Electrically evoked isokinetic plantar flexor torque in males

The involuntary angle-specific isokinetic plantar flexor torques of seven male subjects aged 18-21 yr were measured using a Cybex II dynamometer (Lumex) modified by the addition of a strain-gauge load cell to improve the dynamic response of the instrument. Supramaximal electrical stimuli were used to evoke a maximal tetanic response from the triceps surae and ensure constant muscle activation at each angular velocity studied. Angle-specific torques were measured over a range (0.5-5.0 rad/s) of preset velocities, torque decreasing in a nonlinear manner with increasing angular velocity. The torque-velocity data was adequately described by an exponential equation of the form: V = a(e-1/b - e-Po/b) where V = velocity (rad/s), P = torque (N.m), Po = isometric torque (N.m), and a and b are constants. The mean intrasubject coefficient of variation of torque over the range of velocities studies was 7.9 +/- 1.88% (SD).     

Isokinetic plantar flexion: experimental results and model calculations

In isokinetic experiments on human subjects, conducted to determine moments that can be exerted about a joint at different angular velocities, joint rotation starts as soon as the moment increases above the resting level. This contraction history differs from the one in experiments on isolated muscle, where the force is allowed to increase to an isometric level before shortening is initiated. The purpose of the present study was to determine the influence of contraction history on plantar flexing moments found during maximal voluntary plantar flexion on an isokinetic dynamometer. In ten subjects, plantar flexing moments were measured as a function of ankle angle at different angular velocities. They were also calculated using a model of the muscle-tendon complex of the human triceps surae. The model incorporates elastic tendinous tissue in series with muscle fibers. The input of the model consists of time histories of active state (the force generating capacity of contractile elements) and shortening velocity of the muscle-tendon complex. Different time courses of active state were offered at fixed length of the muscle-tendon complex. The time course yielding a close match between the calculated rise of plantar flexing moment and the rise measured during fixed angle contractions was used to calculate moment-angle curves for isokinetic plantar flexion. The active state value reached when a peak occurred in calculated moment-angle curves was found to be lower if the angular velocity was made higher. Comparing measured and calculated results, it was concluded that moment-angular velocity diagrams determined in studies of isokinetic plantar flexion in human subjects reflect not only the influence of shortening velocity of contractile elements on the force which can be produced by plantar flexors.     

Stretch-shortening cycle during plantar flexion in young and elderly women and men

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.     

Scapular kinematics during unloaded and maximal loaded isokinetic concentric and eccentric shoulder flexion and extension movements

Characterization of scapular kinematics under demanding load conditions might aid to distinguish between physiological and clinically relevant alterations. Previous investigations focused only on submaximal external load situations. How scapular movement changes with maximal load remains unclear. Therefore, the present study aimed to evaluate 3D scapular kinematics during unloaded and maximal loaded shoulder flexion and extension. Twelve asymptomatic individuals performed shoulder flexion and extension movements under unloaded and maximal concentric and eccentric loaded isokinetic conditions. 3D scapular kinematics assessed with a motion capture system was analyzed for 20° intervals of humeral positions from 20° to 120° flexion. Repeated measures ANOVAs were used to evaluate kinematic differences between load conditions for scapular position angles, scapulohumeral rhythm and scapular motion extent. Increased scapular upward rotation was seen during shoulder flexion and extension as well as decreased posterior tilt and external rotation during eccentric and concentric arm descents of maximal loaded compared to unloaded conditions. Load effects were further seen for the scapulohumeral rhythm with greater scapular involvement at lower humeral positions and increased scapular motion extent under maximal loaded shoulder movements. With maximal load applied to the arm physiological scapular movement pattern are induced that may imply both impingement sparing and causing mechanisms.     

Palmar and plantar pads and flexion creases of the rat (Rattus norvegicus)

The recent detection of dermal ridge configurations on the volar pads of the rat (Rattus norvegicus) has created opportunities for experimental studies of dermatoglyphics. In the present work, the palmar and plantar surfaces of the rat were studied to establish the feasibility of comparative rat and human dermatoglyphic investigations. The studied features included the volar pads and flexion creases. The number and location of the palmar and plantar pads in the rat were found to be similar to those of humans. The exception was a previously unrecognized small pad on the palms and soles of the rat, located on the radial and tibial side, respectively, of the proximal component of the first interdigital pad. This pad has no parallel in human embryos. Rats were found to have flexion creases in the non-pad areas between the neighboring pads, similar in location and appearance to those of humans. Unlike humans, however, rats also have boundary creases, separating the pad and non-pad areas. The marked similarities in the morphology of the volar areas between rats and humans make the rat ideally suitable for experimental studies of dermatoglyphics and flexion creases. Results of such studies should be applicable to human developmental dermatoglyphics, including those pertaining to medical disorders. © 1994 Wiley-Liss, Inc.     

Palmar and plantar pads and flexion creases of genetic polydactyly mice (Pdn)

Attempts to gain a better understanding of the relationship between the epidermal ridge patterns (dermatoglyphics) and flexion creases on the volar aspects of human hands and feet and specific medical disorders led to a search for a suitable animal model, allowing studies of the fetal development of the pertinent structures. A common experimental animal, the rat (Rattus norvegicus), was found to be an excellent candidate, owing to the strong resemblance of the volar pads and flexion creases on its palmar and plantar surfaces to those of human subjects. A hereditary preaxial polydactyly mouse (Pdn) provides an opportunity to study the effects of this malformation on the surrounding morphological structures and, specifically, on the volar pads, i.e., the sites over which the dermatoglyphic patterns develop. The hands and feet of the wild‐type (+/+) mice show no anomalies, and their major pad and flexion crease configurations correspond to those of normal rats. The heterozygous (Pdn/+) mice, in spite of having a thumb/big toe with a duplicated distal phalanx on their hands/feet, did not display any alterations in palmar/plantar pads. The homozygous (Pdn/Pdn) mice have a protrusion in the thenar area and one to three supernumerary digits on the preaxial portion of both the hands and feet. The effect of these anomalies was found to be limited to the pad and flexion crease configurations in the preaxial areas; the postaxial sites were not affected. The original number of pads on the thenar/first interdigital areas of Pdn/Pdn mice was apparently identical to that of the +/+ and Pdn/+ mice. The preaxial protrusion, however, affected the number, size, and location of the pads observed in the newborn mice, resulting in varying pad configurations, such as fused and scattered pads or a pad cluster formed by gathering the neighboring pads. These pad modifications were induced by the preaxial plantar/palmar protrusion only and were not affected by the presence of supernumerary preaxial digits. In view of the similarities in the morphology and fetal development of human and mouse distal limbs, the present study is relevant to human subjects, particularly to the understanding of the significance of dermatoglyphic variations in individuals with specific medical disorders. Future studies of naturally occurring or experimentally induced limb malformations in mice or rats should provide valuable insights into the development of human hands and feet and into factors contributing to their congenital anomalies. J. Morphol. 239:87–96, 1999. © 1999 Wiley‐Liss, Inc.     

Effect of muscle model parameter scaling for isometric plantar flexion torque prediction

This paper uses a EMG-driven Hill-type muscle model to estimate individual muscle forces of the triceps surae in isometric plantar flexion contractions. A uniform group of 20 young physical-active adult males was instructed to follow a specific contraction protocol with low (20%MVC) and medium-high (60%MVC) contractions, separated by relaxing intervals. The torque calculated by summing the individual muscle forces multiplied by the respective moment arms was compared to the torque measured by a dynamometer. Musculoskeletal parameters from the literature were used. Then, three different “correction factors” or bias have been applied on some of the muscle model parameters. These factors were based on anthropometric and dynamometric measurements: moment arm scaled by bimalleolar diameter, tendon slack length by leg length and optimal force by the maximum torque. Model torque agreement with dynamometer was recalculated with the parameter scales. It was observed that the relative torque estimation error decreased slightly but significantly when all factors were applied simultaneously (12.92±4.94% without scaling to 10.12±1.73%), which resulted mainly from the correction of the maximal muscle force parameter.     

Fluctuations in plantar flexion force are reduced after prolonged tendon vibration.

The purpose of the study was to examine the effect of prolonged vibration on the force fluctuations during a force-matching task performed at low-force levels. Fourteen young healthy men performed a submaximal force-matching task of isometric plantar flexion before and after Achilles tendon vibration (n = 8, vibration subjects) or lying without vibration (n = 6, control subjects) for 30 min. The target forces were 2.5-10% of the previbration maximal voluntary contraction force. The standard deviation of force decreased by a mean of 29 +/- 20% across target forces after vibration, whereas it did not decrease significantly in control subjects (-5 +/- 12%). This change was significantly greater compared with control subjects (P < 0.01 for both). Power spectral density of the force was predominantly composed of signals of low-frequency bandwidth (相似文献   

Measurement of the isometric dorsiflexion and plantar flexion force in the ankle joint]

This article describes an easy to use test equipment for measuring the isometric force in the ankle joints in dorsiflexion and plantar flexion. The combination of the test equipment for measuring the voluntary maximal isometric muscle force in the ankle joint, the surface electromyograms and the motion analysis of the measured leg allow an objective comparison of the strength of the muscular force between the left and right leg. It might be also used as a control setup during rehabilitation after surgical treatment or injuries.     

Age-related decreases in motor unit discharge rate and force control during isometric plantar flexion

Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software “Daisy”. DR was lower in OLD in RECR-10% (17.9%, p < 0.001), RECR-20% (15.8%, p < 0.05), ISO-10% (17.7%, p < 0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p < 0.001) and ISO-20% (55.2%, p < 0.05) which were accompanied with a slight increase in DR variation (n.s.). The observed lower DR in OLD is in line with earlier findings in small distal muscles. Also the larger force fluctuation in OLD was in line with previous studies with smaller hand muscles. These findings suggest that the age-related changes in MU control do exist also in large leg extensors that play an important role in human locomotion and balance control.     

Use of a Kin-Com dynamometer to study the stretch-shortening cycle during plantar flexion

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 degrees.s-1 and 240 degrees.s-1) with the knee at two different angles (0 degree and 90 degrees). 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.     

The mechanism of electromyographic silent periods preceding a ballistic voluntary plantar flexion]

The present study was designed to investigate the neurophysiological mechanism of electromyographic silent periods(SP) preceding a ballistic voluntary movement. Ten male subjects were asked to respond to the flashing light by performing a plantar flexion as strongly and quickly as possible. The myoelectric signals from agonist (m. gastrocnemius, caput laterale: LG, m. soleus: SOL) and antagonist (m. tibialis anterior: TA) were simultaneously recorded together with the isometric contraction force signal. The excitability of the alpha motoneuron pools by means of the H reflex analysis was also determined at various phases of the movement. The results obtained are as follows: 1) In five out of 10 subjects, the electromyographic silent period was consistently observed (SP Group), while the rest of the subjects did not show such changes (NSP Group). 2) The maximum rate of tension raise (dF/dt) in SP Group (32.3 +/- 24.9 N/ms) was significantly (p less than .05) greater than NSP Group (15.1 +/- 12.0 N/ms). 3) In SP Group, the averaged H-wave mean amplitude decreased about 40ms prior to the appearance of SP. From these results, it can be concluded that SP in this study was attributable to the supraspinal influences so as to allow a specific motor program to be executed for selective recruitment of phasic (high threshold) motor units.     

Effects of hyperventilation on phosphocreatine kinetics and muscle deoxygenation during moderate-intensity plantar flexion exercise.

The effects of controlled voluntary hyperventilation (Hyp) on phosphocreatine (PCr) kinetics and muscle deoxygenation were examined during moderate-intensity plantar flexion exercise. Male subjects (n = 7) performed trials consisting of 20-min rest, 6-min exercise, and 10-min recovery in control [Con; end-tidal Pco(2) (Pet(CO(2))) approximately 33 mmHg] and Hyp (Pet(CO(2)) approximately 17 mmHg) conditions. Phosphorus-31 magnetic resonance and near-infrared spectroscopy were used simultaneously to monitor intramuscular acid-base status, high-energy phosphates, and muscle oxygenation. Resting intracellular hydrogen ion concentration ([H(+)](i)) was lower (P < 0.05) in Hyp [90 nM (SD 3)] than Con [96 nM (SD 4)]; however, at end exercise, [H(+)](i) was greater (P < 0.05) in Hyp [128 nM (SD 19)] than Con [120 nM (SD 17)]. At rest, [PCr] was not different between Con [36 mM (SD 2)] and Hyp [36 mM (SD 1)]. The time constant (tau) of PCr breakdown during transition from rest to exercise was greater (P < 0.05) in Hyp [39 s (SD 22)] than Con [32 s (SD 22)], and the PCr amplitude was greater (P < 0.05) in Hyp [26% (SD 4)] than Con [22% (SD 6)]. The deoxyhemoglobin and/or deoxymyoglobin (HHb) tau was similar between Hyp [13 s (SD 8)] and Con [10 s (SD 3)]; however, the amplitude was increased (P < 0.05) in Hyp [40 arbitrary units (au) (SD 23)] compared with Con [26 au (SD 17)]. In conclusion, our results indicate that Hyp-induced hypocapnia enhanced substrate-level phosphorylation during moderate-intensity exercise. In addition, the increased amplitude of the HHb response suggests a reduced local muscle perfusion in Hyp compared with Con.     

The effects of normalization method on antagonistic activity patterns during eccentric and concentric isokinetic knee extension and flexion

The purpose of this study was to compare different normalization methods of electromyographic (EMG) activity of antagonists during isokinetic eccentric and concentric knee movements. Twelve women performed three maximum knee extensions and flexions isometrically and at isokinetic concentric and eccentric angular velocities of 30 °·s⁻¹, 90 °·s⁻¹, 120 °·s⁻¹ and 150 °·s⁻¹. The EMG activity of the vastus lateralis, rectus femoris, vastus medialis and hamstrings was recorded. The antagonist integrated IEMG values were normalized relative to the EMG of the same muscle during an isometric maximal action (static method). The values were also expressed as a percentage of the EMG activity of the same muscle, at the same angle, angular velocity and muscle action (dynamic method) when the muscle was acting as an agonist. Three-way analysis of variance (ANOVA) designs indicated significantly greater IEMG normalized with the dynamic method compared to the EMG derived using the static method (P < 0.05). These differences were more evident at concentric angular velocities and at the first and last 20 ° of the movement. The present findings demonstrate that the method of normalization significantly influences the conclusions on antagonistic activity during isokinetic maximum voluntary efforts. The dynamic method of normalization is more appropriate because it considers the effects of muscle action, muscle length and angular velocity on antagonist IEMG.     

Muscle oxidative metabolism accelerates with mild acidosis during incremental intermittent isometric plantar flexion exercise

BACKGROUND: It has been thought that intramuscular ADP and phosphocreatine (PCr) concentrations are important regulators of mitochondorial respiration. There is a threshold work rate or metabolic rate for cellular acidosis, and the decrease in muscle PCr is accelerated with drop in pH during incremental exercise. We tested the hypothesis that increase in muscle oxygen consumption (o2mus) is accelerated with rapid decrease in PCr (concomitant increase in ADP) in muscles with drop in pH occurs during incremental plantar flexion exercise. METHODS: Five male subjects performed a repetitive intermittent isometric plantar flexion exercise (6-s contraction/4-s relaxation). Exercise intensity was raised every 1 min by 10% maximal voluntary contraction (MVC), starting at 10% MVC until exhaustion. The measurement site was at the medial head of the gastrocnemius muscle. Changes in muscle PCr, inorganic phosphate (Pi), ADP, and pH were measured by 31P-magnetic resonance spectroscopy. o2mus was determined from the rate of decrease in oxygenated hemoglobin and/or myoglobin using near-infrared continuous wave spectroscopy under transient arterial occlusion. Electromyogram (EMG) was also recorded. Pulmonary oxygen uptake (o2pul ) was measured by the breath-by-breath gas analysis. RESULTS: EMG amplitude increased as exercise intensity progressed. In contrast, muscle PCr, ADP, o2mus, and o2pul did not change appreciably below 40% MVC, whereas above 40% MVC muscle PCr decreased, and ADP, o2mus, and o2pul increased as exercise intensity progressed, and above 70% MVC, changes in muscle PCr, ADP, o2mus, and o2pul accelerated with the decrease in muscle pH (~6.78). The kinetics of muscle PCr, ADP, o2mus, and o2pul were similar, and there was a close correlation between each pair of parameters (r = 0.969~0.983, p < 0.001). CONCLUSION: With decrease in pH muscle oxidative metabolism accelerated and changes in intramuscular PCr and ADP accelerated during incremental intermittent isometric plantar flexion exercise. These results suggest that rapid changes in muscle PCr and/or ADP with mild acidosis stimulate accelerative muscle oxidative metabolism.     

Unchanged H-reflex during a sustained isometric submaximal plantar flexion performed with an EMG biofeedback

The aim of this study was to assess H-reflex plasticity and activation pattern of the plantar flexors during a sustained contraction where voluntary EMG activity was controlled via an EMG biofeedback. Twelve healthy males (28.0 ± 4.8 yr) performed a sustained isometric plantar flexion while instructed to maintain summed EMG root mean square (RMS) of gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) muscles fixed at a target corresponding to 80% maximal voluntary contraction torque via an EMG biofeedback. Transcutaneous electrical stimulation of the posterior tibial nerve was evoked during the contraction to obtain the maximal H-reflex amplitude to maximal M-wave amplitude ratio (H_sup/M_sup ratio) from GL, GM and soleus (SOL) muscles. Neuromuscular function was also assessed before and immediately after exercise. Results showed a decrease in SOL activation during sustained flexion (from 65.5 ± 6.4% to 42.3 ± 3.8% maximal EMG, p < 0.001), whereas summed EMG RMS of GL and GM remained constant (59.7 ± 4.8% of maximal EMG on average). No significant change in the H_sup/M_sup ratio was found for SOL, GL and GM muscles. Furthermore, it appears that the decrease in maximal voluntary contraction torque (?20.4 ± 2.9%, p < 0.001) was related to both neural and contractile impairment. Overall, these findings indicate that the balance between excitation and inhibition affecting the motoneuron pool remains constant during a sustained contraction where myoelectrical activity is controlled via an EMG biofeedback or let free to vary.     

Longitudinal and transverse deformation of human Achilles tendon induced by isometric plantar flexion at different intensities

The present study determined in vivo deformation of the entire Achilles tendon in the longitudinal and transverse directions during isometric plantar flexions. Twelve young women and men performed isometric plantar flexions at 0% (rest), 30%, and 60% of the maximal voluntary contraction (MVC) while a series of oblique longitudinal and cross-sectional magnetic resonance (MR) images of the Achilles tendon were taken. At the distal end of the soleus muscle belly, the Achilles tendon was divided into the aponeurotic (ATapo) and the tendinous (ATten) components. The length of each component was measured in the MR images. The widths of the Achilles tendon were determined at 10 regions along ATapo and at four regions along ATten. Longitudinal and transverse strains were calculated as changes in relative length and width compared with those at rest. The ATapo deformed in both longitudinal and transverse directions at 30%MVC and 60%MVC. There was no difference between the strains of the ATapo at 30%MVC and 60%MVC either in the longitudinal (1.1 and 1.6%) or transverse (5.0～11.4 and 5.0～13.9%) direction. The ATten was elongated longitudinally (3.3%) to a greater amount than ATapo, while narrowing transversely in the most distal region (-4.6%). The current results show that the magnitude and the direction of contraction-induced deformation of Achilles tendon are different for the proximal and distal components. This may be related to the different functions of Achilles tendon, i.e., force transmission or elastic energy storage during muscle contractions.     

Evaluation of plantar flexion contracture contribution during the gait of children with Duchenne muscular dystrophy

Because of extensor weakness, children with Duchenne muscular dystrophy (DMD) maintain internal flexion moments at the joints of the lower extremities when they walk. We believe that at the ankle, the plantar flexion moments caused by contractures may contribute significantly to the production of the net ankle flexion moment during the gait in these children. The goal of the present study is to quantify ankle plantar flexion passive moments that may be associated with the presence of flexion contractures and to estimate their contribution to the net moment during the gait of children with DMD. Kinematic and kinetic parameters were collected during gait of eleven subjects with DMD. Ankle plantar flexion passive moments were also measured experimentally during the same session. Fourteen control children participated in the study in order to have normal reference values. The presence of ankle plantar flexion contractures in children with DMD was reflected by a rigidity coefficient obtained at a common moment of ?7 Nm that was higher for these children (0.75 Nm/° vs. 0.48 Nm/°; p < 0.05). The relative passive moment contribution to the net plantar flexion moments was higher for the children with DMD at the end of the lengthening phase of the plantar flexors (25% vs. 18%; p < 0.05). We believe that the passive moments can compensate for the presence of progressive muscle weakness in the children with DMD and help these children with gait.