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排序方式: 共有304条查询结果,搜索用时 15 毫秒
1.
Fatigue during stretch-shortening cycle exercises: changes in mechanical performance of human skeletal muscle 总被引:6,自引:0,他引:6
Stretch-shortening cycle (SSC), which is a normal contraction behavior of muscle, was used as a model to investigate muscular fatigue. Nine male volunteers were subjected to 100 repeated and exhaustive SSC contractions of the forearm extensors using a special sledge apparatus incorporating a force plate system. The fatigue contractions were performed on submaximal levels but the before-after comparison also included maximal drop-jump condition on the sledge as well as falls on to the floor. The results indicated that in the 100 submaximal SSCs the fatigue was characterized by increases in the contact times for both the eccentric and concentric phases of SSC, but the influence was more pronounced on the concentric part. The force-time curves during contact on the platform were influenced by fatigue so that the initial force peak became higher and the subsequent initial drop of force more pronounced. During submaximal and maximal drops, the angular velocities changed in the two phases of SSC. With progressing fatigue, the eccentric maximal angular velocity increased and the corresponding concentric velocities decreased. These changes were accompanied by slight changes in the elbow joint mechanism with respect to the contact, release, and maximal flexion angles. The results suggest that repeated SSC induces fatigue and the fatigue effects on the mechanical behavior of the muscle are very much similar to those induced by either isometric or concentric fatigue contractions. However, the transfer of the energy between eccentric and concentric phases was drastically reduced and this implies that SSCs can be used effectively to examine the fatiguability of the system regulating muscle stiffness during exercise. 相似文献
2.
Biomechanics of sprint running. A review. 总被引:1,自引:0,他引:1
Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future. 相似文献
3.
Neuromuscular changes after long-lasting mechanically and electrically elicited fatigue 总被引:1,自引:0,他引:1
Central fatigue was investigated under an isolated active condition whereby the possible effects of supraspinal fatigue were
minimized. Therefore, ten subjects were fatigued by simultaneously and repeatedly mechanically stretching and electrically
stimulating their calf muscles for 1 h. This was performed using an ankle ergometer. The active fatigue task included a total
of 2400 muscle stretches with an intensity of 10% of the maximal voluntary contraction (MVC). This protocol clearly impaired
neuromuscular function, as revealed by a significant reduction in MVC (P<0.01) and the neural input to the muscle (average EMG) (P<0.01–0.001). The interpolated nerve stimulation compensated for this force loss by 4.28% (P<0.05). Stretch-reflex recordings revealed a notable post-fatigue reduction in the peak-to-peak amplitude (59.1%, P<0.01) and stretch-resisting force of the muscle (14.1%, P<0.01). The maximal H-reflex declined by 50.5% (P<0.001) and did not recover while the leg was kept ischemic. It is suggested that the existing protocol with minor metabolic
loading can induce central fatigue, which seems to be of reflex origin from the fatigued muscle. Although the role of presynaptic
inhibition of Ia terminals is possibly reinforced, disfacilitation via reduced spindle sensitivity cannot be excluded.
Electronic Publication 相似文献
4.
Kyröläinen H Pullinen T Candau R Avela J Huttunen P Komi PV 《European journal of applied physiology》2000,82(4):297-304
The present study was designed to investigate interactions between running economy and mechanics before, during, and after
an individually run marathon. Seven experienced triathletes performed a 5-min submaximal running test on a treadmill at an
individual constant marathon speed. Heart rate was monitored and the expired respiratory gas was analyzed. Blood samples were
drawn to analyze serum creatine kinase activity (S-CK), skeletal troponin I (sTnI), and blood lactate (B-La). A video analysis
was performed (200 frames · s−1) to investigate running mechanics. A kinematic arm was used to determine the external work of each subject. The results of
the present study demonstrate that after the marathon, a standardized 5-min submaximal running test resulted in an increase
in oxygen consumption, ventilation, and heart rate (P < 0.05), with a simultaneous decrease in the oxygen difference (%) between inspired and expired air, and respiratory exchange
ratio (P < 0.05). B-La did not change during the marathon, while sTnI and S-CK values increased (P < 0.05), peaking 2 h and 2 days after the marathon, respectively. With regard to the running kinematics, a minor increase in
stride frequency and a similar decrease in stride length were observed (P < 0.01). These results demonstrate clearly that weakened running economy cannot be explained by changes in running mechanics.
Therefore, it is suggested that the increased physiological loading is due to several mechanisms: increased utilization of
fat as an energy substrate, increased demands of body temperature regulation, and possible muscle damage.
Accepted: 20 March 2000 相似文献
5.
6.
Summary The relationships between ground reaction forces, electromyographic activity (EMG), elasticity and running velocity were investigated
at five speeds from submaximal to supramaximal levels in 11 male and 8 female sprinters. Supramaximal running was performed
by a towing system. Reaction forces were measured on a force platform. EMGs were recorded telemetrically with surface electrodes
from the vastus lateralis and gastrocnemius muscles, and elasticity of the contact leg was evaluated with spring constant
values measured by film analysis. Data showed increases in most of the parameters studied with increasing running speed. At
supramaximal velocity (10.36±0.31 m×s−1; 108.4±3.8%) the relative increase in running velocity correlated significantly (P<0.01) with the relative increase in stride rate of all subjects. In male subjects the relative change in stride rate correlated
with the relative change of IEMG in the eccentric phase (P<0.05) between maximal and supramaximal runs. Running with the towing system caused a decrease in elasticity during the impact
phase but this was significant (P<0.05) only in the female sprinters. The average net resultant force in the eccentric and concentric phases correlated significantly
(P<0.05−0.001) with running velocity and stride length in the maximal run. It is concluded that (1) increased neural activation
in supramaximal effort positively affects stride rate and that (2) average net resultant force as a specific force indicator
is primarily related to stride length and that (3) the values in this indicator may explain the difference in running velocity
between men and women. 相似文献
7.
Electromyographic activity of m. rectus femoris at submaximal and maximal voluntary contractions was quantified by conventional integration technique and also be a more "qualitative" procedure of automated motor unit averaging and frequency spectrum analysis. By relating the EMG parameters to produced muscle tension it was observed that the integrated EMG increased in a slightly nonlinear fashion with the increase in muscle force. The other EMG variables also showed clear changes as a function of muscle tension. The averaged motor unit potential (AMUP) and its specific parameters (number of spikes, amplitude, rise time and amplitude-rise time ratio) showed such changes with muscle tension that they may be useful in estimation of the recruitment pattern of the different types of motor units. 相似文献
8.
Electromyographic activity of m. rectus femoris at submaximal and maximal voluntary contractions was quantified by conventional integration technique and also be a more “qualitative” procedure of automated motor unit averaging and frequency spectrum analysis. By relating the EMG parameters to produced muscle tension it was observed that the integrated EMG increased in a slightly nonlinear fashion with the increase in muscle force. The other EMG variables also showed clear changes as a function of muscle tension. The averaged motor unit potential (AMUP) and its specific parameters (number of spikes, amplitude, rise time and amplitude-rise time ratio) showed such changes with muscle tension that they may be useful in estimation of the recruitment pattern of the different types of motor units. 相似文献
9.
S. Cheng P. V. Komi H. Kyröläinen D. H. Kim K. Häkkinen 《European journal of applied physiology》1989,59(1-2):128-130
Summary Vibrational wave propagation was tested in vivo on the tibial bone of both legs of 56 female volunteers. The impact was produced
by a hammer with a force strain gauge and the response was monitored by two accelerometers. The peak amplitude of the accelerations,
the velocity of the acceleration wave propagation and damping were analysed for comparison among the different age groups.
The results showed significant negative correlations between age and the peak amplitude of acceleration, and the velocity
of acceleration wave propagation (p<0.01). The damping time of the acceleration wave also had a negative correlation with age. These findings suggested that
age differences were related to the differences in the mechanical properties of bone. With reduction of bone mineral density,
the velocity of the vibrational wave propagation would decrease, with simultaneous increase in impedance. In addition, wave
absorption would be accelerated. It is suggested that this method could be used as an indicator of bone density. The method
could also be developed to provide an index to monitor the progress of osteoporosis.
Visiting research assistant from the Department of Sport Medicine, Chengdu College of Physical Education, Chengdu, People's
Republic of China
Visiting research assistant from Seoul National University, Seoul, South Korea 相似文献
10.
Summary Ground reaction forces and mechanical power were investigated when the subjects walked normally, while they were racing or running at four speeds, and when they performed the running long jump take-off. In addition, the apparent spring constants of the support leg in eccentric and concentric phases were investigated at the four running speeds, during the running long jump take-off, and in the triple jump. Six club level track and field athletes, four national level long jumpers, and six national level triple jumpers took part in the study. Cinematographic technique and a mathematical model of hopping (Alexander and Vernon 1975) were employed in the analysis. Force and power values were found to vary in the following order (from highest to lowest): long jump take-off, maximal running speed, submaximal running (80, 60, and 40% of maximum speed), racing gait, and normal gait. The data disclosed that the measured parameters had the highest values in the long jump take-off performed by the long jump athletes. Their peak values were: resultant ground reaction force 3270±74 N and mechanical power 160.1±10.5 J×kg–1×s–1. For the track and field athletes the values were 2010±80 N and 126.0±12.6 J ×kg–1×s–1. The apparent spring constant values of the support leg in the national level jumper group were in eccentric phase 30.54±8.38 N×mm–1 ×kg–1 and in concentric phase 0.129±0.012 N×mm–1×kg–1. In the track and field athletes the values were 13.97±1.01 N×mm–1×kg–1 and 0.093±0.003 N×mm–1×kg–1, respectively. In general, the increase in force and mechanical power output was related to the value of the apparent spring constant of the support leg in the eccentric phase. The spring constant in the eccentric phase increased with the velocity of motion in running, the long jump take-off and the triple jump. This suggests that it may be possible to use this parameter as a measure of mechanical performance, as it may reflect the combined elasticity of muscles, tendons, and bones. 相似文献