Eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man

Summary The primary purpose of this investigation was to study the eccentric and concentric torque-velocity characteristics of the quadriceps femoris in man using a recently developed combined isometric, concentric and eccentric controlled velocity dynamometer (the SPARK System). A secondary purpose was to compare the method error associated with maximal voluntary concentric and eccentric torque output over a range of testing velocities. 21 males (21–32 years) performed on two separate days maximal voluntary isometric, concentric and eccentric contractions of the quadriceps femoris at 4 isokinetic lever arm velocities of 0° · s^–1 (isometric), 30° · s^–1 120° · s^–1 and 270° · s^–1. Eccentric peak torque and angle-specific torques (measured every 10° from 30° to 70°) did not significantly change from 0° · s^–1 to 270° · s^–1 (p>0.05) (with the exception of angle-specific 40° torque, which significantly increased;p<0.05). The mean method error was significantly higher for the eccentric tests (10.6%±1.6%) than for the concentric tests (8.1%±1.7%) (p<0.05). The mean method error decreased slightly with increasing concentric velocity (p>0.05), and increased slightly with increasing eccentric velocity (p>0.05). A tension restricting neural mechanism, if active during maximal eccentric contractions, could possibly account for the large difference seen between the present eccentric torque-velocity results and the classic results obtained from isolated animal muscle.     

Muscle activation during maximal voluntary eccentric and concentric knee extension

Summary The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360° · s^–1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30°–70°) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%–146%,P < 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%–31%,P < 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P > 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P < 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions.     

Effects of electrical stimulation on eccentric and concentric torque-velocity relationships during knee extension in man

The purpose of this study was to examine the effects of electrical stimulation on torque output during knee extension. Nine well-trained males (19-43 years) performed maximal voluntary, electrically evoked and superimposed eccentric and concentric knee extensions at velocities of 60, 180 and 360 degrees s-1, plus an isometric test (torque was always recorded at a 60 degree knee angle). Fifty-hertz stimulation was applied percutaneously at the maximum tolerated voltage (140-200 V). By superimposing electrical stimulation, eccentric torque could be increased by an average of 21-24% above the voluntary level (P less than 0.05). No corresponding differences were observed between superimposed and voluntary torques under isometric or concentric conditions. Electrically evoked torque also exceeded voluntary torque under eccentric conditions (11-12%, P less than 0.05), but was less under isometric and concentric conditions (-10 to -52%, P less than 0.05). Within the limitations of the study, it was concluded that eccentric knee extension torque under maximal voluntary conditions does not represent the maximal torque-producing capacity. The action of a neural inhibitory mechanism was proposed as an explanation for this finding. If active, this mechanism may protect against the extreme muscle tension that could otherwise develop under truly maximal eccentric conditions.     

Trunk muscle strength in eccentric and concentric lateral flexion

The aim of this study was to investigate the position and velocity dependency of the strength (torque) output of lateral flexor muscles of the trunk. Twelve male volunteers with no history of back pain participated. Movement was constrained to the frontal plane and the velocity was controlled by an isokinetic dynamometer. The eccentric and concentric strength of lateral flexor muscles on the left side was measured in a supine position at velocities of 15, 30, 45 and 60° · s⁻¹ and static strength at 20, 10, 0, −10 and −20° of lateral trunk flexion. Average peak torque values ranged between 211 and 218 Nm (eccentric) and between 66 and 140 Nm (concentric) over all tested velocities, and the average static torque ranged between 80 and 172 Nm over all tested positions. The shape of the torque–position curves was unaffected by speed and peak torque occurred at an average position of 11–15° to the contralateral (right) side in both eccentric and concentric actions. In eccentric actions, torque output was significantly higher than that during concentric and static actions. Increasing the speed of contraction did not affect eccentric torque values, whereas both peak and angle-specific concentric torque decreased with increasing speed. These results are in general accordance with earlier findings from other muscle groups, such as the knee extensors. However, they are partially at variance with results obtained in studies of lateral lifting and lowering, indicating that there are other limiting factors in complex tasks that do not just involve the trunk muscles. Accepted: 24 July 2000     

Electromechanical delay in human skeletal muscle under concentric and eccentric contractions

Summary In contraction of skeletal muscle a delay exists between the onset of electrical activity and measurable tension. This delay in electromechanical coupling has been stated to be between 30 and 100 ms. Thus, in rapid movements it may be possible for electromyographic (EMG) activity to have terminated before force can be detected. This study was designed to determine the dependence of the EMG-tension delay upon selected initial conditions at the time of muscle activation. The rigth forearms of 14 subjects were passively oscillated by a motor-driven dynamometer through flexion-extension cycles of 135 deg at an angular velocity of 0.5 rad/s. Upon presentation of a visual stimulus the subjects maximally contracted the relaxed elbow flexors during flexion, extension, and under isometric conditions. The muscle length at the time of the stimulus was the same in all three conditions. An on-line computer monitoring surface EMG (Biceps and Brachioradialis) and force calculated the electromechanical delay. The mean value for the delay under eccentric condition, 49.5 ms, was significantly different (p<0.05) from the delays during isometric (53.9 ms) and concentric activity (55.5 ms). It is suggested that the time required to stretch the series elastic component (SEC) represents the major portion of the measured delay and that during eccentric muscle activity the SEC is in a more favorable condition for rapid force development.     

Effects of arm acceleration and behavioral conditions on the organization of postural adjustments during arm flexion

Summary Nine standing subjects performed unilateral arm flexion movements over an eight-fold range of speeds, under two behavioral conditions. In the visually-guided condition, a visual target informed subjects about the correct movement speed. Seven subjects also made movements of different speeds during a self-paced condition, without a visual target. Angular displacement and acceleration of the arm, and EMG activity from the hamstrings (HM), erector spinae (ES) and the anterior deltoid (AD) muscles were measured. The following results were observed. (1) Mean rectified amplitudes of EMG activity in HM and ES were typically correlated with the average arm acceleration and presumably the disturbance to posture and/or balance. HM and ES amplitudes were correlated for only six subjects. Functions relating the ratios of HM/ES EMG amplitudes to acceleration varied between subjects. (2) HM onset latencies were highly variable for slow movements and usually lagged movement. For movements above a threshold-like point in acceleration, HM latencies were correlated with arm acceleration and recruited before movement. ES latencies were constant for fast movements, and negatively correlated with acceleration for slower movements. (3) The recruitment order of HM and AD was influenced by the behavioral condition but not by arm acceleration for fast movements. HM and AD were recruited coincidentally for visually-guided movements, while for self-paced movements, HM was recruited before AD. We conclude that for the arm flexion task: (1) HM and ES are not tightly coupled; (2) both behavioral and mechanical conditions affect the recruitment of postural muscles; and (3) postural and focal components of the movement are probably organized by parallel processes.     

Strength-velocity relationship and fatiguability of unilateral versus bilateral arm extension

Summary Strength-velocity relations and fatigue resistance in an arm bench press manoeuvre were compared between conditions of bilateral (BL, both arms acting together) and unilateral muscle contraction in 9 young men. BL and UL (sum of the 2 arms acting singly) strength was similar for isometric and slow isokinetic maximal voluntary contractions (MVC); at high velocities BL MVC declined more than UL. In both types of contractions a curvilinear relation was observed between strength and velocity, with significantly higher peak torques (PT) being produced under isometric conditions than for slow velocity efforts (p<0.01). Mean declines in PT during 100 repetitive MVCs of approximately 70s were to 25% of initial values for the BL fatigue test and to 37% for UL (p<0.01). In contrast to results of a similar investigation of leg extension in the same subjects, the arms showed (1) no BL deficit of strength in the initial part of the strength-velocity curve and (2) approximately twice as much fatigue in repetitive contractions. These physiological differences may stem from the varying habitual activity patterns of the arms and legs.     

Effect of prior isometric muscle action on concentric torque output during plantar flexion

The influence of different levels of prior isometric muscle action on the concentric torque output during plantar flexion was examined at two angular velocities (60°·s^–1 and 120°·s^–1) in ten healthy female subjects. The levels of the prior muscle actions were 25%, 50%, 75% and 100% of the maximal voluntary isometric contraction (MVIC). A KINetic-COMmunicator II dynamometer was used to measure torque output during plantar flexion within a range of motion of 78°-120° of the ankle joint. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the gastrocnemius medialis muscle and the soleus muscle. Torque-angle curves were made for the plantar flexions using different prior muscle actions. Up to 75% of MVIC, the torque output in the first part of the range of motion increased with the level of the prior isometric muscle action; at higher levels of MVIC the torque did not appear to increase any further. Later in the range of motion, after 24° in the plantar flexion at a velocity of 60°·s^–1 and 31° at 120°·s^–1, the prior muscle actions had no further influence. No increase was found in the electromyograms, with one exception, during the concentric movements when preceded by higher levels of MVIC. It would seem therefore that the increase in torque output early in the range of motion cannot be explained on the basis of differences in electrical muscle activation in this study.     

头部前屈运动过程中颈肌特性的研究

目的分析人体头部前屈运动过程中头颈部肌群活动特性,探索人体头颈部肌肉疲劳原因。方法基于AnyBody软件建立人体头颈部肌骨模型,以Vicon运动捕捉系统测量数据为输入,对头部前屈运动过程中的肌力进行仿真,并结合文献数据进行分析。结果颈后肌群在头部前屈运动中起主要作用。在头部前屈45%和75%行程位置肌力分配模式不同。肌力对前屈角位移的积分WM一定程度上反映了肌肉的疲劳特性,其中颈半棘肌和多裂肌在头部前屈运动过程中WM最大,容易出现疲劳。结论本文建立的头颈部肌骨模型可为分析人体运动状态下肌肉分析提供技术平台。     

The relationships among peak torque, mean power output, mechanomyography, and electromyography in men and women during maximal, eccentric isokinetic muscle actions

The purpose of the present investigation was to examine the velocity-related patterns of peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, and electromyographic (EMG) amplitude of the vastus lateralis (VL) muscle in men and women during maximal, eccentric isokinetic muscle actions of the leg extensors. Eight women [mean (SD)] [aged 23 (3) years] and seven men [aged 23 (2) years] volunteered for this investigation. Their PT was measured on a calibrated dynamometer at randomly ordered velocities of 30, 90, and 150°·s^–1. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes (Ag-AgCl) over the VL muscle. Their MP was determined using the dynamometer software. The results indicated no sex-related differences (P>0.05) for the patterns of PT, MP, MMG amplitude, or EMG amplitude across velocity. The normalized values for MP and MMG amplitude increased (P<0.05) from 30 to 150°·s^–1 (30°·s^–1<90°·s^–1<150°·s^–1), while PT and EMG amplitudes remained unchanged across velocity. The results indicated close associations between the velocity-related patterns of MP and MMG amplitudes as well as PT and EMG amplitudes. Thus, MMG amplitude reflected the velocity-related changes in muscle power output, but not torque production, while EMG amplitude reflected torque production, but not muscle power output. During maximal, eccentric isokinetic muscle actions, EMG and MMG signals provided unique information regarding the electrical and mechanical aspects of muscle strength and power. Electronic Publication     

Anatomical predictors of maximum isometric and concentric knee extensor moment

The most important anatomical determinants of in vivo joint moment magnitude have yet to be defined. Relationships between maximal knee extensor moment and quadriceps muscle volume, anatomical (ACSA) and physiological (PCSA) cross-sectional area, muscle architecture and moment arm (MA) were compared. Nineteen untrained men and women performed maximal isokinetic knee extensions under isometric conditions (90° joint angle) and at 30° and 300° s⁻¹. Magnetic resonance and ultrasound imaging techniques were used to measure vastus lateralis PCSA and fascicle length (FL), quadriceps ACSA, volume and patellar tendon MA. Muscle volume was the best predictor of extensor moment measured isometrically (R ² = 0.60) and at 30° s⁻¹ (R ² = 0.74). PCSA × FL was the best predictor of moment at 300° s⁻¹ (R ² = 0.59). MA was not an important predictor. ACSA was the second best predictor at all three speeds and could be recommended as an ideal measure given its relative ease of measurement.     

Software for determining lower extremity muscle-tendon kinematics and moment arm lengths during flexion/extension movements.

A computer program was developed to calculate lower extremity muscle-tendon (MT) kinematics and flexion/extension moment arm (MA) lengths for any subject performing movements constrained to occur in the sagittal plane. The program requires as input subject anthropometric and time series ankle, knee, and hip angle data. Using these data a lower extremity link-segment model is constructed for each time element. Muscle-tendon attachment data and a straight line muscle model are used to calculate MT and flexion/extension moment arm lengths. A finite difference technique is used to determine MT shortening velocity. The utility of this program is demonstrated by calculating MT kinematics and MA lengths for six muscles of a single subject both as a function of joint angles and during gait.     

Neuromuscular performance of lower limbs during voluntary and reflex activity in power- and endurance-trained athletes

Neural, mechanical and muscle factors influence muscle force production. This study was, therefore, designed to compare possible differences in the function of the neuromuscular system among differently adapted subjects. A group of 11 power-trained athletes and 10 endurance-trained athletes volunteered as subjects for this study. Maximal voluntary isometric force and the rate of force production of the knee extensor and the plantar flexor muscles were measured. In addition, basic reflex function was measured in the two experimental conditions. The power athletes produced higher voluntary forces (P<0.01-0.001) with higher rates for force production (P<0.001) by both muscle groups measured. Unexpectedly, however, no differences were noticed in the electromyogram time curves between the groups. During reflex activity, the endurance group demonstrated higher sensitivity to the mechanical stimuli, i.e. the higher reflex amplitude caused a higher rate of reflex force development, and the reflex amplitude correlated with the averaged angular velocity. The differences in the isometric conditions could be explained by obviously different muscle fibre distribution, by different amounts of muscle mass, by possible differences in the force transmission from individual myofibrils to the skeletal muscle and by specificity of training. In addition, differences in nervous system structure and muscle spindle properties could explain the observed differences in reflex activity between the two groups.     

Muscle cross-sectional area and voluntary force production characteristics in elite strength- and endurance-trained athletes and sprinters

Summary Seven male elite strength-trained athletes (SA) from different weight categories, six elite sprinters (SPA) and seven elite endurance-trained athletes (EA) volunteered as subjects for examination of their muscle cross-sectional area (CSA), maximal voluntary isometric force, force-time and relaxation-time characteristics of the leg extensor muscles. The SA group demonstrated slightly greater CSA and maximal absolute strength than the SPA group, while the EA group demonstrated the smallest values both in CSA and especially in maximal strength (p<0.05). When the maximal forces were related to CSA of the muscles, the mean value for the SA group of 60.8±10.0 N·cm⁻² remained slightly greater than that recorded in the SPA group 55.0±3.1 N·cm⁻² and significantly greater (p<0.05) than that recorded in the EA group 49.3±4.0 N·cm⁻². The mean value in the SPA was also significantly greater (p<0.05) than that of the EA group. The isometric force-time curves differed between the groups (p<0.05−0.01) so that the times taken to produce the same absolute force were the shortest in the SPA group and the longest in the EA group. With force expressed as a percentage of the maximum, the force-time curves showed that the SPA group demonstrated still shorter times to a given value (p<0.05), especially at the lower force levels, than the other two groups. With regard to the differences in force production per CSA and in the shape of the force-time curves, the present findings may be explained by possible differences both in the rate and the amount of neural activation of the muscles and/or in the qualitative characteristics of the muscle tissue itself. The present findings characterize the very specific nature of high resistance strength-, sprint- and endurance-training stimuli over a very prolonged period of time.     

A new method for measuring power output in a single leg extension: feasibility,reliability and validity

Summary A method is described for measuring the explosive power of the leg in extension which has been found safe and acceptable for all age groups and levels of physical capability. The extension movement takes 0.25–0.40 s in a push through 0.165 m against a flat pedal. At the end of the push the leg is fully extended. The movement is made seated so that the forces are contained between the buttocks and the foot. The seat position is adjusted for leg length and the push is transmitted by a lever and chain to spin a flywheel. The gearing is such that resistance to the movement remains nearly constant throughout the extension. The final angular velocity of the flywheel is measured by an optoswitch and used to calculated the average leg extensor power (LEP) in the push. The reliability of the power measurement was evaluated in 46 subjects ranging in age from 20 to 86 years; they included medical students and geriatric day patients. They were tested on two occasions separated by a week. The maximal values on the first occasion (best of at least five trials) ranged from 30 to 300 W (mean ± 1 SD = 154 ± 88 W). There was no significant difference on re-test and the coefficient of variation was 9.4%. In a subgroup of 9 non-naive subjects who were measured by an experienced observer it was 6.3%. As expected, power was lower in women than in men and declined sharply with age. The sex difference was less when the values were expressed as power per body mass; a sharp age-related decline remained. The results from the LEP rig were compared with results obtained in the same subjects on the same occasion from similar pushes against an isokinetic dynamometer and two-legged jumps on a force plate. There was a highly significant correlation in both cases, Spearman's rank correlation (rho) = 0.73,P < 0.001,n = 16 subjects (age 27 ± 7.5 years) and rho = 0.86,P < 0.001,n = 13 subjects (age 39 ± 10.4 years) respectively.     

A dynamometric comparison of maximum eccentric,concentric, and isometric contractions using EMG and energy expenditure measurements

Summary In fourteen subjects we compared maximum voluntary eccentric, concentric, and isometric contractions. The maximum voluntary forces by the subjects on a weight-lifting rod when changing from standing to squatting and from squatting to standing, and during a halfway knee-bend, were measured. The rod was placed on a special stand and moved up and down at a constant speed of 8.5 m/s by a motor. Energy expenditure was measured by the indirect method and EMG activity was measured in the quadriceps femoris. It was found that the force which the muscles generated was greatest during eccentric contraction, lower during isometric and lowest during concentric contraction. Energy expenditure was slightly greater during concentric than eccentric contraction. The level of difference in EMG activity of the quadriceps femoris was statistically insignificant. An energy comparison with isometric contractions was not undertaken in view of the very complex nature of these relationships.     

Viscosity of the elbow flexor muscles during maximal eccentric and concentric actions

The aim of the present study was to estimate the damping coefficient (B factor) of the elbow flexor muscles during both eccentric and concentric muscle actions. We used a muscle model consisting of a viscous damper associated in parallel with a contractile component, both in series with an elastic component. The viscous damper allowed the concentric loss and the eccentric gain of force to be modelled. Eight volunteer subjects performed maximal eccentric and concentric elbow movements on an isokinetic dynamometer at angular velocities of 0.52, 1.04 and 2.09 rad·s^–1. Torques at an elbow joint angle of 90° were recorded. Electromyogram (EMG) signals from the belly of the right elbow flexor and from the long head of the triceps brachia muscles were recorded using two pairs of bipolar surface electrodes. The root mean square (rms) of the EMG was determined. Eccentric and concentric rms were not significantly different (P>0.05). The B factor was higher in the concentric than in the eccentric conditions (P<0.05), and, whatever the muscle action type it decreased as the velocity increased. These results indicated that the concentric loss and the eccentric gain of force were attributable to the behaviour of the contractile machinery. Furthermore, whatever the exact cause of loss and gain of tension, our study showed that the total effect can be modelled by the viscous damper of a three-component muscle model.     

Paradoxical variation of strength determinants with different rotation axes in trunk flexion and extension strength tests

The aim of this study was to illustrate the influence of different levels of the fulcrum (the axis of sagittal rotation) on measured trunk flexion and extension strength and compare force and torque as a unit of measure. The isometric trunk strength was measured in 16 healthy female subjects. The dynamometer was kept at the shoulder level and the moment arm was lengthened step by step by moving the fulcrum caudally from the level of the posterior superior iliac spine to the level of the gluteal fold. The moment of force (torque) increased from 117.0 to 208.5 N · m in flexion and from 182.2 to 292.5 N · m in extension,P < 0.0001. An attempt to quantify this change was made. Paradoxically, the measured force remained at a constant level (in flexion) or slightly decreased (in extension). We concluded that torque as a measure of trunk flexion and extension strength is highly dependent on the level of the rotation axis and force appears to be less sensitive for variations with the height of the fulcrum. We would suggest that the observed increase in torque is physiological and reflects to what extent hip flexor or extensor muscles are recruited. The force, on the other hand, may better characterize a person's capability to perform functional tasks. Force and torque should strictly be distinguished from one another.     

Relationship between the efficiency of muscular work during jumping and the energetics of running

Summary The running economy of seventeen athletes was studied during running at a low speed (3.3 m · s^–1) on a motor-driven treadmill. The net energetic cost during running expressed in kJ·kg^–1·km^–1 was on average 4.06. As expected, a positive relationship was found between the energetic cost and the percentage of fast twitch fibres (r=0.60,n=17,p<0.01). In addition, the mechanical efficiency during two different series of jumps performed with and without prestretch was measured in thirteen subjects. The effect of prestretch on muscle economy was represented by the ratio between the efficiency of muscular work performed during prestretch jumps and the corresponding value calculated in no prestretch conditions. This ratio demonstrated a statistically significant relationship with energy expenditure during running (r=–0.66,n=13,P<0.01), suggesting that the elastic behaviour of leg extensor muscles is similar in running and jumping if the speeds of muscular contraction during eccentric and concentric work are of similar magnitudes.     

Time of day effects on isometric and isokinetic torque developed during elbow flexion in humans

 The aim of this study was, firstly, to confirm or refute the existence of circadian rhythms during several velocities of concentric action of the elbow flexor muscles and, secondly, to compare the characteristics of these circadian rhythms with those obtained during isometric actions. Eight volunteer subjects participated in this study. The circadian rhythms were obtained from six test sessions (TS) carried out at different times of day over 6 days with only one TS a day. During each TS, oral temperature and the torque of the muscle action were measured. The subjects made, on an isokinetic ergometer, two maximal isokinetic concentric elbow flexions at five angular velocities (60, 120, 180, 240 and 300° · s⁻¹) and at an angle of 60°. Torque-angular velocity relationships, which characterised the functioning of the muscle during concentric and isometric actions, were established for the different times of day. The values of the torque recorded at each of the angular velocities presented a clear circadian rhythm. After normalisation of the torque values, no significant differences were observed among the computed characteristics of the circadian rhythms obtained at different angular velocities. Since the circadian rhythms during isometric and concentric torque were the same, the characteristics of the circadian rhythms of the musculo-skeletal system can be studied using either type of muscle action. The results indicated that torque and temperature varied concomitantly during the day. Thus, the recording of body temperature allows one to estimate the times of occurrence of maximal and minimal values in the circadian rhythm of muscle torque. Accepted: 10 October 2000