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1.
The purpose of this investigation was to compare children and adults of both genders with respect to torque-velocity, electromyogram (EMG)-velocity and torque-EMG relationships during maximal voluntary knee extensor muscle actions. Four groups of ten subjects each were studied comprising 11-year-old girls and boys and female and male physical education students (22–35 years). Maximal voluntary eccentric (lengthening) and concentric (shortening) actions of the knee extensors were performed at the constant velocities of 45, 90 and 180° · s–1. Average values for torque and EMG activity, recorded by surface electrodes from the quadriceps muscle, were taken for the mid 40° of the 80° range of motion. The overall shapes of the torque- and EMG-velocity relationships were similar for all four groups, showing effects of velocity under concentric (torque decrease and EMG increase) but not under eccentric conditions. Eccentric torques were always greater than velocity-matched concentric ones, whereas the eccentric EMG values were lower than the concentric ones at corresponding velocities. Torque output per unit EMG activity was clearly higher for eccentric than for concentric conditions and the difference was of similar magnitude for all groups. Thus, the torque-EMG-velocity relationships would appear to have been largely independent of gender and to be fully developed at a prepubertal age. 相似文献
2.
The aim of this study was to investigate the position and velocity dependency of the strength (torque) output of lateral
flexor muscles of the trunk. Twelve male volunteers with no history of back pain participated. Movement was constrained to
the frontal plane and the velocity was controlled by an isokinetic dynamometer. The eccentric and concentric strength of lateral
flexor muscles on the left side was measured in a supine position at velocities of 15, 30, 45 and 60° · s−1 and static strength at 20, 10, 0, −10 and −20° of lateral trunk flexion. Average peak torque values ranged between 211 and
218 Nm (eccentric) and between 66 and 140 Nm (concentric) over all tested velocities, and the average static torque ranged
between 80 and 172 Nm over all tested positions. The shape of the torque–position curves was unaffected by speed and peak
torque occurred at an average position of 11–15° to the contralateral (right) side in both eccentric and concentric actions.
In eccentric actions, torque output was significantly higher than that during concentric and static actions. Increasing the
speed of contraction did not affect eccentric torque values, whereas both peak and angle-specific concentric torque decreased
with increasing speed. These results are in general accordance with earlier findings from other muscle groups, such as the
knee extensors. However, they are partially at variance with results obtained in studies of lateral lifting and lowering,
indicating that there are other limiting factors in complex tasks that do not just involve the trunk muscles.
Accepted: 24 July 2000 相似文献
3.
The purpose of this study was to examine the effects of moment of antagonistic muscle on the resultant joint moment during
isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum eccentric and concentric knee
extension and flexion efforts on a Biodex dynamometer at 0.52 rad · s−1 (30° · s−1). Electromyographic (EMG) activity of vastus medialis and biceps femoris (hamstrings) was also recorded. The antagonistic
moment of the hamstrings was determined by recording the integrated EMG (iEMG)/moment relationship at different levels of
muscle effort. The iEMG/moment curves were fitted using second-degree polynomials. The polynomials were then used to predict
the antagonistic moment exerted by the hamstrings from the antagonist iEMG. The antagonistic moment had a maximum of 42.92
Nm and 28.97 Nm under concentric and eccentric conditions respectively; paired t-tests indicated that this was a significant difference (P < 0.05). These results indicate that the resultant joint moment of knee extensors is the result of both agonist and antagonist
muscle activation. The greater antagonist muscle activity under concentric activation conditions may be partly responsible
for the lower resultant joint concentric moment of knee extensors compared with the corresponding eccentric activation. The
antagonist moment significantly affects comparisons between the isokinetic moments and agonist EMG and in vitro force measurements
under different testing (muscle action and angular velocity) conditions.
Accepted: 25 February 1997 相似文献
4.
The human voluntary force:velocity relationship frequently fails to demonstrate the expected high eccentric forces. Possible
explanations include unique activation strategies which might be affected by neural learning mechanisms. We investigated the
effect of practicing eccentric contractions on (1) the force: velocity relationship of the human knee extensor muscles and
(2) the extent of agonist and antagonist muscle activity. Eight healthy adults [seven women, group mean age 31 (SEM 5) years ± ]
practised twice a week for 4 weeks using their non-dominant legs. Each session comprised three isokinetic concentric and eccentric
maximal voluntary contractions (MVC) at randomised angular velocities of 100, 200 and 300° · s−1. Before and after, the force:velocity relationship was determined bilaterally (angular velocities 0–300° · s−1). There were no significant differences in the forces generated or relative electromyogram (EMG) activity after practice,
although there was a trend for dynamic forces to increase. Beforehand, the bilateral eccentric MVC forces were lower than
isometric (P < 0.0025); afterwards they were broadly similar. The agonist EMG was similar during isometric and eccentric contractions, but
lower during concentric (P < 0.03). Antagonist EMG activity showed considerable individual variation, was similar during all contraction types and tended
to be greater during dynamic contractions. These data indicate that neither central learning mechanisms nor total muscle activation
strategies underlie the human failure to produce the expected high eccentric voluntary forces in humans.
Accepted: 19 September 2000 相似文献
5.
S. H. Westing A. G. Cresswell A. Thorstensson 《European journal of applied physiology》1991,62(2):104-108
Summary The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360° · s–1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30°–70°) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%–146%,P < 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%–31%,P < 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P > 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P < 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions. 相似文献
6.
In a stretch-shortening cycle (SSC) the concentric muscle action is enhanced by a preceding eccentric muscle action. The hypothesis of the present study is that a preceding isometric action can also have an effect on a following concentric action, but to a lesser degree. A KINetic-COMmunicator II dynamometer was used to test muscle strength of the plantar flexion of the right foot in 20 healthy women. Maximal voluntary torque measurements were made at different angular velocities (120o s-1 and 240o s-1) and the range of motion of the ankle joint was 78–125o. The assessment was based on concentric torque output and EMG recording from the gastrocnemius muscle under three different types of testing conditions (concentric actions with and without preceding eccentric or isometric actions, all with maximal efforts). The results showed that preceding muscle actions led to greater concentric torque output (P < 0.01) between 90 and 99o plantar flexion. However, the increase in the concentric action was significantly (P < 0.01) larger with eccentric than with isometric preceding action, regardless of velocity. The EMG activity of the concentric action showed unchanged or lower values when preceded by a muscle action. In this model our conclusion is that the main reason for larger concentric torque values after a preceding muscle action is that time is sufficient for maximal muscle tension development; in addition, elastic energy is stored, particularly during the preceding eccentric action. Our results show that the effect of preceding muscle actions should be taken into account when measuring isokinetic muscle strength at relatively small angular movements. 相似文献
7.
Reichard LB Croisier JL Malnati M Katz-Leurer M Dvir Z 《European journal of applied physiology》2005,95(4):371-376
The main objective of this study was to explore the mechanical and electrical output of thigh muscles derived from a range
of motion (RoM) of 90° (0–90° flexion, LR) and the three successive RoMs: 0–30° (SR1), 30–60° (SR2) and 60–90° (SR3). Thirteen
men took part in the study. In view of the torque–velocity relationship and in order to render the test conditions as equivalent
as possible, LR was tested at 90°/s while the corresponding velocity for all SRs was 30°/s. The findings indicated very good
agreement between LR and SR2 in terms of absolute strength (particularly the concentric), within muscle eccentric to concentric
strength ratios, between muscles (agonist to antagonist) strength ratios and the normalized IEMG (expressed in μV/Nm). An
agreement was also noted between the mean eccentric peak torque of the knee flexors at LR and SR1 and between the mean eccentric
peak torque of the knee extensors at LR and SR3. However, in general there was a lesser agreement between LR and SR1 or SR3.
It is suggested that testing thigh muscles in the middle sector of knee motion (SR2) yields strength and EMG data that are
close and well correlated with those derived from testing the knee along the commonly used (0–90°) RoM. 相似文献
8.
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
9.
Determining the mechanisms of co-activation around the knee joint with respect to age and sex is important in terms of our greater understanding of strength development. The purpose of this study was to examine the effects of age, sex and muscle action on moment of force and electromyographic (EMG) activity of the agonist and antagonist muscle groups during isokinetic eccentric and concentric knee extension and flexion. The study comprised nine pubertal boys [mean age 12.6 (SD 0.5) years], nine girls [12.7 (SD 0.5) years] nine adult men [23.1 (SD 2.1) years] and nine adult women [23.7 (SD 3.1) years] who performed maximal isometric eccentric and concentric efforts of knee extensors and flexors on a dynamometer at 30°?·?s?1. The moment of force and surface EMG activity of vastus lateralis and biceps femoris muscles were recorded. The moment of force:agonist averaged EMG (aEMG) ratios were calculated. The antagonist aEMG values were expressed as a percentage of the aEMG activity of the same muscle, at the same angle, angular velocity and muscle action when the muscle was acting as agonist. Three-way analysis of variance (ANOVA) designs indicated no significant effects of age or sex on moment:aEMG ratios. Eccentric ratios were significantly higher than the corresponding concentric ones (P?0.05). The results also indicated no significant effect of age and sex on the aEMG of the vastus lateralis and biceps femoris muscles when acting as antagonists. The antagonist aEMG was significantly greater during concentric agonist efforts compared with the corresponding eccentric ones (P?0.05). These findings would suggest that the moment exerted per unit of agonist EMG and the antagonist activity are similar in children compared with adults and are not sex dependent. Future comparisons between eccentric and concentric moments of force and agonist ENG should take into consideration the antagonist effects, irrespective of age or sex. 相似文献
10.
The stretch-shortening cycle (SSC) is a combination of eccentric and concentric muscle actions. The purpose of the study was to compare the SSC of four different groups comprising a total of 29 women and 30 men, divided according to sex and age (i.e. 20–40 years and 70–85 years). A KIN-COM dynamometer was used for strength measurements of the plantar flexion of the right foot. An electromyogram (EMG) from the gastroenemius muscle was recorded simultaneously. Maximal voluntary concentric muscle actions at 120° · s–1 and 240° · s–1 with and without prior eccentric muscle actions were performed. Average torque values of the range of motion between 90° and 99° of the ankle joint were extracted. All four groups were significantly stronger at 120° · s–1 than at 240° · s–1 for pure concentric actions. The average torque values of the concentric phases in the SSC movement were significantly higher than the torque values for pure concentric actions in all four groups and at both velocities. The EMG was significantly lower or unchanged in the SSC movement compared to a pure concentric action in all groups. A larger percentage increase in torque with prior eccentric action was found in young women compared to young men at both velocities. Our results suggested that the enhanced performance was even more marked when a concentric action was preceded by an eccentric action in the young women than in the young men, probably due to better utilization of elastic forces, but we could not demonstrate any age-related differences in enhanced performance with SSC. 相似文献
11.
The stretch-shortening cycle (SSC) is a natural muscle function where a concentric action is preceded by an eccentric action, and this leads to a higher concentric torque value in healthy persons. This study aimed to investigate the concentric torque output with and without preceding eccentric or isometric actions in patients with upper motor neuron lesions due to cerebro-vascular disease. Strength measurements of the plantar flexions were made in a dynamometer at different angular?velocities (120°?·?s?1 and 240°?·?s?1) and recordings of electromyogram (EMG) were made simultaneously. The assessment was based on comparisons of the concentric torque values with and without preceding actions. The study showed a significantly higher percentage increase in concentric torque values after preceding actions in the affected leg compared with the nonaffected leg except at 120°?·?s?1 with preceding isometric action. Relative EMG changes showed no differences between the legs except at 120°?·?s?1 with preceding isometric action. We would suggest that the higher performance of the affected leg was caused by better utilization of elastic energy due to muscle stiffness which, despite reduced muscle strength, may have returned the patient's functional ability towards normal. 相似文献
12.
Use of a Kin-Com dynamometer to study the stretch-shortening cycle during plantar flexion 总被引:1,自引:0,他引:1
Ulla Svantesson Brian Ernstoff Peter Bergh Gunnar Grimby 《European journal of applied physiology》1991,62(6):415-419
Summary The aim of this study was to evaluate the Kin-Com II dynamometer in the study of the stretch-shortening cycle (a concentric muscle action preceded by an eccentric muscle action). Measurements were made of plantar flexion at different angular velocities (120° · s–1 and 240° · s–1) with the knee at two different angles (0° and 90°). Ten healthy women ranging in age from 22 to 41 years were studied. Torque values were recorded simultaneously with surface electromyograms (EMG); maximal voluntary concentric torque values were recorded and, after a short rest, the torque values of the concentric action which followed immediately after an eccentric action of the same velocity, both with maximal effort. Mean values were taken at different ankle positions and also averaged over different ranges. A concentric action preceded by an eccentric action generated a torque value on an average about 100% larger than a concentric action alone. The EMG activity was lower or unchanged. It was concluded that the present method could be useful in the study of the stretch-shortening cycle in plantar flexion and in the testing of the behaviour of the elastic components in people with disabilities in the lower limbs. 相似文献
13.
Changes in the elastic properties of tendon structures following 20 days bed-rest in humans 总被引:3,自引:1,他引:3
Kubo K Akima H Kouzaki M Ito M Kawakami Y Kanehisa H Fukunaga T 《European journal of applied physiology》2000,83(6):463-468
The purpose of this study was to investigate the effects of 20 days bed-rest on the elastic properties of tendon structures
of the human knee extensor muscles in vivo. Six healthy men carried out a 6° head-down bed-rest for 20 days. Muscle volume
and maximal voluntary contraction (MVC) torque of the quadriceps femoris muscle significantly decreased by an average of 7.8 (SD 2.7)%
and 14.9 (SD 6.9)%, respectively. Before and after bed-rest, the elongation (l) of the tendon and aponeurosis of vastus lateralis muscle was measured directly by ultrasonography, while the subjects performed
ramp isometric knee extension up to MVC. The extent of l tended to be greater after bed-rest. The l above 110 N was significantly greater after bed-rest. Furthermore, the mean stiffness after bed-rest [35.5 (SD 7.8) N · mm−1] was significantly lower than that before bed-rest [52.6 (SD 19.2) N · mm−1]. The rate of torque development significantly reduced after bed-rest by an average of 47%, and the bed-rest induced a lengthening
in the electromechanical delay (mean 21%). These results suggest that bed-rest results in a decrease in the stiffness of tendon
structures with a reduction of muscle strength and volume. These adaptations of the tendon structures to bed-rest would bring
about the changes in electromechanical delay and rate of torque development.
Accepted: 28 July 2000 相似文献
14.
Spurway NC Watson H McMillan K Connolly G 《European journal of applied physiology》2000,82(5-6):374-380
Ten male and ten female young adults trained the knee extensors of one leg eccentrically and those of the other concentrically
for 6 weeks, using a gymnasium leg-extension machine. Before and after training, both legs of each subject were tested isometrically
for maximum voluntary knee-extensor force, and in both eccentric and concentric isokinetic modes at 30–250° · s−1. All limbs showed improvements in mean eccentric force (ranging from 18% in the concentrically trained legs of the females
to 31% in the eccentrically trained legs of the males, P < 0.01–0.001). Upward trends in isometric and concentric forces were smaller and less- or non-significant. In three of the
four groups, mean eccentric forces after training were significantly greater than mean isometric forces, a difference that
was not evident before training. Ten further subjects of each gender, not trained but tested isometrically and isokinetically
three times in 2 weeks, showed no significant improvement over the series of tests. The explanation suggested is that the
increased percentage activation (“decreased inhibition”), often regarded as the main mechanism of strength gain in the early
weeks of training, had been displayed particularly in the subjects' eccentric performance. This implies that the activation-shortfall,
which is reduced by the initial phase of strength training, is largely or completely the same as that responsible for the
fact that untrained, voluntary eccentric force is less than that of isolated muscle.
Accepted: 18 February 2000 相似文献
15.
MacIntyre DL Sorichter S Mair J Berg A McKenzie DC 《European journal of applied physiology》2001,84(3):180-186
The purpose of this study was to examine the time-course and relationships of technetium-99m (99mTc) neutrophils in muscle, interleukin-6 (IL-6), myosin heavy chain fragments (MHC), eccentric torque, and delayed onset muscle
soreness (DOMS) following eccentric exercise in humans. Twelve male subjects completed a pre-test DOMS questionnaire, performed
a strength test and had 100 ml blood withdrawn for analysis of plasma IL-6 and MHC content. The neutrophils were separated,
labelled with 99mTc, and re-infused into the subjects immediately before the exercise. Following 300 eccentric repetitions of the right quadriceps
muscles on an isokinetic dynamometer, the subjects had 10 ml of blood withdrawn and repeated the eccentric torque exercise
tests and DOMS questionnaire at 0, 2, 4, 6, 20, 24, 48, 72 h, and 6 and 9 days. Bilateral images of the quadriceps muscles
were taken at 2, 4, and 6 h. Computer analysis of regions of interest was used to determine the average count per pixel. The
99mTc neutrophils and IL-6 increased up to 6 h post-exercise (P < 0.05). The neutrophils were greater in the exercised muscle than the non-exercised muscle (P < 0.01). The DOMS was increased from 0 to 48 h, eccentric torque decreased from 2 to 24 h, and MHC peaked at 72 h post-exercise
(P < 0.001). Significant relationships were found between IL-6 at 2 h and DOMS at 24 h post-exercise (r=0.68) and assessment of the magnitude of change between IL-6 and MHC (r=0.66). These findings suggest a relationship between damage to the contractile proteins and inflammation, and that DOMS is
associated with inflammation but not with muscle damage.
Accepted: 31 October 2000 相似文献
16.
Caserotti P Aagaard P Simonsen EB Puggaard L 《European journal of applied physiology》2001,84(3):206-212
Elderly people (age 75 years; n=48 males and 34 females) were studied in order to elucidate gender differences in elderly subjects on the determinants of
muscle power (force and velocity) during a stretch-shortening cycle. All subjects performed three maximal counter-movement
vertical jumps using both legs, on a force platform (Kistler 9281 B). The eccentric (Ep) and concentric (Cp) phases of the
jumps were analyzed. The Ep was further divided into an acceleration phase (Epacc: from the start of the downward movement to the maximal negative velocity) and deceleration phase (Epdec: from the maximal negative velocity to the end of the downward movement). Jump height for the men was higher than for the
women (P < 0.001). During both Epacc and Epdec no significant differences were observed between males and females in force and power generation. However, the men had a
higher peak muscle power during the Cp, which may be explained exclusively by the velocity determinant (P < 0.001). No specific gender-related strategy appeared to influence the motor pattern of the movement. The comparable eccentric
force generation of the leg extensors in both genders suggests a similar ability to cope with eccentric muscle actions during
everyday activities. In contrast, the marked lower capacity for concentric contractions in women may result in an impaired
performance, especially in activities where intense and rapid movements are essential, for example when reversing a forward
fall. This may be one reason why elderly women are more prone to falls than are elderly men.
Accepted: 19 September 2000 相似文献
17.
Jan Y. Seger B. Arvidsson A. Thorstensson Jan Y Seger 《European journal of applied physiology》1998,79(1):49-57
The purpose of this study was to compare pure eccentric and concentric isokinetic training with respect to their possible specificity in the adaptation of strength and morphology of the knee extensor muscles. Ten moderately trained male physical education students were divided into groups undertaking eccentric (ETG) and concentric (CTG) training. They performed 10 weeks of maximal isokinetic (90°?·?s?1) training of the left leg, 4?×?10 repetitions – three times a week, followed by a second 10-week period of similar training of the right-leg. Mean eccentric and concentric peak torques increased by 18% and 2% for ETG and by 10% and 14% for CTG, respectively. The highest increase in peak torque occurred in the eccentric 90°?·?s?1 test for ETG (35%) whereas in CTG strength gains ranged 8%–15% at velocities equal or lower than the training velocity. Significant increases in strength were observed in the untrained contra-lateral leg only at the velocity and mode used in ipsilateral training. Cross-sectional area of the quadriceps muscle increased 3%–4% with training in both groups, reaching statistical significance only in ETG. No major changes in muscle fibre composition or areas were detected in biopsies from the vastus lateralis muscle for either leg or training group. In conclusion, effects of eccentric training on muscle strength appeared to be more mode and speed specific than corresponding concentric training. Only minor adaptations in gross muscle morphology indicated that other factors, such as changes in neural activation patterns, were causing the specific training-induced gains in muscle strength. 相似文献
18.
Gauthier A Davenne D Martin A Van Hoecke J 《European journal of applied physiology》2001,84(3):249-252
The aim of this study was, firstly, to confirm or refute the existence of circadian rhythms during several velocities of
concentric action of the elbow flexor muscles and, secondly, to compare the characteristics of these circadian rhythms with
those obtained during isometric actions. Eight volunteer subjects participated in this study. The circadian rhythms were obtained
from six test sessions (TS) carried out at different times of day over 6 days with only one TS a day. During each TS, oral
temperature and the torque of the muscle action were measured. The subjects made, on an isokinetic ergometer, two maximal
isokinetic concentric elbow flexions at five angular velocities (60, 120, 180, 240 and 300° · s−1) and at an angle of 60°. Torque-angular velocity relationships, which characterised the functioning of the muscle during
concentric and isometric actions, were established for the different times of day. The values of the torque recorded at each
of the angular velocities presented a clear circadian rhythm. After normalisation of the torque values, no significant differences
were observed among the computed characteristics of the circadian rhythms obtained at different angular velocities. Since
the circadian rhythms during isometric and concentric torque were the same, the characteristics of the circadian rhythms of
the musculo-skeletal system can be studied using either type of muscle action. The results indicated that torque and temperature
varied concomitantly during the day. Thus, the recording of body temperature allows one to estimate the times of occurrence
of maximal and minimal values in the circadian rhythm of muscle torque.
Accepted: 10 October 2000 相似文献
19.
Adaptation to chronic eccentric exercise in humans: the influence of contraction velocity 总被引:1,自引:0,他引:1
Paddon-Jones D Leveritt M Lonergan A Abernethy P 《European journal of applied physiology》2001,85(5):466-471
We compared changes in muscle fibre composition and muscle strength indices following a 10 week isokinetic resistance training
programme consisting of fast (3.14 rad.s–1) or slow (0.52 rad.s–1) velocity eccentric muscle contractions. A group of 20 non-resistance trained subjects were assigned to a FAST (n=7), SLOW (n=6) or non-training CONTROL (n=7) group. A unilateral training protocol targeted the elbow flexor muscle group and consisted of 24 maximal eccentric isokinetic
contractions (four sets of six repetitions) performed three times a week for 10 weeks. Muscle biopsy samples were obtained
from the belly of the biceps brachii. Isometric torque and concentric and eccentric torque at 0.52 and 3.14 rad.s–1 were examined at 0, 5 and 10 weeks. After 10 weeks, the FAST group demonstrated significant [mean (SEM)] increases in eccentric
[29.6 (6.4)%] and concentric torque [27.4 (7.3)%] at 3.14 rad.s–1, isometric torque [21.3 (4.3)%] and eccentric torque [25.2 (7.2)%] at 0.52 rad.s–1. The percentage of type I fibres in the FAST group decreased from [53.8 (6.6)% to 39.1 (4.4)%] while type IIb fibre percentage
increased from [5.8 (1.9)% to 12.9 (3.3)%; P<0.05]. In contrast, the SLOW group did not experience significant changes in muscle fibre type or muscle torque. We conclude
that neuromuscular adaptations to eccentric training stimuli may be influenced by differences in the ability to cope with
chronic exposure to relatively fast and slow eccentric contraction velocities. Possible mechanisms include greater cumulative
damage to contractile tissues or stress induced by slow eccentric muscle contractions.
Electronic Publication 相似文献
20.
Neuromuscular adaptations to detraining following resistance training in previously untrained subjects 总被引:1,自引:0,他引:1
Andersen LL Andersen JL Magnusson SP Aagaard P 《European journal of applied physiology》2005,93(5-6):511-518
Resistance training has been shown to considerably increase strength and neural drive during maximal eccentric muscle contraction; however, less is known about the adaptive change induced by subsequent detraining. The purpose of the study was to examine the effect of dynamic resistance training followed by detraining on changes in maximal eccentric and concentric isokinetic muscle strength, as well as to examine the corresponding adaptations in muscle cross-sectional area (CSA) and EMG activity. Maximal concentric and eccentric isokinetic knee extensor moment of force was measured in 13 young sedentary males (age 23.5±3.2 years), before and after 3 months of heavy resistance training and again after 3 months of detraining. Following training, moment of force increased during slow eccentric (50%, P<0.001), fast eccentric (25%, P<0.01), slow concentric (19%, P<0.001) and fast concentric contraction (11%, P<0.05). Corresponding increases in EMG were observed during eccentric and slow concentric contraction. Significant correlations were observed between the training-induced changes in moment of force and EMG (R2=0.33–0.77). Muscle CSA (measured by MRI) increased by 10% (P<0.001). After 3 months of detraining maximal muscle strength and EMG remained preserved during eccentric contraction but not concentric contraction. The present findings suggest that heavy resistance training induces long-lasting strength gains and neural adaptations during maximal eccentric muscle contraction in previously untrained subjects. 相似文献