Effect of resisted knee flexion on knee extension torque

We tested the principle of "reversal of antagonists" by measuring the effect of resisted knee flexion on subsequent peak knee extension torque at velocities of 60 degrees/sec and 120 degrees/sec using an isokinetic dynamometer. We determined peak knee extension torques from torque curves produced during knee extension that was performed reciprocally with either passive or maximum voluntary resisted knee flexion. We used a crossover design so that all 18 healthy adult subjects performed knee extension reciprocally with both passive and resisted knee flexion. Paired means t tests revealed no statistically significant difference between the peak knee extension torques produced under the two knee flexion conditions either at 60 degrees/sec or 120 degrees/sec. We, therefore, concluded that resisted knee flexion does not augment peak knee extension torque under our conditions of testing. The concept of reversal of antagonists was not supported. Antagonistic muscle functioning, therefore, may be irrelevant to agonist isokinetic testing and training in neurologically healthy persons.     

Reliability of concentric and eccentric torque during isokinetic knee extension in post-stroke hemiparesis

BACKGROUND: Emerging evidence on the velocity-dependent nature of force impairment in post-stroke hemiparesis has emphasized the complexity of strength and motor performance assessments in this clinical population. The need to establish reliability and responsiveness of muscle performance measures across a broad range of concentric and eccentric movement speeds is therefore clear, as these metrics will provide benchmarks both for making clinical inference and evaluating meaningful clinical change following interventions. METHODS: Isokinetic knee extensor strength was tested at 14 angular velocities in 17 adults with chronic post-stroke hemiparesis (>18 months), and 13 non-disabled controls. Identical tests were conducted on two occasions separated by two days. Test-retest reliability of maximal isokinetic torque was evaluated using intraclass correlation. Absolute reliability was assessed using standard error of measurement from which smallest real differences were derived. FINDINGS: Overall, intraclass correlation coefficients were excellent for both hemiparetic (0.891) and control (0.937) groups. Intraclass correlation coefficients for each criterion speed were also high for both groups (>0.86). Measurement error relative to the mean torque varied between 14.1% and 26.3% for hemiparetic subjects and 6.0-18.1% for controls. The smallest real difference relative to mean torque was 39.0-72.7% and 16.6-50.2% for hemiparetic and control subjects, respectively. INTERPRETATION: Isokinetic knee extension torque can be measured reliably in persons with chronic post-stroke hemiparesis and in non-disabled controls across a full functional range of concentric and eccentric speeds. Established measurement error and smallest real differences will aid interpretation of longitudinal observations of muscle performance in this clinical population.     

Validity of knee flexion and extension peak torque prediction models

The primary purpose of this study was to test the validity of predictive models relating isokinetic knee torque production to anthropometric and demographic variables. Subjects were 23 healthy female and 15 healthy male volunteers between the ages of 10 and 77 years. We measured subjects' peak knee flexion and extension torque production at two angular velocities. For each torque dependent variable, we calculated a Pearson product-moment correlation coefficient between the measured torque values and the values obtained with prediction equations. The difference between the squared value of the correlation coefficients and the regression multiple R2 values obtained for an original group of 134 subjects ranged between .05 and .10 for the torque dependent variables. The results indicate the validity of the regression models at the level specified by the multiple regression R2 values. Clinicians can use the prediction equations presented in this article to establish rehabilitation goals for patients and can estimate the error involved in applying each prediction equation.     

Relative decreases in knee extension torque with increased knee extension velocities in stroke patients with hemiparesis

I examined the isokinetic knee extension torque (KET) produced by the paretic and nonparetic lower limbs of 27 stroke patients, with hemiparesis, at knee extension velocities (KEVs) of 30 degrees, 60 degrees, 120 degrees, and 180 degrees/sec. The purpose of this study was to determine whether the relative decreases in KET at velocities greater than 30 degrees/sec were different on the two sides. To further investigate this relative decrease, the relationship between the torque at 30 degrees/sec and those at higher speeds also was examined on each side. Relative decreases in KET differed between speeds, but not between sides. Torques at speeds greater than 30 degrees/sec were correlated significantly with the torque at 30 degrees/sec. These findings suggest that patients with hemiparesis and minimal muscle spasticity may have difficulty moving forcefully at higher speeds because they are weak. Therapeutic interventions, therefore, might be most beneficial when they are directed toward helping patients with hemiparesis activate their weak muscles.     

Effect of quadriceps femoris muscle stretch on knee extension torque

Peak and angle specific knee extension torques produced after a quadriceps femoris muscle stretch and after a 15-second rest were compared to determine the effect of stretch on knee extension torque. Twenty healthy subjects performed eight maximum voluntary knee extensions at 90 degrees/sec under each condition. Although peak torque and torques at 15, 30, 45, and 60 degrees from full extension were measured, knee extension torque was only significantly greater (p less than .02) at 60 degrees of knee flexion after quadriceps femoris muscle stretch. The absolute difference, which was only a mean 4.9 N X m (3.6 ft-lb), was not substantial. When quadriceps femoris muscle stretch is a consequence of passive knee flexion at 90 degrees/sec, knee extension torque is apparently facilitated only during the initial part of the knee extension movement. Therefore, in healthy patients, a muscle stretch, such as used in this study, is probably of little therapeutic value.     

Patellar forces during knee extension

A radiographical study of 20 loaded knees of healthy subjects and a knee dissection study of 20 specimens were performed in order to present a two-dimensional patello-femoral joint biomechanical model. A constant knee-extending moment gave 25-40% lower force magnitudes in the patellar tendon than in the quadriceps tendon if the knee was flexed to 60-120 deg. The magnitude of the patello-femoral joint compressive force reached its maximum at 90 deg knee angle and decreased slightly towards 120 deg. A compressive force between quadriceps tendon and femoral intercondylar groove was present above 60 deg knee angle and its magnitude was estimated. The patellar forces in women were about 20% higher than in men. The biomechanical model may be used in knee rehabilitation activities to optimize and individualize exercise programmes. The model may also be applied to daily activities in order to quantify patellar forces.     

Effect of electrical stimulation current frequencies on isometric knee extension torque

The purpose of this study was to compare the isometric knee extension torques of male and female subjects during maximal voluntary contractions (MVCs), electrical stimulation only, and electrical stimulation superimposed onto MVCs at electrical stimulation current frequencies of 20, 50, and 100 Hz. An asymmetrical, bidirectional, nonionizing waveform of 1-msec pulse duration was delivered through the femoral nerve and the superficial quadriceps femoris muscles at maximally tolerated intensity for each subject. The male subjects (n = 20) demonstrated significantly greater absolute torques under all contraction conditions than did the female subjects (n = 20) (p less than .01); when the torques were expressed as a percentage of each subject's MVC torque, however, no significant differences were observed between the sexes. Overall, the superimposed contractions at 50 and 100 Hz and the MVCs had similar torque values, all being significantly greater than the torque values produced by electrical stimulation only at frequencies of 20, 50, and 100 Hz and by the superimposed contractions at 20 Hz. Superimposing electrical stimulation onto MVCs did not result in greater torques than those produced by the MVCs alone. The three most effective contraction conditions, in terms of subject comfort (minimal discomfort) and increased torque, were the superimposed contractions at 50 and 100 Hz and MVCs alone, all of which involved a voluntary component.     

Knee extensor and flexor torque characteristics before and after unilateral total knee arthroplasty

OBJECTIVE: The purpose of this study was to document torque characteristics and strength recovery of the knee extensors and flexors before and up to 1 yr after unilateral total knee arthroplasty. Our goal was to also document the responsiveness of isokinetic testing over repeated measures. DESIGN: Thirteen individuals voluntarily participated in this study. Torque production of the knee extensors and flexors was assessed isokinetically at 1.047 and 3.142 radians/sec. RESULTS: Regardless of time, the knee extensors and flexors on the involved side generated a range of 76 and 82% of the average peak torque produced by the uninvolved side at both 1.047 and 3.142 radians/sec, respectively. At 30 days after surgery, there was a "dip" in both knee extensor and flexor torque production. Responsiveness indices for the knee extensors and flexors ranged from 0.95 to 2.12 at 1.047 radians/sec. At 3.142 radians/sec, the responsiveness indices for the knee extensors and flexors ranged from 0.65 to 2.87. CONCLUSION: One year after surgery, there continues to be knee extensor and flexor strength asymmetry between limbs. Moreover, within the first month after surgery, the knee extensors and flexors are at the weakest point compared with before, 60 days, and 1 yr after surgery. Isokinetic testing is a useful tool to document torque production before and in the early time after unilateral total knee arthroplasty.     

Decreased isometric knee flexion torque with hip extension in hemiparetic patients

I measured the 90-degree isometric knee flexion torque of 12 hemiparetic patients while they performed unilateral knee flexion in sitting and supine positions. The measurements were taken to clarify why hemiparetic patients have difficulty flexing their involved knees when their involved hip is extended. The patients generated more torque in the sitting position than in the supine position and more torque on their nonparetic side than on their paretic side. The ratio of supine-to-sitting knee flexion torque did not differ significantly between sides. This finding suggests that hemiparetic patients do not have relatively greater difficulty generating knee flexion torque on their involved side with the hip extended than with the hip flexed. Recommendations for assessment and treatment are made with this finding in mind.     

脑卒中后偏瘫侧膝关节屈伸的脑功能性磁共振成像研究

目的探讨脑卒中后偏瘫侧下肢运动功能恢复的机制。 方法通过血氧水平依赖性功能磁共振成像（BOLD-fMRI）技术研究7例脑卒中患者屈伸偏瘫侧膝关节时脑激活情况并与8例健康志愿者屈伸单侧膝关节时脑激活情况进行比较，用SPM5图像处理软件处理功能磁共振成像(fMRI)资料。 结果8例正常志愿者实际屈伸单侧膝关节时，对侧旁中央小叶、对侧辅助运动区Brodmann 6区（BA6）、右侧颞上回及两侧顶下小叶明显激活。7例脑卒中患者中有6例屈伸偏瘫侧膝关节时脑激活区主要位于健侧半球顶叶BA7、BA5等脑区。 结论健侧半球的代偿激活是脑卒中偏瘫下肢运动功能恢复的一个主要机制，脑卒中后偏瘫侧膝关节屈伸可能直接依赖于健侧半球顶叶BA7、BA5的激活。     

Isokinetic knee flexion and extension torque in the upright sitting and semireclined sitting positions

We undertook this study to determine whether the isokinetic knee extension and flexion torque generated by 14 young healthy women was greater in the upright sitting test position or in the semireclined sitting test position. Testing was performed at 60 degrees/sec. Knee extension torque did not differ significantly between the two test positions. The subjects, however, did produce significantly greater knee flexion torque when upright compared with when semireclined (p less than .001). Therapists should recognize that the results of testing isokinetic knee extension in the two positions may be similar, but that the results of testing isokinetic knee flexion may be significantly different.     

膝关节屈肌和伸肌等速向心性收缩峰力矩角度的研究

目的　了解影响峰力矩角度 (AOPT)的因素 ,确定向心性屈、伸膝峰力矩角度的正常值范围。方法　共 3 0 0名小于 65岁的正常成人 ,用Cybex3 3 0型等速仪器测试 60 (°) /s、180 (°) /s和 3 0 0 (°) /s屈、伸双膝的AOPT ,利用多因素方差分析和多元线性回归分析年龄、性别、速度、峰力矩和加速度对AOPT的影响 ,建立回归方程。结果　除女性屈膝组外 ,年龄对慢速AOPT无明显影响 ;女性屈、伸膝AOPT均较男性后移 ;随速度增快屈、伸膝AOPT均后移 ;60 (°) /s屈膝峰力矩与AOPT呈负相关 ,伸膝峰力矩与AOPT呈正相关 ;屈膝加速度时间与AOPT呈正相关 ,伸膝加速度与AOPT呈负相关。结论　慢速屈、伸膝AOPT主要受峰力矩的影响 ,本研究所确定的正常值范围可作为诊断或评价膝关节功能的一种辅助指标     

膝关节角度对屈伸肌共同收缩及伸膝力矩的影响

目的 应用表面电极肌电图（EMG）测量膝关节在不同角度做开放链最大等长伸膝时屈膝肌的共同兴奋能力，比较不同角度膝屈伸肌的共同兴奋水平。方法 12名健康在校大学生参与测试。每名受试者在Cybex测试仪上髋关节屈曲90°，单侧膝关节分别于屈膝10，60和90°时各做1组开放链的最大等长伸膝动作。使用表面电极EMG测量每次膝关节伸展时股四头肌与胭绳肌的电信号。在每次伸膝的同时用cy—bex测量股四头肌的最大伸膝力矩。结果所有角度下股四头肌的最大等长收缩均伴胭绳肌的共同兴奋。平均最大伸膝力矩出现在屈膝60°（P〈0．05）。结论膝关节在屈膝60°时可产生最大等长伸膝力矩，开放链的伸膝肌等长收缩伴有屈膝肌的共同兴奋。     

Diagnostic value of knee extension torque tracings in suspected anterior cruciate ligament tears

The purpose of this study was to determine the diagnostic accuracy of knee extensor muscle torque tracings in patients suspected of having damage to the anterior cruciate ligament of the knee joint. The knee extensor torque tracings of 30 patients suspected of having anterior instability of the knee joint were reviewed independently for abnormalities believed to be associated with anterior cruciate ligament damage. These results were compared blindly with an arthroscopic evaluation. The diagnostic accuracy of the torque tracing approach was determined by calculating the prevalence, sensitivity, specificity, and positive and negative predictive values. The sensitivity and specificity were calculated to be 25.0% and 85.7%, respectively. These results suggest that the curve patterns examined in this article have poor diagnostic accuracy and are of little benefit as a clinical diagnostic aid.     

Test-retest reliability of isokinetic knee extension and flexion torque measurements in persons with spastic hemiparesis

The purpose of this study was to evaluate and compare the test-retest reliability of isokinetic torque measurements in the involved and uninvolved knee musculature of 20 subjects with spastic hemiparesis. An isokinetic dynamometer was used to measure maximal voluntary knee extension and flexion at 60 degrees and 120 degrees/s. Peak torque (PT) and average peak torque (APT) data were collected from five repetitions on two separate occasions. Average peak torque was defined as the mean of the PT values obtained during each of the five repetitions. Spasticity was measured in the involved knee musculature prior to isokinetic testing using the Ashworth Scale. Pearson Product-Moment Correlation Coefficients and intraclass correlation coefficients (ICCs) were high (greater than or equal to .90) for both knees for PT and APT at both angular velocities. No clinically meaningful differences were found between the Pearson correlation coefficients and the ICCs of the involved versus the uninvolved knee for any testing conditions. We concluded that isokinetic evaluation of torque, as measured by PT and APT in subjects with spastic hemiparesis, can yield reliable results in both extremities.     

Isometric and isokinetic knee extension and flexion torque in men and women aged 20-70

An investigation was made of the influence of age and sex on peak muscle torque in knee extension and flexion during maximal isokinetic and isometric contraction. The study was performed on both legs of 139 clinically healthy men and 141 clinically healthy women aged 20, 30, 40, 50, 60 or 70 years. Maximum knee extension and flexion muscle torque (Newtonmetre, Nm) was measured isokinetically at various angles of velocity (12, 90 and 150 degrees/s) and isometrically under standardized conditions (Cybex II). No significant differences were found between the right and the left leg in the whole material. Muscle torque was higher in men than in women in all age groups (p less than 0.001). Both isokinetic and isometric torque decreased with age in both sexes. Isokinetic torque decreased significantly (p less than 0.05) between 20 and 30 years of age in men and between 40 and 50 years of age in women (at all velocities studied; p less than 0.05). A significant decrease (p less than 0.05) was found between the ages of 60 and 70 years in both sexes. Maximum isometric torque showed a significant decrease (p less than 0.05) between 60 and 70 years in men and women. There were no significant differences in isokinetic or isometric torque between moderately active and inactive men or women. Significant correlations were found between muscle torque and body weight, height and body surface area.     

Knee extension isometric torque production differences based on verbal motivation given to introverted and extroverted female children

To date, little research has been conducted to test the efficacy of different forms of motivation based on a female child's personality type. The purpose of this study was to evaluate the ability of female children to perform a maximal knee extension isometric torque test with varying forms of motivation, based on the child's personality type (introvert vs. extrovert). The subjects were asked to perform a maximal isometric knee extension test under three different conditions: 1) with no verbal motivation, 2) with verbal motivation from the evaluator only, and 3) with verbal motivation from a group of their peers and the evaluator combined. A 2×3 mixed ANOVA was significant for an interaction (F 2,62=17.530; p<0.0005). Post hoc testing for the introverted group showed that scores without verbal motivation were significantly higher than with verbal motivation from the evaluator or the evaluator plus the peers. The extroverted group revealed that scores with verbal motivation from the evaluator or the evaluator plus the peers were significantly higher than without verbal motivation. Results suggest that verbal motivation has a varying effect on isometric knee extension torque production in female children with different personality types. Extroverted girls perform better with motivation, whereas introverted girls perform better without motivation from others.     

关节镜下松解和伸屈膝训练治疗膝关节粘连的6个月随访评估

目的:观察膝关节镜手术松解和术后膝关节伸屈主被动训练治疗膝关节粘连的随访效果。方法:对象为2002-12/2004-08南京医科大学第一附属医院关节中心收治的24例膝关节粘连患者,均为经正规保守治疗,膝关节活动度小于90°。所有患者接受膝关节镜下松解治疗:连续硬膜外阻滞麻醉,术前手法推拿松解,了解活动度增加的情况;术中屈曲膝关节对关节内、外间隙及髁间窝粘连进行松解;退出关节镜后轻柔手法松解。手法松解与镜下松解清理交替反复进行,直至膝关节屈曲达110°以上,伸直为0°。再次行关节镜下全面清理及软骨修整。术后行膝关节的主被动屈伸康复训练:①伸膝训练:术后第1～2天,首先行伸膝功能训练,膝关节达到或接近伸直位后,转为股四头肌等长收缩训练,股四头肌内侧头的收缩每次维持10s,20次为1组,每天练习3～5组。②屈膝训练:术后第1天开始持续被动活动机功能训练,每天两三次,1.0～1.5h/次,其起始角度设置为术前活动度增加5°～10°,每天增加5°～10°,直至达到或接近术中最大活动度,10d左右。出院后继续每天进行膝关节伸屈主被动训练,连续半年以上。所有病例术后每月随诊1次,记录膝关节的伸屈度数(膝关节活动范围110°～125°为优,90°～109°为良,60°～89°为可,60°以下为差)、行走的改善情况及并发症发生情况。结果:术后平均随访6个月,按实际完成处理,24例均进入结果分析。①膝关节功能恢复评价:3个月平均活动度从54°(20°～90°)增加至103°(70°～125°),平均增加49°;优8例,良12例,可4例。半年增加至115°(75°～130°),平均增加61°(40°～100°);优10例,良11例,可3例。无一例患者发生再粘连,步态改善,跛行消失,关节无肿痛,能交替上下楼,有22例患者自觉关节不灵活,增加活动后可缓解。②术后并发症:10例患者出现关节腔积血,行关节穿刺治疗;有1例发生关节内感染,在关节镜下冲洗,控制感染后,3周后再次手法松解,膝关节屈曲达95°;无骨折、韧带断裂等严重并发症发生。结论:采用关节镜下松解的方法治疗关节粘连具有创伤小,并发症少等优点;结合早期膝关节的伸屈主被动训练能有效的维持和巩固手术效果,加快膝关节功能恢复,预防再次粘连。