共查询到20条相似文献,搜索用时 31 毫秒
1.
The purpose of this study was to investigate whether acute passive stretching (APS) reduced maximal isometric voluntary contraction (MVC) of the plantar flexors (PF) and if so, by what mechanisms. The PF in 15 female volunteers were stretched for 10 min (5×120 s) by a torque motor to within 2° of maximum dorsiflexion (D) range of motion (ROM). MVC with twitch interpolation, maximal Hoffmann reflex (Hmax) and compound action potentials (Mmax) were recorded at 20° D. Stretch reflexes (SR) were mechanically induced at 200° s–1 between 0° and 10° D and SR torque and EMG amplitude were determined. All tests were assessed pre- (pre) and post-APS (post-test1). MVC, SR, and Mmax were again assessed after additional stretch was applied [mean 26 (1)° D; post-test2] to test if the optimal angle had been altered. EMG was recorded from soleus (SOL), medial gastrocnemius (MG) and tibialis anterior (TA) using bipolar surface electrodes. APS resulted in a 27% decrease in mean peak passive torque (P<0.05). MVC and SR torque were 7% (P<0.05) and 13% lower at post-test1 (P<0.05), respectively. SR EMG amplitude of SOL and MG was reduced by 27% (P<0.05) and 22% (P<0.05), respectively. The Hmax/Mmax EMG and Hmax/Mmax torque ratios were unchanged at post-test1. At post-test2, MVC and SR EMG recovered to pre-APS values, while the SR and Mmax torque increased by 19% and 13%, respectively (P<0.05). The decrease in MVC during post-test1 was attributed to changes in the mechanical properties of PF and not to reduced muscle activation. 相似文献
2.
This study determined the effects of a short period of knee isometric training on the quadriceps muscles accessible to surface
electromyography (EMG). For this purpose, a training (n=9) and a control (n=7) group were tested on five identical occasions at 1 week intervals during 4 weeks. The training group exercised three times
a week by making isometric knee extensions at 80% of the maximal voluntary contraction (MVC). During the test sessions, maximal
and submaximal torque and associated activations of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM)
muscles were analysed. As a result of training, differences between MVC values of the two groups were highly significant (P < 0.001), whereas only RF-EMG showed significant differences (P < 0.05). The VL and VM did not present any significant changes in maximal activation. The EMG–torque relationships were analysed
individually before and after the training period. For the control subjects, EMG–torque relationships did not present significant
changes while for the training group, these relationships showed a significant increase in RF, VL, and VM maximal activation
in 6, 6 and 4 subjects, respectively, and a significant decrease in 1, 2 and 5 subjects, respectively. In almost all cases,
a significant downward shift of the relationship was observed. This study confirmed that the parts of the quadriceps muscle
tested present different adaptation capacities and demonstrate inter-individual variability in the strategies used to enhance
muscle strength. In conclusion, to analyse the neural effects resulting from training in a large and compartmentalized muscle
like the quadriceps femoris, it is desirable to take into account each muscle independently. Moreover, we suggest that overall
results obtained from the experiment population should be completed by an analysis on individuals.
Accepted: 1 September 2000 相似文献
3.
Cramer JT Housh TJ Evetovich TK Johnson GO Ebersole KT Perry SR Bull AJ 《European journal of applied physiology》2002,86(3):226-232
The purpose of the present investigation was to examine the velocity-related patterns of peak torque (PT), mean power output
(MP), mechanomyographic (MMG) amplitude, and electromyographic (EMG) amplitude of the vastus lateralis (VL) muscle in men
and women during maximal, eccentric isokinetic muscle actions of the leg extensors. Eight women [mean (SD)] [aged 23 (3) years]
and seven men [aged 23 (2) years] volunteered for this investigation. Their PT was measured on a calibrated dynamometer at
randomly ordered velocities of 30, 90, and 150°·s–1. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes (Ag-AgCl) over the VL muscle. Their
MP was determined using the dynamometer software. The results indicated no sex-related differences (P>0.05) for the patterns of PT, MP, MMG amplitude, or EMG amplitude across velocity. The normalized values for MP and MMG amplitude
increased (P<0.05) from 30 to 150°·s–1 (30°·s–1<90°·s–1<150°·s–1), while PT and EMG amplitudes remained unchanged across velocity. The results indicated close associations between the velocity-related
patterns of MP and MMG amplitudes as well as PT and EMG amplitudes. Thus, MMG amplitude reflected the velocity-related changes
in muscle power output, but not torque production, while EMG amplitude reflected torque production, but not muscle power output.
During maximal, eccentric isokinetic muscle actions, EMG and MMG signals provided unique information regarding the electrical
and mechanical aspects of muscle strength and power.
Electronic Publication 相似文献
4.
Robert M. Erskine David A. Jones Alun G. Williams Claire E. Stewart Hans Degens 《European journal of applied physiology》2010,110(6):1117-1125
Considerable variation exists between people in the muscle response to resistance training, but there are numerous ways muscle
might adapt to overload that might explain this variable response. Therefore, the aim of this study was to quantify the range
of responses concerning the training-induced change in maximum voluntary contraction (MVC) knee joint torque, quadriceps femoris
(QF) maximum muscle force (F), physiological cross-sectional area (PCSA) and specific tension (F/PCSA). It was hypothesized that the variable change in QF specific tension between individuals would be less than that of
MVC. Fifty-three untrained young men performed progressive leg-extension training three times a week for 9 weeks. F was determined from MVC torque, voluntary muscle activation level, antagonist muscle co-activation and patellar tendon moment
arm. QF specific tension was established by dividing F by QF PCSA, which was calculated from the ratio of QF muscle volume to muscle fascicle length. MVC torque increased by 26 ± 11%
(P < 0.0001; range −1 to 52%), while F increased by 22 ± 11% (P < 0.0001; range −1 to 44%). PCSA increased by 6 ± 4% (P < 0.001; range −3 to 18%) and specific tension increased by 17 ± 11% (P < 0.0001; range −5 to 39%). In conclusion, training-induced changes in F and PCSA varied substantially between individuals, giving rise to greater inter-individual variability in the specific tension
response compared to that of MVC. Furthermore, it appears that the change in specific tension is responsible for the variable
change in MVC. 相似文献
5.
This study examines the effect of fascicle length change on motor-unit recruitment and discharge rate in the human tibialis anterior (TA) during isometric contractions of various intensities. The torque produced during dorsiflexion and the surface and intramuscular electromyograms (EMGs) from the TA were recorded in eight subjects. The behavior of the same motor unit (n = 59) was compared at two ankle joint angles (+10 and -10 degrees around the ankle neutral position). Muscle fascicle length of the TA was measured noninvasively using ultrasonography recordings. When the ankle angle was moved from 10 degrees plantarflexion to 10 degrees dorsiflexion, the torque produced during maximal voluntary contraction (MVC) was significantly reduced [35.2 +/- 3.3 vs. 44.3 +/- 4.2 (SD) Nm; P < 0.001] and the average surface EMG increased (0.47 +/- 0.08 vs. 0.43 +/- 0.06 mV; P < 0.05). At reduced ankle joint angle, muscle fascicle length declined by 12.7% (P < 0.01) at rest and by 18.9% (P < 0.001) during MVC. Motor units were activated at a lower recruitment threshold for short compared with long muscle fascicle length, either when expressed in absolute values (2.1 +/- 2.5 vs. 3.6 +/- 3.7 Nm; P < 0.001) or relative to their respective MVC (5.2 +/- 6.1 vs. 8.8 +/- 9.0%). Higher discharge rate and additional motor-unit recruitment were observed at a given absolute or relative torque when muscle fascicles were shortened. However, the data indicate that increased rate coding was mainly present at low torque level (<10% MVC), when the muscle-tendon complex was compliant, whereas recruitment of additional motor units played a dominant role at higher torque level and decreased compliance (10-35% MVC). Taken together, the results suggest that the central command is modulated by the afferent proprioceptive information during submaximal contractions performed at different muscle fascicle lengths. 相似文献
6.
Mark Jesunathadas Thorsten Rudroff Roger M. Enoka 《European journal of applied physiology》2010,110(6):1175-1186
This study examined the associations between the fluctuations of foot acceleration during shortening and lengthening contractions
with the electromyographic (EMG) activity of lower leg muscles and ultrasound measures of tibialis anterior fascicle length
and pennation angle. Young (24.9 ± 4.17 years) and old (74.8 ± 3.31 years) adults lifted and lowered a submaximal load with
the foot at different speeds (3°/s–50°/s). The standard deviation (SD) of foot acceleration normalized to the load lifted
was similar for young (12.2 ± 7.22 cm s−2/kg) and old adults (14.3 ± 8.03 cm s−2/kg; P = 0.093). The changes in tibialis anterior muscle fascicle length and pennation angle were similar for young and old adults
(P ≥ 0.233), but greater for shortening (fascicle length: 0.937 ± 0.633 cm, pennation angle: 1.61 ± 0.918o) than for lengthening
contractions (fascicle length: 0.806 ± 0.521 cm, pennation angle: 0.966 ± 0.632o; P ≤ 0.014). The changes in fascicle length and pennation angle were not associated with the SD of foot acceleration (r
2 ≤ 0.031; P ≥ 0.092). The surface EMG of tibialis anterior was greater for the shortening contractions than for the lengthening contractions
(P < 0.001), but triceps surae EMG was similar for the two types of contractions (P = 0.304). The results suggested that the influence of movement speed on variability in performance was similar for shortening
and lengthening contractions with the dorsiflexor muscles; furthermore, old adults were able to match the performance of young
adults. 相似文献
7.
Force-generating capacity and electromyographic (EMG) activity of the knee extensor muscles were studied before and after short-term (10 d) unilateral lower limb unloading and during 4 days of recovery. Ten healthy males used crutches to prevent one of their lower limbs from weight-bearing while maintaining joint mobility as well as daily ambulatory activities. Knee extensor torque and quadriceps rectified EMG during maximal voluntary isometric contraction (MVC) was measured repeatedly before and after the intervention. Also, EMG at a fixed submaximal level (100 Nm; 30–45% MVC) and maximal angular velocity (AVmax), during unresisted knee extension, were assessed. Maximum torque decreased (P<0.05) by 13±8% in response to unloading while maximum EMG activity did not change after unloading or during recovery (P=0.35). Submaximum EMG increased (P<0.05) by 25±16% after unloading. Maximum and submaximum torque/EMG ratios decreased (P<0.05) after unloading. AVmax decreased (P<0.05) by 9±8% after unloading. The post value, however, was not different from that of the weight-bearing limb. Torque, EMG and AVmax were recovered (P>0.05) after 4 days of resumed weight-bearing. The pronounced decrease and the rapid recovery in maximum torque appears not to be attributed to a change in muscle mass alone. Because the findings of unchanged maximum EMG and increased EMG at a submaximal force level suggest no change in neural drive, we propose that unspecific tissue factors in part impair muscle function in response to short-term loss of weight-bearing activity. Results also indicate that recovery in muscle function after short-term unloading seems to be completed in a time span shorter than the period of preceding inactivity. 相似文献
8.
The purpose of the present study was to investigate the fatigue effect of repeated exhaustive stretch-shortening cycle (SSC)
exercise on concentric muscle function. Ten healthy male subjects performed SSC exercise [92 (30) jumps] on a special sledge
apparatus. Exhaustion occurred on average within 3 min. A squat jump (SJ) test utilizing a concentric-only action was performed
immediately before and after the SSC exercise, and then 10 min, 20 min, 2 days and 4 days later. In addition, a drop jump
(DJ) test using an SSC was also performed immediately before and 20 min after the SSC exercise, and 2 days and 4 days later.
During jump tests, lower limb joint moment, power, and work contributions were analyzed by using the kinetic and kinematic
data. The fatigue exercise was characterized by a relatively high blood lactate concentration [7.2 (0.8) mmol·l–1] and a 2-day delayed increase in serum creatine kinase activity [486 (300) U·l–1]. SJ performance decreased markedly immediately after the SSC exercise (P<0.05) and then recovered within 10 min. In contrast, DJ performance and knee joint contribution showed a delayed decrease
2 days after the SSC exercise bout. The surface electromyographic (EMG) activity of the lower limb muscles showed no obvious
change in the SJ in comparison to the DJ, although in the latter there was a delayed decrease of knee extensor EMG during
the pre-activation and braking phases. The results suggest that isolated concentric muscle function is affected mainly by
acute metabolic fatigue after SSC exercise. During a follow-up period after the exercise, changes in hip and knee joint contribution
in SJ showed a different recovery pattern compared to those in eccentric DJ. It could be suggested that exhaustive SSC exercise
would mainly influence the relative power–work balance between the hip and knee joints during the eccentric phase of SSC.
Thus different motor control strategies may account for the distinctive fatigue responses observed in SJ and DJ.
Electronic Publication 相似文献
9.
Relationship between myoelectric and mechanical manifestations of fatigue in the quadriceps femoris muscle group 总被引:1,自引:0,他引:1
Anne F. Mannion P. Dolan A. F. Mannion P. Dolan 《European journal of applied physiology》1996,74(5):411-419
Fatigue is commonly defined as “the failure to maintain the required force”. As such, it may be argued that the use of electromyographic
(EMG) power spectral statistics to monitor muscle fatigue is inappropriate, because, during the maintenance of a submaximal
force of contraction, EMG changes are readily observable in the absence of any decline in the muscle's mechanical output.
However, it is possible that the EMG changes reflect the changing metabolic status of the muscle and hence its inability to
generate its normal maximal force. The present study sought to examine whether the decline in EMG median frequency, which
occurs during the maintenance of a submaximal force, is correlated with a reduction in the muscle's maximum force-generating
capacity. The maximum voluntary contraction (MVC) of the knee extensors in ten young, healthy subjects was determined. On
five separate occasions, randomly assigned forces of 20, 30, 40, 50 and 60% MVC were held to the limit of endurance. At intervals
throughout the sustained contractions, subjects were required to rapidly generate an MVC for 1–2 s, then return to the fixed
submaxial target force. Surface EMG signals were recorded throughout the contractions from the rectus lemons and vastus lateralis
muscles, from which the power spectrum median frequency was calculated. Regression analysis revealed highly significant relationships
between the rate of decline in MF and the rate of decline in MVC, and between each of these parameters and endurance time
to fatigue (P = 0.0001, in each case). It is concluded that the decline in MF can be used to monitor fatigue, where fatigue is defined
as the inability to generate the maximum force that can be produced by the muscle in its fresh state. 相似文献
10.
To examine whether postactivation potentiation (PAP) was related to changes in the electromyogram (EMG) and in the mechanomyogram
(MMG), evoked twitch torque properties were compared before and after a 10 s plantar flexion MVC in ten male subjects. Peak
twitch torque (Pt), and the peak acceleration of the twitch torque development (d2
T/dt
2) were measured from electrical tibial nerve stimulation. In addition, from the medial gastrocnemius muscle, peak to peak
MMG (p-p MMG) by means of accelerometer, and peak to peak EMG (M-wave) amplitudes were recorded. Immediately (2 s) following
the MVC there were significant increases in Pt (47%), d2
T/dt
2 (86%), and p-p MMG (70%), but no change in the M-wave. At 2 s, 15 s, 30 s after the MVC, individual percent changes in p-p
MMG were significantly and positively correlated with individual percent changes in both Pt and d2
T/dt
2. These results indicate that evoked MMG reflects acute enhanced force output elicited by PAP, and that the increases in twitch
contraction properties represent intrinsic mechanical changes of the muscle, that are not associated with electrical changes.
Furthermore, measurements of the evoked p-p MMG signal following PAP support the utility of describing the gross lateral movement
phase of the MMG signal. 相似文献
11.
Reflex responses to unexpected stretches are well documented for selected muscles in both animal and human. Moreover, investigations
of their possible functional significance have revealed that stretch reflexes can contribute substantially to the overall
stiffness of a joint. In the lower extremity only the muscles spanning the human ankle joint have been investigated in the
past. This study implemented a unique hydraulic actuator to study the contributions of the knee extensor stretch reflex to
the overall knee joint torque. The quadriceps muscles were stretched at various background torques, produced either voluntarily
or by electrical stimulation, and thus the purely reflex mediated torque could be calculated. The stretch had a velocity of
67°/s and an amplitude of 20°. A reflex response as measured by electromyography (EMG) was observed in all knee extensors
at latencies of 26 – 36 ms. Both phasic and tonic EMG stretch responses increased with increasing background torques. Lines
of best fit produced correlation coefficients of 0.59 – 0.78. This study is the first to examine the reflex contribution of
the knee extensors to the total torque at background torques of 0 – 90% MVC. The contribution of the reflex mediated torque
is initially low and peaked at background torques of 20 – 40% MVC. In terms of the total torque the reflex contributed 16
– 52% across all levels of background torque. It is concluded that during medium background torque levels such as those obtained
during walking, the stretch reflex of the quadriceps muscle group contributes substantially to the total torque around the
knee joint. 相似文献
12.
Pääsuke M Saapar L Ereline J Gapeyeva H Requena B Oöpik V 《European journal of applied physiology》2007,101(5):577-585
This study compared postactivation potentiation (PAP) in knee extensor muscles after a 10 s conditioning isometric maximal
voluntary contraction (MVC) in female power- (PT, n = 12) and endurance-trained (ET, n = 12) athletes, and untrained (UT, n = 12) women aged 20–24 years. Isometric twitch characteristics of the knee extensor muscles were assessed in pre-MVC condition
and during 15 min post-MVC period using supramaximal electrical stimulation of the femoral nerve by rectangular pulses of
1 ms duration. A significant (P < 0.05) potentiation of twitch peak torque (Pt, 30–51% in different groups), maximal rates of torque development (50–125%)
and relaxation (76–124%) occurred immediately (2 s) post-MVC. PAP declined sharply at 1–3 min of recovery, whereas a significant
potentiation of twitch Pt was still present for ET athletes at 1 min, and for UT women and PT athletes at 5 min of recovery,
respectively. There were no significant (P > 0.05) changes in twitch contraction and half-relaxation times after a 10 s conditioning MVC. We concluded that PAP in knee
extensor muscles is enhanced in PT but not in ET female athletes. The magnitude of PAP was greater when measured immediately
after the conditioning MVC and its decline was slower in PT compared with ET athletes. Immediately post-MVC, twitch speed-related
characteristics were potentiated to a greater extent than twitch Pt. The time-course of isometric twitch was not significantly
altered by conditioning MVC. 相似文献
13.
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
14.
This study investigates the changes in mechanomyographic (MMG) topographical maps of the upper trapezius muscle during short
and sustained isometric contractions until task failure. MMG signals were detected over the dominant upper trapezius muscle
of 12 volunteers using an unstructured grid of 12 accelerometers. The subjects performed isometric shoulder elevation at (1)
maximal voluntary contraction (100% MVC), (2) 10–20–40–60–80–100% MVC for 10 s and (3) 20% MVC until task failure. Maps of
absolute and normalised average rectified value (ARV) and mean power frequency (MNF) were obtained from the two-dimensional
MMG recordings. Entropy (measure of heterogeneity of maps) of the MMG ARV and MNF distributions, changes over time of ARV
and MNF, and the ratio between ARV at the task failure and at 100% MVC (activation ratio) were analysed in relation to the
time to task failure. For the short duration and sustained contractions, MMG ARV and MNF depended on accelerometer location
(P < 0.001) while normalised values did not. The activation ratio was positively correlated with the time to task failure (R
2 = 0.36, P < 0.05). Lower ARV entropy values (P < 0.05), greater MMG ARV increase during the endurance test (P < 0.001) and higher values of ARV activation ratio (P < 0.001) were observed in the subjects with longer time to task failure. The results demonstrate an association between time
to task failure and MMG activation ratio and ARV entropy, which indicates that spatial variations in MMG activity and its
changes over time underlie functional mechanisms for the maintenance of force during fatiguing contractions. 相似文献
15.
This study investigated the contribution of muscle architecture to the differences in the torque–velocity and power–velocity
relationships between older (OM n = 9, aged 69–82 years) and younger men (YM n = 15, aged 19–35 years). Plantarflexors’ (PF) maximal isometric and concentric torques were recorded at 0.87, 1.75, 2.62,
3.49 and 4.36 rad s−1. Physiological cross-sectional area (PCSA) was calculated as the ratio of muscle volume (determined by magnetic resonance
imaging) to muscle fascicle length (L
f, measured by ultrasonography). GM PCSA and L
f of the OM were, respectively, 14.3% (P < 0.05) and 19.3% (P < 0.05) smaller than of the YM. In the OM, GM maximum isometric torque and maximum contraction velocity (V
max), estimated from Hill’s equation were, respectively, 48.5 and 38.2% lower (P < 0.001) than in the YM. At all contraction velocities, the OM produced less torque than the YM (46.3% of YM at 0.87 rad s−1 to 14.7% at 4.36 rad s−1, P < 0.001). Peak power (PP) of the OM was 80% lower than that of the YM and normalisation of PP to muscle volume only reduced
this difference by 10%. Normalisation of torque to PCSA reduced, but did not eliminate, differences in torque between YM and
OM (9.6%) and differences in torque/PCSA increased with contraction velocity (P < 0.05). After normalisation of velocity to L
f, the difference in V
max between the OM and the YM was reduced to 15.9%. Thus, although muscle architecture contributes significantly to the differences
in the torque– and power–velocity properties of OM and YM, other contractile factors, intrinsic to the muscle, seem to play
a role. It is noteworthy that the deficit in PP between OM and YM is far greater than that of muscle torque, even after normalisation
of PP to muscle volume. This finding likely plays an important role in the loss of mobility in old age. 相似文献
16.
The purpose of this study was to examine whether the human gastrocnemius medialis (GM) fascicle length and pennation angle alter during a sustained submaximal isometric plantar flexion. Fourteen male subjects performed maximal voluntary plantar flexions (MVC) on a dynamometer before and after a fatiguing task. This task consisted of a sustained submaximal isometric fatiguing contraction (40% MVC) until failure to hold the defined moment. Ultrasonography was used to visualise the muscle belly of the GM. Leg kinematics were recorded (120 Hz) to calculate the joint moment using inverse dynamics. The exerted moments and the EMG signals from GM and lateralis, soleus and tibialis anterior were measured at 1,080 Hz. The root mean square (RMS) of the EMG signal of the three triceps surae muscles increased significantly (P0.05) between 17% and 28% with fatigue. Further, the fascicle length of the GM significantly decreased from 47.1±8.0 mm at the beginning to 41.8±6.7 mm at the end of fatigue and the pennation angle increased from 23.5±4.1° to 26.3±2.2° (P0.05). The changes in fascicle length and pennation angle of the GM during the contraction can influence the force potential of the muscle due to the force–length relationship and the force transmission to the tendon. This provides evidence on that an additional mechanical mechanism, namely tendon creep, can contribute to the increase in the EMG activity of the GM during submaximal isometric sustained contractions. 相似文献
17.
Robert M. Erskine David A. Jones Constantinos N. Maganaris Hans Degens 《European journal of applied physiology》2009,106(6):827-838
It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific
tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris
(QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate
QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F
t) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary
activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated
as volume divided by fascicle length during MVC. Dividing F
t by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension.
Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus
lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension
from Method 1 (30 ± 5 N cm−2) was similar to and correlated with that of Method 2 (29 ± 5 N cm−2; R
2 = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore,
a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling
accurate estimations of QF specific tension where time and resources are limited. 相似文献
18.
Gajdosik RL 《European journal of applied physiology》2002,87(3):220-227
The purpose of this study was to use a model of aging to examine the relationships between passive properties of the calf
muscles and plantarflexion concentric isokinetic torque characteristics. Eighty-one active women 20–84 years of age were tested
using a Kin-Com isokinetic dynamometer interfaced with electromyography (EMG). The passive properties were tested by stretching
the muscles from relaxed plantarflexion to a maximal dorsiflexion (DF) angle at a rate of 5°·s–1 (0.087 rad·s–1) with minimal raw EMG activity (<0.05 mV). The maximal concentric torque was tested from maximal passive DF into plantarflexion
at four randomly ordered velocities of 30, 60, 120, and 180°·s–1. Pearson correlation coefficients (Bonferroni adjusted) indicated a hierarchical order of high to moderate positive correlations
between four passive properties and the peak and mean concentric torque for all test velocities. Correlation coefficients
for the four passive properties ranged from 0.50 to 0.78 (P<0.001), and the coefficients of determination (r
2) from higher to lower were: (1) maximal DF passive resistive torque (r
2: 0.50–0.62), (2) length extensibility (r
2: 0.40–0.49), (3) maximal muscle length (r
2: 0.28–0.41), and (4) passive elastic stiffness in the last half of the full-stretch range of motion (r
2: 0.25–0.31). The maximal DF passive resistive torque and the length extensibility accounted for 50–62% and 40–49% of the
variability in the concentric torque, respectively. The results indicate that the concentrically stronger calf muscles of
active women were positively correlated with passively stronger, longer, and stiffer calf muscles, which are characteristics
of the calf muscles of younger women. Further studies are needed to examine whether therapeutic interventions, such as stretching
and strengthening, can promote adaptations in the calf muscles of older women to attain these more youthful characteristics.
Electronic Publication 相似文献
19.
R. M. Erskine D. A. Jones A. G. Williams C. E. Stewart H. Degens 《Acta physiologica (Oxford, England)》2010,199(1):83-89
Aim: The present study investigated whether in vivo human quadriceps femoris (QF) muscle specific tension changed following strength training by systematically determining QF maximal force and physiological cross-sectional area (PCSA). Methods: Seventeen untrained men (20 ± 2 years) performed high-intensity leg-extension training three times a week for 9 weeks. Maximum tendon force (Ft) was calculated from maximum voluntary contraction (MVC) torque, corrected for agonist and antagonist muscle activation, and moment arm length (dPT) before and after training. QF PCSA was calculated as the sum of the four component muscle volumes, each divided by its fascicle length. Dividing Ft by the sum of the component muscle PCSAs, each multiplied by the cosine of the respective fascicle pennation angle, provided QF specific tension. Results: MVC torque and QF activation increased by 31% (P < 0.01) and 3% (P < 0.05), respectively, but there was no change in antagonist co-activation or dPT. Subsequently, Ft increased by 27% (P < 0.01). QF volume increased by 6% but fascicle length did not change in any of the component muscles, leading to a 6% increase in QF PCSA (P < 0.05). Fascicle pennation angle increased by 5% (P < 0.01) but only in the vastus lateralis muscle. Consequently, QF specific tension increased by 20% (P < 0.01). Conclusion: An increase in human muscle specific tension appears to be a real consequence of resistance training rather than being an artefact of measuring errors but the underlying cause of this phenomenon remains to be determined. 相似文献
20.
Effects of equivolume isometric training programs comprising medium or high resistance on muscle size and strength 总被引:1,自引:0,他引:1
Kanehisa H Nagareda H Kawakami Y Akima H Masani K Kouzaki M Fukunaga T 《European journal of applied physiology》2002,87(2):112-119
Isometric unilateral elbow extension training was conducted for 10 weeks (3 times per week) on 12 young adult men to investigate
the effects of equivolume exercise programs with different combinations of intensity and duration on the morphological and
functional aspects of the triceps brachii muscle. One group of 6 subjects trained by developing maximal voluntary contraction
(MVC) for 6 s per set with 12 sets per session (100%G), while the other group of 6 subjects trained at 60% of MVC for 30 s
per set with 4 sets per session (60%G). Training significantly increased the muscle volume (V
m), fascicle pennation angle of the triceps brachii, and torque output during concentric and eccentric elbow extensions at
three constant velocities of 0.52, 1.57, and 3.14 rad·s–1 as well as under the training condition, with no significant differences in the relative gains between the two programs.
However, 100%G showed significantly greater V
m than 60%G after training, when V
m before training was normalized. Thus, only 60%G significantly increased the ratio of torque to V
m developed in the eccentric actions at the three velocities and concentric action at 1.57 rad·s–1. The present results indicate that isometric training programs of medium resistance/long duration and high resistance/short
duration produce different effects on V
m and dynamic strength relative to V
m, even if the training volume is equalized between the two protocols.
Electronic Publication 相似文献