共查询到20条相似文献,搜索用时 31 毫秒
1.
Nicola A. Maffiuletti Jonas Saugy Marco Cardinale Jean-Paul Micallef Nicolas Place 《European journal of applied physiology》2013,113(6):1625-1634
The aim of this study was to examine the magnitude and the origin of neuromuscular fatigue induced by half-squat static whole-body vibration (WBV) exercise, and to compare it to a non-WBV condition. Nine healthy volunteers completed two fatiguing protocols (WBV and non-WBV, randomly presented) consisting of five 1-min bouts of static half-squat exercise with a load corresponding to 50 % of their individual body mass. Neuromuscular fatigue of knee and ankle muscles was investigated before and immediately after each fatiguing protocol. The main outcomes were maximal voluntary contraction (MVC) torque, voluntary activation, and doublet peak torque. Knee extensor MVC torque decreased significantly (P < 0.01) and to the same extent after WBV (?23 %) and non-WBV (?25 %), while knee flexor, plantar flexor, and dorsiflexor MVC torque was not affected by the treatments. Voluntary activation of knee extensor and plantar flexor muscles was unaffected by the two fatiguing protocols. Doublet peak torque decreased significantly and to a similar extent following WBV and non-WBV exercise, for both knee extensors (?25 %; P < 0.01) and plantar flexors (?7 %; P < 0.05). WBV exercise with additional load did not accentuate fatigue and did not change its causative factors compared to non-WBV half-squat resistive exercise in recreationally active subjects. 相似文献
2.
Stéphane Perrey Sébastien Racinais Khaled Saimouaa Olivier Girard 《European journal of applied physiology》2010,109(6):1027-1036
This study aimed to reveal the neural and muscular adjustments following a repeated-sprint (RS) running exercise. Sixteen
subjects performed a series of neuromuscular tests before, immediately after and 30 min (passive recovery) post-RS exercise
(12 × 40 m sprints interspaced by 30 s of passive recovery). Sprint times significantly lengthened over repetitions (+17%
from the first to the last sprint; P < 0.05). After RS running exercise, maximal voluntary contraction torque of the plantar flexors (−11 ± 7.3%), muscle activation
(twitch interpolation) (−2.7 ± 3.4%) and soleus maximal M-wave amplitude (−20 ± 17%) were significantly (P < 0.05) reduced but returned close to baseline after 30 min. Both soleus EMG activity and maximal Hoffmann reflex normalized with respect to M-wave amplitude did not change during the whole experiment.
From pre- to post-RS exercise, evoked twitch response was characterized by lower peak torque and maximal rate of torque development
(−13 and −11%, respectively, P < 0.05), but was not different from baseline after recovery. Peak tetanus at 20 and 80 Hz were 17 and 8% lower (P < 0.05) in the fatigued state, respectively. Acute muscle fatigue induced by RS running exercise is mainly peripheral as
the short-term (30 min) recovery pattern of plantar flexors contractile properties follows that of the voluntary force-generating
capacity. 相似文献
3.
Fimland MS Moen PM Hill T Gjellesvik TI Tørhaug T Helgerud J Hoff J 《European journal of applied physiology》2011,111(12):3041-3049
The objective of this study was to compare the neuromuscular function of the paretic and non-paretic plantar flexors (i.e.
soleus, gastrocnemius medialis, lateralis) in chronic stroke patients. It was hypothesized that the contractile rate of force
development (RFD) and neural activation, assessed by electromyogram (EMG) and V-waves normalized to the M-wave, and voluntary
activation (twitch interpolation) would be reduced during plantar flexor maximum voluntary isometric contraction and that
the evoked muscle twitch properties would be reduced in the paretic limb. Ten chronic stroke survivors completed the study.
The main findings were that the paretic side showed deteriorated function compared to the non-paretic leg in terms of (1)
RFD in all analyzed time windows from force onset to 250 ms, although relative RFD (i.e. normalized to maximum voluntary force)
was similar; (2) fast neural activation (for most analyzed time windows), assessed by EMG activity in time windows from EMG
onset to 250 ms; (3) V-wave responses (except for gastrocnemius medialis); (4) voluntary activation; (5) the evoked peak twitch
force, although there was no evidence of intrinsic muscle slowing; (6) EMG activity obtained at maximal voluntary force. In
conclusion, this study demonstrates considerable neuromuscular asymmetry of the plantar flexors in chronic stroke survivors.
Effective rehabilitation regimes should be investigated. 相似文献
4.
Horstman AM de Ruiter CJ van Duijnhoven NT Hopman MT de Haan A 《European journal of applied physiology》2012,112(1):135-144
We measured changes in maximal voluntary and electrically evoked torque and rate of torque development because of limb unloading.
We investigated whether these changes during single joint isometric muscle contractions were related to changes in jump performance
involving dynamic muscle contractions and several joints. Six healthy male subjects (21 ± 1 years) underwent 3 weeks of unilateral
lower limb suspension (ULLS) of the right limb. Plantar flexor and knee extensor maximal voluntary contraction (MVC) torque
and maximal rate of torque development (MRTD), voluntary activation, and maximal triplet torque (thigh; 3 pulses at 300 Hz)
were measured next to squat jump height before and after ULLS. MVC of plantar flexors and knee extensors (MVCke) and triplet
torque decreased by 12% (P = 0.012), 21% (P = 0.001) and 11% (P = 0.016), respectively. Voluntary activation did not change (P = 0.192). Absolute MRTD during voluntary contractions decreased for plantar flexors (by 17%, P = 0.027) but not for knee extensors (P = 0.154). Absolute triplet MRTD decreased by 17% (P = 0.048). The reduction in MRTD disappeared following normalization to MVC. Jump height with the previously unloaded leg
decreased significantly by 28%. No significant relationships were found between any muscle variable and jump height (r < 0.48), but decreases in torque were (triplet, r = 0.83, P = 0.04) or tended to be (MVCke r = 0.71, P = 0.11) related to decreases in jump height. Thus, reductions in isometric muscle torque following 3 weeks of limb unloading were significantly related
to decreases in the more complex jump task, although torque in itself (without intervention) was not related to jump performance. 相似文献
5.
Morse CI Thom JM Davis MG Fox KR Birch KM Narici MV 《European journal of applied physiology》2004,92(1-2):219-226
Previous studies have reported a decrease in muscle torque per cross-sectional area in old age. This investigation aimed at determining the influence of agonists muscle activation and antagonists co-activation on the specific torque of the plantarflexors (PF) in recreationally active elderly males (EM) and, for comparison, in young men (YM). Twenty-one EM, aged 70–82 years, and 14 YM, aged 19–35 years, performed isometric maximum voluntary contractions (MVC). Activation was assessed by comparing the amplitude of interpolated supramaximal twitch doublets at MVC, with post-tetanic doublet peak torque. Co-activation of the tibialis anterior (TA) was evaluated as the ratio of TA-integrated EMG (IEMG) activity during PF MVC compared to TA IEMG during maximal voluntary dorsiflexion. Triceps surae muscle volume (VOL) was assessed using magnetic resonance imaging (MRI), and PF peak torque was normalised to VOL (PT/VOL) since the later approximates physiological cross-sectional area (CSA) more closely than anatomical CSA. Also, physical activity level, assessed by accelerometry, was significantly lower (21%) in the elderly males. In comparison to the YM group, a greater difference in PT (39%) than VOL (19%) was found in the EM group. PT/VOL and activation capacity were respectively lower by 25% and 21% in EM compared to YM, whereas co-activation was not significantly different. In EM PT/VOL correlated with activation (R2=0.31, P<0.01). In conclusion, a reduction in activation capacity may contribute significantly to the decline in specific torque in the plantar flexors of elderly males. The hypothesis is put forward that reduced physical activity is partialy responsible for the reduced activation capacity in the elderly. 相似文献
6.
Jubeau M Muthalib M Millet GY Maffiuletti NA Nosaka K 《European journal of applied physiology》2012,112(2):429-438
This study compared between maximal voluntary (VOL) and electrically stimulated (ES) isometric contractions of the elbow flexors
for changes in indirect markers of muscle damage to investigate whether ES would induce greater muscle damage than VOL. Twelve
non-resistance-trained men (23–39 years) performed VOL with one arm and ES with the contralateral arm separated by 2 weeks
in a randomised, counterbalanced order. Both VOL and ES (frequency 75 Hz, pulse duration 250 μs, maximally tolerated intensity)
exercises consisted of 50 maximal isometric contractions (4-s on, 15-s off) of the elbow flexors at a long muscle length (160°).
Changes in maximal voluntary isometric contraction torque (MVC), range of motion, muscle soreness, pressure pain threshold
and serum creatine kinase (CK) activity were measured before, immediately after and 1, 24, 48, 72 and 96 h following exercise.
The average peak torque over the 50 isometric contractions was greater (P < 0.05) for VOL (32.9 ± 9.8 N m) than ES (16.9 ± 6.3 N m). MVC decreased greater and recovered slower (P < 0.05) after ES (15% lower than baseline at 96 h) than VOL (full recovery). Serum CK activity increased (P < 0.05) only after ES, and the muscles became more sore and tender after ES than VOL (P < 0.05). These results showed that ES induced greater muscle damage than VOL despite the lower torque output during ES. It
seems likely that higher mechanical stress imposed on the activated muscle fibres, due to the specificity of motor unit recruitment
in ES, resulted in greater muscle damage. 相似文献
7.
S. E. Alway R. L. Hughson H. J. Green A. E. Patla J. S. Frank 《European journal of applied physiology》1987,56(4):461-466
Summary Twitch potentiation was studied in the human triceps surae complex before and after intermittent maximal voluntary contractions or electrical stimulation at 20 Hz. Both forms of exercise were conducted with intact circulation for a maximum of 10 min or with circulatory occlusion until force output declined 50%. The relative potentiation was determined when a control twitch was compared to a twitch obtained after 5 s of maximal voluntary plantar flexion. The unpotentiated twitch torque (PT) and potentiated twitch torque (PT*) were reduced most severely after voluntary ischemic exercise (63.2% and 52.5% respectively, (P<0.001)). However, the relative potentiation (PT*/PT) immediately after voluntary ischemic exercise increased to 1.65±0.18 from 1.22±0.13 at rest. Both PT and PT* recovered quickly after exercise. At rest, twitch contraction time (CT) and one-half relaxation time (1/2 RT) in the unpotentiated twitch were longer than that of contraction (CT*) and one-half relaxation time (1/2 RT*) in the potentiated twitch. Following non-occluded exercise, CT, CT*, 1/2 RT and 1/2 RT* were shortened relative to rest. After ischemic exercise CT and CT* were shortened although 1/2 RT and 1/2 RT* increased relative to rest. Both CT* and 1/2 RT* quickly recovered to pre-exercise values by 5 min post-exercise. Ratios of potentiated/control twitch parameters were not altered after nonoccluded exercise, but were increased after ischemic exercise. These results suggest that the mechanisms of fatigue which depress voluntary torque and twitch and potentiated twitch torques, do not interfere with the extent of potentiation after fatiguing exercise.This study was supported by the Medical Research Council of Canada 相似文献
8.
Sigitas Kamandulis Albertas Skurvydas Marius Brazaitis Laimutis Škikas Jacques Duchateau 《European journal of applied physiology》2010,108(6):1065-1074
The aim of this study was to compare the possible changes in muscle activation level between a first and second bout of damaging
eccentric exercise performed at 2 weeks interval (i.e. repeated bout effect). To that purpose, ten physically active males
took part in this study. The eccentric exercise consisted of 10 sets of 12 maximal voluntary contractions (MVC) produced by
the knee extensors during movements performed at a constant speed of 160°s−1. Changes in voluntary and electrically evoked torque in concentric and/or isometric conditions were assessed at the following
time points: pre-exercise, and 2 min, 1 and 24 h after each eccentric exercise. At the same time points, voluntary activation
was quantified by the superimposed electrical stimulation technique. Muscle soreness and plasma CK activity were measured
within 48 h after the eccentric exercise. The results showed that the decrease in eccentric peak torque was linear throughout
the exercise protocol. At the end of bouts 1 and 2, torque was significantly reduced by 27.7 ± 9.1 and 23.4 ± 11.2, respectively,
with no difference between bouts (P > 0.05). At 24 h post-exercise, a lower reduction (P < 0.05) in MVC (17.8 ± 5.4%) and electrically evoked (16.7 ± 4.6%) isometric torque was observed for bout 2. In contrast,
no statistical difference was found in the deficit in voluntary activation between the two bouts. In conclusion, our results
indicate that the repeated bout effect of eccentric exercise appears to reduce muscle damage, but does not influence the level
of voluntary activation. 相似文献
9.
Requena B Gapeyeva H García I Ereline J Pääsuke M 《European journal of applied physiology》2008,104(3):463-472
Twitch potentiation in knee extensor (KE) muscles after a 7-s conditioning isometric maximal voluntary contraction (MVC trial),
submaximal (25% MVC) voluntary contraction (SVC trial) and submaximal tetanic contraction (25% MVC) induced by percutaneous
electrical stimulation at 100 Hz (PES trial) was compared in 12 men aged 19–25 years. Isometric twitch characteristics of
KE muscles were measured before conditioning contraction and following 10-min recovery by supramaximal electrical stimulation
of the femoral nerve. During MVC trial, twitch peak torque (Pt) potentiated (P < 0.05) immediately after the conditioning contraction with sharp decline during the first and third minute of recovery.
No significant potentiation of twitch Pt was observed in SVC trial. During PES trial, twitch Pt was potentiated (P < 0.05) within 3–10 min of recovery. The time-course of isometric twitch was not significantly altered by conditioning contractions.
It was concluded that twitch potentiation in the KE muscles differed markedly following the three conditioning contractions. 相似文献
10.
Darryl J. Cochrane Stephen R. Stannard Elwyn C. Firth Jörn Rittweger 《European journal of applied physiology》2010,108(2):311-319
Whole-body vibration (WBV) leads to a rapid increase in intra-muscular temperature and enhances muscle power. The power-enhancing
effects by WBV can, at least in part, be explained by intra-muscular temperature. However, this does not exclude possible
neural effects of WBV occurring at the spinal level. The aim of this study was to examine if muscle twitch and patellar reflex
properties were simultaneously potentiated from an acute bout of WBV in a static squat position. Six male and six female athletes
performed three interventions for 5 min, static squat with WBV (WBV+, 26 Hz), static squat without WBV (WBV−) and stationary
cycling (CYCL, 70 W). Transcutaneous muscle stimulation consisting of a single 200 μs pulse and three patellar tendon taps
were administered prior to and then 90 s, 5, 10 min post-intervention. Ninety-seconds after WBV+ muscle twitch peak force
(PF) and rate of force development (RFD) were significantly higher (P < 0.01) compared to WBV− and CYCL. However the patellar tendon reflex was not potentiated. An acute continuous bout of WBV
caused a post-activation potentiation (PAP) of muscle twitch potentiation (TP) compared to WBV− and CYCL indicating that a
greater myogenic response was evident compared to a neural-mediated effect of a reflex potentiation (RP). 相似文献
11.
Trevor C. Chen Hsin-Lian Chen Ming-Ju Lin Chang-Jun Wu Kazunori Nosaka 《European journal of applied physiology》2009,106(2):267-275
Since little is known about the repeated bout effect of more than two eccentric exercise bouts, this study compared muscle
damage responses among four exercise bouts. Fifteen young (21.8 ± 1.9 years) men performed four bouts of 30 maximal isokinetic
eccentric contractions of the elbow flexors every 4 weeks. Maximal voluntary elbow flexion isometric and concentric strength,
range of motion at the elbow joint (ROM), upper arm circumference, blood markers of muscle damage, and muscle soreness were
measured before and up to 120 h following each bout. Changes in all measures following the second to fourth bouts were significantly
(P < 0.05) smaller than those after the first bout. The decreases in strength and ROM immediately after the fourth bout were
significantly (P < 0.05) smaller than other bouts. It is concluded that the first bout confers the greatest adaptation, but further adaptation
is induced when the exercise is repeated more than three times. 相似文献
12.
The effects of whole body vibration on balance,joint position sense and cutaneous sensation 总被引:1,自引:0,他引:1
Pollock RD Provan S Martin FC Newham DJ 《European journal of applied physiology》2011,111(12):3069-3077
Whole body vibration (WBV) may enhance muscular strength and power but little is known about its influence on sensory-motor
function. Vibration of a single muscle or tendon affects the afferent system in a manner that depends on amplitude and frequency.
WBV stimulates many muscle groups simultaneously and the frequencies and amplitudes used are different from many of the studies
on single musculotendinous units. We investigated the effects of WBV at two amplitudes on balance, joint position sense (JPS)
and cutaneous sensation in young healthy subjects. Eighteen adults (24.3 ± 1.5 years, 15 females) were assessed before WBV
(five 1 min bouts, 30 Hz) then immediately, 15 and 30 min afterwards. Two amplitudes (4 and 8 mm peak to peak) were investigated
on different occasions. Standing balance was assessed with feet together and eyes closed, and standing on one leg with eyes
open and closed. JPS at the knee and ankle was assessed by repositioning tasks while cutaneous sensation was recorded from
six sites in the lower limb using pressure aesthesiometry. Neither amplitude affected JPS (P > 0.05). There were minimal effects on balance only in the vertical plane and only 30 min after WBV (P < 0.05). Low amplitude vibration only reduced sensation at the foot and ankle immediately after WBV (P < 0.008). High amplitude vibration impaired sensation at the foot, ankle and posterior shank for the entire test period (P < 0.008). In young healthy individuals WBV did not affect JPS or static balance, but reduced cutaneous sensation. These data
may have implications for older and clinical populations with compromised postural control. 相似文献
13.
Gondin J Guette M Maffiuletti NA Martin A 《European journal of applied physiology》2004,93(3):359-365
The purpose of this study was to investigate the effect of 2 weeks of ankle joint immobilization on triceps surae neural activation, with particular emphasis on the potential differences between the monoarticular soleus and the biarticular gastrocnemius muscles. Seventeen male volunteers were divided into the immobilized group (IG, n=8) and the control group (CG, n=9). Elastic adhesive bandages and an ankle stabilization orthosis were used to immobilize the ankle joint only. The plantar flexor torque obtained during maximal voluntary contractions (MVC) and after single, paired and tetanic stimuli applied at rest was measured. The associated EMG activity from the soleus and gastrocnemius muscles was also recorded, and their activation levels were estimated by means of the twitch interpolation technique. After immobilization, triceps surae maximal voluntary torque significantly decreased by 17% (P<0.001). Strength losses were accompanied by a decrement in activation level (–6%, average of the three techniques used) and in maximal 100 Hz tetanic force (–11%). A significant decrease in the soleus (–22%, P<0.05) but not in the gastrocnemius EMG activity, normalized to respective M-waves, was also found. It was concluded that the reduced voluntary torque output after immobilization could be attributed to both muscular and neural alterations. These latter selectively involved the monoarticular soleus muscle, while neural drive to the biarticular gastrocnemii, which had not been immobilized in their function as knee flexors, was preserved. 相似文献
14.
This study was designed to investigate if the relationship between the interpolated twitch-torque (IT) and voluntary torque
(VT) is affected by the number of electrical stimuli (single vs. double) and the stimulation site (nerve trunk vs. muscle).
The results showed that the IT–VT relationship of the plantar flexors is appropriately described by a composite (linear + curvilinear)
model. Indeed, whatever the stimulation method, the IT–VT relationship was linear between approximately 25 and 75% of the
maximal voluntary torque (MVT) and curvilinear for higher contraction intensities. The four stimulation conditions are equivalent
in assessing the maximal voluntary activation (VA% range 96.2 ± 5.0 to 98.5 ± 3.1%) as well as in determining the true maximal
torque expected for total twitch occlusion (MTexp range 171.4 ± 21.2 to 179.0 ± 26.8 Nm). The gap between the MVT and MTexp should be viewed as an index of muscle inactivation. This gap was comparable for the four stimulation methods (2–6%) and
close to the deficit in VA% (2–4%). No pulse-number effect was found on the IT–VT relationship when the nerve was stimulated
but an effect on the concavity of the composite relationship was observed when the stimulation was applied over the muscle.
Even though the four stimulation techniques are equivalent in assessing the maximal activation capacity our results demonstrate
that the neural stimulation method is the most consistent as it guarantees the same motor pool recruitment independently from
the number of pulses. 相似文献
15.
Milesi S Capelli C Denoth J Hutchinson T Stüssi E 《European journal of applied physiology》2000,82(3):197-205
Maximal voluntary isometric torque values of the ankle plantar (T
im,PF) and dorsal flexors (T
im,DF) were assessed in eight healthy adult males at 5° and 15° of dorsal flexion (DF) and at 5°, 15° and 25° of plantar flexion
(PF) with the knee at right angles, before (two times), during (three times) and after (three times) 17 days of 6° head-down
tilt bedrest (BR). Integrated electromyograms (iEMG) were also recorded from the gastrocnemius medialis and tibialis anterior.
T
im,PF and the iEMG of the gastrocnemius medialis were significantly larger (by 14% and by 27%, respectively) at the end of recovery
than before BR. This was probably the consequence of training and/or habituation leading to: (1) increased activation of the
plantar flexors; and (2) decreased co-activation of the antagonist muscles. Neither T
im,DF nor the tibialis anterior iEMG changed significantly. The effects of BR on muscle performance were evaluated as follows.
The net torque generated by a given muscle group was assumed to be the algebraic sum of the torque generated by the agonists
and by the antagonists. Thus, for the plantar flexors Tim,PF=αiEMGGm − βiEMGTa, where: (1) iEMGGm and iEMGTa are the iEMGs of gastrocnemius medialis and of tibialis anterior during maximal PF; and (2) the constants α and β represent
the electromechanical coupling of the plantar (α) and dorsal (β) flexors. Similarly for the dorsal flexors: Tim,DF=βiEMGTa − αiEMGGm, where iEMGTa and iEMGGm are the iEMGs of tibialis anterior and gastrocnemius medialis during maximal DF. Torque and iEMG values were assessed for
all subjects under all experimental conditions. Thus, since the biomechanical leverage of the system was constant, α and β
could be calculated. During BR, α decreased by 25% and it dropped by a further 30% during recovery. In contrast, β remained
almost unchanged. This suggests that, in spite of training and/or habituation, BR significantly impaired the maximal isometric
performance of the plantar flexors, an effect that continued during the initial 10 days of recovery.
Accepted: 4 February 2000 相似文献
16.
Cornelis Jo de Ruiter Alex de Korte Sander Schreven Arnold de Haan 《European journal of applied physiology》2010,108(2):247-255
We hypothesized that maximal unilateral isometric knee extensor torque, the rate of torque development during maximally fast
isometric contractions and unilateral squat jump performance would be better with the dominant than non-dominant leg. Limb
dominancy was established using the step up, balance recovery, and ball kick test. On two days, eight men (21.5 ± 2.2 years,
means ± SD) performed unilateral maximal isometric contractions with their knee extensors (120° knee angle) with superimposed
electrical stimulation to determine maximal torque and voluntary activation for both limbs. In addition, maximally fast isometric
contractions without countermovement and unilateral squat jumps (SJ) starting from 120° knee angles were performed. Torque
time integral (contractile impulse) over the first 40 ms after torque onset (TTI40) and maximal rates of torque development
(MRTD) during voluntary and maximal electrical nerve stimulation were used to quantify initial torque rise. Limb dominancy
tests were very consistent, but none of the parameters was (or tended to be) significantly different between limbs, neither
during maximal electrical stimulation nor during voluntary attempts. Between limbs there were significant relationships for
voluntary TTI40 (r
2 = 0.94) and maximal SJ height (r
2 = 0.88) and both parameters were significantly related in both limbs (r
2 = 0.69 and 0.75). In conclusion, unilateral fast torque generating capacity, muscle activation and squat jump performance
were similar in both limbs, but differed substantially among subjects, with strong correlations between fast voluntary isometric
torque development and jump height. These findings further challenge the concept of lower limb dominancy in dynamometry testing
in sports and rehabilitation. 相似文献
17.
Girard O Millet GP Micallef JP Racinais S 《European journal of applied physiology》2012,112(6):2323-2330
The aim of this study was to characterize the effect of a 5 km running time trial on the neuromuscular properties of the plantar flexors. Eleven well-trained triathletes performed a series of neuromuscular tests before and immediately after the run on a 200 m indoor track. Muscle activation (twitch interpolation) and normalized EMG activity were assessed during maximal voluntary contraction (MVC) of plantar flexors. Maximal soleus H-reflexes and M-waves were evoked at rest (i.e. H (MAX) and M (MAX), respectively) and during MVC (i.e. H (SUP) and M (SUP), respectively). MVC significantly declined (-27%; P < 0.001) after the run, due to decrease in muscle activation (-8%; P < 0.05) and M (MAX)-normalized EMG activity (-13%; P < 0.05). Significant reductions in M-wave amplitudes (M (MAX): -13% and M (SUP): -16%; P < 0.05) as well as H (MAX)/M (MAX) (-37%; P < 0.01) and H (SUP)/M (SUP) (-25%; P < 0.05) ratios occurred with fatigue. Following exercise, the single twitch was characterized by lower peak torque (-16%; P < 0.001) as well as shorter contraction (-19%; P < 0.001) and half-relaxation (-24%; P < 0.001) times. In conclusion, the reduction in plantar flexors strength induced by a 5 km running time trial is caused by peripheral adjustments, which are attributable to a failure of the neuromuscular transmission and excitation-contraction coupling. Fatigue also decreased the magnitude of efferent motor outflow from spinal motor neurons to the plantar flexors and part of this suboptimal neural drive is the result of an inhibition of soleus motoneuron pool reflex excitability. 相似文献
18.
Steve McGaraughty Stanislav Reinis John Tsoukatos 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1995,105(2):283-290
The present study was designed to determine the relative contribution of the gastrocnemius muscle to isometric plantar flexor torque production at varying knee angles, while investigating the activation of the gastrocnemius muscle at standardised non-optimal lengths. Voluntary plantar flexor torque, supramaximally stimulated twitch torque and myoelectric activity (EMG) from the triceps surae were measured at different knee angles. Surface and intra-muscular EMG were recorded from the soleus muscle and the medial and lateral heads of the gastrocnemius muscle in 10 male subjects. With the ankle angle held constant, knee angle was changed in steps of 30° ranging from 180° (extended) to 60° (extreme flexion), while voluntary torque from a 5-s contraction was determined at 10 different levels of voluntary effort, ranging from 10% of maximal effort to maximal effort. To assess effort, supramaximal twitches were superimposed on all voluntary contractions, and additionally during rest. Maximal plantar flexor torque and resting twitch torque decreased significantly in a sigmoidal fashion with increasing knee flexion to 60% of the maximum torque at 180° knee angle. For similar levels of voluntary effort, the EMG root mean square (RMS) of gastrocnemius was less with increased knee flexion, whereas soleus RMS remained unchanged. From these data, it is concluded that the contribution of gastrocnemius to plantar flexor torque is at least 40% of the total torque in the straight leg position. The decrease of gastrocnemius EMG RMS with decreasing muscle length may be brought about by a decrease in the number of fibres within the EMG electrode recording volume and/or impaired neuromuscular transmission. 相似文献
19.
Maffiuletti NA Pensini M Scaglioni G Ferri A Ballay Y Martin A 《European journal of applied physiology》2003,90(5-6):601-607
When muscle is artificially activated, as with electromyostimulation (EMS), action potentials are evoked in both intramuscular nerve branches and cutaneous receptors, therefore activating spinal motoneurons reflexively. Maximal soleus and gastrocnemii H- and T-reflex and the respective mechanical output were thus quantified to examine possible neural adaptations induced at the spinal level by EMS resistance training. Eight subjects completed 16 sessions of isometric EMS (75 Hz) over a 4-week period. Maximal soleus and gastrocnemii M wave (Mmax), H reflex (Hmax) and T reflex (Tmax) were compared between before and after training, together with the corresponding plantar flexor peak twitch torque. No significant changes were observed for electromechanical properties of Hmax reflex following EMS. On the other hand, peak twitch torque produced by Tmax, but not by equal-amplitude H reflex, significantly increased as a result of training (+21%, P<0.05). These changes were associated with a trend towards a significant increase for normalized gastrocnemii (+21%, P=0.07) but not soleus Tmax reflex. It is concluded that, contrary to results previously obtained after voluntary physical training, EMS training of the plantar flexor muscles did not affect alpha motoneuron excitability and/or presynaptic inhibition, as indicated by H-reflex results. On the other hand, in the absence of change in a control group, Tmax electromechanical findings indicated that: (1) equal-amplitude H- and T-reflex adapted differently to EMS resistance training; and (2) EMS had an effect on gastrocnemii but not on soleus muscle, perhaps because of the differences in respective motor unit characteristics (e.g., axon diameter). 相似文献
20.
Oya T Cresswell AG 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2008,185(4):699-707
To determine whether the soleus (SOL) H-reflex is modulated during shortening contractions in a manner that has been observed
for isometric contractions, SOL H-reflexes and M-waves were elicited via percutaneous electrical stimulation to the tibial
nerve at an intensity that evoked an H-reflex at 50% of its maximum in 11 healthy subjects. Paired electrical stimuli were
delivered as the ankle angle passed through 90° at an interval of 400 ms while the subject performed shortening contractions
at levels of plantar flexion torque ranging between 2 and 30% of that during a maximal voluntary contraction (MVC). H-reflexes
were also recorded during the performance of isomeric contractions of plantar flexors at similar levels of plantar flexion
torque and at the same joint angle (muscle length) in an additional five healthy subjects. Correlations were examined between
the peak-to-peak amplitude of the first H-reflexes, M-waves and plantar flexion torques in both protocols. It was revealed
that no significant correlation was found between the SOL H-reflex and increasing plantar flexion torque during shortening
contractions (ρ = −0.07, P = 0.15), while a strong positive correlation was observed for the isometric conditions (ρ = 0.99, P < 0.01). No significant change was observed in the SOL M-wave for either contraction type. Furthermore, the H-reflexes elicited
via paired stimuli with the same background activity in voluntary shortening contractions showed almost identical amplitudes,
suggesting that the level of homosynaptic post-activation depression did not change in response to the varying levels of activation
in voluntary shortening contractions. Therefore, the lack of increase in the H-reflex during shortening contractions at increasing
intensities is possibly due to a centrally regulated increase in presynaptic inhibition. Such a downward modulation of the
reflex suggests that Ia-excitatory input onto the SOL motoneurone pool needs to be reduced during the performance of shortening
contractions. 相似文献