Effect of antagonist muscle fatigue on knee extension torque

The effect of hamstring fatigue on knee extension torque was examined at different knee angles for seven male subjects. Before and after a dynamic flexion fatigue protocol (180° s^–1, until dynamic torque had declined by 50%), maximal voluntary contraction extension torque was measured at four knee flexion angles (90°, 70°, 50° and 30°). Maximal torque generating capacity and voluntary activation of the quadriceps muscle were determined using electrical stimulation. Average rectified EMG of the biceps femoris was determined. Mean dynamic flexion torque declined by 48±11%. Extensor maximal voluntary contraction torque, maximal torque generating capacity, voluntary activation and average rectified EMG at the four knee angles were unaffected by the hamstring fatigue protocol. Only at 50° knee angle was voluntary activation significantly lower (15.7%) after fatigue (P<0.05). In addition, average rectified EMG before fatigue was not significantly influenced by knee angle. It was concluded that a fatigued hamstring muscle did not increase the maximal voluntary contraction extension torque and knee angle did not change coactivation. Three possible mechanisms may explain the results: a potential difference in recruited fibre populations in antagonist activity compared with the fibres which were fatigued in the protocol, a smaller loss in isometric torque generating capacity of the hamstring muscle than was expected from the dynamic measurements and/or a reduction in voluntary activation.     

Interdependence of torque,joint angle,angular velocity and muscle action during human multi-joint leg extension

Purpose

Force and torque production of human muscles depends upon their lengths and contraction velocity. However, these factors are widely assumed to be independent of each other and the few studies that dealt with interactions of torque, angle and angular velocity are based on isolated single-joint movements. Thus, the purpose of this study was to determine force/torque–angle and force/torque–angular velocity properties for multi-joint leg extensions.

Methods

Human leg extension was investigated (n = 18) on a motor-driven leg press dynamometer while measuring external reaction forces at the feet. Extensor torque in the knee joint was calculated using inverse dynamics. Isometric contractions were performed at eight joint angle configurations of the lower limb corresponding to increments of 10° at the knee from 30 to 100° of knee flexion. Concentric and eccentric contractions were performed over the same range of motion at mean angular velocities of the knee from 30 to 240° s^?1.

Results

For contractions of increasing velocity, optimum knee angle shifted from 52 ± 7 to 64 ± 4° knee flexion. Furthermore, the curvature of the concentric force/torque–angular velocity relations varied with joint angles and maximum angular velocities increased from 866 ± 79 to 1,238 ± 132° s^?1 for 90–50° knee flexion. Normalised eccentric forces/torques ranged from 0.85 ± 0.12 to 1.32 ± 0.16 of their isometric reference, only showing significant increases above isometric and an effect of angular velocity for joint angles greater than optimum knee angle.

Conclusions

The findings reveal that force/torque production during multi-joint leg extension depends on the combined effects of angle and angular velocity. This finding should be accounted for in modelling and optimisation of human movement.     

Relative torque contribution of vastus medialis muscle at different knee angles

Aim: We investigated the relative contribution of the vastus medialis (VM) muscle to total isometric knee extension torque at 10°, 30°, 60° and 90° knee flexion. In the past a more prominent role of the VM muscle at more extended knee angles has been put forward. However, different components of the quadriceps muscle converge via a common distal tendon. We therefore hypothesized that the relative contribution of the VM to total knee extension torque would be similar across angles. Methods: At each knee angle the EMG isometric torque relations [20%, 25%, 30%, 35% maximal voluntary contraction (MVC)] of the rectus femoris (RF), vastus lateralis (VL) and VM muscle were established in 10 healthy male subjects; rectified surface EMG was normalized to M‐wave area. Subsequently, the VM was functionally eliminated by selective electrical surface stimulation with occluded blood flow. Results: There was no evidence for preferential activation of VM at any of the knee angles. Following VM elimination, total knee extension torque during maximal femoral nerve stimulation (three pulses at 300Hz) at 10°, 30°, 60° and 90°, respectively, decreased (P < 0.05) to (mean ± SD): 75.7 ± 12.2, 75.1 ± 9.3, 78.2 ± 7.2 and 76.0 ± 5.8% (P > 0.05 among knee angles). In addition, during voluntary contractions at 20% MVC the increases in torque output of RF and VL compensating for the loss of VM function were calculated from the increases in EMG and found to be similar (P > 0.05) at 10°, 30°, 60° and 90° values (%MVC), respectively, were: 9.1 ± 6.8, 7.5 ± 2.9, 5.9 ± 3.7 and 6.9 ± 3.4. Conclusion: The present findings support our hypothesis that the VM contributes similarly to total knee extension torque at different knee angles.     

Activation of agonist and antagonist muscles at different joint angles during maximal isometric efforts

The purpose of this study was to investigate the influence of different angles of the knee joint on the activation level of an agonist (quadriceps femoris muscle) and antagonist (biceps femoris muscle) from electromyographic activities and activation levels (twitch interpolation). Isometric torque measurements were performed on 23 healthy subjects at 10° intervals between 40° and 110° of knee joint flexion. Superimposed twitches at maximal voluntary contraction were applied and the voluntary activation estimated. To quantify the antagonist muscle activity, we normalized its integrated EMG (iEMG) value at each joint angle with respect to its iEMG value at the same angle when acting as an agonist at maximal effort. The activation levels at the knee-flexed position (80–110°) were higher than that at the knee-extended position (40–70°). The co-activation levels at 90, 100, and 110° were significantly higher than that the other knee angle. These results suggest that the activation level of an agonist (quadriceps femoris) muscle and the co-activation level of an antagonist (biceps femoris) muscle were higher in longer muscles than in shorter muscles. It was also concluded that the risk of knee injuries could be reduced by applying these mutual relationships between activation levels of agonist and antagonist muscles.     

Angle- and velocity-specific alterations in torque and semg activity of the quadriceps and hamstrings during isokinetic extension-flexion movements

The purpose of this study was to investigate the effect of movement velocity (100 degrees, 200 degrees , 300 degrees s(-1), and 400 degrees s(-1)) and joint position (0 degrees - 15 degrees [L0], 25 degrees - 40 degees [L25], 55 degrees - 70 degrees [L55], and 75 degrees - 90 degrees [L75]) on peak torque (PT) parameters and surface electromyography (SEMG) of the knee-joint muscles during reciprocal isokinetic extension and flexion movements. Thirteen subjects (age = 22.7 +/- 2.1 years, mean height = 161.1 +/- 6.6 cm, mean weight = 63.5 +/- 5.8 kg) participated in the study. Bipolar surface electrodes were placed over the vastus medialis, vastus lateralis, biceps femoris, and medial hamstrings for determination of the root mean square (SEMGrms) and median frequency (SEMGmf) of the SEMG. Peak torque, angle of peak torque (PTang), percentage of peak torque (PTper), SEMGrms, and SEMGmf were analyzed using separate repeated measures analysis of variance (ANOVA). The following main results, significant at p < or = 0.05 or better, were found: The PTang was influenced by movement velocity (in extension there was a decrease in PTang moving from 300 degrees x s(-1) to 400 degrees x s(-1) and inflexion there was an increase in PTang moving from 300 degrees x s(-1) to 400 degrees x s(-1)). Secondly, a greater percentage of peak torque (PTper) was maintained during knee flexion than knee extension. And thirdly, both the quadriceps and hamstrings exhibited changing amplitudes and spectral frequencies based on joint position and movement velocity. There was a trend of decreasing SEMGrms for the quadriceps as the knee moved into extension, and a lower SEMGmf during early (L75) and end stages of knee extension (L0). For the hamstrings, SEMGrms was lowest at the more shortened position (L75) and highest near the mid-position (L25); the lowest SEMGmf occurred at the more lengthened position (L0) and the highest occurred at the more shortened position (L75). Finally, velocity influenced hamstrings and quadriceps muscle amplitude such that SEMGrms was highest at the slower velocities and lowest at the higher velocities. Velocity had no impact on quadriceps spectral properties (p > 0.05), but had a cyclic effect on hamstrings spectral properties. Changes in amplitude and frequency spectrum in tested muscles could be explained, in part, by neural drive to these muscles. Data support the hypothesis of lower activation levels of the quadriceps muscle in the extended position espoused by several authors as a way to protect the knee-joint in the knee-extended position.     

Reliability of a practicable EMG-moment model for antagonist moment prediction

Although the use of practicable EMG-moment models for knee joint moment prediction appears promising, the repeatability of the estimated forces remains unclear. The purpose of this study was to apply an EMG-moment model to predict the antagonist moment of the knee flexors (Mflx) during maximal isometric knee extension efforts. Nine healthy males performed maximal isometric knee extension and flexion contractions at 0 degrees , 45 degrees and 90 degrees angles with recordings of the net moment and EMG of thigh muscles. Calibration knee flexion efforts were performed at different levels of intensity and the resulting EMG-moment curves were fitted using second-order polynomials. The polynomials were then used to predict Mflx. This procedure was repeated a week after. The results indicated non-significant differences in test-retest Mflx. Intraclass correlation coefficients ranged from 0.852 to 0.912 indicating high test-retest reliability of the estimated Mflx. For isometric contractions, the present model is suitable as a method to estimate antagonist muscle moments.     

A correlogram analysis of the activity in the rostral ventromedial medulla of awake rats and in rats anesthetized with ketamine or pentobarbital following the administration of morphine

The present study was designed to determine the relative contribution of the gastrocnemius muscle to isometric plantar flexor torque production at varying knee angles, while investigating the activation of the gastrocnemius muscle at standardised non-optimal lengths. Voluntary plantar flexor torque, supramaximally stimulated twitch torque and myoelectric activity (EMG) from the triceps surae were measured at different knee angles. Surface and intra-muscular EMG were recorded from the soleus muscle and the medial and lateral heads of the gastrocnemius muscle in 10 male subjects. With the ankle angle held constant, knee angle was changed in steps of 30° ranging from 180° (extended) to 60° (extreme flexion), while voluntary torque from a 5-s contraction was determined at 10 different levels of voluntary effort, ranging from 10% of maximal effort to maximal effort. To assess effort, supramaximal twitches were superimposed on all voluntary contractions, and additionally during rest. Maximal plantar flexor torque and resting twitch torque decreased significantly in a sigmoidal fashion with increasing knee flexion to 60% of the maximum torque at 180° knee angle. For similar levels of voluntary effort, the EMG root mean square (RMS) of gastrocnemius was less with increased knee flexion, whereas soleus RMS remained unchanged. From these data, it is concluded that the contribution of gastrocnemius to plantar flexor torque is at least 40% of the total torque in the straight leg position. The decrease of gastrocnemius EMG RMS with decreasing muscle length may be brought about by a decrease in the number of fibres within the EMG electrode recording volume and/or impaired neuromuscular transmission.     

Effects of patellar resurfacing on contact area and contact stress in total knee arthroplasty

The objective of this study was to examine the effects of patellar resurfacing on patellofemoral joint contact pressure and contact area in total knee arthroplasty. We tested seven fresh-frozen cadaveric knees using a custom knee jig which permits the simulation of physiologic quadriceps loading. Before patellar resurfacing, the mean peak contact pressure of medial and lateral patellofemoral joints was less than 10 MPa at knee flexion angles of 30 degrees, 60 degrees and 90 degrees, that of medial and lateral patellofemoral joints were 11.63 MPa and 11.42 MPa at a knee flexion angle of 120 degrees respectively, and the mean contact area of patellofemoral joint ranged from 70 to 150 mm2. After patellar resurfacing, the mean peak contact pressure of medial and lateral patellofemoral joints ranged from 50 to 100 Mpa (P<0.05), which exceeds the yield strength of ultrahigh molecular weight polyethylene, and the mean contact area of patellofemoral joint reduced to 10-15 mm2 (P<0.05). The contact pressure of patellofemoral joint was lower than the yield strength of articular cartilage before patellar resurfacing. Our results indicate that the yield stress of UHMWPE is exceeded after patellar resurfacing.     

Quadriceps voluntary activation at different joint angles measured by two stimulation techniques

People are able to fully activate their quadriceps at mid-length during a brief isometric contraction but it is uncertain whether this is the case at other muscle lengths. With the twitch superimposition technique for determining levels of voluntary activation (VA), the muscle may be stimulated through the intramuscular branches of the nerve or via the nerve trunk itself. The former technique is easier to use, but different populations of motor units may be stimulated if the joint position is changed to alter muscle length. The purpose of this study was to investigate quadriceps VA at a range of knee joint angles using both magnetic stimulation of the motor nerve and percutaneous electrical stimulation over the muscle belly. Eight healthy subjects (six females, mean age 29 years) performed maximal voluntary contractions of the quadriceps at knee joint angles at 10–110° of flexion. Surface electromyography (EMG) of quadriceps and hamstrings was recorded as an indication of the amount of muscle activity. Nearly all subjects showed >95% VA at all joint angles. VA did not vary with joint angle nor were there significant differences between the two stimulation techniques. Similarly, there was no significant effect of knee joint angle on the EMG activity of either muscle group. These findings indicate that VA of the quadriceps during a brief isometric contraction is not affected by muscle length and can be measured by either stimulation technique. Electronic Publication     

Interrater reliability of isokinetic measures of knee flexion and extension

The purpose of this investigation was to determine the interrater reliability of peak torque and total work values obtained with isokinetic measures of knee flexion and extension. Eight male and eight female students were evaluated on four occasions by four different examiners (range of isokinetic test experience: 0 to 10 yrs) using a standardized isokinetic measurement protocol. Subjects were randomly assigned to participate in a test sequence determined by a 4 x 4 balanced Latin square. Peak torque and total work values at 60 degrees /sec and 180 degrees /sec were obtained for the concentric measures of knee extension and flexion. The measures of peak torque and total work were corrected for the effects of gravity. Intraclass correlation coefficients and standard error of measurement estimates were used to estimate the interrater reliability for each test condition (test speed x muscle group). Intraclass correlation coefficient values ranged from .90 to .96 for peak torque and .90 to .95 for total work. Standard error of measurement estimates ranged from 8.9 to 13.3 Nm for peak torque and 11.3 to 16.8 Nm for total work. The results of this investigation demonstrate that reliable measures of isokinetic muscle performance of knee extension and flexion may be obtained by four clinicians with varied experience when following a standardized measurement protocol.     

Surface EMG signal alterations in Carpal Tunnel syndrome: a pilot study

Fatigability and muscle oxygen consumption (mVO₂) during sustained voluntary isometric knee extensions are less at extended (30° knee angle; 0°, full extension) versus flexed knee angles (90°). This lower energy consumption may partially result from lower neural activation at extended knee angles. We hypothesized a smaller difference in mVO₂ between extended and flexed knee angles during electrical stimulation, which guaranteed maximal activation, than during maximal voluntary contractions (MVC). In eight healthy young males, MVC extension torque was obtained at 30°, 60° and 90° knee angles. mVO₂ of the rectus femoris (RF), vastus lateralis (VL) and medialis muscle was measured using near-infrared spectroscopy during tetanic (10 s) and maximal voluntary (15 s) contractions (MVC₁₅). For electrically induced contractions, steady state mVO₂ was reached at similar (P > 0.05) times after torque onset (4.6 ± 0.7 s) at all knee angles. In contrast, during MVC₁₅ at 30° mVO₂ was reached at 7.1 ± 1.1 s, significantly later compared to 60° and 90° knee angles. The knee angle dependent differences in mVO₂ were not lower in electrically induced contractions (as hypothesised) but were similar as in voluntary contractions. Normalized mVO₂ at 30° (percentage 90° knee angle) was 79.0 ± 9.4% (across muscles) for electrically induced and 79.5 ± 7.6% (across muscles) for voluntary contractions (P < 0.05). We conclude that the slower onset of mVO₂ during voluntary effort at 30° may have been due to a lower maximal activation. However, because steady state mVO₂ both during electrically induced and voluntary contractions was ~20% less at extended versus flexed knee angles, the causes for the lower mVO₂ must reside within the muscle itself.     

Segmental reflexes and ankle joint stiffness during co-contraction of antagonistic ankle muscles in man

The size of soleus H-reflexes and short-latency stretch reflexes was measured at different levels of plantar flexion or co-contraction (simultaneous activation of dorsi- and plantar flexors) in seven healthy subjects. In four of seven subjects the short-latency stretc reflex was smaller during weak co-contraction than during isolated plantar flexion at matched background electromyogram (EMG) levels in the soleus muscle. In three of these four subjects the stretch reflex was larger during strong co-contraction than during plantar flexion, whereas it had the same size during the two tasks in the last subject. In the remaining subjects the stretch reflex either had the same size or was larger at all levels of co-contraction than at similar levels of plantar flexion. In contrast, the H-reflex was found to decrease with co-contraction at all contraction levels in all subjects. The decrease in the reflexes during weak co-contraction might be caused by presynaptic inhibition of Ia afferents. It is unclear why only the H-reflex decreased during strong co-contraction. The stiffness of the ankle joint was measured from the torque increment following the stretch of the plantar flexors divided by the stretch amplitude. In all subjects the total stiffness of the ankle joint was larger during strong co-contraction than during plantar flexion of similar strength. The stiffness was smaller during weak co-contraction than during weak plantar flexion in three out of seven subjects. The medial gastrocnemius muscle was more active at a given level of soleus activity during the co-contraction task than during the isolated plantar flexion task. It is suggested that the increase in the stiffness during co-contraction as compared to isolated plantar flexion was mainly due to the mechanical contribution of the activity in the tibialis anterior and medial gastrocnemius muscles. The decrease in stiffness during weak co-contraction was, in contrast, most likely mainly caused by modulation of reflex stiffness.     

Differences in the electromyographic activity of the hamstring muscles during maximal eccentric knee flexion

This study investigated the effects of the knee joint angle and angular velocity on hamstring muscles’ activation patterns during maximum eccentric knee flexion contractions. Ten healthy young males (23.4 ± 1.3 years) performed eccentric knee flexion at constant velocities of 10, 60, 180, and 300 deg/s in random order. The eccentric knee flexion torque and the surface electromyographic (EMG) activity of the biceps femoris (BF), semitendinosus (ST), and semimembranosus (SM) muscles were measured. The results of torque during 10 deg/s were lower than the faster velocities. No significant change was found in eccentric torque output and the EMG amplitude with change in the faster test velocities, although those values showed a decreasing tendency as the knee approached extension. Furthermore, the EMG amplitude of the BF decreased significantly as the knee approached extension, although the EMG activity of the ST and SM remained constant. These results suggest that the neural inhibitory mechanism might be involved in decreasing in maximal voluntary force and hamstring muscles activation toward the knee extension during high-velocity eccentric movement and therefore subjects have difficulties to maintain high eccentric force level throughout the motion. Moreover, the possible mechanism reducing the BF muscle activation as the knee approaches extension was architectural differences in the hamstring muscles, which might reflect each muscle’s function.     

Elbow flexion strength curves in untrained men and women and male bodybuilders

Summary The influence of elbow joint angle on voluntary isometric elbow flexion strength was assessed in 15 young women (F), 18 young men (M) and 11 male body-builders (BB). Measurements were made at elbow joint angles of 1.31, 1.57, 1.83, 2.09, 2.36, 2.62 and 2.88 rad (3.14 rad = 180° = full extension). The peak voluntary strength [mean (SE), N.m] in M [69.5 (4.3)] and BB [93.3 (4.8)] occurred at 2.09 rad (120°), but occurred at 1.57 rad (90°) in F [35.4 (2.4)]. Peak torque at 1.31 rad was 20% and 25% lower than at 2.09 rad in M and BB, respectively, but did not differ between these two angles in F. The larger elbow flexor muscle and fibre size in M and BB may have been responsible for their impaired torque production at joint angles corresponding to the shortest muscle lengths.     

Flexor reflex responses triggered by imposed knee extension in chronic human spinal cord injury

Hypersensitivity of the flexor reflex pathways to input from force-sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injury (SCI). In this study, we triggered flexor reflexes with constant velocity knee movements in 15 subjects with SCI. Ramp and hold knee extension perturbations were imposed on one leg while the hip and ankle were held in an isometric position using an instrumented leg brace. Knee, ankle and hip torque responses and electromyograms from six muscles of the leg were recorded following controlled knee extension at four different velocities. Tests were conducted with the hip in both flexed and extended positions. During the movement into knee extension, a velocity-dependent stretch reflex, represented by a progressively increasing knee flexion torque, was observed. In addition, another type of reflex that resembled a flexor reflex (flexion of the hip and ankle) was also triggered by the imposed knee extension. The magnitude of the ankle dorsiflexion torque responses was significantly correlated to the stretch reflex torque at the knee in 9 of the 15 subjects. We concluded that stretch reflexes initiate a muscle contraction that then can contribute to a flexor reflex response, possibly through muscle group III/IV afferent pathways. These results suggest that spasticity in SCI consists of a myriad of complex reflex responses that extend beyond stretch reflexes.     

Biomechanics of passive knee joint in drawer: load transmission in intact and ACL-deficient joints

A non-linear 3D finite element model of the passive human tibiofemoral knee joint consisting of two bony structures and their articular cartilage layers, menisci, and four principal ligaments was used to investigate the detailed response of the unconstrained joint under up to 100 N posterior femoral force at different flexion angles from 0 to 90 degrees. The analysis was repeated after the transection of the anterior cruciate ligament (ACL). The boundary conditions were selected to assure a stable and unconstrained response of the joint throughout the range of motion. The results indicated the ACL as the primary structure to resist the drawer load throughout the range of flexion considered and that the joint primary and coupled laxities substantially increased in its absence. At full extension under drawer, forces in collateral ligaments increased significantly resulting in larger overall contact forces as the ACL was transected. In the ACL-deficient joint, such large forces in collateral ligaments, however, diminished as flexion angle varied from 0 to 90 degrees. At full extension or flexion angles up to approximately 30 degrees, the medial meniscus and adjacent medial tibial and femoral cartilage layers were subjected to substantially larger loads and stresses following the transection of the ACL. Adequate consideration of such couplings is important in avoiding further damage to joint structures subsequent to an injury and restoring adequate function following injuries to primary components.     

胫骨结节前移的生物力学分析

本研究的目的是评估胫骨结节前移术（Ｍａｑｕｅｔ手术）降低髌股关节接触力的效果。采用膝关节活体几何学数据结合生物力学模型模拟Ｍａｑｕｅｔ手术。６例健康青年人在膝关节负重屈伸时（上一级楼梯）以视屏系统连续记录膝关节的动态Ｘ线影像，采用计算机系统分析数字化Ｘ线影像得到膝关节的几何学数据。根据上述数据对６例右膝进行计算机手术模拟，将髌腱止点前移３、５、１０、１５和２０°，随后，对模拟结果作生物力学分析。结果显示，膝屈曲角度达９０°时，Ｍａｑｕｅｔ手术仅能使髌股关节接触力减少２０％，只有在膝关节屈角度小于２０°及髌腔前移１５°或２０°时，髌股关节接触力才有明显下降，达５０％。髌腱前移１５°或２０°意味着胫骨结节前移几乎达１英寸。结果还显示，Ｍａｑｕｅｔ手术可使髌股装置的力传导效率下降２０％，因而在膝关节屈曲角度大于２０°时，手术效果变得很小。上述发现提示Ｍａｑｕｅｔ手术仅适用于屈膝角度较小的老年人或活动较少的病人。     

Effect of contraction history on torque deficits by stretches of active rat skeletal muscles.

Effects of contraction history on torque deficits by stretches of active skeletal muscles were examined. After three contractions using maximal and submaximal activation (80 and 20 Hz) at an ankle position of 40 degrees (i.e., long muscle length) and with maximal activation at 120 degrees (i.e., short muscle length), the isometric and stretch torques (15 stretches) of rat plantar flexor muscles (bout 1) were measured. Controls were unconditioned. Stretches (i.e., ankle rotation from 90 degrees to 40 degrees, velocity: 50 degrees. s-1) were imposed on maximal isometric contractions at 90 degrees (i.e., preloaded stretches). All groups performed a second bout following 2 hours of rest after bout 1. After maximal contractions at long muscle length, preload torque at 90 degrees and stretch torque at 40 degrees for stretch 1 of bout 1 were 25% and 18% lower than the other groups. However, for all groups, bout 1 ended and bout 2 began and ended with similar isometric and stretch torques. Stretches early in bout 2, with preloads similar to stretches in bout 1, had greater stretch torques resulting in larger torque deficits. Torque deficits, possibly caused by damage to muscle structures and excitation-contraction uncoupling, were not prevented by a history of isometric contractions. Different contraction histories can result in similar isometric torques but different stretch torques.     

Moment arms of the knee extensor mechanism in children and adults

In the present study we investigated whether there are differences in the patellar tendon moment arm (PTMA)-knee angle relationship between pre-pubertal children and adults, and whether the PTMA length scales to relevant anthropometric measurements in the two groups. Anthropometric characteristics and the PTMA length-joint angle relationships were determined in 20 adults and 20 pre-pubertal children of both genders. The anthropometric characteristics measured were height, body mass, knee circumference, medio-lateral knee breadth, anterior-posterior knee depth, leg length, femur length and tibia length. The PTMA was quantified from magnetic resonance images using the geometric centre of the femoral condyle method, at every 5° between 55° and 90° of knee flexion (0° is full extension). Adults had a significantly greater PTMA length at all joint angles (4.2 ± 0.4 vs. 3.6 ± 0.3 cm at 90°; P  < 0.01), with the PTMA length decreasing from knee extension to knee flexion similarly in both adults and children. There were no significant and strong correlations between the PTMA and anthropometric measures in adults for any joint angle. In contrast, the PTMA correlated and scaled with anthropometric characteristics for the children ( P  < 0.05, r  = 0.49–0.9) at all joint angles. The PTMA length in children was most accurately predicted at 85° of flexion from the equation PTMA = –0.25 + 0.083·tibia length + 0.02·leg length ( R ² = 0.83). These findings indicate that the knee extensor mechanism in pre-pubertal children should not be considered to be a 'scaled-down' version of that in adults.     

A mathematical modelling study investigating the influence of knee joint flexion angle and extension moment on patellofemoral joint reaction force and stress

BackgroundPatellofemoral pain (PFP) is the most common orthopaedic condition among runners. Individuals with PFP exhibit greater patellofemoral joint (PFJ) reaction force and stress when compared with pain-free controls. However, it is not clear whether PFJ reaction force and stress are the highest (or lowest) when knee joint flexion angle and extension moment are in which combinations. We aimed to investigate the influence of knee joint flexion angle and extension moment on PFJ reaction force and stress.MethodsA PFJ sagittal model was used to quantify PFJ reaction force and stress. Based on the public dataset of the previous study, peak knee joint flexion angle and extension moment at various running speeds was calculated. Based on the calculated peak value, simulation ranges were set to knee joint flexion angle of 10–45° and extension moment of 0–240 Nm. The quadriceps force, effective lever arm length at quadriceps muscle, and PFJ contact area were determined as a function of the knee joint flexion angle and extension moment, and finally PFJ forces and stress were estimated.ResultsPFJ reaction force increased as the knee flexion angle and extension moment increased. Although PFJ stress also increased as the knee extension moment increased, it was at the highest and lowest at 10° and about 30° knee joint flexion angles, respectively.ConclusionsIncorporating knee flexion posture (approximately 30°) during running may help in reducing PFJ stress, which would be useful in the prevention of pain and act as an optimal treatment program for PFP.