblique and gluteus maximus muscle activation. The anteverted pelvis with trunk extension significantly increased multifidus muscle activity. The neutral pelvis position led to significantly lower activity of all muscles. Rectus abdominis muscle activation to maintain body posture was similar in all exercises and was not influenced by position of the pelvis and trunk.Conclusions: Variations in the pelvic and trunk positions in the knee stretch exercises change the activation pattern of the multifidus, gluteus maximus, rectus abdominis, and oblique muscles. The lower level of activation of the rectus abdominis muscle suggests that pelvic stability is maintained in the 4 exercise positions.

Comparative mechanical study of isolated papillary muscle from Wistar-Kyoto and Wistar rats

Isolated papillary muscles have often been used in myocardial mechanical function studies. The objective of the present study was to compare the mechanical function of papillary muscle isolated from left ventricle between Wistar (W) and Wistar-Kyoto (WKY) rats of different ages (1, 3, 6 and 12 months), in order to examine whether there is a difference in intrinsic mechanical properties of muscle between the two rat strains. Muscles were perfused with Krebs-Henseleit solution at 28°C and studied isometrically and isotonically at a stimulation rate of 0.2 Hz. The W and WKY showed statistically significant differences during both isometric and isotonic contractions. During isometric contraction? (l) the peak developed tension (DT) and + dT/dt were lower in WKY rats in the 1 mo groups, (2) the resting tension (RT) was greater in WKY at 3, 6 and 12 mo. (3) time to peak tension (TPT) was greater in WKY at 3 and 12 mo, (4) time for tension to fall from peak to 50% of peak tension (RT 1/2) was greater in WKY at 3 mo and (5) - dT/dt was lower in WKY at 1 and 3 mo. During isotonic contraction, (1) the peak shortening (PS) and -dL/dt were lower in WKY at 12 mo, (2) the time to peak shortening (TPS) was greater in WKY at 3 and 12 mo; (3) + dL/dt was lower in WKY at 3, 6, and 12 mo and (4) the relative variation of length (Lmax-PS)/Lmax was greater in WKY at 6 and 12 mo. These data showed a difference in mechanical behaviour of the papillary muscle between Wistar and Wistar-Kyoto rats of different age.

Food restriction-induced myocardial dysfunction demonstrated by the combination of in vivo and in vitro studies

The aim of this study was to test the hypothesis that protein-calorie undernutrition decreases myocardial contractility jeopardizing ventricular function, and that ventricular dysfunction can be detected noninvasively. Five-month-old male Wistar-Kyoto rats were fed with regular rat chow ad libitum for 90 days (Control group, n = 14). A second group of rats received 50% of the amount of diet consumed by de control group (Food restricted group, n = 14). Global LV systolic function was evaluated in vivo, noninvasively, by transthoracic echocardiogram. After echocardiographic study, myocardial contractility was assessed in vitro in the isovolumetrically beating isolated heart in eight animals from each group (Langendorff preparation). The in vivo LV fractional shortening showed that food restriction depressed LV systolic function (p < 0.05). Myocardial contractility was impaired as assessed by the maximal rate of rise of LV pressure (+dP/dt), and developed pressure at diastolic pressure of 25 mmHg (p < 0.05). Furthermore, food restriction induced eccentric ventricular remodeling, and reduced myocardial elasticity and LV compliance (p < 0.05). In conclusion, food restriction causes systolic dysfunction probably due to myocardial contractility impairment and reduction of myocardial elasticity. © 2002 Elsevier B.V. All rights reserved.

Electromyographic analysis of the pectoralis major and deltoideus anterior muscles in horizontal flyer exercises with loads

The effective activity of the pectoralis major and deltoideus anterior muscles in horizontal flyer exercises with external loads of 25, 50, 75 and 100% of the maximum load was studied in 11 male volunteers. The electromyographic analysis was done by using MEDI-TRACE-200 surface electrodes connected to a biological signal acquisition mode coupled to a PC/AT computer. The electromyographic signals were processed and the values obtained were normalized through maximum voluntary isometric contraction. It was statistically observed that in all types and loads of this exercise, the muscles presented significant differences in the concentric and eccentric phases. In the concentric phase, when different loads were compared, the muscles were more active with 75 and 100% of the maximum load, while in the eccentric phase, higher activity was observed with 100% of the maximum load. By analyzing each load effect in the concentric phase, it was verified that the muscles on the left side were more active than those on the right side with 25, 75 and 100% of the maximum load.

Neuromuscular recovery of the biceps brachii muscle after resistance exercise

The aim of this study was to determine the time to restore the biceps brachii (BB) electromyographic (EMG) activity after the biceps curl (BC) exercise, at different intensities. Ten males performed initially maximal voluntary isometric contractions (MVC) of the elbow flexors, followed by one isometric submaximal contraction at 50% MVC (reference contraction). After this, four bouts of the BC at 25%, 30%, 35%, and 40% 1 RM during 1 minute (randomly assigned, with 10 minutes rest between them) were performed. During the rest intervals at preestablished moments (15 seconds, 1, 3, 5, and 10 min), isometric 50% MVC were performed. The EMG variables (root mean square [RMS], zero crossings [ZC], median frequency, [MF] and peak power [PP]) at rest were compared with reference values. Immediately after the exercise, RMS and PP increased, while ZC and MF decreased, indicating fatigue. After 1 minute most of the variables were similar to the reference. Different load levels did not affect the EMG recovery. In conclusion, the EMG variables recovered after 1 minute rest, indicating the optimal muscular condition for subsequent bouts. Copyright © Taylor & Francis Group, LLC.

Electromyographic evaluation of the temporal muscle after the use of interocclusal splints with a vibrating device in individuals with sleep bruxism

This is the first study performed with an interocclusal splint with a vibrating device on patients with sleep bruxism. The purpose of the present study was to evaluate the effectiveness of the splint with vibrating device on patients who suffer from sleep bruxism through computerized electromyography (EMG) of the anterior temporal muscles. Eight male and female patients, ranging in age from 18 to 28 years, with evident signs and symptoms of bruxism were selected. The splint were made for the upper arch. The patients was treated with the interocclusal splint with a vibrating device, and submitted to EMG evaluations of the anterior temporal muscles on both sides. The evaluations were performed at the beginning of treatment and after 21 days of splint use. Electromyography was performed in an isometric contractions measuring of the temporal muscles. The following results obtained revealed that: when closing the mandible (isometric contraction), the anterior temporal muscles had an expressive reduction in electromyographic activity (p. < 0.10), so this splints were considered effective for patients who suffer from sleep bruxism. © 2009 Springer-Verlag.

Hypertrophied myocardium is more dependent on extracellular calcium than the normal cardiac muscle

Background: The aim of this study was to analyze stable hypertrophied myocardial function and its response to inotropic maneuvers in rats submitted to renovascular hypertension for a 10-week period (RHT group, n=10). Material/Methods: Myocardial performance was studied in isolated left ventricle papillary muscles in isometric contraction under the following conditions: at postrest contraction of 30 seconds (PRC), at extracellular calcium (ECa 2+) chloride concentration of 1.25 and 5.20 mM, and after beta-adrenergic stimulation with 10 -6 M isoproterenol (ISOP). Results: The results were compared with normotensive Wistar controls rats (C group, n=10). In basal condition, resting tension, and contraction time (TPT) were greater, while relaxation time (RT 50) tended to be longer in RHT than C group. PRC and ISOP promoted a similar change in muscle function response intensity (Δ) in both groups. ECa 2+ shift did not change TPT in the C group and decreased TPT in the RHT animals; Δ was different between these groups. RT 50 increased in C and decreased in RHT, both without statistical significance; however, Δ was different. Conclusions: These results suggest that hypertrophied myocardial dysfunction may be attibuted to changes in intracellular calcium cycling. © Med Sci Monit, 2010.

Muscle strength and ankle mobility for the gait parameters in diabetic neuropathies

Aims: To evaluate the spatio-temporal variables of gait and the isometric muscle strength component of the ankle in patients with peripheral diabetic neuropathy. Also, verify the relationship between these variables and gait parameters. Methods: This study involved 25 diabetic peripheral neuropathy (DPN) participants (62.4 ± 8.36 years) and 27 age-matched healthy control individuals (64.48 ± 6.21 years). The assessment of the spatio-temporal parameters of gait was performed using an electronic baropodometry treadmill. Prior to the collection data, each participant was instructed to walk on the treadmill in her/his habitual self-selected speed. Results: Diabetic neuropathy group showed impairment of gait, with a smaller stride and length speed of the cycle, and increased duration of support time. Restricted dorsiflexion mobility and increased plantarflexion mobility were found, with a decrease in muscle strength of the dorsiflexors and plantiflexors. There was a significant relationship between plantiflexor muscle strength and the length and speed of the gait cycle. Also the muscle strengths of the plantiflexors and dorsiflexors, and the range of motion of dorsiflexion were predictors of gait performance. Conclusions: The ankle, muscle strength and ankle mobility variables could explain changes in gait speed and range of motion in patients with DPN, allowing for the application of preventive strategies. © 2012 Elsevier Ltd.

Exercise-induced muscle damage and running economy in humans

Running economy (RE), defined as the energy demand for a given velocity of submaximal running, has been identified as a critical factor of overall distance running performance. Plyometric and resistance trainings, performed during a relatively short period of time (15-30 days), have been successfully used to improve RE in trained athletes. However, these exercise types, particularly when they are unaccustomed activities for the individuals, may cause delayed onset muscle soreness, swelling, and reduced muscle strength. Some studies have demonstrated that exercise-induced muscle damage has a negative impact on endurance running performance. Specifically, the muscular damage induced by an acute bout of downhill running has been shown to reduce RE during subsequent moderate and high-intensity exercise (>65% VOax). However, strength exercise (i.e., jumps, isoinertial and isokinetic eccentric exercises) seems to impair RE only for subsequent high-intensity exercise (90% VOax). Finally, a single session of resistance exercise or downhill running (i.e., repeated bout effect) attenuates changes in indirect markers of muscle damage and blunts changes in RE. © 2013 Cláudio de Oliveira Assumpção et al.

The acute effects of static stretching on peak force, peak rate of force development and muscle activity during single- and multiple-joint actions in older women

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeitos do treinamento resistido concêntrico versus excêntrico sobre respostas funcionais, clínicas e bioquímicas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)