We examined the effect of illusionary perception on anticipatory postural control associated with arm flexion with subjects in a standing position, using vibration stimulation of the Achilles’ tendon. Arm flexion was performed five times under each of the following conditions: (1) quiet standing, (2) vibration of the Achilles’ tendon at 100 Hz frequency and 1.5 mm amplitude with the trunk fixed by a stopper during quiet standing, and (3) a perceived standing position during vibration. The reproduced positions were located forward by about 20% of the foot length compared with the quiet standing position; these positions showed no significant differences among the five trials. In the first trial of arm flexion during vibration, the biceps femoris began activating approximately 40 ms before the anterior deltoid. The same time difference between activation of the two muscles was observed in the reproduced condition. As the vibration trials were repeated, this activation timing approached the value in the quiet standing condition. In both the biceps femoris and erector spinae, the mean amplitude of electromyogram for the first 50 ms after the start of activation did not differ significantly among the three conditions. 相似文献
Lower extremity muscle activations during crossover and side step cut tasks are hypothesized to play an important role in controlling knee motion, and therefore, impact the design of knee injury prevention and rehabilitation programs. However, the contribution of lower extremity muscles to frontal and transverse plane moments during cutting tasks is unclear. The purpose of this study was to compare the muscle activation patterns of selected lower extremity muscles (vastus lateralis, medial/lateral hamstrings and medial/lateral gastrocnemius) of subjects performing a stepping down and side step cut, a stepping down and crossover cut and an equivalent straight ahead task. Ground reaction force was used to determine the cut angle, stance time and compare the lower limb loading during each task. Electromyography data during all tasks were normalized to the average activation during the straight ahead tasks to determine relative changes in muscle activation between the straight ahead and different cut styles (crossover and side step). There were no differences in the pattern of muscle activation of the vastus lateralis, or lateral hamstring muscles when comparing the cutting tasks to the equivalent straight ahead task. However, the crossover cut task resulted in significantly higher muscle activation of the medial hamstrings and lateral gastrocnemius muscles relative to both the side step cut and straight ahead tasks. These results suggest the medial/lateral hamstrings and medial/lateral gastrocnemius play a role in transverse and frontal plane control during cut tasks. 相似文献
Muscle fatigue limits the effectiveness of FES when applied to regain functional movements in spinal cord injured (SCI) individuals. The stimulation intensity must be manually increased to provide more force output to compensate for the decreasing muscle force due to fatigue. An artificial neural network (ANN) system was designed to compensate for muscle fatigue during functional electrical stimulation (FES) by maintaining a constant joint angle. Surface electromyography signals (EMG) from electrically stimulated muscles were used to determine when to increase the stimulation intensity when the muscle’s output started to drop.
In two separate experiments on able-bodied subjects seated in hard back chairs, electrical stimulation was continuously applied to fatigue either the biceps (during elbow flexion) or the quadriceps muscle (during leg extension) while recording the surface EMG. An ANN system was created using processed surface EMG as the input, and a discrete fatigue compensation control signal, indicating when to increase the stimulation current, as the output. In order to provide training examples and test the systems’ performance, the stimulation current amplitude was manually increased to maintain constant joint angles. Manual stimulation amplitude increases were required upon observing a significant decrease in the joint angle. The goal of the ANN system was to generate fatigue compensation control signals in an attempt to maintain a constant joint angle.
On average, the systems could correctly predict 78.5% of the instances at which a stimulation increase was required to maintain the joint angle. The performance of these ANN systems demonstrates the feasibility of using surface EMG feedback in an FES control system. 相似文献
Cl− currents (ICl) were measured in short fibers (1–2 mm) from the lumbricalis muscle of toads (Bufo arenarum) with two microelectrodes (15°C). Initially the fibers were equilibrated in a high K+-containing solution: (mm) K2SO4 68; Na2SO4 20; KCl 60; CaSO4 8; MgSO4 1; HEPES 2.5. Constant pulses were applied when all the external K+ was replaced by Cs+: Cs2SO4 68; Na2SO4 20; CsCl 60; CaSO4 8; HEPES 2.5 (pH 7.5). Under these conditions about 80–90% of the current is carried by Cl−. The current-voltage relation is almost linear implying constant conductance and hence voltage-independent permeability.
The voltage dependence of the net Cl− current could be fitted by constant field equation with a PCl of 3.3 × 10−6 cm/sec. In a separate group of experiments a two-pulse technique was used to estimate the availability and the inactivation
of the initial ICl during a test pulse. After returning the potential to the holding potential for various times, test pulses of the same amplitude
and duration of the prepulses were applied. The initial current during the test pulse was 70% of the initial current during
the prepulse and the recovery was complete in less than 300 msec with a linear relationship between the current during the
test pulse and the amplitude of the preceding prepulse. When the test pulses were preceded by a positive prepulse, the initial
current for any given test pulse was larger than with a negative prepulse. If we assumed that the initial current during the
test pulse is a measure of the number of channels open at the end of the prepulse, these results suggest that hyperpolarizing
pulses inactivate and depolarizing prepulses activate the ICl.
Received: 31 March 1995/Revised: 27 October 1995 相似文献
The aim of the study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling at different work loads and speeds. Six healthy subjects pedalled a weight-braked cycle ergometer at 0, 120 and 240 W at a constant speed of 60 rpm. The subjects also pedalled at 40, 60, 80 and 100 rpm against the same resistance, giving power outputs of 80, 120, 160 and 200 W respectively. The subjects were filmed with a cine-film camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work for the hip, knee and ankle joint muscles was calculated using a model based upon dynamic mechanics and described elsewhere. The total work during one pedal revolution significantly increased with increased work load but did not increase with increased pedalling rate at the same braking force. The relative proportions of total positive work at the hip, knee and ankle joints were also calculated. Hip and ankle extension work proportionally decreased with increased work load. Pedalling rate did not change the relative proportion of total work at the different joints. 相似文献
Greater hamstring musculotendinous stiffness is associated with lesser ACL loading mechanisms. Stiffness is enhanced via training, but previous investigations evaluated tendon rather than musculotendinous stiffness, and none involved the hamstrings. We evaluated the effects of isometric and isotonic training on hamstring stiffness and ACL loading mechanisms. Thirty-six healthy volunteers were randomly assigned to isometric, isotonic, and control groups. Isometric and isotonic groups completed 6 weeks of training designed to enhance hamstring stiffness. Stiffness, anterior tibial translation, and landing biomechanics were measured prior to and following the interventions. Hamstring stiffness increased significantly with isometric training (15.7%; p = 0.006), but not in the isotonic (13.5%; p = 0.089) or control (0.4%; p = 0.942) groups. ACL loading mechanisms changed in manners consistent with lesser loading, but these changes were not statistically significant. These findings suggest that isometric training may be an important addition to ACL injury prevention programs. The lack of significant changes in ACL loading mechanisms and effects of isotonic training were likely due to the small sample sizes per group and limited intervention duration. Future research using larger sample sizes and longer interventions is necessary to determine the effects of enhancing hamstring stiffness on ACL loading and injury risk. 相似文献
The expression of three microRNAs, miR-1, miR-206 and miR-133 is restricted to skeletal myoblasts and cardiac tissue during embryo development and muscle cell differentiation, which suggests a regulation by muscle regulatory factors (MRFs). Here we show that inhibition of C2C12 muscle cell differentiation by FGFs, which interferes with the activity of MRFs, suppressed the expression of miR-1, miR-206 and miR-133. To further investigate the role of myogenic regulators (MRFs), Myf5, MyoD, Myogenin and MRF4 in the regulation of muscle specific microRNAs we performed gain and loss-of-function experiments in vivo, in chicken and mouse embryos. We found that directed expression of MRFs in the neural tube of chicken embryos induced ectopic expression of miR-1 and miR-206. Conversely, the lack of Myf5 but not of MyoD resulted in a loss of miR-1 and miR-206 expression. Taken together our results demonstrate differential requirements of distinct MRFs for the induction of microRNA gene expression during skeletal myogenesis. 相似文献