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1.
Todd G Petersen NT Taylor JL Gandevia SC 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,150(3):308-313
A long-duration, submaximal contraction of a hand muscle increases central fatigue during a subsequent contraction in the
other hand. However, this 'cross-over' of central fatigue between limbs is small and the location within the central nervous
system at which this effect occurs is unknown. We investigated this 'cross-over' by measurement of the force and EMG responses
to transcranial magnetic stimulation of the motor cortex (TMS). To produce central fatigue, we used sustained maximal voluntary
contractions (MVCs). In the first study, subjects (n=10) performed four 1-min sustained MVCs of the elbow flexors, alternating between the left and right arms (two MVCs per arm).
The sustained MVCs were performed consecutively with no rest periods. In the second study, the same subjects made two sustained
1-min MVCs with the same arm with a 1-min rest between efforts. During each sustained MVC, a series of TMS and brachial plexus
stimuli were delivered. Surface EMG was recorded from biceps brachii and brachioradialis muscles bilaterally. Voluntary activation
was estimated during each MVC using measurement of the force increments to TMS. On average during each sustained MVC, voluntary
activation declined by 7–12% (absolute change, P<0.001) and voluntary force declined by 35–45% MVC (P<0.001), whereas the cortical motor-evoked potential increased (P<0.001) and the subsequent silent period lengthened (P<0.001). The average voluntary activation and voluntary force were similar during two sustained MVCs performed by the same
arm, when separated by 1 min of rest. However, when the 1-min rest interval was replaced with a sustained contraction performed
by the other arm, the average voluntary activation was 2.9% worse in the second contraction (absolute change, P<0.05), while it did not alter voluntary force production or the EMG responses to TMS. Therefore, in maximal exercise of 4 min
duration, the 'cross-over' of central fatigue between limbs is small in the elbow flexors and has a minor functional effect.
Our data suggest that voluntary drive from the motor cortex is slightly less able to drive the muscle maximally after a fatiguing
voluntary contraction on the contralateral side.
Electronic Publication 相似文献
2.
Rattey J Martin PG Kay D Cannon J Marino FE 《Pflügers Archiv : European journal of physiology》2006,452(2):199-207
The purpose of this investigation was to examine the effects of voluntary muscular fatigue in one lower limb and determine whether a ‘cross-over’ of fatigue is evident in the contralateral limb. Twenty-eight subjects (13 males and 15 females) performed a series of voluntary and evoked isometric contractions of both the dominant (exercised) and non-dominant (non-exercised) leg extensor muscles, prior to and after a fatigue protocol consisting of a 100-s sustained maximal isometric contraction (MVC) performed by the dominant limb only. Force values and surface electromyography (EMG) from the vastus lateralis muscle were obtained allowing for the determination of twitch and compound action potential (M-wave) values. Maximal twitch tension and peak-to-peak amplitude were significantly decreased after the fatigue test in the dominant limb, as was maximal voluntary force (∼65 N reduction), EMG activity (∼0.1 mV decrease) and voluntary activation (∼17% decline). However, no significant changes were observed in the non-dominant limb with respect to twitch and M-wave properties nor in MVC force. The voluntary activation of the non-dominant limb decreased significantly by 8.7% after the fatigue test, which was performed only on the dominant limb. The results of the present study suggest that the decrease in force production in the exercised limb was primarily related to peripheral fatigue mechanisms, with central fatigue making a lesser contribution. Centrally mediated mechanisms appear to be the sole contributor to fatigue in the non-exercised limb suggesting an anticipatory fatigue response and a ‘cross-over’ of central fatigue between the exercised and non-exercised contralateral limb. 相似文献
3.
Biro A Griffin L Cafarelli E 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2007,177(2):157-166
There are conflicting observations of the effects of fatigue on the sensitivity of large diameter Ia afferents. Our goal was
to characterize any fatigue-related changes in the spinal reflex pathways during fatigue. Manipulation of the Ia afferent
response by vibration and tendon tap, in which the motor neuron pool is modulated by both short- and long-loop activation
from muscle spindles, were elicited before and after a fatigue task. The fatigue task consisted of intermittent submaximal
and maximal voluntary contractions (MVCs). Percent voluntary activation fell from 98.75% MVC to 80.92% MVC following the fatigue
task as measured by the twitch interpolation technique. Voluntary contractions of the same force profile as the force produced
by 30 s of vibration were produced by having participants (n = 10) follow the trajectory on a computer monitor, before and after the fatigue task. Recruitment thresholds (RTs) of voluntarily
activated units showed no change during fatigue; however, units activated via the reflex pathway were recruited ∼30% sooner
during fatigue (P < 0.05). The ratio of the electrical-to-mechanical response of the tendon tap increased significantly with fatigue. Our findings
of decreased RTs in response to vibration and increased EMG activity during the tendon tap following the fatigue task indicate
that Ia afferent input to the motoneuron pool was increased. The decrease in MVC force indicates that during this time the
descending drive was compromised. These results provide evidence that the gain of the gamma loop is increased during fatigue,
indicating possible peripheral neural compensation to the motor neuron pool in order to preserve force output. 相似文献
4.
Maffiuletti NA Jubeau M Munzinger U Bizzini M Agosti F De Col A Lafortuna CL Sartorio A 《European journal of applied physiology》2007,101(1):51-59
The present study aimed to compare quadriceps femoris muscle strength and fatigue between obese (grade II and III) and nonobese
adults. Ten obese (mean age: 25 years; mean BMI: 41 kg/m2) and ten lean (mean age: 27 years; mean BMI: 23 kg/m2) men were
tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions
at 180°/s) and an electrostimulated (40 Hz) isometric protocol (5 min, 10% of the maximal torque). Maximal voluntary isometric
and isokinetic torque and power were also measured. Voluntary torque loss was significantly higher (P < 0.05) in obese (−63.5%) than in lean subjects (−50.6%). Stimulated torque decreased significantly (P < 0.05) but equally in the two subject groups. Obese subjects displayed higher absolute (+20%; P < 0.01) but lower relative (i.e., normalized to body mass) (−32%; P < 0.001) muscle torque and power than their lean counterparts. Obese individuals demonstrated lower fatigue resistance during
voluntary but not during stimulated knee extensions compared to their nonobese counterparts. Peripheral mechanisms of muscle
fatigue—at least those associated to the present stimulated test—were not influenced by obesity. The observed quadriceps muscle
function impairments (voluntary fatigue and relative strength) probably contribute to the reduced functional capacity of obese
subjects during daily living activities. 相似文献
5.
The effects of muscle fatigue on the temporal neuromuscular control of the vastus medialis (VM) muscle were investigated
in 19 young male subjects. The electromyogram (EMG) activities of VM and the force generation capacities of the quadriceps
muscle were monitored before and after a fatigue protocol. In response to light signals, which were triggered randomly, the
subjects made three maximal isometric knee extensions. This was then followed by the fatigue protocol which consisted of 30
isometric maximal voluntary contractions at a sequence of 5-s on and 5-s off. Immediately after the exercise to fatigue, the
subjects performed another three maximal isometric contractions in response to the light signals. The effects of fatigue on
the temporal neuromuscular control were then investigated by dividing the total reaction time (TRT) into premotor time (PMT)
and electromechanical delay (EMD). The TRT was defined as the time interval between the light signal and the onset of the
knee extension force. The PMT was defined as the time from the light signal to the onset of EMG activities of VM, and EMD
as the time interval between onset of EMG activities to that of force generation. Following the contractions to fatigue there
was a significant decrease in peak force (F
peak, P = 0.016), an increase in the root mean square (rms)-EMG: F
peak quotient (P = 0.001) but an insignificant change in the median frequency (P = 0.062) and rms-EMG (P = 0.119). Significant lengthening of mean EMD was found after the fatigue protocol [0.0396 (SD 0.009) vs 0.0518 (SD 0.016) s
P < 0.001]. The lengthening of EMD in VM would affect the stabilizing effect of the patella during knee extension. The faster
mean PMT [0.2445 (SD 0.093) vs 0.2075 (SD 0.074) s, P = 0.042] following the fatigue protocol might have compensated for the lengthened EMD and contributed to the insignificant
change in the mean TRT [0.284 (SD 0.09) vs 0.259 (SD 0.073) s, P = 0.164]. This was probably related to the low level of fatigue (15% decrease in force) and the stereotyped nature of the
action such that the effects of the fatigue on neuromuscular control were likely to have been attributable to peripheral processes.
Accepted: 26 April 1999 相似文献
6.
Effects of knee joint angles and fatigue on the neuromuscular control of vastus medialis oblique and vastus lateralis muscle in humans 总被引:1,自引:0,他引:1
The effects of different knee joint angles and fatigue on the neuromuscular control of the vastus medialis oblique (VMO)
and vastus lateralis (VL) muscles were investigated in 17 (11 men, 6 women) young subjects. The electromyogram (EMG) activities
and the force generation capacities were monitored before and after a fatigue protocol at three different knee joint angles,
90°, 150°, 175° of knee extension, on three occasions. In response to randomly triggered light signals, the subjects performed
three isometric maximal voluntary contraction (IMVC) that lasted for 4 to 8 s. This was then followed by the fatigue protocol
which consisted of six bursts of contractions fixed at 30 s on and 10 s off. Immediately after the exercise to fatigue, the
subjects performed another three IMVC in response to the light signals. Repeated measures ANOVA were performed to examine
the effects of fatigue at these three positions on the electromechanical delay (EMD), median frequency (f
med), peak force (F
peak) and root mean square (rms)-EMG:F
peak quotient of VMO and VL. The results revealed a significant effect of the three knee joint angles on the EMD before the fatigue
(P < 0.05). The fatigue protocol induced a significant decrease in F
peak at all the three positions (P < 0.01). However, the fatigue induced a significant decrease of f
med at only 90° and 150° of knee extension (P < 0.01). This occurred in parallel with the lengthening of EMD at these two joint angles (P < 0.01 and P < 0.05). The effects of fatigue on the f
med and EMD were not significant between VMO and VL at all three angles. The insignificant difference in f
med and EMD between VMO and VL at the three knee positions before and after fatigue indicated that no preferential onset activation
between VMO and VL had occurred.
Accepted: 1 September 2000 相似文献
7.
Electromyogram changes during sustained contraction after resistance training in women in their 3rd and 8th decades 总被引:3,自引:1,他引:3
The present study aimed at investigating the neuromuscular adaptations to 6 weeks of resistance training in women in their
third (6 experimental, 8 controls) and eighth decades (8 experimental, 8 controls). The surface electromyogram (sEMG) was
measured from the biceps brachii muscle during constant-force isometric contractions lasting 12 s at 80% of maximal voluntary
contraction (MVC). All the signals were analysed adopting in the time domain the root mean square (RMS) as a measure of amplitude
and in the frequency domain the median frequency (MDF) of the power spectrum. Quantitative analysis was performed from the
3rd to the 6th second, to describe the early phase of the contraction (“Early”), starting from point at which 80% of the MVC
was reached, and from the 9th to the 12th second, to describe the last part of the constant-force sustained contraction (“Late”).
After training, the MVC increased by 22.4% in the young (P < 0.0001) and by 13.4% in the older (P < 0.05) women. The “Early” RMS increased by 60.4% with respect to the pre-training condition in the young (P < 0.01) but not in the older women. In contrast, the “Late” RMS increased by 46.7% in the older (P < 0.05) but not in the young women. The MDF remained unchanged in both groups. These results indicate that young and older
women showed different training-induced adaptation of the motor unit (MU) activation pattern, in order to keep a constant
level of force during a sustained isometric contraction at 80% of MVC.
Accepted: 11 March 2000 相似文献
8.
Effects of neuromuscular fatigue on the electromechanical delay of the leg extensors and flexors in young and old men 总被引:1,自引:0,他引:1
E. C. Conchola B. J. Thompson D. B. Smith 《European journal of applied physiology》2013,113(9):2391-2399
Purpose
The purpose of this study was to investigate the effects of a fatigue-inducing bout of submaximal, intermittent isometric contractions on the electromechanical delay (EMD) of the leg extensors and flexors in young and old men.Methods
Twenty young (mean ± SD: age = 25 ± 2.8 years) and sixteen old (age = 70.8 ± 3.8) recreationally active men performed maximal voluntary contractions (MVCs) followed by a fatigue-inducing protocol consisting of intermittent isometric contractions of the leg extensors or flexors using a 0.6 duty cycle (6 s contraction, 4 s relaxation) at 60 % of MVC until volitional fatigue. MVCs were again performed at 0, 7, 15, and 30 min post fatigue. A three-way mixed factorial ANOVA was used to analyze the EMD data.Results
There was a two-way muscle × time interaction (P = 0.039) where the EMD of the leg flexors was greater (P = 0.001–0.034) compared with baseline at all post fatigue time periods, but was only greater at immediately post fatigue for the extensors (P = 0.001). A significant two-way interaction for muscle × age (P = 0.009) revealed that the EMD was greater (P = 0.003) for the extensors for the old compared with the young men, but not different for the flexors (P = 0.506).Conclusions
These findings showed differential fatigue-induced EMD recovery patterns between the leg extensors and flexors with the flexors being slower to recover and also that age-related increases of EMD are muscle group specific. The sustained increased EMD of the flexors during recovery may have important injury and performance implications in a variety of populations and settings. 相似文献9.
Neuromuscular adaptation during prolonged strength training, detraining and re-strength-training in middle-aged and elderly people 总被引:6,自引:0,他引:6
Häkkinen K Alen M Kallinen M Newton RU Kraemer WJ 《European journal of applied physiology》2000,83(1):51-62
Effects of a 24-week strength training performed twice weekly (24 ST) (combined with explosive exercises) followed by either
a 3-week detraining (3 DT) and a 21-week re-strength-training (21 RST) (experiment A) or by a 24-week detraining (24 DT) (experiment
B) on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris,
maximal isometric and one repetition maximum (1-RM) strength and jumping (J) and walking (W) performances were examined. A
group of middle-aged (M, 37–44 years, n=12) and elderly (E, 62–77, n=10) and another group of M (35–45, n=7) and E (63–78, n=7) served as subjects. In experiment A, the 1-RM increased substantially during 24 ST in M (27%, P < 0.001) and E (29%, P < 0.001) and in experiment B in M (29%, P < 0.001) and E (23%, P < 0.01). During 21 RST the 1-RM was increased by 5% at week 48 (P < 0.01) in M and 3% at week 41 in E (n.s., but P < 0.05 at week 34). In experiment A the integrated electromyogram (IEMG) of the vastus muscles in the 1-RM increased during
24 ST in both M (P < 0.05) and E (P < 0.001) and during 21 RST in M for the right (P < 0.05) and in E for both legs (P < 0.05). The biceps femoris co-activation during the 1-RM leg extension decreased during the first 8-week training in M (from
29 ± 5% to 25 ± 3%, n.s.) and especially in E (from 41 ± 11% to 32 ± 9%, P < 0.05). The CSA increased by 7% in M (P < 0.05) and by 7% in E (P < 0.001), and by 7% (n.s.) in M and by 3% in E (n.s.) during 24 ST periods. Increases of 18% (P < 0.001) and 12% (P < 0.05) in M and 22% (P < 0.001) and 26% (P < 0.05) in E occurred in J. W speed increased (P < 0.05) in both age groups. The only decrease during 3 DT was in maximal isometric force in M by 6% (P < 0.05) and by 4% (n.s.) in E. During 24 DT the CSA decreased in both age groups (P < 0.01), the 1-RM decreased by 6% (P < 0.05) in M and by 4% (P < 0.05) in E and isometric force by 12% (P < 0.001) in M and by 9% (P < 0.05) in E, respectively, while J and W remained unaltered. The strength gains were accompanied by increased maximal voluntary
neural activation of the agonists in both age groups with reduced antagonist co-activation in the elderly during the initial
training phases. Neural adaptation seemed to play a greater role than muscle hypertrophy. Short-term detraining led to only
minor changes, while prolonged detraining resulted in muscle atrophy and decreased voluntary strength, but explosive jumping
and walking actions in both age groups appeared to remain elevated for quite a long time by compensatory types of physical
activities when performed on a regular basis.
Accepted: 2 May 2000 相似文献
10.
Neuromuscular changes after long-lasting mechanically and electrically elicited fatigue 总被引:1,自引:0,他引:1
Central fatigue was investigated under an isolated active condition whereby the possible effects of supraspinal fatigue were
minimized. Therefore, ten subjects were fatigued by simultaneously and repeatedly mechanically stretching and electrically
stimulating their calf muscles for 1 h. This was performed using an ankle ergometer. The active fatigue task included a total
of 2400 muscle stretches with an intensity of 10% of the maximal voluntary contraction (MVC). This protocol clearly impaired
neuromuscular function, as revealed by a significant reduction in MVC (P<0.01) and the neural input to the muscle (average EMG) (P<0.01–0.001). The interpolated nerve stimulation compensated for this force loss by 4.28% (P<0.05). Stretch-reflex recordings revealed a notable post-fatigue reduction in the peak-to-peak amplitude (59.1%, P<0.01) and stretch-resisting force of the muscle (14.1%, P<0.01). The maximal H-reflex declined by 50.5% (P<0.001) and did not recover while the leg was kept ischemic. It is suggested that the existing protocol with minor metabolic
loading can induce central fatigue, which seems to be of reflex origin from the fatigued muscle. Although the role of presynaptic
inhibition of Ia terminals is possibly reinforced, disfacilitation via reduced spindle sensitivity cannot be excluded.
Electronic Publication 相似文献
11.
Place N Matkowski B Martin A Lepers R 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2006,174(4):595-603
The aims of the present study were to examine (1) endurance time and (2) activation pattern of vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles during fatiguing isometric knee extensions performed with different EMG biofeedbacks. Thirteen men (27 ± 5 year) volunteered to participate in three experimental sessions. Each session involved a submaximal isometric contraction held until failure at an EMG level corresponding to 40% maximal voluntary contraction torque (MVC), with visual EMG biofeedback provided for either (1) RF muscle (RF task), (2) VL and VM muscles (Vasti task) or (3) the sum of the VL, VM and RF muscles (Quadriceps task). EMG activity of VL, VM and RF muscles was recorded during each of the three tasks and further analyzed. Time to task failures and MVC loss (P < 0.001) after exercises were similar (P > 0.05) between the three sessions (182 s and ∼28%, respectively) (P > 0.05). Moreover, the magnitude of central and peripheral fatigue was not different at failure of the three tasks. Activation pattern was similar for knee extensors at the beginning of each task (P > 0.05). However, RF EMG activity decreased (P < 0.05) during the Vasti and the Quadriceps tasks (from ∼33 to ∼25% maximal EMG), whereas vasti EMG activity remained constant during the RF task (∼41% maximal EMG). These findings suggest that (1) task failure occurs when sustaining a submaximal level of EMG activity for as long as possible and (2) CNS is not able to differentiate descending drive to the different heads of the quadriceps at the beginning of a sustained contraction, despite a different activation pattern for the bi-articular RF muscle compared to the mono-articular vasti muscles during fatigue. 相似文献
12.
Purpose
Few studies have assessed the time-dependent response of fatigue (i.e., loss of force) during submaximal exercise without the use of maximum contractions. There is unexplored potential in the use of the superimposed muscle twitch (SIT), evoked by transcranial magnetic stimulation (TMS) or motor nerve stimulation (MNS), to assess fatigue during voluntary submaximal contractions. For the human triceps surae muscles, there are also no data on TMS-evoked twitches.Methods
To optimise the TMS stimulus for assessment of fatigue, we first tested the effects of TMS power (40, 55, 70, 85, 100 % max) on SIT force during contractions (0–100 % MVC in 10 % increments) in six subjects. Then, we compared SIT responses (TMS and MNS) during submaximal contractions and MVCs (all at 60 s intervals) during a continuous protocol of intermittent contractions (30 % MVC) consisting of consecutive 5 min periods of baseline, fatigue (ischaemia) and recovery.Results
For TMS, SIT force increased as a diminishing function of TMS power (P < 0.05), the relationships between SIT force and the force of voluntary contraction at all TMS powers were parabolic, and SIT force was maximised at ~20–40 % MVC. During intermittent contractions, MVC and SIT forces were stable during baseline, decreased similarly during ischaemia by 40–50 % (P < 0.05), and recovered similarly to baseline values (P > 0.05) before the end of the protocol.Conclusion
TMS can be used to evoke twitches during submaximal contractions of the human calf muscle and, along with MNS, used to assess fatigue during submaximal exercise. 相似文献13.
We investigated the effects of age on changes in the force and velocity components of knee extension (KE) power during 16 weeks
of traditional progressive resistance training (PRT). Thirty-one young (27 ± 1 years, 16 men, 15 women) and 30 older (64 ± 1 years,
14 men, 16 women) adults trained by KE, leg press, and squat 3 days/week. PRT consisted of three sets with an appropriate
load for 8–12 repetitions to fatigue. Testing occurred at baseline, 8, and 16 weeks. Thigh lean mass (TLM) was measured by
DEXA. KE load–power and load–velocity curves were generated from peak concentric contractions against loads equivalent to
20, 30, 40, 50, and 60% maximum voluntary isometric contraction (MVC) force. Quadriceps neural activation relative to maximum
was assessed during a sit-to-stand task. Participants increased KE 1RM (P < 0.05) by 8 weeks with young adults also increasing strength from 8 to 16 weeks. Adjusting for TLM, all groups increased
KE specific strength (P < 0.05). MVC improved by 8 weeks in older adults and by 16 weeks in young subjects (P < 0.05). Neural activation requirements during standing and sitting declined in older adults by 8 weeks (P < 0.05). The KE load–power curve improved for all groups (P < 0.05) by 8 weeks with only young adults improving from 8 to 16 weeks. Peak concentric velocity increased only in older
adults (P < 0.05). Training improvements in power resulted primarily from increases in strength both early and late for young adults
while older adults realized early improvements in both strength and peak concentric velocity.
Grants: This study was supported by National Institute on Aging Grant R01 AG017896 (MMB), Department of Veterans’ Affairs
Merit Grant (MMB), and General Clinical Research Center Grant M01 RR00032. 相似文献
14.
M: Shinohara Motoki Kouzaki Takeshi Yoshihisa Tetsuo Fukunaga 《European journal of applied physiology》1997,77(1-2):189-191
To investigate the efficacy of ischemia in strength training with low mechanical stress, tourniquet ischemia was utilized
in low-resistance training. Five untrained subjects conducted one-legged isometric knee extension training with one leg ischemic
(I-leg) and the other non-ischemic (NI-leg). Repeated isometric contractions for 2 s with 3 s relaxation in between were continued
for 3 min and conducted 3 days/week for 4 weeks as training. Training resistance was 40% of maximal voluntary contraction
(MVC) of respective leg and tourniquet ischemia was applied during I-leg training. MVC in I-leg after 2 weeks (9% gain) and
4 weeks (26% gain) were significantly higher than pre-training value (p < 0.05). A significant increase in maximal rate of torque development in I-leg was observed after 4 weeks (p < 0.05). On the contrary, there was no significant changes in either of the parameters in NI-leg. As a consequence, the differences
between legs for both parameters were significant after 2 and 4 weeks (p < 0.05 or p < 0.01). The substantial gain in strength and maximal rate of torque development in I-leg demonstrated the efficacy of tourniquet
ischemia during low-resistance training of short duration, and suggested the importance of neuromuscular and/or metabolic
activity, other than high mechanical stress, to the adapting responses to strength training.
Accepted: 17 July 1997 相似文献
15.
Zijdewind I Butler JE Gandevia SC Taylor JL 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2006,175(3):526-535
During strong voluntary contractions, activity is not restricted to the target muscles. Other muscles, including contralateral muscles, often contract. We used transcranial magnetic stimulation (TMS) to analyse the origin of these unintended contralateral contractions (termed “associated” contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right elbow-flexor muscles followed by submaximal contractions with their left elbow flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were ∼1.5–2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts. 相似文献
16.
Plasma catecholamine responses and neural adaptation during short-term resistance training 总被引:1,自引:0,他引:1
Low exercise-induced plasma adrenaline (A) responses have been reported in resistance-trained individuals. In the study reported
here, we investigated the interaction between strength gain and neural adaptation of the muscles, and the plasma A response
in eight healthy men during a short-term resistance-training period. The subjects performed 5 resistance exercises (E1–E5),
consisting of 6 sets of 12 bilateral leg extensions performed at a 50% load, and with 2 days rest in between. Average electromyographic
(EMG) signal amplitude was recorded before and after the exercises, from the knee extensor muscles in isometric maximal voluntary
contraction (MVC) as well as during the exercises (aEMGmax and aEMGexerc, respectively). Total oxygen consumed during the exercises (V˙O2tot) was also measured. All of the exercises were exhaustive and caused significant decreases in MVC (34–36%, P < 0.001). As expected, the concentric one-repetition maximum (1-RM), MVC and aEMGmax were all higher before the last exercise (E5) than before the first exercise (E1; 7, 9 and 19%, respectively, P < 0.05). In addition, in E5 the aEMGexerc:load and V˙O2tot:load ratios were lower than in E1 (−5 and −14%, P < 0.05), indicating enhanced efficiency of the muscle contractions, However, the post-exercise plasma noradrenaline (NA)
and A were not different in these two exercises [mean (SD) 10.2 (3.8) nmol · l−1 vs 11.3 (6.0) nmol · l−1, ns, and 1.2 (1.0) nmol · l−1 vs 1.9 (1.1) nmol · l−1, ns, respectively]. However, although NA increased similarly in every exercise (P < 0.01), the increase in A reached the level of statistical significance only in E1 (P < 0.05). The post-exercise A was also already lower in E2 [0.7 (0.7) nmol · l−1, P < 0.05) than in E1, despite the higher post-exercise blood lactate concentration than in the other exercises [9.4 (1.1) mmol · l−1, P < 0.05]. Thus, the results suggest that the observed attenuation in the A response can not be explained by reduced exercise-induced
strain due to the strength gain and neural adaptation of the muscles. Correlation analysis actually revealed that those individuals
who had the highest strength gain during the training period even tended to have an increased post-exercise A concentration
in the last exercise as compared to first one (r=0.76, P < 0.05).
Accepted: 10 February 2000 相似文献
17.
Marc Jubeau Raphaël Zory Julien Gondin Alain Martin Nicola A. Maffiuletti 《Neuroscience letters》2007
The aim of this study was to evaluate the effects of neuromuscular electrical stimulation (NMES) training and subsequent detraining on neuromuscular fatigue mechanisms. Ten young healthy men completed one NMES fatigue protocol before and after a NMES training program of 4 weeks and again after 4 weeks of detraining. Muscle fatigue (maximal voluntary torque loss), central fatigue (activation failure), and peripheral fatigue (transmission failure and contractile failure) of the plantar flexor muscles were assessed by using a series of electrically evoked and voluntary contractions with concomitant electromyographic and torque recordings. At baseline, maximal voluntary torque decreased significantly with fatigue (P < 0.001), due to both activation and transmission failure. After detraining, maximal voluntary torque loss was significantly reduced (P < 0.05). In the same way, the relative decrease in muscle activation after training and detraining was significantly lower compared to baseline values (P < 0.05). Short-term NMES training–detraining of the plantar flexor muscles significantly reduced the muscle fatigue associated to one single NMES exercise session. This was mainly attributable to a reduction in activation failure, i.e., lower central fatigue, probably as a result of subject's accommodation to pain and discomfort during NMES. 相似文献
18.
N. Boisseau P. Delamarche F. Rannou D. Bentue-Ferrer A. Gratas-Delamarche 《European journal of applied physiology》2000,81(1-2):93-99
To test glucose tolerance during exercise, the effects of oral glucose ingestion (0.5 g · kg−1) on plasma glucose and hormonal responses (insulin, catecholamines) were investigated in 11 women [mean (SEM) age 21.6 (1.3)
years] and 10 men [22.0 (0.3) years] during cycle ergometer exercise (30 min at 60% maximum oxygen consumption, V˙O2max). The two groups exhibited similar V˙O2max values, when expressed per kg of lean body mass. Venous blood samples (5 ml) were withdrawn immediately before the exercise,
during the exercise (at 3, 5, 10, 15 and 30 min) and at the 30th min of the recovery period. Glucose was ingested orally between
the 2nd and the 3rd min of the exercise. As compared to men, plasma glucose concentrations were lower in women during exercise
(P < 0.05 at 3, 15 and 30 min) and at the 30th min of the recovery period (P < 0.001), while plasma insulin concentrations were higher in women during exercise (P < 0.05 at 3, 15 and 30 min). The ratio of the area under the curve for glucose over the area under the curve for insulin
was lower in women during exercise (P < 0.0002). A linear relationship between glucose and insulin concentrations was found only for women during exercise (r = 0.615, P < 0.0001). No gender difference was observed for the catecholamine concentration during exercise. In conclusion, this study
postulates that an oral glucose load given at the onset of a prolonged and moderate exercise bout induced lesser plasma glucose
and greater insulin concentrations in women as compared to men. These data argue in favour of a greater glucose tolerance
in women during exercise.
Accepted: 5 June 1999 相似文献
19.
Kawakami Y Akima H Kubo K Muraoka Y Hasegawa H Kouzaki M Imai M Suzuki Y Gunji A Kanehisa H Fukunaga T 《European journal of applied physiology》2001,84(1-2):7-12
Nine healthy men carried out head-down bed rest (BR) for 20 days. Five subjects (TR) performed isometric, bilateral leg extension
exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured.
Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional
magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated
(uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [−10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but
after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography,
showed no significant changes in either group. The PCSA decreased in NT by −7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [−3.8 (SD 3.8)%]. Changes in force were related
more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by
BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective
as a countermeasure.
Accepted: 18 September 2000 相似文献
20.
Kubo K Kanehisa H Kawakami Y Fukunaga T 《European journal of applied physiology》2001,84(1-2):162-166
The purpose of this study was to investigate the changes in the elastic properties of tendons in humans in relation to fatigue
of knee extensor muscles. The muscle fatigue test (MFT) consisted of maximal isometric contractions performed 50 times. The
decline in peak moment was 43.6 (SD 19.5)%. After MFT, the muscle thickness and pennation angle of the vastus lateralis muscle
(VL) significantly increased 1.5 (SD 0.7) mm (5%) and 1.7 (SD 1.8)° (11%), respectively. Before and after MFT, the elongation
(l) of the tendon and aponeurosis of VL was directly measured by ultrasonography, while the subjects performed ramp isometric
knee extensions up to maximal voluntary contraction . The l tended to be greater after MFT than before MFT. This difference in the l was statistically significant (P < 0.05) at force developments beyond 220 N. Furthermore, the compliance increased significantly from 2.0 (SD 0.6) · 10−2 mm · N−1 before MFT to 2.6 (SD 0.7) · 10−2 mm · N−1 after MFT (22.7%). In addition, the electromechanical delay was significantly increased from 60.6 (SD 5.9) ms before to 70.0 (SD 4.4) ms
after MFT. These results suggested that the repeated muscle contractions made the tendon structures more compliant.
Accepted: 15 August 2000 相似文献