Muscular and tibiofemoral joint forces during isokinetic concentric knee extension

The purpose of this study was the examination of muscular and tibiofemoral forces during concentric isokinetic knee extension at angular velocities ranging from 30 to 210 deg s(-1), using a two-dimensional biomechanical model. Five males without knee joint injury history participated in the study. The maximum moment ranged from 226.2 Nm at 30 deg s(-1) to 166.4 Nm at 210 deg s(-1). The maximum muscular force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1). The compressive tibiofemoral force ranged from 7.5 times body weight at 30 deg s(-1) to 5.7 at 210 deg s(-1) and the shear tibiofemoral force ranged from 0.9 to 0.8 times body weight respectively. These results indicate that the forces developed during maximal isokinetic knee extension are significantly reduced relative to other powerful dynamic activities but are higher than joint forces during simple walking and cycling activities. Appropriate precautions and adjustment of the isokinetic protocol are required in the final phases of joint injury rehabilitation. RELEVANCE: Isokinetic dynamometry has widespread applications in rehabilitation and training of muscle function. It is therefore important to examine the joint and muscular forces under different conditions in order to alter rehabilitation and training programmes and prevent exercise-induced injuries.     

Knee joint forces during isokinetic knee extensions: a case study.

OBJECTIVE: To describe the procedures to obtain knee joint forces during isokinetic knee extensions and evaluate the patellar ligament force, quadriceps tendon force, patellofemoral and tibiofemoral joint forces at different speeds measured from a female subject. DESIGN: A technical note with a case study. BACKGROUND: Two previous studies examined knee joint forces during isokinetic knee extension using different techniques reported inconsistent findings. Also, the highest speed used in these two studies (180 degrees s(-1)) were much lower than the maximum speeds available in modern isokinetic dynamometers. METHODS: The subject performed maximum effort isokinetic knee extensions at 16 different speeds ranged from 25 to 400 degrees s(-1). The gravitational and inertial effects were included in determining the resultant knee torque. Knee radiographs were used to determine the knee joint geometry. A combination of knee torque and geometric data was used to determine different knee joint forces. RESULTS: All knee joint forces were found to decrease with increasing isokinetic speed. The tibiofemoral shears forces indicated that the anterior cruciate ligament was loaded throughout the range of motion. CONCLUSIONS: The magnitudes of knee joint forces are largely depending on the knee torque values. RELEVANCE: Isokinetic knee extensions are considered appropriate for the early part of the rehabilitation for patients with knee dysfunctions due to the lesser demand of coordination. However, to reduce the knee joint forces, submaximal efforts at lower speeds or maximal efforts at higher speeds are recommended.     

Knee joint mechanics under quadriceps--hamstrings muscle forces are influenced by tibial restraint

BACKGROUND: To investigate the role of quadriceps and hamstrings muscle recruitments on knee joint mechanics, measurement studies constrain the tibial anterior-posterior translation at a point away from the joint. This generates a restraining force perpendicular to the tibia thus introducing an artefact shear force that likely alters joint mechanics and forces in cruciate ligaments. METHODS: A 3D nonlinear finite element model of the entire knee joint, including tibiofemoral and patellofemoral joints, was used to investigate joint mechanics in flexion (0 degrees -90 degrees ) under isolated and combined hamstrings and quadriceps activation. The effect of tibial restraint at two locations on results was studied and compared with the reference boundary condition of tibia constrained by pure moments. FINDINGS: Tibial restraint by a force rather than a pure moment substantially influences the joint response. For identical forces, hamstrings have much greater moment generating capacity at larger flexion angles while quadriceps are more effective at smaller angles. INTERPRETATION: Tibial constraint by a restraining force rather than a pure moment causes an artefact force on the joint that vary with muscle forces and restraining location. These artefact shear forces, especially when placed closer to the joint, considerably reduce forces in cruciate ligaments; in anterior cruciate ligament at near full extension and in posterior cruciate ligament at larger flexion angles. The beneficial effects of muscle co-contraction in reducing anterior cruciate ligament forces at near full extension and in posterior cruciate ligament forces at near 90 degrees , however, disappear as the restraint on the tibia approaches the joint. The artefact forces could distort results and their interpretations.     

Efficacy of isokinetic exercise on joint position sense and muscle strength in patellofemoral pain syndrome

OBJECTIVE: The objective of this study was to demonstrate the impairment of knee joint position sense in individuals with patellofemoral pain syndrome and investigate the effects of isokinetic exercise on knee joint position sense and muscle strength. DESIGN: A total of 24 male patients complaining of anterior knee pain caused by overexertion and 24 male healthy individuals without symptoms were included for this investigation. Isokinetic exercise protocol was carried out at angular velocities of 60 degrees/sec and 180 degrees/sec. These sessions were repeated three times per week and lasted for 6 wks. At the beginning and after 6 wks of knee passive joint position sense, quadriceps and hamstring muscle strength and pain assessments were performed. RESULTS: After the isokinetic exercise, flexion peak torque (P < 0.05), extension peak torque (P < 0.01), flexion total work (P < 0.001), extension total work (P < 0.001), passive reproduction of knee joint position sense for 40 degrees of flexion (P < 0.05) and 50 degrees of extension (P < 0.01), and pain score (P < 0.001) improved significantly in the patellofemoral pain syndrome group. CONCLUSION: Isokinetic exercises have positive effects on passive position sense of knee joints, increasing the muscular strength and work capacity. These findings show that using the present isokinetic exercise in rehabilitation protocols of patients with patellofemoral pain syndrome not only improves the knee joint stabilization but also the proprioceptive acuity.     

等速离心肌力训练治疗膝关节骨关节炎的研究

运动Ｃｙｂｅｘ－６０００型等还肌力测试和训练系统对２０例膝关节骨关节炎患者进行 量等速离心肌力训练，观察训练对患膝肌力、疼痛及下肢功能的影响。结果表明：经过４周的训练，患膝 伸肌群各项测试指标均有不同程度提高，疼痛明显缓解，下肢功能显著改善。说明亚极量等速离心训练对膝关节骨关节炎２的近期疗效是明显的。     

Improvement of muscle strength in osteoarthritic knee patients after intraarticular knee injection of hyaluronan

OBJECTIVE: The objective of this study was to investigate whether the knee concentric and eccentric muscle strengths can be improved in patients with bilateral knee osteoarthritis after intraarticular hyaluronan injections. DESIGN: A total of 25 patients with bilateral knee osteoarthritis and with a radiographic Ahlb?ck grading scale of I or II participated in this study. One session of intraarticular knee injection of hyaluronan was given to both knees (weekly intraarticular knee hyaluronan injections for a total of 5 wks). Knee concentric and eccentric muscle strengths were recorded between 10 and 90 degrees of knee flexion. The recordings were done on two angular velocities, 80 and 240 degrees/sec. This study took place in a tertiary medical center with a gait laboratory and a KIN-COM isokinetic dynamometer. RESULTS: An increase in concentric and eccentric muscle strength adjusted for body weight (P < 0.01) was observed in both knees, ranging between 5.1% and 27.7%. CONCLUSION: The decreased knee muscle contraction strength (concentric and eccentric) can be improved in knee osteoarthritis patients with an Ahlb?ck grading scale of I or II after five weekly intraarticular knee injections of hyaluronan.     

Does saddle height affect patellofemoral and tibiofemoral forces during bicycling for rehabilitation?

The aim of the present study was to measure saddle height effects on knee joint load. Nine uninjured non-cyclists were evaluated in three saddle heights: 100% of trochanteric height-REF; 103% of REF-HIGH; and 97% of REF-LOW. Two-dimensional sagittal plane force applied on the pedal and kinematics were recorded. After inverse dynamics of the lower limb, knee resultant force was computed as tibiofemoral normal and shear components and compressive patellofemoral force. Peak patellofemoral compressive force and peak compressive and shear tibiofemoral forces did not differ when saddle height was changed. Knee angle at the lower crank position increased at LOW compared to REF and HIGH saddle height (p<0.02). Small saddle height changes (±3%) did not affect knee joint load, at low workloads on uninjured subjects, while changes in knee angle did not relate to effects on joint forces. These findings suggest that setting saddle height by knee angle secures the maintenance of joint load at low workloads on uninjured subjects.     

关节镜术后等速训练对膝半月板损伤恢复的影响

背景:运动损伤后的康复训练是保持和减缓运动能力的重要途径,开展此领域的研究具有重要意义。目的:观察膝半月板损伤施以关节镜手术后,等速训练对膝关节功能恢复及关节周围肌肉力量的影响。设计:病例-对照观察。单位:辽宁警官高等专科学校警训系。对象:于2004-09/2005-01选择大连医科大学附属医院外科收治的单侧膝关节半月板急性损伤患者22例为观察对象。随机数字表法分为实验组和对照组,各11例。方法:实验组和对照组患者进行关节镜手术治疗,对照组进行常规封闭、理疗、按摩等方法恢复。实验组患者术后第2～4天开始功能恢复,3周后采用Cybex-6000型等速运动测试仪对患侧膝屈伸肌进行等速运动训练。主要观察指标:不同测试速度[60,120,180(°)/s]时的屈伸肌峰力矩、单次最大做功量、力矩加速能、平均功率。结果:纳入患者22例,均进入结果分析。①关节镜手术配合等速肌力训练后,膝关节运动范围加大,训练前患膝的最大屈曲角度为(132±25)°,训练后患膝的最大屈曲角度为(158±21)°,经配对t检验,两者差异有非常显著性意义(P<0.01)。而对照组手术后最大屈曲角度为(133±31)°,实验结束后最大屈曲角度为(139±34)°,差异无显著性意义(P>0.05)。且两组实验后差异有显著性意义(P<0.05)。②实验组膝屈伸肌峰力矩、单次最大做功量、力矩加速能及平均功率在60,120,180(°)/s的变化与对照组相比差异均有显著性意义(P<0.05)。结论:膝关节等速训练,可加速膝半月板损伤后的康复过程,对增加膝关节周围肌肉力量、保持膝关节的稳定性和运动能力均具有重要的意义。     

Isometric and isokinetic measurement of hamstring and quadriceps strength.

This study evaluates quadriceps strength at varying movement velocities in a group of healthy subjects. Specific objectives included (1) investigating the effect of angular velocity on peak torque (PT) (2) investigating the effect of angular velocity on joint angle at peak torque (JAPT) and (3) evaluating whether the use of a relatively new isokinetic testing device yields new insights to previously accepted relationships between angular velocity and PT or JAPT. Twenty healthy subjects were tested for isometric and isokinetic knee extension and flexion strength on a LIDO Active Isokinetic Rehabilitation System at velocities of 0 degrees, 60 degrees, 120 degrees, and 180 degrees/sec. Isometric PT (0 degrees/sec) was found to be highly correlated with isokinetic PT for both extensors and flexors at all velocities (r = .88-.93, p less than .01). PT declined significantly as angular velocity increased for both extension (p less than .01) and flexion (p less than .05). A relationship between isometric and isokinetic JAPT was significant for extension only at 60 degrees and 180 degrees/sec (r = .48-.52, p less than .05). These results indicate that knee isometric and isokinetic PT as measured on the LIDO Active system are highly related for both extension and flexion. PT declined as isokinetic angular velocity increased. Isometric and isokinetic JAPT are significantly related only for extension.     

Conséquences et prédiction des lésions musculaires des ischiojambiers à partir des paramètres isocinétiques concentriques et excentriques du joueur de football professionnelConsequences and prediction of hamstring muscle injury with concentric and eccentric isokinetic parameters in elite soccer players

OBJECTIVE: To know if isokinetic parameters identify previous hamstring (H) injury and predict a new muscle injury in high-level soccer player. METHOD: Concentric (con) and eccentric (ecc) isokinetic torque was measured at the angular speed of 60 degrees /s in 28 elite soccer players (23 years +/- 3.3; 74 kg +/- 7.5; 178 cm +/- 6.5). First, 11 players, victims of 15 moderate or major hamstring injuries in the preceding 2 years, were compared with 17 players without previous hamstring injury. Comparisons were carried out from isokinetic knee flexors-extensors ratios [Hcon/Qcon and Hecc/Qcon] and bilateral knee flexors ratios [Hcon/Hcon and Hecc/Hecc]. Secondly, all the population was followed during 12 months and the isokinetic muscular profile of players who presented a recurrence or a new hamstring muscle injury was analysed. RESULTS: A concentric ratio hamstring-to-quadriceps lower than 0.6 and a hamstring asymmetry of more than 10% do not allow to identify previous hamstring injury. On the other hand, the mixed ratio eccentric hamstring-to-concentric quadriceps lower than 0.6 represents the best indicator (probability: 77.5%). The rate of recurrence is 30% (three cases of 10) and the rate of new hamstring muscle injury is 31% (five cases of 16) (P > 0.05). One of the five injured soccer players presented a concentric ratio hamstring-to-quadriceps lower than 0.6 and no player presented a mixed ratio lower than 0.6. However, four of the five injured players presented a concentric and an eccentric asymmetry. But, it is the strongest side, which presented a new hamstring muscle injury. CONCLUSION:The mixed ratio eccentric hamstring-to-concentric quadriceps lower than 0.6 identify a previous hamstring injury despite the resumption of competitive soccer. However, this ratio and the others isokinetic studied parameters do not predict a recurrence or a new hamstring muscle injury.     

Use of ultrasound to increase effectiveness of isokinetic exercise for knee osteoarthritis

OBJECTIVE: To investigate the effects of ultrasound (US) in isokinetic muscle strengthening exercises on functional status of patients with knee osteoarthritis (OA). DESIGN: Effectiveness of isokinetic muscle strengthening exercises for treatment of periarticular soft tissue disorders was compared with and without pulsed and continuous US. SETTING: Outpatient exercise program in a Taiwan medical university hospital. PARTICIPANTS: One hundred twenty subjects with bilateral knee OA (Altman grade II). INTERVENTION: Subjects were randomized sequentially into 1 of 4 groups. Group I received isokinetic muscular strengthening exercises, group II received isokinetic exercise and continuous US, group III received isokinetic exercise and pulsed US treatment, and group IV was the control group. MAIN OUTCOME MEASURES: Therapeutic effects of isokinetic exercise were evaluated by changes in ambulation speed and the Lequesne index. In addition, changes in knee range of motion (ROM), visual analog scale for pain, and muscle peak torques during knee flexion and extension were compared. Compliance in each group was recorded. RESULTS: Each treated group had increased muscle peak torques and significantly reduced pain and disability after treatment and at follow-up. However, only patients in groups II and III had significant improvement in ROM and ambulation speed after treatment. Fewer participants in group III discontinued treatment due to knee pain during exercise. Patients in group III also showed the greatest increase in walking speed and decrease in disability after treatment and at follow-up. Gains in muscular strength in 60 degrees /s angular velocity peak torques were also noted in groups II and III. However, group III showed the greatest muscular strength gains with 180 degrees /s angular velocity peak torques after treatment and follow-up. CONCLUSIONS: US treatment could increase the effectiveness of isokinetic exercise for functional improvement of knee OA, and pulsed ultrasound has a greater effect than continuous US.     

Effects of the posterior cruciate ligament reconstruction on the biomechanics of the knee joint: a finite element analysis

BACKGROUND: Previous experimental studies have been conducted to evaluate the biomechanical effects of posterior cruciate ligament reconstruction; but no consensus has been reached on the preferred method of reconstruction. METHODS: The 3D finite element mesh of a knee joint was reconstructed from computed tomography and magnetic resonance images. The ligaments were considered as hyperelastic materials. The tibiofemoral and patellofemoral joints were modeled with large sliding contact elements. The 3D model was used to simulate knee flexion from 0 degrees to 90 degrees in four cases: a knee with a "native" posterior cruciate ligament, a resected posterior cruciate ligament, a reconstructed single graft posterior cruciate ligament, and a reconstructed double graft posterior cruciate ligament. FINDINGS: A resected posterior cruciate ligament induced high compressive forces in the medial tibiofemoral and patellofemoral compartments. The pressures generated in the tibiofemoral and patellofemoral compartments were nearly the same for the two reconstruction techniques (single graft and double graft). The single graft resulted in lower tensile stresses inside the graft than for the double graft. INTERPRETATION: Firstly, a resected posterior cruciate ligament should be replaced to avoid excessive compressive forces, which are a source of cartilage degeneration. Secondly, the two types of posterior cruciate ligament reconstruction techniques partially restored the biomechanics of the knee in flexion, e.g. contact pressures were restored for pure flexion of the knee. The reconstruction techniques therefore partially restore the biomechanics of the knee in flexion. A double graft reconstruction is subjected to the highest tensile stresses.     

Reliability of knee extensor and flexor torques during continuous concentric-eccentric cycles

Peak and average torques of the knee extensors and flexors were determined on three occasions within ten days. On each occasion, 20 healthy women and 15 healthy men performed three continuous concentric-eccentric cycles with no pause between muscle actions or between cycles at 45 degrees and 90 degrees/sec angular velocities. Peak and average torques did not vary significantly or systematically over the three test occasions. Intraclass correlation coefficients (ICCs), based on one occasion, ranged from 0.79 to 0.91 for peak torques and from 0.75 to 0.88 for average torques. At 45 degrees/sec angular velocity, the ICCs for peak torque tended to be greater than those for average torque, whereas at 90 degrees/sec angular velocity the ICCs were similar whether calculated using peak or average torque. The ICCs during knee extension were greater than those during knee flexion. Eccentric muscle actions produced significantly higher torques than did concentric actions (p less than 0.01). A continuous concentric-eccentric cycle protocol which emphasizes teaching the subject to perform the test maneuvers and using at least three submaximal practice contractions and one maximal practice contraction can produce reliable isokinetic torques.     

铅球运动员主要关节等速肌力配布特征

背景：目前,国内外利用等速仪器针对铅球运动主要环节肌肉力量特征方面研究的文献较少。目的：查找铅球运动员不同速度下各主要环节肌力配布特征和存在的不足。方法：利用德国ISOMED2000等速肌力测试系统,对第十一届全运会男子铅球冠军膝关节、髋关节、腰背环节和肩关节进行慢速60（°）/s和快速180（°）/s等速测试。结果与结论：1膝关节慢速左右侧屈伸肌比值为25.6%、39.4%,快速屈伸肌比值为28.5%、29.8%,屈肌群肌力较小。2髋关节在快、慢速时,右侧伸肌群分别为左侧的2.11和1.87倍,屈肌群为1.25和1.64倍,右髋非常显著性大于左髋。3腰背环节慢速屈伸肌比值为93.3%,快速测试屈伸肌比值为84.3%。4肩关节自然位屈伸,慢速屈伸肌力右肩分别为左肩的1.27和1.34倍,快速为左肩的1.40和1.92倍。5各环节根据人体模型相对质量按膝关节为基准膝、髋、躯干、肩为1∶2.38∶3.30∶0.70。结果表明：1膝关节屈伸肌群绝对肌力、快速屈肌群肌力均较弱,肌群配备不合理。2躯干肌力在右侧最大力量伸肌群、左右侧快速伸肌群非常薄弱,增加腰背肌力伸肌训练,特别是慢速和快速肌肉力量和伸展性训练。3右侧各环节伸肌群薄弱,加强右肩伸肌群的绝对肌肉力量。     

Effect of tibial tubercle elevation on biomechanics of the entire knee joint under muscle loads

BACKGROUND: Anterior elevation of the tibial tubercle, known as Maquet procedure, is performed to reduce excessive patellofemoral contact stresses in knee joints with patellofemoral osteoarthritis and anterior pain. Previous investigations, however, have entirely focused on the likely effect of tibial tubercle elevation procedure on biomechanics of contact at the patellofemoral joint with no attention what-so-ever to associated alterations in biomechanics of the tibiofemoral joint. METHODS: Using a validated 3D nonlinear finite element model of the entire knee joint, the effect of 1.25 cm and 2.5 cm tubercle elevations on the entire knee joint biomechanics was investigated under constant quadriceps load of 411 N alone or combined with hamstrings co-activation of 205.5 N under joint angles of 0-90 degrees. FINDINGS: Results confirm the effectiveness of this procedure in reducing patellofemoral contact forces, especially at smaller flexion angles. Maximum contact stress substantially decreased at full extension but increased at 90 degrees. Substantial effects of tuberosity elevation on tibial kinematics, cruciate ligament forces, tibiofemoral contact forces and extensor lever arm were found. The posterior cruciate ligament and tibiofemoral contact forces at larger flexion angles considerably increased whereas the anterior cruciate ligament and tibiofemoral contact forces at near full extension angles decreased. Overall, the extent of changes depended on the magnitude of anterior elevation, joint flexion angle and loading considered. INTERPRETATION: Biomechanics of the tibiofemoral joint were significantly influenced by tibial tubercle elevation. Current results advocate the need for an integral view of the entire knee joint in management of various joint disorders rather than a view in which each component is considered and treated in isolation with no due attention to perturbations caused and associated consequences.     

Dynamic in vitro measurement of posterior cruciate ligament load and tibiofemoral stress after TKA in dependence on tibiofemoral slope

BACKGROUND: To prevent excessive tension on the posterior cruciate ligament, some knee prosthesis-systems offer the option of creating a posterior tibiofemoral slope of the tibial component. The objective of this study was to investigate the effect of the amount of tibiofemoral slope on the posterior cruciate ligament load and tibiofemoral contact stress after total knee arthroplasty under isokinetic in vitro conditions. METHODS: Twelve fresh frozen knee specimens were tested in a knee simulator. After implantation of the Interax I.S.A. knee prosthesis-system with a mobile bearing inlay, a bow shaped load transducer was fixed in the medial fibres of the posterior cruciate ligament. A pressure sensitive film was fixed on the femoral inlay surface. The test cycle simulated an isokinetic extension cycle from 120 degrees of flexion to full extension. First, posterior cruciate ligament load and tibiofemoral peak contact stress were measured with the tibial component implanted with a neutral tibial slope and then with 10 degrees posterior slope. FINDINGS: After implantation of the tibial component without tibial slope, posterior cruciate ligament load reached a maximum load of 29.5 N (SD 17.1 N) at 97.8 degrees knee flexion. Tibiofemoral contact stress on the medial compartment reached a maximum of 11.9 MPa (SD 2.4 MPa) on the medial compartment and 15.0 MPa (SD 6.1 MPa) on the lateral compartment. With a tibial slope of 10 degrees , posterior cruciate ligament load reached a maximum of 14.5N (SD 4.9N, P = 0.04) at 100.5 degrees knee flexion and tibiofemoral stress increased to a maximum of 13.3 MPa (SD 4.7 MPa, P = 0.38) medial and 17.4 MPa (SD 8.2 MPa, P = 0.22) lateral in knee extension. INTERPRETATION: Maximum posterior cruciate ligament load was observed at high knee flexion angles, decreasing to full extension. The implantation of the tibial base plate with 10 degrees dorsal slope reduced posterior cruciate ligament load significantly in knee flexion above 50 degrees and slightly increased tibiofemoral contact stress in knee extension. Therefore a posterior tibial slope prevents an excessive load on the posterior cruciate ligament while having little effect on tibiofemoral stress at high knee flexion angles.     

Hip and knee joint loading during vertical jumping and push jerking

Background

The internal joint contact forces experienced at the lower limb have been frequently studied in activities of daily living and rehabilitation activities. In contrast, the forces experienced during more dynamic activities are not well understood, and those studies that do exist suggest very high degrees of joint loading.

Methods

In this study a biomechanical model of the right lower limb was used to calculate the internal joint forces experienced by the lower limb during vertical jumping, landing and push jerking (an explosive exercise derived from the sport of Olympic weightlifting), with a particular emphasis on the forces experienced by the knee.

Findings

The knee experienced mean peak loadings of 2.4–4.6 × body weight at the patellofemoral joint, 6.9–9.0 × body weight at the tibiofemoral joint, 0.3–1.4 × body weight anterior tibial shear and 1.0–3.1 × body weight posterior tibial shear. The hip experienced a mean peak loading of 5.5–8.4 × body weight and the ankle 8.9–10.0 × body weight.

Interpretation

The magnitudes of the total (resultant) joint contact forces at the patellofemoral joint, tibiofemoral joint and hip are greater than those reported in activities of daily living and less dynamic rehabilitation exercises. The information in this study is of importance for medical professionals, coaches and biomedical researchers in improving the understanding of acute and chronic injuries, understanding the performance of prosthetic implants and materials, evaluating the appropriateness of jumping and weightlifting for patient populations and informing the training programmes of healthy populations.     

What change in isokinetic knee muscle strength can be detected in men and women with hemiparesis after stroke?

OBJECTIVE: To assess the intra-rater (between occasions) test-retest reliability of isokinetic knee muscle strength measurements in subjects with chronic poststroke hemiparesis and to define limits for the smallest change that indicates real (clinical) improvements for stroke patients. SUBJECTS: Fifty men and women (mean age 58 +/- 6.4 years) 6-46 months post stroke, able to walk at least 300 m with or without a unilateral assistive device. METHODS: Maximal concentric knee extension and flexion contractions at 60 degrees/s and 120 degrees/s, and maximal eccentric knee extension contractions at 60 degrees/s, with the paretic and nonparetic limbs, were performed seven days apart using a Biodex dynamometer. MEASURES: Reliability of the maximum peak torque measurements was evaluated with the intraclass correlation coefficient (ICC(2,1)), the Bland and Altman analyses, the standard error of measurement (SEM and SEM%) and the smallest real difference (SRD and SRD%). RESULTS: Test-retest agreements were high (ICC(2,1) 0.89-0.96) with no discernible systematic differences between limbs, angular velocities and modes. The SEM%, representing the smallest change that indicates a real (clinical) improvement for a group of subjects, was relatively small (8-20%). The SRD%, representing the smallest change that indicates a real improvement for a single subject ranged from 26% to 33% for concentric knee extension, from 39% to 55% for concentric knee flexion, and from 22% to 25% for eccentric knee extension. CONCLUSION: Isokinetic knee muscle strength can be reliably measured and used to detect real improvements following an intervention for single subjects as well as for groups of subjects with chronic mild to moderate hemiparesis after stroke.     

Continuous versus separate isokinetic test protocol: the effect of estradiol on the reproducibility of concentric and eccentric isokinetic measurements in knee muscles.

OBJECTIVE: To investigate the effects of estradiol on the reliability of concentric and eccentric isokinetic measurements of knee muscles and to compare the reproducibility of measurements in a continuous test protocol and a separate test protocol. DESIGN: Repeated measurements. SETTING: A university exercise physiology laboratory. PARTICIPANTS: Twenty healthy sedentary women volunteers, aged 19 to 37 years, who had regular menstrual cycles (ranging from 27 to 35 days). Subjects were randomly divided into two groups: continuous test group (n = 10) and separate test group (n = 10) and tested at the menstrual phase (days 1 to 3) and preovulatory phase (days 12 to 14) in both legs. METHODS: Continuous reciprocal flexion-extension contractions were used in the continuous test group, and separated flexion and extension contractions were used in the separate test group. Four different test protocols were designed to determine the effects of test mode and number of contractions on the isokinetic measurements: Group A, 4 reciprocal flexion-extension repetitions at each angular velocity of 60 degrees/sec and 180 degrees/sec in one leg in the continuous test group; Group B, 4 and 20 reciprocal flexion-extension repetitions at 60 degrees/sec and 180 degrees/sec, respectively, in the contralateral leg in the same group; Group C, 4 repetitions in extensors and flexors at each angular velocity of 60 degrees/sec and 180 degrees/sec with a 5-minute rest between the two muscle groups in one leg in the separate test group; and Group D, 4 repetitions at 60 degrees/sec and 20 repetitions at 180 degrees/sec for extensors and flexors with a 5-minute rest between the two muscle groups in the contralateral leg in the same group. Blood samples were analyzed for sex hormones, creatine kinase, and lactate dehydrogenase before the tests at the menstrual phase and the preovulatory phase. In addition subjective assessment of muscle soreness was made at each blood sampling. RESULTS: Concentric and eccentric peak torque, average power, total work, and endurance ratio at both angular velocities were not significantly different in the two phases of the cycle by paired observation t test for each of the four groups. Except for concentric and eccentric endurance ratios of quadriceps and hamstrings, and concentric peak torque and average power of hamstrings at 180 degrees/sec in Group D, intraclass correlation coefficients of tested variables showed correlations that were moderate to excellent (p < .05) between two phases. In addition, there were no significant correlations between estradiol and the tested variables. Resting serum creatine kinase and lactate dehydrogenase activities and the score of muscle soreness were at the baseline and not significantly different prior to the tests performed at preovulatory and menstrual phases. CONCLUSIONS: The results suggest that: (1) reproducibility of isokinetic tests during the menstrual cycle is not influenced by sex hormone fluctuations, particularly estradiol; (2) when compared with the separate test protocol used in this study, the continuous test protocol is more appropriate to measure peak torque, average power, total work, and endurance ratio for both muscle groups of the knee even if the number of contractions is changed. However, these conclusions are specific to sedentary individuals; to make more valid conclusions, further studies with different subject groups are needed.