Stimulated and voluntary fatiguing contractions of quadriceps femoris differently disturb postural control

Muscle fatigue affects muscle strength and postural control. However, it is not known whether impaired postural control after fatiguing muscular exercise depends on the nature of the muscle contraction. To answer this question, the present study analyzes changes in postural control after two fatiguing exercises of equal duration and intensity but that induced different magnitudes of strength loss. The effects of fatiguing contractions of the femoris quadriceps were compared for voluntary muscular contraction (VOL) and neuromuscular electrical stimulation (ES) on muscle strength and postural control. Seventeen subjects completed these two fatiguing exercises. Maximal voluntary contraction (MVC) and postural control were recorded using an isokinetic dynamometer and a force platform that recorded the center of foot pressure. Recordings were performed before and after the completion of both fatiguing tasks. Results indicate that, after a fatiguing exercise, the ES exercise affected MVC more than the VOL exercise. Inversely, postural control was disturbed more after VOL exercise than after ES exercise. In conclusion, postural control disturbance is influenced by the nature of the muscular contraction (voluntary vs. non-voluntary) and the type of the motor unit solicited (tonic vs. phasic) rather than by the magnitude of strength loss.     

Normalized EMG to normalized torque relationship of vastus intermedius muscle during isometric knee extension

The purpose of the present study was to investigate the electromyography (EMG) to torque relationship of the vastus intermedius (VI) muscle. Thirteen healthy men performed maximal voluntary contraction (MVC) and submaximal contraction during isometric knee extension at 10% of the MVC to 90% of the MVC at intervals of 10% of the MVC level. Surface EMG was detected from four muscle components of the QF muscle group, i.e., VI, vastus lateralis (VL), vastus medialis, and rectus femoris (RF) muscles. Normalized muscle activation in the VI muscle was significantly lower than in the VL muscle at a lower torque level (20 and 40% of MVC) and significantly lower compared to the RF muscle at a higher torque level (from 60 to 90% of MVC). These results suggest that neuromuscular activation in the VI muscle is not consistent with the other components of QF muscle group during submaximal knee extension contractions.     

Perceived exertion and maximal quadriceps femoris muscle strength during dynamic knee extension exercise in young adult males and females

The objectives of the present study were to: (1) examine perceived exertion across different target voluntary-contraction intensities; (2) compare perceived exertion ratings with actual target intensities, and (3) compare perceived exertion ratings between males and females. Subjects for this study included 30 healthy, college-aged male (n=15) and female (n=15) volunteers. All subjects were free of orthopedic, cardiopulmonary, systemic and neurological disease. Subjects were evaluated for their one-repetition maximum (1-RM) during inertial knee extension exercise. All subjects then completed, in a random order, two sub-maximal inertial contractions at 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of their 1-RM. Perceived exertion was measured by asking subjects to provide a number that corresponded to the feelings in their quadriceps after completion of the two repetitions, by viewing a modified category-ratio (CR-10) scale. The results showed that males lifted a significantly greater absolute (P<0.05) and relative (P<0.05) amount of mass than females; allometric-modeled strength values also demonstrated significant sex differences. The results revealed a significant intensity main effect (P<0.001) but no significant gender main effect (P=0.97) nor intensity-by-gender interactions (P=0.50) for the perceived exertion responses. The findings demonstrated that perceived exertion was significantly (P<0.05) lower than the specific expected values on the CR-10 scale from 10% to 60% of 1-RM, but was not different from 70% to 90% 1-RM. The results revealed that the increase in perceived exertion was fit to both linear and quadratic trends, and that the exponent of the power function was found to be 1.437 (SD 0.22) for the males, and 1.497 (0.295) for the females. The major findings demonstrate that although males were able to lift more absolute and relative mass than females, the perceptual response to relative load was similar between genders. The increase in perceived exertion, as a function of relative load, showed a strong linear trend; however, enhanced perceptual sensitivity at high contraction intensities was evident from the positively accelerating power function. Electronic Publication     

Stimulated and voluntary fatiguing contractions of quadriceps femoris similarly disturb postural control in the bipedal stance

The aim of this work was to compare the effects of fatigue of the quadriceps femoris after fatiguing voluntary contractions (VOL) and fatiguing neuromuscular electrical stimulation (ES) on bipedal postural control. Nineteen active male subjects (22.2 ± 1.7 years) completed these two fatiguing exercises. Isometric maximal voluntary contraction (MVC) and postural control were recorded using an ergometer and a force platform that registered the center of foot pressure (COP). We analyzed the COP surface, the mean COP velocity and the spectral power density given by the wavelet transform. Recordings were performed before (PRE condition) and after the completion of each fatiguing task (immediately POST condition, after a 5 min recovery POST 5 condition). In POST condition, the ES exercise affected MVC more than the VOL exercise. However, bipedal postural control was similarly deteriorated for both exercises. In POST 5 condition, for both fatiguing exercises, muscle strength and postural control did not recover their initial level. These results suggest that the postural control disturbance could not be distinguished for the two fatiguing exercises in the bipedal stance. In addition, the recovery speeds of postural control and muscle strength abilities did not differ for the ES exercise and the VOL exercise.     

Intramuscular pressure and electromyographic responses of the vastus lateralis muscle during repeated maximal isokinetic knee extensions

The purpose of the study was to investigate changes in intramuscular pressure (IMP) (maximal during contraction - peak IMP, and between contraction, relaxation IMP - RxIMP) and surface electromyographic activity (EMG) parameters [mean frequency of the power spectrum (fmean), and signal amplitude, root mean square (RMS)] throughout 100 repetitive isokinetic contractions for six healthy subjects. Parameters were recorded simultaneously from the vastus lateralis muscle during maximal knee extension. Regression analyses revealed significant decreases for peak IMP and fmean, and an increase in RxIMP; RMS, however, did not change. All parameters demonstrated trends of change throughout the contractions that were non-linear. Details and inter relations for RxIMP and fmean were highlighted to express intramuscular fluid accumulation and fatigue development, respectively. Individual regression analyses for RxIMP revealed significant positive correlations for all subjects (range of r=0.62 to 0.89). At group level, mean RxIMP increased from 6.0 mmHg for the 1st contraction to 14.0 mmHg for the 100th contraction. For fmean, individual regressions were significantly negative for all subjects (r=-0.75 to -0.89). Fmean decreased from 89.2 Hz for the 1st contraction to 63.3 Hz for the 100th contraction. When the data were delineated between the fatigue (contractions 1-40) and endurance phases (41-100), the slopes of increase for RxIMP, and of decrease for fmean were significantly greater during the fatigue phase. RxIMP throughout the 100 contractions correlated negatively with fmean for each subject (r=-0.54 to -0.78); when delineated, the correlation between parameters was significantly greater for the fatigue as compared with the endurance phase. Relaxation IMP trends are mainly attributed to intramuscular water accumulations during repetitive contractions. In spite of consistent correlations between RxIMP and fmean a causal association could not be established. It may be suggested that a common factor occurring during the fatiguing process governs changes in RxIMP and fmean.     

Recruitment order of motor units in human vastus lateralis muscle is maintained during fatiguing contractions

Motor-unit firing patterns were studied in the vastus lateralis muscle of five healthy young men [21.4 +/- 0.9 (SD) yr] during a series of isometric knee extensions performed to exhaustion. Each contraction was held at a constant torque level, set to 20% of the maximal voluntary contraction at the beginning of the experiment. Electromyographic signals, recorded via a quadrifilar fine wire electrode, were processed with the precision decomposition technique to identify the firing times of individual motor units. In repeat experiments, whole-muscle mechanical properties were measured during the fatigue protocol using electrical stimulation. The main findings were a monotonic decrease in the recruitment threshold of all motor units and the progressive recruitment of new units, all without a change of the recruitment order. Motor units from the same subject showed a similar time course of threshold decline, but this decline varied among subjects (mean threshold decrease ranged from 23 to 73%). The mean threshold decline was linearly correlated (R2 >or= 0.96) with a decline in the elicited peak tetanic torque. In summary, the maintenance of recruitment order during fatigue strongly supports the notion that the observed common recruitment adaptations were a direct consequence of an increased excitatory drive to the motor unit pool. It is suggested that the increased central drive was necessary to compensate for the loss in force output from motor units whose muscle fibers were actively contracting. We therefore conclude that the control scheme of motor-unit recruitment remains invariant during fatigue at least in relatively large muscles performing submaximal isometric contractions.     

Association between regional quadriceps oxygenation and blood oxygen saturation during normoxic one-legged dynamic knee extension

It is not clear whether muscle oxygenation (O_2-NIRS) measured by near-infrared spectroscopy (NIRS) correlates with femoral venous SO₂ (S_fvo₂) during normoxic exercise. Therefore, the purpose of this study was to compare physiologically calibrated O_2-NIRS with S_fvo₂ in subjects performing one-legged dynamic knee extension exercise (1L-KEE). Five healthy male subjects (age 25±2 year, height 177.8±4.8 cm, body weight 67.1 ± 5.0 kg; mean ± SD) performed 1L-KEE at 20, 40, and 60% of peak work rate (WR-peak) each for 4 min. S_fvo₂ was measured at rest and during the 3rd minute of each work rate. O_2-NIRS was continuously monitored in a proximal region of the vastus lateralis (VL-p), a distal region of VL (VL-d), and a proximal region of the rectus femoris (RF-p). S_fvo₂ was 56.0% at rest and decreased to 36.6 at 20% WR-peak, 35.8 at 40% WR-peak, and 31.1 at 60% WR-peak. There was a significant correlation between O_2-NIRS and S_fvo₂(VL-p: r ² = 0.62, VL-d: r ² = 0.35, RF-p: r ² = 0.62, with a moderate variation among individuals at each site; residual values = 4.83 – 11.75). These data indicate that NIRS measurement provides a reflection of S_fvo₂ during 20–60% WR-peak of normoxic 1L-KEE.     

The influences of muscle fibre proportions and areas upon EMG during maximal dynamic knee extensions

This study is an investigation of the relationship between muscle morphology and surface electromyographic (EMG) parameters [mean frequency of the power spectrum (MNF), signal amplitude (root mean square, RMS) and the signal amplitude ratio (SAR; i.e. the ratio between the RMS level during the passive part of the contraction cycle and the RMS level during the active part of the contraction cycle)] during 100 maximal dynamic knee extensions at 90° · s⁻¹. Each contraction cycle comprised of 1 s of active knee extension and 1 s of passive knee flexion. The surface EMG was recorded from the vastus lateralis muscle. Twenty clinically healthy subjects participated in the study, and muscle biopsy samples of the vastus lateralis were obtained from 19 of those subjects. The relationships between muscle morphology and EMG were investigated at three stages of the test: initially, during the fatigue phase (initial 40 contractions), and at the endurance level (the final 50 contractions). Major findings on correlations are that SAR and MNF tended to correlate positively with the proportion of type 1 fibres, and RMS correlated positively with the proportion of type 2 muscle fibres. The muscle fibre areas showed little correlation with the EMG variables under investigation. The results of the present study showed that the three EMG variables of a dynamic endurance test that were investigated (RMS, MNF and SAR) were clearly correlated with the proportions of the different fibre types, but only to a small extent with fibre areas. These findings contradict some of the theoretical models of the EMG, especially for parameters in the frequency domain. Accepted: 17 June 1999     

Effects of different strength training regimes on moment and power generation during dynamic knee extensions

This study examined the effect of different training regimes on moment and power generation during maximal knee extensions at low to very high extension velocities (0–1000°·s^–1 individual range). A group of 24 soccer players performed 12 weeks of progressively adjusted strength training of the knee extensors at either high resistance (HR,n=7), low resistance (LR,n=6), loaded kicking movements (FU,n=6), while one group served as controls (n=5). Moment and power generation of the knee extensors were determined before and after the training period with a nonisokinetic measuring method recently described. Following HR training, knee extension moment increased 9%–10% at knee angular velocities 0 (isometric) and 30° · s^–1 (P<0.05), peak moment increased 20% at 240–300°·s^–1 (P<0.05), while power generation increased 5%–29% at 240–480° · s^–1 (P<0.01). In addition, in the HR group maximal recorded power increased 45% (P<0.01). After FU training a 7%–13% increase in moment and power was observed at 30–180° · s^–1 (P<0.05). Following LR training, peak moment increased 9% at 120° · s^–1 (P<0.05). Improvements in knee extension moment and power were generally related to the angular velocities employed during training. However, as evaluated using the present measuring method, moment and power increased not only at very low but also at high knee angular velocities following the high-resistance strength training.     

Regional differences in blood flow, glucose uptake and fatty acid uptake within quadriceps femoris muscle during dynamic knee-extension exercise

The purpose of the present study was to investigate the regional differences in glucose and fatty acid uptake within skeletal muscle during exercise. Blood flow (BF), glucose uptake (GU) and free fatty acid uptake (FFAU) were measured in four different regions (vastus lateralis, VL; rectus femoris, RF; vastus intermedius, VI; and vastus medialis, VM) of the quadriceps femoris (QF) muscle during low-intensity, knee-extension exercise using positron emission tomography. BF was higher in VI than in VL, RF and VM (P < 0.05). FFAU was higher in VI (P < 0.001) but also in VM (P < 0.05) compared with VL and RF. In contrast, GU was higher in RF compared with VL (P < 0.05) but was not significantly different to VM or VI (both P = NS). FFAU within these four muscle regions correlated significantly with BF (r = 0.951, P < 0.05), whereas no significant relationship was observed between GU and BF (r = 0.352, P = NS). Therefore, skeletal muscle FFAU, but not GU, appears to be associated with BF during low-intensity exercise. The present results also indicate considerable regional differences in substrate use within working QF muscle. As such, an important methodological outcome from these results is that one sample from a specific part of the QF muscle does not represent the response in the entire QF muscle group.     

Differential effect of knee extension isometric training on the different muscles of the quadriceps femoris in humans

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     

The development of the tensor vastus intermedius during the human embryonic period and its clinical implications

The tensor vastus intermedius (TVI) is a newly discovered muscle located in the anterolateral thigh area and is considered the fifth component of the quadriceps femoris muscle. There have been several papers describing its anatomical and morphological features in detail; however, many features of this muscle, such as its ontology or kinetic functions, remain unknown. The purpose of this study was to determine the initial appearance of the TVI muscle in human embryonic development and to investigate its growth and development. Histological observations were performed on 30 lower limbs of 15 human embryos from Carnegie stage (CS) 21, 22, and 23 (with crown-rump length ranging from 18.7 to 28.7 mm). Myocyte clusters of the TVI were observed between the vastus lateralis and intermedius muscles in 7 out of 10 limbs in CS 22, indicating that the TVI arises during this stage. In CS 23, the TVI was clearly present in all specimens except one. However, neither the aponeurosis nor the tendonous structure of the TVI were observed in these embryonic stages. Formation of the conventional four components of the quadriceps muscle is completed within CS 21; therefore, our results suggest that the TVI is the last element to develop in the quadriceps femoris complex. It is posited that after the embryonic period, the TVI continues to grow, while forming the tendinous structure toward the patella and receiving vascular supply from certain vascular branches. The clinical significance of these findings is that orthopedists and plastic surgeons who perform surgical procedures within the anterolateral thigh (ALT) area should be aware of the anatomy and development of the TVI in order to reduce surgical complications. Our present research aims to contribute to a deeper understanding of the morphogenesis of the TVI and the other femoral extensor muscles.     

Force enhancement during and following muscle stretch of maximal voluntarily activated human quadriceps femoris

Force enhancement during and following muscle stretch has been observed for electrically and voluntarily activated human muscle. However, especially for voluntary contractions, the latter observation has only been made for adductor pollicis and the ankle joint muscles, but not for large muscles like quadriceps femoris. Therefore, the aim of this study was to investigate the effects of active muscle stretch on force production for maximal voluntary contractions of in vivo human quadriceps femoris (n = 15). Peak torques during and torques at the end of stretch, torques following stretch, and passive torques following muscle deactivation were compared to the isometric torques at corresponding muscle length. In addition, muscle activation of rectus femoris, vastus medialis and vastus lateralis was obtained using surface EMG. Stretches with different amplitudes (15, 25 and 35° at a velocity of 60° s⁻¹) were performed on the plateau region and the descending limb of the force–length relation in a random order. Data analysis showed four main results: (1) peak torques did not occur at the end of the stretch, but torques at the end of the stretch exceeded the corresponding isometric torque; (2) there was no significant force enhancement following muscle stretch, but a small significant passive force enhancement persisted for all stretch conditions; (3) forces during and following stretch were independent of stretch amplitude; (4) muscle activation during and following muscle stretch was significantly reduced. In conclusion, although our results showed passive force enhancement, we could not provide direct evidence that there is active force enhancement in voluntarily activated human quadriceps femoris.     

股四头肌腱的临床应用解剖

目的　为临床应用股四头肌腱重建膝关节交叉韧带提供临床解剖学资料。 方法　在10具成人尸体标本上（20只膝关节）解剖观察股四头肌腱的形态和走行关系以及在髌骨附着点的解剖学特点,测量股直肌腱起止点宽度、长度以及髌骨上极的厚度。 结果　股直肌止点的宽度为（3.20±0.33）cm。起点的宽度为（1.28±0.25）cm。完全为腱性组织的长度为（6.96±0.80）cm。股直肌腱近侧端约4/5完全游离,远侧端约1/5与股外侧肌和股中间肌融合,共同构成股四头肌腱,附着于髌骨上极前方约3/4部分。髌上极的平均厚度为(2.22±0.14)cm。 结论　股四头肌腱的的解剖学特点,完全使其可以作为临床上行膝关节交叉韧带重建的供区之一。     

Severe degeneration of rabbit vastus intermedius muscle immobilized in shortened position

The authors have previously shown that passive daily mobilization of the rabbit hind limb immobilized with the knee in extension leads to necrosis of the deep thigh muscles and myositis ossificans-like periosteal bone formation. In this study the effect of immobilization alone on the rabbit hind limb muscles was examined similarly to that of immobilized limbs. Serum creatine kinase activities increased significantly and intravenously administered Evans blue albumin showed increased vascular permeability in the deep vastus intermedius muscle even on day 1. Necrotic fibers were clearly present in the deep part of the vastus intermedius muscle on day 5 in light and electron microscopy and in enzyme histochemistry. Fibrosis and atrophy were found later. The superficial portion of the vastus intermedius and the deep contralateral nonimmobilized vastus intermedius showed degenerative changes. Bone formation was not noted. The conclusion was that the deep vastus intermedius muscle composed almost exclusively of type I fibers is exceptionally prone to damage when immobilized in a shortened position. Contact of the necrotic muscle with the underlying periosteum is not alone sufficient to induce heterotopic ossification. The additional trauma caused by daily mobilization is needed for the myositis ossificans-like bone formation.