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1.
Paola Sbriccoli Massimo Sacchetti Francesco Felici Leonardo Gizzi Mauro Lenti Alessandro Scotto Giuseppe De Vito 《Journal of electromyography and kinesiology》2009,19(6):e380-e386
Muscle fiber conduction velocity (MFCV) gives critical information on neuromuscular control and can be considered a size principle parameter, being suggestive of motor unit recruitment strategies. MFCV has been recently measured during constant-load sub-maximal cycling exercise and was found to correlate positively with percentage of type I myosin heavy chain.The aim of this study was to test the hypothesis that MFCV measured during an incremental cycling test using surface electromyography (sEMG), can be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (T-vent), V′O2max and MFCV was explored.Eleven male physically active subjects (age 30 ± 9 years) undertook a 1-min incremental cycling test to exhaustion. T-vent and V′O2max were measured using an open circuit breath by breath gas analyzer. The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed on each sEMG burst over the last 30-s of each step.The mean V′O2max obtained during the maximal test was 53.32 ± 2.33 ml kg?1 min?1, and the T-vent was reached at 80.77 ± 3.49% of V′O2max. In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.28 ± 0.67 m s?1 at an intensity corresponding to the T-vent. Thereafter, MFCV declined until maximal work intensities. This study demonstrates that MFCV can be used as non-invasive tool to infer MUs recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities. 相似文献
2.
Dario Farina Andrea Macaluso Richard A Ferguson Giuseppe De Vito 《Journal of applied physiology》2004,97(6):2035-2041
Muscle fiber conduction velocity (MFCV) provides indications on motor unit recruitment strategies due to the relation between conduction velocity and fiber diameter. The aim of this study was to investigate MFCV of thigh muscles during cycling at varying power outputs, pedal rates, and external forces. Twelve healthy male participants aged between 19 and 30 yr cycled on an electronically braked ergometer at 45, 60, 90, and 120 rpm. For each pedal rate, subjects performed two exercise intensities, one at an external power output corresponding to the previously determined lactate threshold (100% LT) and the other at half of this power output (50% LT). Surface electromyogram signals were detected during cycling from vastus lateralis and medialis muscles with linear adhesive arrays of eight electrodes. In both muscles, MFCV was higher at 100% LT compared with 50% LT for all average pedal rates except 120 rpm (mean +/- SE, 4.98 +/- 0.19 vs. 4.49 +/- 0.18 m/s; P < 0.001). In all conditions, MFVC increased with increasing instantaneous knee angular speed (from 4.14 +/- 0.16 to 5.08 +/- 0.13 m/s in the range of instantaneous angular speeds investigated; P < 0.001). When MFCV was compared at the same external force production (i.e., 90 rpm/100% LT vs. 45 rpm/50% LT, and 120 rpm/100% LT vs. 60 rpm/50% LT), MFCV was higher at the faster pedal rate (5.02 +/- 0.17 vs. 4.64 +/- 0.12 m/s, and 4.92 +/- 0.19 vs. 4.49 +/- 0.11 m/s, respectively; P < 0.05) due to the increase in inertial power required to accelerate the limbs. It was concluded that, during repetitive dynamic movements, MFCV increases with the external force developed, instantaneous knee angular speed, and average pedal rate, indicating progressive recruitment of large, high conduction velocity motor units with increasing muscle force. 相似文献
3.
Samuels SE McAllister TA Thompson JR 《Canadian journal of physiology and pharmacology》2000,78(7):557-564
A study was undertaken to determine the long-term effects of a hot environment on protein turnover in skeletal and cardiac muscles of young homeothermic animals. Three groups of 36 male 28 day old rats were housed at 35 degrees C (hot group), 25 degrees C (control group), or 25 degrees C but pair-fed to the intake of the hot group (pair-fed group). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. By day 20, soleus and gastrocnemius (skeletal muscle) protein masses were 7 and 14% lower in the hot group and 31 and 21% lower in the pair-fed group compared with the control group (P < 0.05). The fractional rate of protein synthesis (k(syn)) was on average 11% lower (P < 0.05) in the hot group compared with control rats and was not different from pair-fed rats. The fractional rate of skeletal muscle protein degradation (k(deg)) in hot rats was slightly lower than in control rats; k(deg) was on average 18% higher (P < 0.05) in the pair-fed group compared with the hot group and this difference appeared to be most prominent on day 5. In heart, by day 20, protein mass was 30% lower in the hot group and 40% lower in the pair-fed group compared with control rats (P < 0.05). k(syn) was on average 19% lower (P < 0.05) in the hot group compared with the control group, but not different from pair-fed rats. In the heart there were no differences in k(deg) among treatments. Plasma triiodothyronine (T3) concentration was lower in the hot group, but not in the pair-fed group, compared with controls. In conclusion, chronic exposure to hot environments was associated with lower skeletal and cardiac muscle mass and protein turnover; lower protein mass in this tissue was due to decreased k(syn); this is consistent with lower plasma T3 concentrations. In pair-fed rats, k(syn) was also reduced, but interestingly k(deg) was not, resulting in a greater loss of skeletal muscle mass. These results suggest that heat exposure invokes physiological adaptations to preserve skeletal muscle mass despite decreased food intake. In the heart, loss of protein was a result of decreased k(syn), which can be primarily ascribed to lower food intake. 相似文献
4.
Skeletal muscle fiber type composition and performance during repeated bouts of maximal, concentric contractions 总被引:2,自引:0,他引:2
E B Colliander G A Dudley P A Tesch 《European journal of applied physiology and occupational physiology》1988,58(1-2):81-86
Force output and fatigue and recovery patterns were studied during intermittent short-term exercise. 27 men performed three bouts of 30 maximal unilateral knee extensions on 2 different occasions. Blood flow was maintained or occluded during recovery periods (60 s). Blood flow was restricted by inflating a pneumatic cuff placed around the proximal thigh. Muscle biopsies from vastus lateralis were analyzed for identification of fast twitch (FT) and slow twitch (ST) fibers and relative FT area. Peak torque decreased during each bout of exercise and more when blood flow was restricted during recovery. Initial peak torque (IPT) and average peak torque (APT) decreased over the three exercise bouts. This response was 3 fold greater without than with blood flow during recovery. IPT and APT decreased more in individuals with mainly FT fibers than in those with mainly ST fibers. It is suggested that performance during repeated bouts of maximal concentric contractions differs between individuals with different fiber type composition. Specifically, in high intensity, intermittent exercise with emphasis on anaerobic energy release a high FT composition may not necessarily be advantageous for performance. 相似文献
5.
P J Blijham H J ter Laak H J Schelhaas B G M van Engelen D F Stegeman M J Zwarts 《Journal of applied physiology》2006,100(6):1837-1841
To determine the relation between muscle fiber conduction velocity (MFCV) and muscle fiber diameter (MFD) in pathological conditions, we correlated invasively measured MFCV values with MFD data obtained from muscle needle biopsies in 96 patients with various neuromuscular disorders. MFCV was significantly correlated with MFD and independent of the underlying disorder. Pathological diameter changes were fiber-type dependent, with corresponding MFCVs. A linear equation expresses the relation well: MFCV (m/s)=0.043.MFD (microm)+0.83. We conclude that fiber diameter determines MFCV largely independent of the underlying neuromuscular disorders studied. 相似文献
6.
Hintzy F Belli A Grappe F Rouillon JD 《European journal of applied physiology and occupational physiology》1999,79(5):426-432
The aim of this study was to compare optimal pedalling velocities during maximal (OVM) and submaximal (OVSM) cycling in human, subjects with different training backgrounds. A group of 22 subjects [6 explosive (EX), 6 endurance (EN) and 10 non-specialised subjects] sprint cycled on a friction-loaded ergometer four maximal sprints lasting 6 s each followed by five 3-min periods of steady-state cycling at 150 W with pedalling frequencies varying from 40 to 120 rpm. The OVM and OVSM were defined as the velocities corresponding to the maximal power production and the lowest oxygen consumption, respectively. A significant linear relationship (r2 = 0.52, P < 0.001) was found between individual OVM [mean 123.1 (SD 11.2) rpm] and OVSM [mean 57.0 (SD 4.9) rpm, P < 0.001] values, suggesting that the same functional properties of leg extensor muscles influence both OVM and OVSM. Since EX was greater than EN in both OVM and OVSM (134.3 compared to 110.9 rpm and 60.8 compared to 54.0 rpm, P < 0.01 and P < 0.05, respectively) it could be hypothesised that the distribution of muscle fibre type plays an important role in optimising both maximal and submaximal cycling performance. 相似文献
7.
Objectives:
To examine the relationship between the biceps brachii muscle innervation zone (IZ) width and the mean muscle fiber conduction velocity (MFCV) during a sustained isometric contraction.Methods:
Fifteen healthy men performed a sustained isometric elbow flexion exercise at their 60% maximal voluntary contraction (MVC) until they could not maintain the target force. Mean MFCV was estimated through multichannel surface electromyographic recordings from a linear electrode array. Before exercise, IZ width was quantified. Separate non-parametric one-way analyses of variance (ANOVAs) were used to examine whether there was a difference in each mean MFCV variable among groups with different IZ width. In addition, separate bivariate correlations were also performed to examine the relationships between the IZ width and the mean MFCV variables during the fatiguing exercise.Results:
There was a significant difference in the percent decline of mean MFCV (%ΔMFCV) among groups with different IZ width (χ2 (3)=11.571, p=0.009). In addition, there was also a significant positive relationship between the IZ width and the %ΔMFCV (Kendall’s tau= 0.807; p<0.001).Conclusions:
We believe that such relationship is likely influenced by both muscle fiber size and the muscle fiber type composition. 相似文献8.
Influence of contraction force and speed on muscle fiber conduction velocity during dynamic voluntary exercise. 总被引:2,自引:0,他引:2
T Masuda T Kizuka J Y Zhe H Yamada K Saitou T Sadoyama M Okada 《Journal of electromyography and kinesiology》2001,11(2):85-94
Before using electromyographic (EMG) variables such as muscle fiber conduction velocity (MFCV) and the mean or median frequency (MDF) of an EMG power spectrum as indicators of muscular fatigue during dynamic exercises, it is necessary to determine the influence of a joint angle, contraction force and contraction speed on the EMG variables. If these factors affect the EMG variables, their influence must be removed or compensated for before discussing fatigue. The vastus lateralis of eight normal healthy male adults was studied. EMG signals during non-fatiguing dynamic knee extension exercises were detected with a three-bar active surface electrode array. EMG variables were calculated from the detected signals and compared with the angle of the knee joint, the extension torque and the extension speed. The extension torque was set at four levels with 10% intervals between 40 and 70% of the maximum voluntary contraction. The extension speed was set at five levels with 60 degrees /s intervals between 0 and 240 degrees /s. Because the joint angle unsystematically affected the MFCV, EMG variables at a given joint angle were extracted for comparison. The influence of the extension torque and speed on the extracted EMG variables was clarified with an ANOVA and a regression analysis. The statistical analyses showed that MFCV increased with the extension torque but did not depend on the extension speed. In contrast, MDF was independent of the extension torque but was dependent on the extension speed. MDF thus showed a behavior different from that of MFCV. It became clear that if MFCV is used as an indicator of muscular fatigue during dynamic exercises, it is at least necessary to extract MFCV at a predetermined joint angle and then remove the influence of extension torque on MFCV. 相似文献
9.
Active drag, useful mechanical power output and hydrodynamic force coefficient in different swimming strokes at maximal velocity. 总被引:8,自引:0,他引:8
By comparing the time of the same distance swum with and without an added resistance, under the assumption of an equal power output in both cases, the drag of 73 top swimmers was estimated. The active drag Fr(a.d.) at maximal swimming velocities varied considerably across strokes and individuals. In the females Fr(a.d.) ranged from 69.78 to 31.16 N in the front-crawl, from 83.04 to 37.78 N in dolphin, from 93.56 to 45.19 N in breaststroke, and from 65.51 to 37.79 N in back-stroke. In the males Fr(a.d.) ranged from 167.11 to 42.23 N in front-crawl, from 156.09 to 46.95 N in dolphin, from 176.87 to 55.61 N in breaststroke, and from 146.28 to 46.36 N in back-stroke. Also, the ratio of Fr(a.d.) to the passive drag Fr(a.d.) as determined for the analogical velocity in a tugging condition (in standard body position-front gliding) shows considerable individual variations. In the female swimmers variations in Fr(a.d.)/Fr(p.d.) ranged from 145.17 to 59.94% in front-crawl, from 192.39 to 85.57% in dolphin, from 298.03 to 124.50% in breaststroke, and from 162.87 to 85.61% in back-stroke. In the male swimmers variations in Fr(a.d.)/Fr(p.d.) ranged from 162.24 to 62.39% in front-crawl, from 191.70 to 70.38% in dolphin, from 295.57 to 102.83% in breaststroke, and from 198.82 to 74.48% in back-stroke. The main reason for such variations is found in the individual features of swimming technique and can be quantitatively estimated with the hydrodynamic force coefficient, which thus provides an adequate index of technique. 相似文献
10.
Maria Claudia Cardoso Pereira Valdinar de Araújo Rocha Júnior Martim Bottaro Marcelino Monteiro de Andrade Fabiano Peruzzo Schwartz André Martorelli Rodrigo Celes Jake Carvalho Carmo 《Journal of electromyography and kinesiology》2013,23(2):448-454
The relationship between surface electromyography (SEMG) amplitude and the ventilatory threshold has been extensively studied. However, previous studies of muscle fiber conduction velocity (MFCV) are scarce and present insufficient evidence concerning the relationship between MFCV and metabolic responses during cycling. Based on that fact, the purpose of this study is twofold: (1) to investigate the existence of a MFCV threshold (MFCVT) during cycling and (2) to verify if this possible breakpoint is correlated with the ventilatory threshold (VT) and the SEMG threshold (SEMGT). Eight trained male cyclists (age 36.0 ± 9.7 years) performed an incremental cycling test with initial workload of 150 W gradually incremented by 20 W min?1 until the exhaustion. Gas analyses were conducted using a breath-by-breath open-circuit spirometry and SEMG were registered from vastus lateralis in each pedaling cycle with a linear array of electrodes. A bi-segmental linear regression computer algorithm was used to estimate VT, MFCVT and SEMGT respectively in the carbon dioxide production (VCO2), MFCV and electromyography root mean square (EMG RMS) curves. The one way ANOVA for repeated measures did not reveal any significant difference among VT (77.1 ± 7.5% of VO2max), MFCVT (80.3 ± 10.4% of VO2max) and SEMGT (81.9 ± 11.7% of VO2max). The Bland and Altman procedure confirmed a good concordance between SEMGT and VT (Bias = 5.5 of %VO2max) as well as MFCVT and VT (Bias = 5.2 of %VO2max). The present findings suggest that muscle fiber conduction velocity threshold is a valid and reliable non-invasive tool to obtain information about ventilatory threshold in trained cyclists. 相似文献
11.
McAllister TA Thompson JR Samuels SE 《American journal of physiology. Regulatory, integrative and comparative physiology》2000,278(3):R705-R711
The effect of long-term cold exposure on skeletal and cardiac muscle protein turnover was investigated in young growing animals. Two groups of 36 male 28-day-old rats were maintained at either 5 degrees C (cold) or 25 degrees C (control). Rates of protein synthesis and degradation were measured in vivo on days 5, 10, 15, and 20. Protein mass by day 20 was approximately 28% lower in skeletal muscle (gastrocnemius and soleus) and approximately 24% higher in heart in cold compared with control rats (P < 0.05). In skeletal muscle, the fractional rates of protein synthesis (k(syn)) and degradation (k(deg)) were not significantly different between cold and control rats, although k(syn) was lower (approximately -26%) in cold rats on day 5; consequent to the lower protein mass, the absolute rates of protein synthesis (approximately -21%; P < 0. 05) and degradation (approximately -13%; P < 0.1) were lower in cold compared with control rats. In heart, overall, k(syn) (approximately +12%; P < 0.1) and k(deg) (approximately +22%; P < 0.05) were higher in cold compared with control rats; consequently, the absolute rates of synthesis (approximately +44%) and degradation (approximately +54%) were higher in cold compared with control rats (P < 0.05). Plasma triiodothyronine concentration was higher (P < 0.05) in cold compared with control rats. These data indicate that long-term cold acclimation in skeletal muscle is associated with the establishment of a new homeostasis in protein turnover with decreased protein mass and normal fractional rates of protein turnover. In heart, unlike skeletal muscle, rates of protein turnover did not appear to immediately return to normal as increased rates of protein turnover were observed beyond day 5. These data also indicate that increased rates of protein turnover in skeletal muscle are unlikely to contribute to increased metabolic heat production during cold acclimation. 相似文献
12.
Jane A. Kent-Braun 《European journal of applied physiology and occupational physiology》1999,80(1):57-63
The purpose of this study was to estimate the relative contributions of central and peripheral factors to the development of human muscle fatigue. Nine healthy subjects [five male, four female; age = 30 (2) years, mean (SE)] sustained a maximum voluntary isometric contraction (MVC) of the ankle dorsiflexor muscles for 4 min. Fatigue was quantitated as the fall in MVC. Three measures of central activation and one measure of peripheral activation (compound muscle action potential, CMAP) were made using electromyography (EMG) and electrical stimulation. Measures of intramuscular metabolism were made using magnetic resonance spectroscopy. After exercise, MVC and electrically stimulated tetanic contraction (50 Hz, 500 ms) forces were 22.2 (3.7)% and 37.3 (7.1)% of pre-exercise values, respectively. The measures of central activation suggested some central fatigue during exercise: (1) the central activation ratio [MVC/(MVC + superimposed tetanic force)] fell from 0.94 (0.03) to 0.78 (0.09), (2) the MVC/tetanic force ratio fell from 2.3 (0.7) to 1.3 (0.7), and (3) the integral of the EMG (iEMG) signal decreased to 72.6 (9.1)% of the initial value, while the CMAP amplitude was unchanged. Intramuscular pH was associated by regression with the decline in MVC force (and therefore fatigue) and iEMG. The results indicate that central factors, which were not associated with altered peripheral excitability, contributed approximately 20% to the muscle fatigue developed, with the remainder being attributable to intramuscular (i.e., metabolic) factors. The association between pH and iEMG is consistent with proton concentration as a feedback mechanism for central motor drive during maximal effort. 相似文献
13.
Effect of muscle temperature on leg extension force and short-term power output in humans 总被引:4,自引:0,他引:4
The effect of changing muscle temperature on performance of short term dynamic exercise in man was studied. Four subjects performed 20 s maximal sprint efforts at a constant pedalling rate of 95 crank rev.min-1 on an isokinetic cycle ergometer under four temperature conditions: from rest at room temperature; and following 45 min of leg immersion in water baths at 44; 18; and 12 degrees C. Muscle temperature (Tm) at 3 cm depth was respectively 36.6, 39.3, 31.9 and 29.0 degrees C. After warming the legs in a 44 degrees C water bath there was an increase of approximately 11% in maximal peak force and power (PPmax) compared with normal rest while cooling the legs in 18 and 12 degrees C water baths resulted in reductions of approximately 12% and 21% respectively. Associated with an increased maximal peak power at higher Tm was an increased rate of fatigue. Two subjects performed isokinetic cycling at three different pedalling rates (54, 95 and 140 rev.min-1) demonstrating that the magnitude of the temperature effect was velocity dependent: At the slowest pedalling rate the effect of warming the muscle was to increase PPmax by approximately 2% per degree C but at the highest speed this increased to approximately 10% per degree C. 相似文献
14.
Carlo Capelli Guglielmo Antonutto Paola Zamparo Massimo Girardis Pietro Enrico di Prampero 《European journal of applied physiology and occupational physiology》1993,66(3):189-195
The mechanical power (Wtot, W·kg–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO2max)] of 20–40 min duration. The oxygen uptake [VO2 (W·kg–1, 1 ml O2 = 20.9 J)] and venous blood lactate concentration ([la]b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, Wtot decreased linearly with the intensity of the priming exercise (Wtot = 11.9–0.25·VO2). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO2max, Wtot, VO2 and [la]b remained constant until the end of the exercise. For exercise intensities greater than 60% VO2max, VO2 and [la]b showed continuous upward drifts and Wtot continued decreasing. Under these conditions, the rate of decrease of Wtot was linearly related to the rate of increase of V [(d Wtot/dt) (W·kg–1·s–1) = 5.0·10–5 –0.20·(d VO2/dt) (W·kg–1·s–1)] and this was linearly related to the rate of increase of [la]b [(d VO2/dt) (W·kg–1·s–1) = 2.310–4 + 5.910–5·(d [la]b/dt) (mM·s–1)]. These findings would suggest that the decrease of Wtot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO2 (upwards) and of Wtot (downwards) during intense exercise at constant Wtot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles). 相似文献
15.
Relationship between average muscle fibre conduction velocity and EMG power spectra during isometric contraction, recovery and applied ischemia 总被引:2,自引:0,他引:2
M J Zwarts T W Van Weerden H T Haenen 《European journal of applied physiology and occupational physiology》1987,56(2):212-216
The relationship between muscle fibre conduction velocity (MFCV) and the power spectrum of surface EMGs in 3 human volunteers was studied during isometric contractions at 40% maximum voluntary contraction. In addition, the recovery of these two parameters was measured during short lasting contractions at the same force level every 30 s. The recovery phase was also studied during ischaemia, thereby preventing the recovery of MFCV. The mean MFCV was calculated by the cross-correlation method. The measurements were facilitated by a real-time estimation of the cross-correlation and the MFCV and by a graphic display of the digitised signal. During contraction a nearly linear relation was found between MFCV and the median frequency of the power spectrum (MPF). During recovery this relationship was lost in one subject: MPF restored much faster then MFCV. During recovery under ischemia MFCV did not recover, but MPF recovered partially in all subjects. It is concluded that the shift of the power spectrum to lower frequencies during fatigue cannot be explained by changes in MFCV alone. Central mechanisms also influence the power spectrum and studying the recovery of local muscle fatigue during ischemia may separate these influences from that of MFCV on the power spectrum during fatigue. 相似文献
16.
Claes Krogh-Lund Kurt J?rgensen 《European journal of applied physiology and occupational physiology》1993,66(2):161-173
A brief survey of the literature on manifestations of myo-electric fatigue has disclosed a surprisingly sharp conflict between early studies, focusing on neuromotor regulatory mechanisms, and more recent studies which stress the determinant influence of local metabolism and skewed homeostasis. Favoured explanations concerning changes in the electromyographic (EMG) spectrum were synchronization/grouping of motor unit (MU) firing and conduction velocity (CV) decreases of the action potential propagation. The notion of mutual exclusivity interwoven with these theories prompted us to reinvestigate the EMG of moderate level, static endurance contraction. Ten men in their twenties performed isometric elbow flexion (elbow angle 135°) at 30%6 maximal voluntary contraction (MVC), and the surface EMG of the brachioradialis (BR) and biceps brachii (BB) muscles was recorded. Initially the CV — determined by cross-correlation — was 4.3 m · s–1 (BR) and 4.6 m · s–1 (BB). At exhaustion the CV of the BR muscle had declined by 33%, roughly twice the decrease of the BB CV. Substantially larger relative median frequency (fm) reductions of 50% (BR) and 43% (BB) were found. Simultaneously, the root-mean-square amplitudes grew by 150% (BR) and 120% (BB). All changes during contraction reached the same level of significance (P<0.001, both muscles). From the largely uniform relative increases infm and CV during the last 4 min of a 5-min recovery period, variations in CV were suggested to produce equivalent shifts infm. The gradually increasing discrepancies between relative decreases infm and CV during contraction presumably reflected centrally mediated regulation of MU firing patterns (notably synchronization). After the 5-min recovery another 11 endurance contractions at 30% MVC were executed, separated by 5-min intervals. The series of contractions reduced the endurance time to one-third of the 153 s initially sustained, while the terminal CV recordings increased by 1.0 (BR) and 0.6 (BB) m · s–1, and the terminalfm increased by 24 (BR) and 14 (BB) Hz. The relative CV decreased in direct proportion to the endurance time and thefm decreases varied with the CV; the findings did not support a causal link between CV decrease (signifying impaired fibre excitability) and the force failure of exhaustion. 相似文献
17.
Weissland T Marais G Robin H Vanvelcenaher J Pelayo P 《European journal of applied physiology and occupational physiology》1999,79(3):230-236
The aim of this study was to assess the relationship between spontaneously chosen crank rate (SCCR) and power output during two upper body exercise tests: firstly, an incremental maximal aerobic power test (T1), with an initial intensity of 50 W followed by 15-W increases at each subsequent 90-s stage and secondly, a test (T2) with consecutive exercise periods set at 50%, 60%, 70%, 80%, 110% and 120% of maximal power (Pmax) separated by passive recovery periods. Eight nationally and internationally ranked kayakers, aged 20 (SD 2) years, performed the tests. During both T1 and T2, mean SCCR values were correlated (r = 1) and increased significantly (P < 0.05) in association with the increases in power output. The finding that the subjects consistently increased their crank rate as the power output increased in different tests, i.e. at submaximal, maximal and supramaximal intensities, strongly suggests that SCCR depended on power output and not on the type of exercise (incremental or rectangular exercise). Moreover, the equation relating crank rate and power output determined from T1 suggests that it may be used to predict the crank rate which will be chosen in upper body exercise, whatever the intensity. Finally, the results of testing at 110% and 120% of Pmax would suggest that a high crank rate (>90 rpm) should be used during the test procedure using supramaximal exercises where accumulated oxygen deficit is calculated, and more particularly when exercise is performed using the upper body. 相似文献
18.
Skeletal muscle tension, flow, pressure, and EMG during sustained isometric contractions in humans 总被引:12,自引:0,他引:12
T Sadamoto F Bonde-Petersen Y Suzuki 《European journal of applied physiology and occupational physiology》1983,51(3):395-408
In five healthy males sustained isometric torques during elbow flexion, knee extension, and plantar flexion correlated positively with intramuscular tissue pressure (MTP) in the range 0-80% of the maximal voluntary contraction (MVC). During passive compression of the muscle at rest 133-Xenon muscle clearance stopped when MTP reached diastolic arterial pressure (DAP) indicating that the muscle vascular bed was occluded. However, during sustained contraction this relation between DAP, flow and MTP was not seen. In two cases 133-Xenon clearance from M. soleus did not stop in spite of an 80% maximal contraction and MTP stayed below DAP. In other cases MTP would reach as high as 240 mm Hg before clearance was zero. In the deeper parts of the muscles MTP during contraction was increased in relation to the more superficial parts. The means values for the % MVC that would stop MBF varied between 50 and 64% MVC for the investigated muscles. Mean rectified EMG (MEMG) showed a high correlation to MTP during sustained exhaustive contractions: When MEMG was kept constant MTP also remained constant while the exerted force decreased; when force was kept constant both MEMG and MTP increased in parallel. This demonstrated that muscle tissue compliance is decreasing during fatigue. Muscle ischemia occurring during sustained isometric contractions is partly due to the developed MTP, where especially the MTP around the veins in the deeper parts of the muscle can be considered of importance. However, ischemia is also affected by muscle fiber texture and anatomical distorsion of tissues. 相似文献
19.
Akar FG Nass RD Hahn S Cingolani E Shah M Hesketh GG DiSilvestre D Tunin RS Kass DA Tomaselli GF 《American journal of physiology. Heart and circulatory physiology》2007,293(2):H1223-H1230
End-stage heart failure (HF) is characterized by changes in conduction velocity (CV) that predispose to arrhythmias. Here, we investigate the time course of conduction changes with respect to alterations in connexin 43 (Cx43) properties and mechanical function during the development of HF. We perform high-resolution optical mapping in arterially perfused myocardial preparations from dogs subjected to 0, 3, 7, 14, and 21 days of rapid pacing to produce variable degrees of remodeling. CV is compared with an index of mechanical function [left ventricular end-diastolic pressure (LVEDP)] and with dynamic changes in the expression, distribution, and phosphorylation of Cx43. In contrast to repolarization, CV was preserved during early stages of remodeling (3 and 7 days) and significantly reduced at later stages, which were associated with marked increases in LVEDP. Measurements of differentially phosphorylated Cx43 isoforms revealed early, sustained downregulation of pan-Cx43 that preceded changes in CV and LVEDP, a gradual rise in a dephosphorylated Cx43 isoform to over twofold baseline levels in end-stage HF, and a late abrupt increase in pan-Cx43, but not dephosphorylated Cx43, lateralization. These data demonstrate that 1) CV slowing occurs only at advanced stages of remodeling, 2) total reduction of pan-Cx43 is an early event that precedes mechanical dysfunction and CV slowing, 3) changes in Cx43 phosphorylation are more closely associated with the onset of HF, and 4) Cx43 lateralization is a late event that coincides with marked CV reduction. These data reveal a novel paradigm of remodeling based on the timing of conduction abnormalities relative to changes in Cx43 isoforms and mechanical dysfunction. 相似文献
20.
Heinonen I Ilkka H Saltin B Bengt S Kemppainen J Jukka K Sipilä HT Oikonen V Vesa O Nuutila P Pirjo N Knuuti J Juhani K Kalliokoski K Kari K Hellsten Y Ylva H 《American journal of physiology. Heart and circulatory physiology》2011,300(4):H1510-H1517
The aim of the present study was to determine the effect of nitric oxide and prostanoids on microcirculation and oxygen uptake, specifically in the active skeletal muscle by use of positron emission tomography (PET). Healthy males performed three 5-min bouts of light knee-extensor exercise. Skeletal muscle blood flow and oxygen uptake were measured at rest and during the exercise using PET with H(2)O(15) and (15)O(2) during: 1) control conditions; 2) nitric oxide synthase (NOS) inhibition by arterial infusion of N(G)-monomethyl-L-arginine (L-NMMA), and 3) combined NOS and cyclooxygenase (COX) inhibition by arterial infusion of L-NMMA and indomethacin. At rest, inhibition of NOS alone and in combination with indomethacin reduced (P < 0.05) muscle blood flow. NOS inhibition increased (P < 0.05) limb oxygen extraction fraction (OEF) more than the reduction in muscle blood flow, resulting in an ~20% increase (P < 0.05) in resting muscle oxygen consumption. During exercise, muscle blood flow and oxygen uptake were not altered with NOS inhibition, whereas muscle OEF was increased (P < 0.05). NOS and COX inhibition reduced (P < 0.05) blood flow in working quadriceps femoris muscle by 13%, whereas muscle OEF and oxygen uptake were enhanced by 51 and 30%, respectively. In conclusion, by specifically measuring blood flow and oxygen uptake by the use of PET instead of whole limb measurements, the present study shows for the first time in humans that inhibition of NO formation enhances resting muscle oxygen uptake and that combined inhibition of NOS and COX during exercise increases muscle oxygen uptake. 相似文献