Receptor mechanisms underlying heterogenic reflexes among the triceps surae muscles of the cat

The soleus (S), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles of the cat are interlinked by rapid spinal reflex pathways. In the decerebrate state, these heterogenic reflexes are either excitatory and length dependent or inhibitory and force dependent. Mechanographic analysis was used to obtain additional evidence that the muscle spindle primary ending and the Golgi tendon organ provide the major contributions to these reflexes, respectively. The tendons of the triceps surae muscles were separated and connected to independent force transducers and servo-controlled torque motors in unanesthetized, decerebrate cats. The muscles were activated as a group using crossed-extension reflexes. Electrical stimulation of the caudal cutaneous sural nerve was used to provide a particularly strong activation of MG and decouple the forces of the triceps surae muscles. During either form of activation, the muscles were stretched either individually or in various combinations to determine the strength and characteristics of autogenic and heterogenic feedback. The corresponding force responses, including both active and passive components, were measured during the changing background tension. During activation of the entire group, the excitatory, heterogenic feedback linking the three muscles was found to be strongest onto LG and weakest onto MG, in agreement with previous results concerning the strengths of heteronymous Ia excitatory postsynaptic potentials among the triceps surae muscles. The inhibition, which is known to affect only the soleus muscle, was dependent on active contractile force and was detected essentially as rapidly as length dependent excitation. The inhibition outlasted the excitation and was blocked by intravenous strychnine. These results indicate that the excitatory and inhibitory effects are dominated by feedback from primary spindle receptors and Golgi tendon organs. The interactions between these two feedback pathways potentially can influence both the mechanical coupling between ankle and knee.     

Length and moment arm of human leg muscles as a function of knee and hip-joint angles

Summary Lengths of muscle tendon complexes of the quadriceps femoris muscle and some of its heads, biceps femoris and gastrocnemius muscles, were measured for six limbs of human cadavers as a function of knee and hip-joint angles. Length-angle curves were fitted using second degree polynomials. Using these polynomials the relationships between knee and hip-joint angles and moment arms were calculated. The effect of changing the hip angle on the biceps femoris muscle length is much larger than that of changing the knee angle. For the rectus femoris muscle the reverse was found. The moment arm of the biceps femoris muscle was found to remain constant throughout the whole range of knee flexion as was the case for the medial part of the vastus medialis muscle. Changes in the length of the lateral part of the vastus medialis muscle as well as the medial part of the vastus lateralis muscle are very similar to those of vastus intermedius muscle to which they are adjacent, while those changes in the length of the medial part of the vastus medialis muscle and the lateral part of the vastus lateralis muscle, which are similar to each other, differ substantially from those of the vastus intermedius muscle. Application of the results to jumping showed that bi-articular rectus femoris and biceps femoris muscles, which are antagonists, both contract eccentrically early in the push off phase and concentrically in last part of this phase.     

Inhomogeneous architectural changes of the quadriceps femoris induced by resistance training

Purpose

This study aimed to clarify whether resistance training-induced changes in muscle architecture are homogeneous among the quadriceps and over different regions within each muscle.

Methods

Eleven recreationally active men (27 ± 2 years) completed a 12-week resistance training program for knee extensors. Before and after the intervention, muscle thicknesses, fascicle lengths, and pennation angles of the four muscles (vastus lateralis, vastus medialis, vastus intermedius, rectus femoris) in several regions (2–4 regions per each muscle) were measured using ultrasonography. Anatomical cross-sectional areas (ACSAs) at the same positions as the ultrasound measurements were determined from magnetic resonance images.

Results

Relative increases in the ACSA, muscle thickness, and pennation angle of the rectus femoris were significantly greater than those of the vasti. Relative increases in the ACSAs of the vastus lateralis and rectus femoris were significantly greater in the distal than in the proximal region, and those in the muscle thickness and pennation angle of the vastus intermedius were significantly greater in the medial than in the lateral region. Fascicle lengths did not change in any muscles. The interrelations between muscle thickness and pennation angle remained unchanged after the intervention, with a significant association between the relative changes of the two variables.

Conclusion

The current results indicate that (1) hypertrophy of the quadriceps femoris is associated with a proportional increase in pennation angle but not necessarily in fascicle length, and (2) training-induced changes in muscle size and pennation do not evenly occur among the quadriceps, along or across a muscle.     

Local loss of proprioception results in disruption of interjoint coordination during locomotion in the cat

To investigate the role of localized, proprioceptive feedback in the regulation of interjoint coordination during locomotion, we substantially attenuated neural feedback from the triceps surae muscles in one hindlimb in each of four cats using the method of self-reinnervation. After allowing the recovery of motor innervation, the animals were filmed during level and ramp walking. Deficits were small or undetectable during walking on the level surface or up the ramp, behaviors that require a large range of forces in the triceps surae muscles. During walking down the ramp, when the triceps surae muscles normally undergo active lengthening, the ankle joint underwent a large yield and the coordination between ankle and knee was disrupted. The correlation of the deficit with the direction of length change and not muscle force suggested that a loss of feedback from muscle spindle receptors was primarily responsible for the deficit. These results indicate an important role for the stretch reflex and stiffness regulation during locomotion.     

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.     

Atlas of the muscle motor points for the lower limb: implications for electrical stimulation procedures and electrode positioning

The aim of the study was to investigate the uniformity of the muscle motor point location for lower limb muscles in healthy subjects. Fifty-three subjects of both genders (age range: 18–50 years) were recruited. The muscle motor points were identified for the following ten muscles of the lower limb (dominant side): vastus medialis, rectus femoris, and vastus lateralis of the quadriceps femoris, biceps femoris, semitendinosus, and semimembranosus of the hamstring muscles, tibialis anterior, peroneus longus, lateral and medial gastrocnemius. The muscle motor point was identified by scanning the skin surface with a stimulation pen electrode and corresponded to the location of the skin area above the muscle in which an electrical pulse evoked a muscle twitch with the least injected current. For each investigated muscle, 0.15 ms square pulses were delivered through the pen electrode at low current amplitude (<10 mA) and frequency (2 Hz). 16 motor points were identified in the 10 investigated muscles of almost all subjects: 3 motor points for the vastus lateralis, 2 motor points for rectus femoris, vastus medialis, biceps femoris, and tibialis anterior, 1 motor point for the remaining muscles. An important inter-individual variability was observed for the position of the following 4 out of 16 motor points: vastus lateralis (proximal), biceps femoris (short head), semimembranosus, and medial gastrocnemius. Possible implications for electrical stimulation procedures and electrode positioning different from those commonly applied for thigh and leg muscles are discussed.     

Effects of firing frequency on length-dependent myofascial force transmission between antagonistic and synergistic muscle groups

Effects of stimulation frequency on myofascial force transmission between rat peroneal and triceps surae and antagonistic anterior crural muscles, and between extensor digitorum longus (EDL) and tibialis anterior and extensor hallucis longus (TA + EHL) muscles were investigated for lengthening of all anterior crural muscles. Muscles contracted isometrically at firing rates of 10, 20, 30 and 100 Hz. EDL and TA + EHL were distally lengthened. Peroneal and triceps surae muscles attained a constant muscle-tendon complex length. Peroneal and triceps surae distal active force decreased significantly as a function of anterior crural muscle length, also at submaximal activation. The absolute decrease was highest for 100 Hz (peroneal muscles -0.87 N; triceps surae muscles -0.92 N), but the highest normalized decrease occurred at 10 Hz stimulation (peroneal muscles -34%; triceps surae muscles -18%). At all muscle lengths, a negative proximo-distal difference in EDL active force was present which decreased with lower firing frequencies (from -0.4 N at 100 Hz to -0.03 N at 10 Hz). The passive proximo-distal force difference attained positive values. EDL and TA + EHL length-force characteristics agree with effects of firing frequency, except for 10 Hz stimulation, where active force was higher than expected and optimum length shifted to lower muscle lengths. It is concluded that also at submaximal stimulation frequencies, extramuscular myofascial force transmission between peroneal and triceps surae muscles and antagonistic anterior crural muscles is substantial. Although lengthening of submaximally active anterior crural muscles decreases the net myofascially transmitted load on EDL, myofascial force transmission significantly alters effects of firing frequency on length-force characteristics.     

Architectural anatomy of the quadriceps and the relationship with muscle strength: An observational study utilising real-time ultrasound in healthy adults

Quadriceps atrophy and morphological change is a known phenomenon that can impact significantly on strength and functional performance in patients with acute or chronic presentations conditions. Real-time ultrasound (RTUS) imaging is a noninvasive valid and reliable method of quantifying quadriceps muscle anatomy and architecture. To date, there is a paucity of normative data on the architectural properties of superficial and deep components of the quadriceps muscle group to inform assessment and evaluation of intervention programs. The aims of this study were to (1) quantify the anatomical architectural properties of the quadriceps muscle group (rectus femoris, vastus intermedius, and vastus lateralis) using RTUS in healthy older adults and (2) to determine the relationship between RTUS muscle parameters and measures of quadriceps muscle strength. Thirty middle aged to older males and females (age range 55–79 years; mean age =59.9 ± 7.08 years) were recruited. Quadriceps muscle thickness, cross-sectional area, pennation angle, and echogenicity were measured using RTUS. Quadriceps strength was measured using hand-held dynamometry. For the RTUS-derived quadriceps morphological data, rectus femoris mean results; circumference 9.3 cm; CSA 4.6 cm²; thickness 1.5 cm; echogenicity 100.2 pixels. Vastus intermedius mean results; thickness 1.8 cm; echogenicity 99.1 pixels. Vastus lateralis thickness 1.9 cm; pennation angle 17.3 ° ; fascicle length 7.0 cm. Quadriceps force was significantly correlated only with rectus femoris circumference (r = 0.48, p = 0.007), RF echogenicity (r = 0.38, p = 0.037), VI echogenicity (r = 0.43, p = 0.018), and VL fascicle length (r = 0.43, p = 0.019). Quadriceps force was best predicted by a three-variable model (adjusted R² = 0.46, p < 0.001) which included rectus femoris echogenicity (B = 0.43, p = 0.005), vastus lateralis fascicle length (B = 0.33, p = 0.025) and rectus femoris circumference (B = 0.31, p = 0.041). Thus respectively, rectus femoris echogenicity explains 43%, vastus lateralis fascicle length explains 33% and rectus femoris circumference explains 31% of the variance of quadriceps force. The study findings suggest that RTUS measures were reliable and further research is warranted to establish whether these could be used as surrogate measures for quadriceps strength in adults to inform exercise and rehabilitation programs.     

Mechanomyographic responses of the superficial quadriceps femoris muscles to incremental isometric muscle actions

The purpose of this study was to compare the composite and individual relationships for mechanomyographic (MMG) amplitude vs. torque during incremental isometric muscle actions. Ten women and six men (mean age +/- SD = 21.8 +/- 1.6 y) performed isometric leg extension muscle actions at 10-100% of peak isometric torque. Accelerometers were placed over the superficial quadriceps femoris muscles to detect the MMG signals. Polynomial regression analyses were used to determine the composite and individual patterns for MMG amplitude vs. isometric torque. The results indicated that the composite MMG amplitude vs. isometric torque relationships for all subjects combined were quadratic for the vastus lateralis and vastus medialis, and linear for the rectus femoris. The results of the individual analyses for the vastus lateralis revealed that the best fit model was linear for six subjects, quadratic for five subjects, cubic for three subjects, while two subjects exhibited no significant relationship. For the rectus femoris, eight subjects demonstrated linear patterns, six were quadratic, and two were cubic. For the vastus medialis, six subjects demonstrated linear patterns, four were quadratic, four were cubic, and two demonstrated no significant relationship. Examination of the patterns between muscles for each individual subject demonstrated that twelve of the sixteen subjects demonstrated different patterns for MMG amplitude vs. isometric torque for at least two of the three muscles examined. The results indicated there were differences in the patterns of responses for the composite MMG amplitude vs. isometric torque relationships for the three muscles. Furthermore, individual patterns for MMG amplitude frequently differed from the composite patterns, as well as between muscles. The results suggested that, in addition to using composite results of MMG responses, individual subject responses should be examined. Furthermore, caution should be used in generalizing the MMG responses of the quadriceps femoris muscles when examining a single muscle.     

Muscle blood flow and flow heterogeneity during exercise studied with positron emission tomography in humans

Blood flow is the main regulator of skeletal muscle's oxygen supply, and several studies have shown heterogeneous blood flow among and within muscles. However, it remains unclear whether exercise changes the heterogeneity of flow in exercising human skeletal muscle. Muscle blood flow and spatial flow heterogeneity were measured simultaneously in exercising and in the contralateral resting quadriceps femoris (QF) muscle in eight healthy men using H2(15)O and positron emission tomography. The relative dispersion (standard deviation/mean) of blood flow was calculated as an index of spatial flow heterogeneity. Average muscle blood flow in QF was 29 (10) ml x (kg muscle)(-1) x min(-1) at rest and 146 (54) ml x (kg muscle)(-1) x min(-1) during exercise (P = 0.008 for the difference). Blood flow was significantly (P < 0.001) higher in the vastus medialis and the vastus intermedius than in the vastus lateralis and the rectus femoris, both in the resting and the exercising legs. Flow was more homogeneous in the exercising vastus medialis and more heterogeneous (P < 0.001) in the exercising vastus lateralis (P = 0.01) than in the resting contralateral muscle. Flow was more homogeneous (P < 0.001) in those exercising muscles in which flow was highest (vastus intermedius and vastus medialis) as compared to muscles with the lowest flow (vastus lateralis and the rectus femoris). These data demonstrate that muscle blood flow varies among different muscles in humans both at rest and during exercise. Muscle perfusion is spatially heterogeneous at rest and during exercise, but responses to exercise are different depending on the muscle.     

Non-uniform mechanical activity of quadriceps muscle during fatigue by repeated maximal voluntary contraction in humans

To determine the non-uniform surface mechanical activity of human quadriceps muscle during fatiguing activity, surface mechanomyogram (MMG), or muscle sound, and surface electromyogram (EMG) were recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles of seven subjects during unilateral isometric knee extension exercise. Time- and frequency-domain analyses of MMG and of EMG fatigued by 50 repeated maximal voluntary contractions (MVC) for 3?s, with 3-s relaxation in between, were compared among the muscles. The mean MVC force fell to 49.5 (SEM 2.0)% at the end of the repeated MVC. Integrated EMG decreased in a similar manner in each muscle head, but a marked non-uniformity was found for the decline in integrated MMG (iMMG). The fall in iMMG was most prominent for RF, followed by VM and VL. Moreover, the median frequency of MMG and the relative decrease in that of EMG in RF were significantly greater (P?) than those recorded for VL and VM. These results would suggest a divergence of mechanical activity within the quadriceps muscle during fatiguing activity by repeated MVC.     

Muscle�Ctendon structure and dimensions in adults and children

Muscle performance is closely related to the architecture and dimensions of the muscle–tendon unit and the effect of maturation on these architectural characteristics in humans is currently unknown. This study determined whether there are differences in musculo‐tendinous architecture between adults and children of both sexes. Fascicle length and pennation angle were measured from ultrasound images at three sites along the length of the vastus intermedius, vastus lateralis, vastis medialis and rectus femoris muscles. Muscle volume and muscle–tendon length were measured from magnetic resonance images. Muscle physiological cross‐sectional area (PCSA) was calculated as the ratio of muscle volume to optimum fascicle length. Fascicle length was greater in the adult groups than in children (P < 0.05) but pennation angle did not differ between groups (P > 0.05). The ratios between fascicle and muscle length and between fascicle and tendon length were not different (P > 0.05) between adults and children for any quadriceps muscle. Quadriceps volume and PCSA of each muscle were greater in adults than children (P < 0.01) but the relative proportion of each head to the total quadriceps volume was similar in all groups. However, the difference in PCSA between adults and children (men ～ 104% greater than boys, women ～ 57% greater than girls) was greater (P < 0.05) than the difference in fascicle length (men ～ 37% greater than boys, women ～ 10% greater than girls). It is concluded that the fascicle, muscle and tendon lengthen proportionally during maturation, thus the muscle–tendon stiffness and excursion range are likely to be similar in children and adults but the relatively greater increase in PCSA than fascicle length indicates that adult muscles are better designed for force production than children’s muscles.     

Atrophy of the lower limbs in elderly women: is it related to walking ability?

This study investigated the relationship between walking ability and age-related muscle atrophy of the lower limbs in elderly women. The subjects comprised 20 young women and 37 elderly women who resided in nursing homes or chronic care institutions. The elderly subjects were divided into three groups according to their walking ability. The muscle thickness of the following ten lower limb muscles were measured by B-mode ultrasound: the gluteus maximus, gluteus medius, gluteus minimus, psoas major, rectus femoris, vastus lateralis, vastus intermedius, biceps femoris, gastrocnemius and soleus. Compared to the young group, muscle thicknesses of all muscles except the soleus muscle were significantly smaller in all the elderly groups. There were no significant differences between the fast- and slow-walking groups in the thickness of any muscle. In the dependent elderly group, noticeable muscle atrophy was observed in the quadriceps femoris muscle. The results of this study suggest that the elderly who are capable of locomotion, regardless of their walking speed, show a moderate degree of age-related atrophy, while those who do not walk exhibit more severe atrophy, especially in the quadriceps femoris muscle.     

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。     

Patterning of muscle activity in static knee extension

Activity patterning of the three agonist muscles (rectus femoris, vastus medialis, vastus lateralis) and one antagonist muscle (semimembranosus) was investigated during static knee extension. Male physical education students performed maximal and submaximal exertions in two test postures with different hip and knee positions corresponding to the postures used in our previous leg extension study. The character of the force curves was found in both postures to be convex with maximum peak force at 120 degrees. The supine posture changed the length of the two-joint muscles so as to produce an ordinary type of force curve. In the recumbent posture the efficient angles of the hip and knee joints did not match, thereby causing more plateau-like maximum peak force. All the agonists worked as a group and were highly activated throughout the entire range of the extension movement. The influence of postural variation also on the activity patterning could be seen in the latter half of the knee extension movement. The recumbent posture decreased whereas the supine posture maintained or tended even to increase the agonist activity. The difference is possibly due to the changing length of the two-joint muscles (rectus femoris and semimembranosus). Though the IEMG-force ratio of the agonist muscles was always nonlinear, the increased curvilinear relationship of the rectus femoris in the recumbent posture fits in with the view that in such conditions the central control system attempts to extend the hip joint. The results indicated that the two-joint muscles work like a single-joint muscle but, at the same time, control muscle coordination in single-joint knee extension movement.     

Biarticular and monoarticular muscle activation and injury in human quadriceps muscle

We hypothesized that activation of the quadriceps femoris muscle group during eccentric exercise is related to the increase in magnitude of several markers of muscle injury that developed during the next week. Fourteen male subjects performed six to eight sets of five to ten repetitions of single-leg eccentric-only seated knee extension exercise. Magnetic resonance (MR) images were collected before and immediately after exercise and on days 2–4 and 6 after eccentric exercise. Changes in maximal voluntary contraction (MVC), perceived soreness, muscle volume and muscle transverse relaxation of water protons (T₂) were determined for the quadriceps femoris muscle group each day. Changes in muscle volume and T₂ were determined every day for each muscle [vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), rectus femoris (RF)] of the quadriceps femoris group. Post-exercise T₂ was greater than pre-exercise T₂ (P<0.05) for all muscles. The acute ΔT₂ (Post-Pre) was similar (P>0.05) among VL, VM, VI, and RF [5.5 (0.3) ms], suggesting that the four muscles were equally activated during eccentric exercise. In the week after eccentric exercise, subjects experienced delayed-onset muscle soreness (DOMS) and all muscles demonstrated a delayed increase in T₂ above pre-exercise values (P<0.05), suggesting that muscle injury had occurred. For the quadriceps femoris muscle group, there was no correlation between acute ΔT₂ and delayed (peak T₂ during days 2, 3, 4, 6 minus pre-exercise T₂) ΔT₂ (r=0.04, P>0.05). Similar results were obtained when VL, VM, VI and RF were examined separately. Of the four muscles in quadriceps femoris, the biarticular RF experienced greater muscle injury [delayed ΔT₂=15.2 (2.0) ms] compared to the three monoarticular vasti muscles [delayed ΔT₂=7.7 (1.3) ms; P<0.05]. We propose that the disproportionate muscle injury to RF resulted from an ineffective transfer of torque from the knee to hip joint during seated eccentric knee extension exercise, thus causing RF to dissipate greater energy than normal. We conclude that in humans, muscle activation is not a unique determinant of muscle injury. Electronic Publication     

Coordination of the thigh muscles in static leg extension

Activation patterns of the four thigh muscles (rectus femoris, vastus medialis, vastus lateralis and semimembranosus) were investigated in static leg extension through the entire range of extension movement in three testing postures: sitting, recumbent and supine. Special interest was focused on the role of the two-joint muscles. Five male students performed both maximal and submaximal efforts. The highest force values were observed when the knee was almost extended (150 degrees), while the agonists were the most active in flexed positions. Maximum peak activity of all the agonist muscles occurred throughout a rather wide movement range of the knee joint (80 degrees-150 degrees) in the sitting posture, but the more extended postures tended by lengthening the two-joint muscle of rectus femoris to reduce the range of peak activity of the agonists. During the latter half of the knee extension the activity of the agonists was greatly reduced (p less than .01) and a fully extended knee joint always resulted in silence on the part of the rectus femoris. In that position the vasti muscles together with the semimembranosus formed a force couple for stabilizing the knee joint. The semimembranosus, the two-joint muscle on the antagonistic side, increased activation toward the end of knee extension. This exceptional activation of the antagonist muscle during static agonist effort is likely to be due to the different role of the semimembranosus which tried as an agonist to extend the hip joint in the sitting posture. This phenomenon is supported by the low maximum peak activity of the rectus femoris.(ABSTRACT TRUNCATED AT 250 WORDS)     

The normal peak of electromyographic activity of the quadriceps femoris muscle in the stair cycle

The quadriceps femoris muscles of 18 subjects with no history of knee joint pathology were analysed climbing stairs. Temporal data was obtained from bilateral contact closing footswitches. Knee joint data was measured using a specially constructed flexible linkage-bar electrogonimeter. Electromyographic activity was obtained from bipolar Beckman surface electrodes placed on four components of the quadriceps femoris, vastus medialis oblique, vastus medialis longus, vastus lateralis and rectus femoris. Results showed that within the stair cycle, stance occupied 60% and swing 40%. Cadence values were greater during descending than ascending stairs. Joint angle data demonstrated 2 changes in direction of the angular motion of the knee joint in both ascending and descending. Electromyographic analysis identified a peak of EMG activity for each component of the quadriceps femoris in both ascending and descending stairs. Results identified the location of peak EMG activity at specific knee joint angles. The quadriceps components also demonstrated a regular sequence of recruitment. EMG amplitude levels obtained were higher in ascending than descending stairs. The results have clinical implications in the design of lower extremity prostheses and in the application of functional electrical stimulation.     

In vivo muscle mechanics during locomotion depend on movement amplitude and contraction intensity

The effects of movement amplitude and contraction intensity on triceps surae and quadriceps femoris muscle function were studied during repetitive hopping. In vivo forces from Achilles and patellar tendons were recorded with the optic fibre technique from eight volunteers. The performances were filmed (200 Hz) to determine changes in muscle-tendon unit length and velocity. When hopping with a small amplitude (23° knee flexion during the ground contact phase), the Achilles tendon was primarily loaded whereas patellar tendon forces were greater in large-amplitude hopping (56° knee flexion). In spite of the different magnitudes of stretch in the quadriceps femoris muscle, the stretching velocity and activity patterns of the quadriceps muscle were similar in both conditions. Simultaneously performed electromyographic (EMG) recordings revealed that preferential preactivation of the gastrocnemius muscle was evident in both jumping conditions. The triceps surae muscle was strongly active in the eccentric phase of small-amplitude hopping. Results from hopping with small knee-joint displacement suggest that there may be a particular frequency and jumping height at which the elastic bouncing is best utilized and at the same time the concentric phase is most economical. Results also support earlier observations that the economy of the shortening phase must be compromised at some point in order to produce more power and improve the jumping height. Electronic Publication     

Growth trend of the quadriceps femoris muscle in junior Olympic weight lifters: an 18-month follow-up survey

Isometric torque and the cross-sectional area (CSA) of the quadriceps femoris muscle (QF) were measured twice at an interval of 18 months in seven junior Olympic weight lifters (aged 15.5–17.1 years at the start of the study) to investigate the growth trend of this muscle group in junior athletes specializing in strength and power events. The CSAs of the QF and its four constituent muscles were determined at 30% (proximal to the knee), 50%, and 70% of femur length (Fl) using a magnetic resonance imaging method. Only at 30%Fl were significant increases found in the CSAs of the QF and all constituent muscles, except for the rectus femoris. At this level, the CSA of the vastus medialis relative to the QF decreased significantly, suggesting a predominant hypertrophy in the vastus intermedius and vastus lateralis muscles. Isometric torque during knee extension increased significantly compared, to the CSA for the QF measured at the three levels. Thus, the present results indicate that, at least at high school age, the QF for junior Olympic weight lifters is characterized by a preferential hypertrophy at the level proximal to the knee joint, with an increase in knee extension torque relative to the CSA. Electronic Publication