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.     

Synchronization of lower limb motor unit activity during walking in human subjects

Synchronization of motor unit activity was investigated during treadmill walking (speed: 3-4 km/h) in 25 healthy human subjects. Recordings were made by pairs of wire electrodes inserted into the tibialis anterior (TA) muscle and by pairs of surface electrodes placed over this muscle and a number of other lower limb muscles (soleus, gastrocnemius lateralis, gastrocnemius medialis, biceps femoris, vastus lateralis, and vastus medialis). Short-lasting synchronization (average duration: 9.6 +/- 1.1 ms) was observed between spike trains generated from multiunit electromyographic (EMG) signals recorded by the wire electrodes in TA in eight of nine subjects. Synchronization with a slightly longer duration (12.8 +/- 1.2 ms) was also found in 13 of 14 subjects for paired TA surface EMG recordings. The duration and size of this synchronization was within the same range as that observed during tonic dorsiflexion in sitting subjects. There was no relationship between the amount of synchronization and the speed of walking. Synchronization was also observed for pairs of surface EMG recordings from different ankle plantarflexors (soleus, medial gastrocnemius, and lateral gastrocnemius) and knee extensors (vastus lateralis and medialis of quadriceps), but not or rarely for paired recordings from ankle and knee muscles. The data demonstrate that human motor units within a muscle as well as synergistic muscles acting on the same joint receive a common synaptic drive during human gait. It is speculated that the common drive responsible for the motor unit synchronization during gait may be similar to that responsible for short-term synchronization during tonic voluntary contraction.     

太极拳转体动作中下肢关节活动顺序性和肌肉力表现及肌肉激活特征

目的 分析太极拳转体与弓步动作中下肢关节活动顺序性、肌肉力表现和肌肉激活程度的差异,揭示太极拳转体动作的特征。 方法 募集 20 名练习时长超过 3 年的健康太极拳练习者,采用三维运动捕捉系统、测力台和表面肌电同步采集转体与弓步两种动作运动学、动力学和肌肉激活信息,并通过 OpenSim 仿真软件获取下肢肌力。结果 与弓步相比,转体动作髋、踝关节外旋幅度显著增大;膝关节外展和外旋力矩显著增大,股二头肌、半腱肌和内外侧腓肠肌峰值肌力显著增强,股二头肌、内外侧腓肠肌峰值肌力时刻显著提前,而股内外侧肌和胫骨前肌峰值肌力显著减小,胫骨前肌肌力最早达到峰值;股二头肌、股内外侧肌和内侧腓肠肌的平均激活水平和激活时间显著增加。 结论 太极拳转体动作由踝、髋关节依次转动组成,肌肉力表现的独特性在于重心两次转移致使支撑腿内外侧肌力曲线呈双峰型,因为全足着地延迟方式引发了腓肠肌与股四头肌激活顺序和肌肉平均激活水平改变。研究结果提示全足着地延迟方式具有调节肌肉激活顺序的作用,合理利用有助于提升临床康复效果。     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis, biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Is there a ‘normal’ profile of EMG activity in gait?

The aim of the present study was to validate the notion that there is a normal profile for electromyographic (EMG) signals in gait. For eight subjects, surface electrodes were used to record signals over ten strides from the soleus, rectus femoris, biceps femoris, vastus medialis and tibialis anterior muscles. Analyses of EMG linear envelopes, normalised with respect to both time and amplitude, demonstrated that statistically significant differences exist in amplitude of activity across subjects for all muscles, and that within subjects the data were highly repeatable. More importantly, differences in profiles of activity were found especially for the rectus femoris muscle. It was also found that a given muscle from a given subject can present specific profiles, but usually these specificities are averaged out in the pooled between-subject data. Thus limits exist with the use or the notion of a normal profile of EMG for gait.     

A comparison of the moment arms of pelvic limb muscles in horses bred for acceleration (Quarter Horse) and endurance (Arab)

Selective breeding for performance has resulted in distinct breeds of horse, such as the Quarter Horse (bred for acceleration) and the Arab (bred for endurance). Rapid acceleration, seen during Quarter Horse racing, requires fast powerful muscular contraction and the generation of large joint torques, particularly by the hind limb muscles. This study compared hind limb moment arm lengths in the Quarter Horse and Arab. We hypothesized that Quarter Horse hind limb extensor muscles would have longer moment arms when compared to the Arab, conferring a greater potential for torque generation at the hip, stifle and tarsus during limb extension. Six Quarter Horse and six Arab hind limbs were dissected to determine muscle moment arm lengths for the following muscles: gluteus medius, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius (medialis and lateralis) and tibialis cranialis. The moment arms of biceps femoris (acting at the hip) and gastrocnemius lateralis (acting at the stifle) were significantly longer in the Quarter Horse, although the length of the remaining muscle moment arms were similar in both breeds of horse. All the Quarter Horse muscles were capable of generating greater muscle moments owing to their greater physiological cross-sectional area (PCSA) and therefore greater isometric force potential, which suggests that PCSA is a better determinant of muscle torque than moment arm length in these two breeds of horse. With the exception of gastrocnemius and tibialis cranialis, the observed muscle fascicle length to moment arm ratio (MFL : MA ratio) was greater for the Arab horse muscles. It appears that the Arab muscles have the potential to operate at slower velocities of contraction and hence generate greater force outputs when compared to the Quarter Horse muscles working over a similar range of joint motion; this would indicate that Arab hind limb muscles are optimized to function at maximum economy rather than maximum power output.     

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)     

Electromyographic characteristics at the onset of independent walking in infancy

In order to elucidate electromyographic characteristics of infant walking at the onset of independent gait, we longitudinally recorded electromyograms from muscles of both legs during the learning process of walking in an infant, from ten months after birth until about three years of age. We found electromyographic characteristics of infant gait up to around one month after learning to walk that are not usually seen in adult gait. In stance phase from foot contact until push off, the role of the vastus medialis for maintaining stability became clear as a slightly squatted position was used to lower the center of gravity. Orderly reciprocal or cocontraction patterns of activity in the rectus femoris and biceps femoris or in the tibialis anterior and gastrocnemius were found to be related to returning the body's center of mass toward its initial position. In the latter half of swing phase, the vastus medialis and gastrocnemius showed strong activities with the knee extending and ankle plantarflexing for active leg extension to prevent falling. These characteristically excessive muscle activities in infant walking are considered to express weak muscle strength and an immature balancing system. As months and years pass, the muscles become stronger and balance matures, obviating the need for so much myoelectric activity.     

Modulation of locomotor activity in complete spinal cord injury

The aim of this study was to evaluate the modulation of muscle activity during locomotor-like movements by different walking speeds in subjects with a motor complete spinal cord injury (SCI) compared to actively- and passively-walking control subjects without neurological deficit. Stepping movements on a treadmill were induced and assisted by a driven gait orthosis. Electromyographic (EMG) muscle activity of one leg (rectus and biceps femoris, tibialis anterior and gastrocnemius) was recorded and analyzed at three stepping velocities with similar body weight support in both subject groups. In SCI subjects, the EMG amplitude of biceps femoris, tibialis anterior and gastrocnemius was in general similar or weaker than in passively- and actively-stepping control subjects, but that of rectus femoris was larger. The degree of co-activation between tibialis anterior and gastrocnemius was higher in SCI than in control subjects. A significant velocity-dependent EMG modulation was present in all four-leg muscles in both subject groups. In SCI subjects, this EMG modulation was similar to that in actively stepping control subjects. It is concluded that in complete spastic SCI subjects, spinal neuronal circuits underlying locomotion can to a large extent adequately respond to a change in external drive to adapt the neuronal pattern to a new locomotion speed. The application of various speeds might enhance the effect of locomotor training in incomplete SCI subjects.     

基于AnyBody仿真和肌电测试分析不同体质量指数男性青年球类运动中的生物力学特征

文题释义： Anybody仿真：使用数学建模技术模拟人体肌肉骨骼在不同载荷中的情况,计算各块肌肉和关节的受力、变形、肌腱的弹性能、拮抗肌肉运动和其他对于工作中的人体有用的特性,以计量方式计算出人体对于环境的反应,兼与人机工程学和生物力学分析,为人体运动建模、人机工程学产品性能改进和生物医学工程研究提供平台。 均方根振幅：是将振幅平方的平均值开平方,把振幅值平均然后开方,最原始的是针对正弦波推导出来的,但实际上对所有的波形都适用,均方根值(RMS)也称作为效值,表示在一段周期内,参加肌肉活动的肌肉瞬间肌电图振幅均方根值,是一定时间内肌电位值平方和的平方根。 背景：Anybody肌肉骨骼建模系统,使用数学建模技术模拟人体骨骼、肌肉和环境的关系,可对人体的逆向动力学进行研究,得出下肢三关节最大肌肉力等指标。 目的：研究24名不同体质量指数男大学生在坐瑞士球一个动作周期的下肢肌肉力值,及受试者在坐瑞士球与平凳的均方根肌电平均值对比情况。 方法：将24名男大学生按体质量指数分为正常组、超重组、肥胖组,用BTS三维红外动作捕捉系统、Kistler 三维测力台、BTS表面肌电测试系统,同步记录动力学和肌电参数,以单因素方差分析定性比较不同组间肌力和肌电参数差异,用定量差异分析法对比均值差异。 结果与结论：①肌肉力量方面,由坐到站过程中,正常组与肥胖组相比,股直肌、半膜肌、股二头肌长头、腘肌、比目鱼肌、胫骨前肌差异显著(P < 0.05,0.47≤QD<0.80),股方肌与耻骨肌的两组肌肉力差异极其显著(P < 0.01,QD≥0.80);超重组与肥胖组肌肉力相比,股方肌具有显著性差异(P < 0.05,0.47≤QD<0.80),由站到坐过程中,正常组与肥胖组相比,缝匠肌、拇长伸肌、腓肠肌肌肉力差异显著(P < 0.05,0.47≤QD<0.80);②均方根肌电值方面,坐平凳状态下,由坐到站过程中,正常组与肥胖组相比,股二头肌和腓肠肌差异显著(P < 0.05,0.47≤QD<0.80),由站到坐过程中,正常组与肥胖组相比,股直肌差异显著(P < 0.05,0.47≤QD<0.80);坐瑞士球状态下,由坐到站过程中,正常组与肥胖组相比,胫骨前肌、股二头肌差异显著(P < 0.05,0.47≤QD<0.80);由站到坐过程中,正常组与肥胖组相比,腓肠肌、右竖脊肌肌电值差异显著(P < 0.05,0.47≤QD<0.80)。提示：①各组由坐到站过程中主导发力肌肉是臀中肌、股外侧肌、股二头肌长头、股直肌、腓肠肌、胫骨前肌、比目鱼肌,由站到坐过程中下肢臀中肌、股外侧肌和股二头肌长头、腓肠肌、胫骨前肌、比目鱼肌主导发力;②与坐平凳相比,受试者在坐瑞士球时胫骨前肌、股直肌、股二头肌、腓肠肌均方根肌电值高。ORCID: 0000-0003-0520-5606(庞博) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

Hamstrings and quadriceps muscle contributions to energy generation and dissipation at the knee joint during stance,swing and flight phases of level running

BackgroundHuman movements involve the generation and dissipation of mechanical energy at the lower extremity joints. However, it is unclear how the individual knee muscles contribute to the energetics during running.ObjectiveThis study aimed to determine how each hamstring and quadricep muscle generates and dissipates energy during stance, swing and flight phases of running.MethodsA three-dimensional lower extremity musculoskeletal model was used to estimate the energetics of the individual hamstrings (semimembranosus, semitendinosus, biceps femoris long and short-heads) and quadriceps (rectus femoris, vastus medialis, vastus intermedius and vastus lateralis) muscles for a male subject during level running on a treadmill at a speed of 3.96 m/s.ResultsOur findings demonstrated that the knee flexors generated energy during stance phase and dissipated energy during swing phase, while the knee extensors dissipated energy during the flexion mode of both stance and swing phases, and generated energy during the extension mode. During flight phase, the knee flexors generated energy during the flight phase transiting from toe-off to swing, while the knee extensors generated energy during the flight phase transiting from swing to heel-strike.ConclusionIndividual knee flexors and extensors in the hamstrings and quadriceps play important roles in knee joint energetics, which are necessary for proper execution and stabilization of the stance, swing and flight phases of running.     

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.     

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.     

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.     

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.     

Modulation of multisegmental monosynaptic responses in a variety of leg muscles during walking and running in humans

Motor responses evoked by stimulating the spinal cord percutaneously between the T11 and T12 spinous processes were studied in eight human subjects during walking and running. Stimulation elicited responses bilaterally in the biceps femoris, vastus lateralis, rectus femoris, medial gastrocnemius, soleus, tibialis anterior, extensor digitorum brevis and flexor digitorum brevis. The evoked responses were consistent with activation of Ia afferent fibres through monosynaptic neural circuits since they were inhibited when a prior stimulus was given and during tendon vibration. Furthermore, the soleus motor responses were inhibited during the swing phase of walking as observed for the soleus H-reflex elicited by tibial nerve stimulation. Due to the anatomical site and the fibre composition of the peripheral nerves it is difficult to elicit H-reflex in leg muscles other than the soleus, especially during movement. In turn, the multisegmental monosynaptic responses (MMR) technique provides the opportunity to study modulation of monosynaptic reflexes for multiple muscles simultaneously. Phase-dependent modulation of the MMR amplitude throughout the duration of the gait cycle period was observed in all muscles studied. The MMR amplitude was large when the muscle was activated whereas it was generally reduced, or even suppressed, when the muscle was quiescent. However, during running, there was a systematic anticipatory increase in the amplitude of the MMR at the end of swing in all proximal and distal extensor muscles. The present findings therefore suggest that there is a general control scheme by which the transmission in the monosynaptic neural circuits is modulated in all leg muscles during stepping so as to meet the requirement of the motor task.     

膝骨关节炎患者膝关节置换后下肢肌的表面肌电图变化

背景：膝骨关节炎患者膝关节置换后下肢肌功能恢复一直存在着争议。 目的：评价膝骨关节炎患者膝关节置换手术后下肢肌肉功能。 方法：应用TELEMYO 2400R G2表面肌电图遥测仪对25例双膝骨关节炎单膝关节置换后患者在平常自然步态下进行双下肢股直肌、胫前肌、股二头肌和腓肠肌内侧的表面肌电信号测试。在肌电图测试前,对患者双膝关节功能进行美国特种外科医院膝关节评分。 结果与结论：患者置换后美国特种外科医院膝关节评置换侧平均分91.44,其优良率达100%;未置换侧平均分54.52。置换侧在疼痛、关节功能方面有明显改善;膝关节置换后置换侧股直肌、胫前肌、股二头肌的肌电振幅、肌电积分、平均频率、中位频率的(平均值、最小值、最大值)与未置换侧相比差异无显著性意义(P > 0.05);置换侧腓肠肌内侧肌电振幅值及肌电积分值显著大于未置换侧(P < 0.05);置换侧腓肠肌内侧平均频率、中位频率与未置换侧相比差异无显著性意义(P > 0.05)。提示膝关节置换后置换侧的下肢肌没有恢复到正常的功能活动水平,因此膝关节置换后康复要特别重视患者的肌肉锻炼。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

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 H¹⁵ ₂O 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 · (kg muscle)⁻¹ · min⁻¹ at rest and 146 (54) ml · (kg muscle)⁻¹ · 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. Accepted: 16 June 2000     

The distribution of blood flow between individual muscles and non-muscular tissues in the hind limb of the young ox (Bos taurus): values at thermoneurality and during exposuer to cold.

1. The radioactive microspheres method was used to measure the distribution of blood flow in the hind leg in conscious young steers exposed to thermoneutral and moderately cold environments. Simultaneous measurement of total leg blood flow allowed calculation of blood flow (ml. 100 g tissue-1 min-1) to individual muscles and the major non-muscular tissues in the leg. 2. In the thermoneutral environment, leg blood flow was distributed approximately according to tissue weight, so that about 65% went to muscle and the remainder to bone, skin, connective tissue and fat; 1-7-11-5% of the injected dose of microspheres was found in the lungs, indicating the presence of functioning arteriovenous anastomoses in the leg. 3. During cold exposure leg blood flow increased two-and-a-half fold and 91% of this increase was due to increased blood flow in muscle. This was accompanied by substantial decreases in both total and capillary blood flow in leg skin in three of the four animals. 4. Values for resting tissue blood flow to the six largest individual leg muscles were compared, as well as that for tissue blood flow to the remaining leg muscle. Blood flow in the three large upper thigh muscles (biceps femoris, semimembranosus and semitendinosus) was about half that in muscles in the rest of the leg. 5. Cold exposure caused a threefold increase in total leg muscle blood flow, but the only individual muscles to respond substantially in all four animals were the vastus lateralis and the rectus femoris. Comparison of results from individual animals suggested a relation between total leg blood flow and the number of muscles (apart from vastus lateralis and rectus femoris) involved in shivering. Leg adipose tissue blood flow also increased significantly in the cold.     

Biomechanical analysis during single-leg squat in individuals with knee osteoarthritis

Backgroud: The single-leg squat (SLS) is a functional task to evaluate the abnormal movement patterns and potential neuromuscular deficits in the lower limbs. Still, it is unknown if SLS could provide information to older adults with knee osteoarthritis (KOA). The study’s objective was to analyze the EMG pattern, kinematics, and postural control in individuals with and without KOA during SLS.Methods: Participated in this study, 60 volunteers of both sexes, 30 had KOA (allocated into the KOA group - KOAG), and 30 were healthy (allocated into the Healthy Group - HG) performing the single-leg squat. Surface electromyography (EMG) was assessed for the gastrocnemius medialis (GM), biceps femoris (BF), gluteus medius (GLM), rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), and tibialis anterior (TA) in two phases (downward – P1 and upward – P2). The kinematic data was evaluated using an electrogoniometer. The center of pressure (CoP) was obtained using data collected from a force plate.Results: EMG activity was increased for GM and TA muscles during the P1 of the movement and the GM and GLM muscles during P2 of the movement. The angular displacement of the KOAG was lower when compared with the HG. There was no statistical difference for the co-contraction and postural control data.Conclusions: The SLS analysis showed that EMG activity of the muscles TA, GM, and GLM was increased in the KOAG, but this pattern could be affected by fear of movement leading to reduced knee angular displacement.