对女子手球运动员膝关节屈伸肌群进行等速测试

目的对广东省女子手球队运动员膝关节进行等速向心测试,探讨手球项目运动员膝关节屈伸肌群等速测试特征,为手球项目运动员的力量训练和相关的体育科研提供参考。方法运用CON-TREX等速测试系统对14名广东省女子手球运动员的膝关节进行等速向心测试,选取相对峰力矩、屈伸肌峰力矩比值、平均功率、总功和疲劳指数5个指标来研究手球项目运动员膝关节屈伸肌群的等速测试特征。选取独立样本t检验比较屈肌和伸肌的测试结果。结果膝关节伸肌相对峰力矩值在慢速测试(60°/s)和快速测试(240°/s)时均明显大于屈肌(P<0.01);女手队员膝关节屈伸肌峰力矩比值在快速测试(240°/s)时为76%左右;膝关节屈伸肌平均功率和总功在慢速测试(60°/s)时表现为伸肌大于屈肌(P<0.01),在快速测试(240°/s)时表现为左膝关节伸肌大于屈肌(P<0.05);女手队员膝关节屈伸肌疲劳指数范围在0～0.49之间。结论女手队员膝关节伸肌的最大力量和快速力量大于屈肌;女手队员膝关节屈伸肌峰力矩比值在快速测试(240°/s)时略微偏低,说明女手队员膝关节屈肌快速力量偏低;女手队员膝关节伸肌的快速力量和肌肉工作能力均大于屈肌;女手队员膝关节屈伸肌疲劳指数偏低,说明女手队员膝关节屈伸肌的力量耐力水平比较低。     

The effect of movement direction on joint torque covariation

It has been proposed that unconstrained upper limb movements are coordinated via a kinetic constraint that produces dynamic muscle torques at each moving joint that are a linear function of a single torque command. This constraint has been termed linear synergy (Gottlieb et al. J Neurophysiol 75:1760–1764, 1996). The current study tested two hypotheses: (1) that the extent of covariation between dynamic muscle torques at the shoulder and elbow varied with the direction of movement and (2) that the extent to which muscle torques deviated from linear synergy would be reproduced by a simulation of pointing movements in which the path of the hand was constrained to be straight. Dynamic muscle torques were calculated from sagittal plane pointing movements performed by 12 participants to targets in eight different directions. The results of principal component analyses performed on the muscle torque data demonstrated direction-dependent variation in the extent to which dynamic muscle torques covaried at the shoulder and elbow. Linear synergy was deviated from substantially in movement directions for which the magnitude of muscle torque was low at one joint. A simulation of movements with straight hand paths was able to accurately estimate the amount of covariation between muscle torques at the two joints in many directions. These results support the idea that a kinematic constraint is imposed by the central nervous system during unconstrained pointing movements. Linear synergy may also be applied as a coordinating constraint in circumstances where its application allows the path of the moving endpoint to remain close to a straight line.     

Effects of hypoxia on cerebral and muscle haemodynamics during knee extensions in healthy subjects

A hypoxic model was used to investigate changes in localized cerebral and muscle haemodynamics during knee extension (KE) in healthy individuals. Thirty-one young healthy volunteers performed one set of KE until failure under hypoxia (14 % O₂) or normoxia (21 % O₂) at 50, 75 or 100 % of 1 repetition maximum, in random order, on three occasions. Prefrontal cerebral and vastus lateralis muscle oxygenation and blood volume (Cox, Mox, Cbv and Mbv, respectively) were recorded simultaneously by near-infrared spectroscopy. Hypoxia induced significant declines in Cox [?0.017 ± 0.016 optical density (OD) units] and Mox (?0.014 ± 0.026 OD units) and increases in Cbv (0.017 ± 0.027 OD units) and Mbv (0.016 ± 0.023 OD units) at rest. Hypoxia significantly reduced total work (TW) performed during KE at each exercise intensity. Cox, Cbv, Mox, and Mbv changes during KE did not differ between normoxia and hypoxia. Correlations between TW done and Cox changes under normoxia (r = 0.04, p = 0.182) and hypoxia (r = 0.05, p = 0.122) were not significant. However, TW was significantly correlated with Mox under both normoxia (R ² = 0.24, p = 0.000) and hypoxia (R ² = 0.15, p = 0.004). Since changes in Cox and Mox reflect alterations in the balance between oxygen delivery and extraction in these tissues, which, in the brain, is an index of neuronal activation, we conclude that: (1) limitation of KE performance was mediated peripherally under both normoxia and hypoxia, with no additional effect of hypoxia, and (2) because of the low common variance with Mox additional intramuscular factors likely play a role in limiting KE performance.     

Gender-specific knee extensor torque,flexor torque,and muscle fatigue responses during maximal effort contractions

The purpose of this study was to examine gender differences in knee extensor and flexor peak torque, work, power, and muscle fatigue during maximal effort isokinetic contractions. Subjects included 19 healthy male and 20 healthy female volunteers. Following a dynamic warm-up period, subjects performed 30 reciprocal, concentric maximal knee extension and flexion contractions at a pre-set angular velocity of 3.14 rad·s^–1 on the Biodex Isokinetic Dynamometer. Values for knee extensor peak torque, work, and power were calculated for each repetition over an angular displacement of 1.05 rad for each repetition. The single highest repetition value for knee extensor and flexor peak torque, work, and power was then calculated relative to body mass (N·m·kg^–1, J·kg^–1, W·kg^–1) and allometric-scaled (N·m·kg^{– n} , J·kg^{– n} , W·kg^{– n} ) units. The allometric-scaled units were derived from a log–log transformation and linear regression analysis to calculate the exponent to which body mass is raised. The rate of quadriceps femoris muscle fatigue was calculated as the decline in each isokinetic variable by the linear slope from the single highest repetition value through the 30th repetition, and by two different fatigue indexes. The results demonstrate higher knee extension and flexion peak torque, work, and power in absolute, relative, and allometric-scaled units for males compared to females. Males exhibited higher fatigue rates for both muscle groups of each isokinetic variable than females, as described by the slope and the fatigue index, except when adjusted for peak values via analysis of covariance. The findings suggest that during maximal-effort muscle contractions, males exhibit a higher susceptibility to muscle fatigue than females, a phenomenon that may be related to an inherent ability to generate higher knee extensor and flexor torque. Electronic Publication     

Influence of hysteresis on joint position sense in the human knee joint

During muscle lengthening in a movement cycle the firing rate of muscle spindles is higher than during shortening. This phenomenon, known as hysteresis, has implications for movement control. Therefore, it should have an impact on joint position sense (JPS), the subject's awareness of the static position of a joint. JPS has been tested on the human knee joint by means of an angle reproduction test. This task included the following sequences. The leg was moved passively, by means of a motor drive, from two different start positions (15 degrees and 75 degrees) to a certain target angle and, after a time of 8 s, it was returned to the start position; subjects had to reproduce the former target angle. Several target angles, mild flexion (30 degrees), intermediate flexion (45 degrees), and strong flexion (60 degrees), were used. Depending on the start position, the movements matching these targets were flexions or extensions. At least for the intermediate position different threshold values should be expected for flexions and extensions, if hysteresis has an impact. Moreover, the JPS measure should show a dependence on movement velocity and independence on distance. Of the variables tested, only movement direction but not movement velocity or distance had a statistically significant impact on the dependent constant angle error (difference between reproduction and target angle). The target angle of 30 degrees was exactly reproduced (-0.14 degrees), independently of the start position. The 45 degrees target angle was significantly underestimated (-4.39 degrees) when matching that position by flexions (starting at 15 degrees) compared to an overestimation (2.27 degrees) when matching that position by extensions (starting at 75 degrees). The target angle of 60 degrees has been constantly underestimated (-3.80 degrees), independently of the start position. Therefore, hysteresis, the dependency of the movement's direction, neglected in the past, should be considered in future tests of JPS or studies considering the role of movement parameters for motor control.     

Isometric and isokinetic torque curves at the knee joint

Isometric and isokinetic torques of bilateral quadriceps and hamstrings were measured with Isokinetic Rehabilitation and Testing System (Model No. Cybex 340) on 40 normal untrained subjects, 20 males and 20 females, ranging between the ages of 23 and 35 years. The mean peak isometric and isokinetic torque values of both muscle groups showed no significant differences between dominant (right) and nondominant (left) limbs in both sexes; however there were significant differences between the male and the female. As the angular velocity increased, the peak torque significantly decreased, and the point of peak torque output occurred significantly later in the range of motion for quadriceps and hamstrings (p less than 0.01). There were no significant changes in the hamstrings to quadriceps (H/Q) ratios as the angular velocity increased. However, there were significant differences of mean H/Q ratio between male and female (p less than 0.01). Height had significant positive correlation with peak isometric and isokinetic torques for both quadriceps and hamstrings (p less than 0.01). Weight was found to correlate significantly with peak isometric and isokinetic torques (p less than 0.01). The mean isometric torques were significantly higher than the mean isokinetic torques for any joint angles in both sexes (p less than .01).     

Psychometric properties of measurement tools for quantifying knee joint position and movement: a systematic review

This systematic review critically evaluates literature on the reliability and validity of measurement tools for quantifying knee joint angles and knee movement. A search was conducted of seven medical databases and one biomedical engineering database, yielding 43 articles that reported reliability or validity. Tools for quantifying knee joint angles included standard handheld goniometers, fluid-based goniometers, gravity-based goniometers, photographs and two dimensional (2-D) motion analysis. Knee movement was measured with electrogoniometers, 2-D and three dimensional (3-D) motion analysis. Intraclass correlation coefficients for testing knee angles ranged from 0.51-1.00 for intratester reliability and 0.43-0.99 for intertester reliability. For quantifying knee position, sequential MRI and 2-D had the least error of measurement, followed by hand held goniometers and photographs. For dynamic measurements, electrogoniometers and 3-D motion analysis were most reliable and had low error of measurement. Strong concurrent validity was found between hand held goniometers and radiographs, as well as between hand held goniometers and 3-D motion analysis.     

Comparison of N-k table offset angles with the human knee flexor torque curve

The purpose of this study was to dynamically examine various offset angles on the N-K table to determine which offset produces a torque pattern corresponding most closely to the isokinetic torque curve of the knee flexor musculature when tested at 60%. Subjects for the study were five college-age male volunteers (age=21.8±1.8 yrs, ht=181.9±4.3 cm, wt=88.4±12.6 kg). Mean peak isokinetic torque values for the five subjects were measured at 5° increments to represent the human knee flexor torque curve. These were converted to relative mean values by dividing each value by the maximum mean peak torque. Torque curves from four offset angles (90°,110°,135°, and 160°) for the N-K table were obtained by using the Kin Com in the passive mode at 20°/s to push the exercise arm of the N-K table through a range of motion of 0° to 90° while recording torque and angular position. The four torque curves were converted to relative values in a similar manner as for the subjects. Qualitative analysis reveals that the 160° offset angle most closely corresponded to the representative knee flexor isokinetic torque curve, while the 90° offset angle corresponded least. Although these findings would seem to support reconsideration of common clinical practice relative to the use of the N-K table for knee flexor strength development, the 160° offset angle is awkward because it has a tendency to force the user into hyperextension at the beginning phase of motion. As such, practical compromises might include the use of the 110° or 135° offset angle in lieu of the traditionally employed 90° offset angle, or the development of an extension stop that would prevent hyperextension of the knee.     

Effects of eccentric strength training on biceps femoris muscle architecture and knee joint range of movement

The aim was to determine whether eccentric strengthening changed the muscle architecture of human biceps femoris and consequently, knee range of motion. Twenty-two subjects were randomly assigned to control and experimental groups. The experimental group completed an eccentric strengthening programme for 8 weeks. Outcome measures included hamstring muscle strength (one repetition maximum), the passive knee extension test (PKE) (knee joint angle at which the onset of passive tension occurs), fascicle length (FL) and pennation angle (PA). One repetition maximum increased by 34% (P < 0.01), the PKE test revealed a 5% increase in joint range of motion (P = 0.01), FL increased by 34% (P = 0.01) and PA did not change (P = 0.38). This is the first report of an increase in FL in the biceps femoris following eccentric resistance training. In addition, the results might imply that this fascicle lengthening could lead to an increase in the range of motion of the knee. Clinical implications for rehabilitation and injury prevention are discussed.     

Effect of prophylactic knee bracing on balance and joint position sense

Prophylactic knee braces are designed to prevent and reduce the severity of ligamentous injuries to the knee. Conflicting evidence is reported concerning their efficacy. The purpose of this study was to determine the effect of prophylactic knee bracing on the proprioceptive parameters of balance and joint position sense. Active and passive joint position sense were assessed using the Cybex II + Isokinetic Dynamometer (Cybex Division of Lumex, Inc, Ronkonkoma, NY). Sway index and center of balance were assessed using the Chattecx Dynamic Balance System (Chattanooga Group, Hixson, TN). Thirty-six male subjects were measured with and without prophylactic knee braces. Joint position sense was measured in degrees of error from four preselected target angles. Sway index and center of balance measures were recorded in centimeters under the following platform conditions: stable, plantar flexion/dorsiflexion, and inversion/eversion. Separate repeated measures ANOVAs were performed to determine if there were differences between the braced and unbraced conditions for center of balance, sway index, and joint position sense. Center of balance with the platform moving in a dorsi/plantar flexion direction was improved while wearing the knee braces. In addition, differences in both center of balance and sway were recorded across the three platform conditions with and without knee bracing. Bracing did not affect joint position sense. The results of this study suggest that prophylactic knee braces have very little impact on proprioceptive feedback mechanisms.     

Effects of body orientation, load and vibration on sensing position and movement at the human elbow joint

Experiments were carried out to study the ability of human subjects to match the position of their forearms relative to the horizontal. The normal, arms-in-front position with the hands aligned and little forward flexion at the shoulder was called the reference position. When the arms were rotated to the side, one arm was raised, or both arms were raised, matching ability deteriorated compared with the reference position, when expressed as an increase in the standard deviation of matching errors. It was concluded that particular significance was assigned by the brain to the arms-in-front position, with the hands in their normal working space. Increases in errors were also observed when the reference arm was made weightless or its weight was increased by means of an adjustable load. This suggested that lifting the arm against gravity provided additional positional information. In a second experiment, dependence of the illusion of muscle lengthening evoked by vibration was tested after two different forms of muscle conditioning, a co-contraction of elbow muscles with the arm held flexed or with it held extended. The speed of the illusory extension of flexor muscles during their vibration increased three-fold after flexion conditioning compared with extension conditioning. Since after flexion conditioning, muscle spindles in flexor muscles are expected to be more sensitive to vibration than after extension conditioning, this observation provides additional support for the view that muscle spindles make an important contribution to kinaesthesia at the elbow joint.     

Effects of altering initial position on movement direction and extent

The purpose of this study was to examine the relative influence of initial hand location on the direction and extent of planar reaching movements. Subjects performed a horizontal-plane reaching task with the dominant arm supported above a table top by a frictionless air-jet system. A start circle and a target were reflected from a horizontal projection screen onto a horizontally positioned mirror, which blocked the subject's view of the arm. A cursor, representing either actual or virtual finger location, was only displayed between each trial to allow subjects to position the cursor in the start circle. Prior to occasional "probe trials," we changed the start location of the finger relative to the cursor. Subjects reported being unaware of the discrepancy between cursor and finger. Our results indicate that regardless of initial hand location, subjects did not alter the direction of movement. However, movement distance was systematically adjusted in accord with the baseline target position. Thus when the hand start position was perpendicularly displaced relative to the target direction, neither the direction nor the extent of movement varied relative to that of baseline. However, when the hand was displaced along the target direction, either anterior or posterior, movements were made in the same direction as baseline trials but were shortened or lengthened, respectively. This effect was asymmetrical such that movements from anterior displaced positions showed greater distance adjustment than those from posterior displaced positions. Inverse dynamic analysis revealed substantial changes in elbow and shoulder muscle torque strategies for both right/left and anterior/posterior pairs of displacements. In the case of right/left displacements, such changes in muscle torque compensated changes in limb configuration such that movements were made in the same direction and to the same extent as baseline trials. Our results support the hypothesis that movement direction is specified relative to an origin at the current location of the hand. Movement extent, on the other hand, appears to be affected by the workspace learned during baseline movement experience.     

Effect of ankle position fixation on peak torque and electromyographic activity of the knee flexors and extensors

The purpose of this study was to examine the effect of ankle position fixation on peak torque (PT) and electromyographic (EMG) activity of knee-joint muscles during isokinetic testing. Twelve female athletes performed isokinetic knee flexion and extension at 60 degrees and 180 degrees/s under two conditions: with the ankle fixed in a position of plantarflexion and with the ankle fixed in a position of dorsiflexion. Bipolar surface electrodes were placed on the vastus lateralis, vastus medialis, biceps femoris, medial hamstrings, and the lateral head of the gastrocnemius for determination of the root mean square of the EMG (rmsEMG) and the median frequency of the EMG (mfEMG). No significant differences in knee extensor PT were noted in either ankle position for each velocity tested. Significant differences were noted, however, in knee flexor PT (p < 0.05) at both 60 degrees and 180 degrees/s, with the greatest PT observed with the ankle fixed in dorsiflexion. Neither quadriceps, hamstrings, nor gastrocnemius rmsEMG activity was affected by ankle position; however, there was a significant difference in mfEMG for the gastrocnemius, with higher frequencies observed with the ankle fixed in plantarflexion (p < 0.01). These results suggest that ankle position effects knee flexor PT during open chain isokinetic movements. The reason for decreased knee flexor PT with the ankle fixed in plantarflexion is probably due to the gastrocnemius muscle being in a too shortened position, thereby preventing it from effectively producing force at the knee joint.     

Effects of esophageal stimulation in healthy subjects

We studied the effects of esophageal electrical stimulation on heart rate variability power spectra (PS/HRV) and cortical evoked potentials (EPs) in healthy subjects. The intensity of stimulation was varied from 2.7 to 20 mA. We found that the amplitude of the cortical evoked potentials (amplitude of the N2/P2 peak) increased from 5.1 +/- 0.7 microV at 5 mA to 16.3 +/- 1.1 microV at 20 mA. The PS/HRV showed an increase in the vagal modulation of the sinus node. When the stimulation frequency was varied from 0.1 to 1 Hz at a constant intensity of 15 mA, the amplitude of cortical EPs (N2/P2 peak) decreased with increase in the frequency of stimulation (p < 0.05). The LF:HF ratio decreased significantly for all frequencies of stimulation (p < 0.005). An experimental paradigm to evoke the cognitive component in the cortical EPs yielded a peak around 354 ms following the stimulus.     

Effects of age on neuromuscular knee joint control

Age-related changes in neuromuscular function may have adverse effects on hamstring reflex activity and may impair knee joint stability. The aim of this study was to investigate whether increasing age affects hamstring short latency responses (SLR), medium latency responses (MLR), and anterior tibial translation. In 40 healthy subjects ranging from 20 to 70 years of age we assessed hamstring muscle latencies and integrals for both hamstring reflex components (SLRs and MLRs) as well as anterior tibial translation in order to quantify knee joint stability in response to induced tibial translation during stance. The results showed no significant differences within the subject population in hamstring SLR and MLR latencies and integrals or anterior tibial translation. More precisely, regression analysis did not reveal any correlation between age and the aforementioned parameters. Our findings suggest that functional knee stability in terms of anterior tibial translation appears to be unaffected from people 20 to 70 years of age. Thus, as compared with younger people, older people - at least those under 70 years of age - do not appear to have a higher risk of ligamentous knee injuries associated with hamstring dysfunction. Further studies should be conducted to assess whether the present findings also apply to dynamic real-world situations. This would improve the understanding of the relationship between knee stability and ageing.     

老年人膝关节和踝关节位置觉的重测信度

背景：目前国内外关节位置觉的研究主要以青年人为对象,而老年人在不同角度关节位置重现的重测信度研究比较缺乏。 目的：观察老年人膝关节和踝关节在不同角度关节复位测试的重测信度。 方法：在Biodex system 3等速系统上用被动复位测试法测试28名健康老年人的膝、踝关节本体感觉,以被动复位绝对误差角度作为个体位置觉能力优劣的代表。重测信度评价指标为组内相关系数(ICC)。 结果与结论：左右两侧膝关节位置觉测试在不同角度都具有良好的重测信度,ICC值为0.851~0.973;左右两侧踝关节位置觉测试在跖屈与背伸位具有中等以上的重测信度,ICC值为0.742~0.964;左侧踝关节复位的绝对误差角度小于右侧踝关节(P < 0.05),且左侧(ICC为0.870~0.964)踝关节重测的相关系数高于右侧(ICC为0.742~0.944)。提示老年人膝关节和踝关节位置觉重测的相关性良好,并且左侧踝关节的相关性高于右侧。     

Perceived horizontal body position in healthy and paraplegic subjects: effect of centrifugation

The perception of body position is mainly mediated by otolith information and visual cues. It has been shown, however, that proprioceptive sources are also involved. To distinguish between the contributions of the vestibular and nonvisual extra-vestibular information to graviception, we tested the effects of a stimulus that leaves the vestibular input unchanged but modifies the information from sense organs located more caudal along the trunk. This was achieved by bringing subjects into a horizontal ear-down position and rotating them around an earth-vertical axis that coincided with the interaural axis. In this paradigm, through centrifugal force, the stimulation of the vestibular and the putative extravestibular graviceptive organs in the body becomes dissociated. Healthy subjects (n = 14) and paraplegic patients with lesions between T4 and T8 (n = 7) adjusted themselves to the perceived horizontal right-ear down body position under two conditions: one with constant velocity rotation (ROT, velocity =120 degrees /s) around the earth-vertical axis of the turntable, and one without rotation (BASE). Among healthy subjects, the individual differences between BASE and ROT varied widely in both the feet-up or feet-down direction. In contrast, adjustments in paraplegic patients during ROT were always in the feet-down direction compared with BASE. A model with two extravestibular graviceptive sensors could explain our results: one sensor is located rostral to T4, and the other is caudal to T8. A load on the rostral graviceptor is interpreted as a tilt of the body in the feet-up direction and shifts the adjustments of perceived body position feet-down; a load on the caudal receptor is interpreted as a tilt in the feet-down direction and shifts the perceived body position feet-up. During ROT, healthy subjects solve the discrepant inputs of both extravestibular graviceptors in a highly variable manner, while paraplegic subjects show less variability because they are restricted to only the rostral graviceptor.     

Effect of movement speed on limb segment motions for reaching from a standing position

The performance of a standing reaching task that necessitates some forward bending requires: (1) the coordination of multiple joints (i.e., the trunk and limb segments) to reach the target, and (2) the preservation of postural stability. It has been proposed that the neural control of multijoint reaching tasks can be simplified by time scaling of joint motions while keeping joint excursions the same. To determine if time scaling of joint motions was used in this more complex reaching task, we had 20 healthy subjects (10 male and 10 female) reach for two targets located in a parasagittal plane while standing on a force platform. Subjects reached for the targets at a comfortable speed and a fast paced speed. Sagittal plane motions of the right shank, thigh, pelvis, trunk, humerus, and forearm were measured. At the fast paced movement speeds subjects had significantly larger excursions of the thigh, pelvis, humerus, and forearm compared to the comfortable speed. Thus, segment motions are not simply time scaled for standing multijoint reaches. We explored three possible reasons for not obeying time scaling: (1) to reduce scaling of peak kinetic energy, (2) to reduce scaling of peak horizontal ground reaction force, and (3) a convergence of movement strategies at faster speeds. While subjects modified their movement strategy in relationship to movement speed, these changes had no significant effect on the expected scaling of peak kinetic energy, or peak horizontal ground reaction forces. Given the intersubject differences in movement strategies used to perform these reaching tasks at the fast speeds, a convergence of movement strategies was ruled out. We propose that the increase in segment motions with speed may be a consequence of rules underlying motor output, the increases being greater for segments in which viscoelastic resistance to movement is more significant compared to inertial resistance. Electronic Publication