Clinical use of the johnson anti-shear device: how and why to use it

The purpose of this paper is to describe the clinical utilization of the Johnson Anti- Shear Device. This device presents a method of controlling the anterior shear forces developed during isokinetic exercise on a Cybex(R) ll or Orthotrone system. The antishear device allows the therapist to alter the amount of anterior shear developed during exercise, thus allowing the therapist to individualize the rehabilitation protocol. This is of special significance following anterior cruciate injury. The clinical use of this device will allow the therapist to more safely develop quadriceps exercise programs with their anterior cruciate deficient knee patients. J Orthop Sports Phys Ther 1986;7(6):304-309.     

Comparison of Quadriceps and Hamstring Torque Values during lsokinetic Exercise

Maximal voluntary muscular torque output of the quadriceps and hamstrings during isokinetic exercise was studied. Both knees of 50 male and 50 female subjects between the ages of 25 and 34 were tested at 60, 180, and 300" per second on the Cybex II isokinetic dynamometer. The means, standard deviations, ranges, absolute value differences, and analysis of variance were calculated on the torque values. The findings were that 1) torque values decreased as speed of exercise increased; 2) quadriceps torque values were significantly greater than the hamstrings at each test speed; 3) the ratio of hamstring torque values to quadriceps torque values significantly increased as the test speed increased; 4) dominant and nondominant knee torque values differed significantly for the males but not for the females; 5) the ratio of nondominant to dominant knee torque values was equal to or greater than 97% in all tests; and 6) the absolute difference in torque values between each subject's knees was 12 foot-pounds or less. J Orthop Sports Phys Ther 1981;3(2):48-56.     

Investigation of the Physiological Overflow Effect from Speed-Specific lsokinetic Activity

This article investigates the concept of physiological overflow during speed-specific isokinetic exercise. The idea was tested on 30 volunteers; 14 female, 16 male; mean age 24.5 years, age range 17-29 years; who were subjected to a repeated m o r e s experimental design. Testing involved 5 repetitions of knee extension/flexion at the velocity spectrum speeds of 80, 7 20, 180,240, and 300 degrees /sec preceded by a warm-up at 3 gradient submaximal repetitions and 1 maximal effort at each speed. The experimental treatment consisted of isokinetic exercise of the knee musculature to the level of 50% quadriceps fatigue at the speed of 180 degrees /sec in a format of 3sessions per week over a period of 8 weeks. Analysis of variance testing with repeated measures revealed statistically significant differences in quadriceps and hamstrings function for peak torque, torque acceleration energy, and watts average power at all velocity spectrum speeds over the period of experimentation. It was concluded that a +/-120 degrees /sec physiological overflow of exercise effects to both slower and faster speeds existed during the program of isokinetic activity. J Orthop Sports Phys Ther 1987;9(3):106-110.     

Comparison of Johnson Anti-Shear Accessory and Standard Dynamometer Attachment for Anterior and Posterior Tibial Translation during Isometric Muscle Contractions

The purpose of this study was to compare the effectiveness of the Johnson Anti-Shear Accessory (JASA) and the standard dynamometer accessory (SDA) in controlling tibial translation for isometric knee flexion and extension exercise on the Cybex(R) II. The subject was a 26-year-old male with known anterior cruciate ligament (ACL) deficiency of the left knee. The subject performed maximum isometric muscle contractions for JASA and SDA conditions. Medial-lateral roentgenograms were obtained while the subject maintained isometric knee flexion and extension muscle contractions at three positions of knee flexion. JASA and SDA trials were analyzed for one extension position and one flexion position. The authors compared JASA and SDA conditions for magnitude of contact pad force and for degree of tibial translation evidenced on the roentgenograms. Tibial translation was greater and contact pad force was less for the SDA condition than the JASA condition. The results suggest the JASA is useful in protecting ACL surgical reconstructions, the partially torn ACL, and secondary supporting structures of the knee as patients perform isometric exercise on Cybex instrumentation. J Orthop Sports Phys Ther 1990;11(11):547-553.     

Effects of Stabilizing the Nontested Lower Extremity during lsokinetic Evaluation of the Quadriceps and Hamstrings*

The purpose of this investigation was to determine if stabilization of the nontested lower extremity influences the peak torque generated by the knee musculature of the opposite extremity during isokinetic testing. The subjects included 15 males and 15 females, between 18 to 30 years of age, who had no history of right knee pain or pathology. A Cybex I isokinetic dynamometer was used to measure the torques generated by the quadriceps and hamstring muscles of the right lower extremity during flexion and extension. Each subject performed two trials of extension and flexion of the right knee; each trial consisted of one set of three contractions at 60 degrees /sec and one set at 180 degrees /sec. One trial was performed with the left lower extremity stabilized and the second trial was performed without stabilization. The results demonstrate that the peak torques generated by the quadriceps and hamstrings of the tested extremity are not significantly influenced by stabilization of the opposite lower extremity at the speeds tested.J Orthop Sports Phys Ther 1984;6(1):18-20.     

Strength relationship of the knee musculature: effects of gravity and sport*

The purposes of this study were to examine the effects of gravity and sport on the hamstrings-quadriceps strength relationships. The peak torques at four speeds of isokinetic exercise (60, 180, 240, 300 degrees /sec) were determined for 20 male college track athletes, including 10 sprinters and 10 distance runners. The runners were tested on a Cybex(R) II isokinetic dynamometer. Peak torque measurements were corrected for the effects of gravity. Results of the present study showed that: 1) the effects of gravity significantly alters the hamstrings to quadriceps ratio at all velocities, and 2) there is no statistically significant difference in the hamstrings quadriceps strength ratios between the two groups of athletes except at 300 O/sec. At that speed, sprinters had a higher ratio than distance runners. J Orthop Sports Phys Ther 1986;7(5);232-235.     

Peak torque and total work relationship in the thigh muscles after anterior cruciate ligament injury

The purpose of the present study was to 1) assess the relationship between the isometric and isokinetic peak torques (speed of movement 0, 60, 180 degrees /sec) and the total work output of multiple contractions (180 degrees /sec) of the quadriceps and hamstrings in 36 patients having a chronic anterior cruciate ligament (ACL) insufficient knee joint, and 2) determine the possible association of these muscle function parameters with the subjective and functional outcome of the ACL insufficient knees. At every test speed the Pearson product moment (r) and the Spearman rank (r,) correlation coefficients between the peak torque and the total work were highly significant for the quadriceps and hamstrings in the uninjured (r = 0.71-0.93, rs = 0.70-0.90) as well as in the anteriorly unstable (r = 0.82-0.89, rs = 0.79-0.86) knees. All correlation coefficients were higher at the highest speed (180 degrees /sec) of the isokinetic test (r = 0.85-0.93, rs = 0.85-0.90) than at the other speeds (0 and 60 degrees /sec) (r = 0.71 -0.90, rs = 0.70-0.85) obviously since the total work was registered at that speed. Both the peak torque and total work parameters of quadriceps as well as hamstrings correlated significantly with the subjective and functional outcome of the ACL insufficient knees (r = 0.75-0.84, rs = 0.76-0.85): the better the muscular function the better the outcome. In conclusion, in anteriorly unstable knees the total work analysis offers little additional information to that attained by the peak torque measurements. J Orthop Sports Phys Ther 1988;10(3):97-101.     

Controlling Anterior Shear During lsokinetic Knee Extension Exercise

The purpose of this paper is to present a means of controlling anterior shear force at the knee during isokinetic exercise. A dual-pad attachment to existing exercise equipment allows selection of the degree of anterior shear placed on the knee during exercise, ranging from a value which apparently places minimal stress on ligamentous restraints, through intermediate shear levels, to a value nearly that of standard exercise equipment. The special problems associated with anterior cruciate ligament (ACL) involvement are reviewed in terms of ACL function, failure, and healing. Calculated loading configurations illustrate the effect on shear afforded by the device. A pilot roentgenographic study indicates restoration of normal tibiofemoral alignment and joint surface velocity vectors during isometric extension with the device. This preliminary finding correlates with clinical observation. Clinical application includes isokinetic exercise of the chronically lax knee and rehabilitation of the knee after ACL repair or reconstruction. J Orthop Sports Phys Ther 1982;4(1):23-31.     

Anterior tibial translation during different isokinetic quadriceps torque in anterior cruciate ligament deficient and nonimpaired individuals

STUDY DESIGN: Factorial quasi-experimental design. OBJECTIVES: To quantify the effect of different levels of isokinetic concentric and eccentric knee extensor torques on the anterior tibial translation in subjects with anterior cruciate ligament (ACL) deficiency. Electromyogram (EMG) activity of 4 leg muscles was recorded in order to detect any co-activation of extensors and flexors. BACKGROUND: The rehabilitation after an ACL injury is of importance for the functional outcome of the patient. In order to construct a rehabilitation program after that injury, it is important to understand the in vivo relationships between muscle force and tibial translation. METHODS AND MEASURES: Twelve patients with unilateral ACL injury and 11 uninjured volunteers performed 36 repetitions of a quadriceps contraction at different isokinetic concentric and eccentric torque levels, on a KinCom machine (60 degrees x s(-1)), with simultaneous recordings of tibial translation (CA-4000) and EMG activity from quadriceps and hamstrings muscles. Tibial translations and EMG levels were normalized to the maximum of each subject. RESULTS: The individual anterior tibial translation increased with increased quadriceps torque in a similar manner in both quadriceps contraction modes in all legs tested. During concentric mode, translation was similar in all groups, but during eccentric mode, the mean translation was 38% larger in the ACL injured knees. No quadriceps-hamstrings co-activation occurred in any test or group. CONCLUSIONS: An ACL deficient knee can limit the translation within a normal space during concentric muscle activity but not during eccentric activity. That limitation depends on other mechanisms than hamstrings co-activation.     

Hamstrings cocontraction reduces internal rotation, anterior translation, and anterior cruciate ligament load in weight-bearing flexion.

Strengthening of the hamstrings is often recommended following injury and reconstruction of the anterior cruciate ligament. It has been suggested that hamstrings activity stabilizes the knee and reduces anterior cruciate ligament load during weight-bearing flexion; however, the effects of hamstrings cocontraction on the kinematics and mechanics of the normal knee have not been assessed at physiological load levels. The aim of this study was to determine whether the addition of hamstrings force affects knee rotations, translations, and joint and quadriceps force during flexion with loads at physiological levels applied to the muscles and joints. Eight cadaveric knee specimens were tested with a servohydraulic mechanism capable of applying controlled dynamic loads to simulate quadriceps and hamstrings muscle forces throughout a physiological range of motion. A constant vertical load of physiologic magnitude was applied to the hip, and quadriceps force was varied to maintain equilibrium throughout flexion. Two conditions were tested: no hamstrings force and a constant hamstrings force equivalent to the vertical load. Hamstrings force significantly reduced internal rotation (p<0.0001) and anterior translation (p<0.0001), increased quadriceps force (p<0.0001) and normal resultant force on the tibia (p<0.0001), and reversed the direction of the shear force on the tibia (p<0.0001). These results suggest that hamstrings strengthening following anterior cruciate ligament injury may benefit anterior cruciate ligament-deficient and reconstructed knees by reducing the load in the ligament; however, they also imply that this comes at the expense of efficiency and higher patellofemoral and joint forces.     

Muscle exercise after the anterior cruciate ligament reconstruction of the knee--Part I: The force given to the anterior cruciate ligament by separate isometric contraction of the quadriceps or the hamstrings

An attempt was made to investigate the force of the anterior cruciate ligament (ACL) in separate isometric contraction (IMC) of the quadriceps and the hamstrings by means of the analysis of two-dimensional models. In IMC of the quadriceps, the average value of the anterior drawer force (ADF) was equal to 14% of the quadriceps tension at the knee flexion of 5 degrees. The ADF decreased as the flexion angle increased. The average value of the angles, where the ADF became zero, was 45.3 degrees, and the standard deviation was 12.5 degrees. In IMC of the hamstrings, the posterior drawer force was given at the every flexion angle. Clinical relevance: In the early stage of the rehabilitation after the ACL reconstruction, the quadriceps exercise by IMC should be performed at the knee flexion of more than 70 degrees (average + 1.96 X S.D.). The hamstrings exercise by IMC can be carried out regardless of flexion angle.     

Exercise after anterior cruciate ligament reconstruction. The force exerted on the tibia by the separate isometric contractions of the quadriceps or the hamstrings

The anterior or posterior drawer force exerted on the tibia by the separate isometric contractions of the quadriceps or hamstrings at various angles of knee flexion was examined in 20 healthy males. A two-dimensional model was analyzed using roentgenographic films. In separate isometric contractions of the quadriceps, the mean value of the anterior drawer force was equivalent to 14% of the tension of the quadriceps at 5 degrees knee flexion. The value decreased with the increase in the angle of knee flexion. The mean angle at which the anterior drawer force became zero was 45.3 degrees +/- 12.5 degrees. When the angle was increased further, the posterior drawer force gradually increased. In separate isometric contractions of the hamstrings, the posterior drawer force was exerted at all angles of flexion. Thus, during the early stage of rehabilitation after the anterior cruciate ligament injury, the quadriceps exercise by isometric muscle contraction should be performed with the knee flexion at more than 70 degrees (mean +/- 1.96). Exercise of the hamstrings by isometric muscle contractions can be carried out regardless of flexion angle.     

Quadriceps protects the anterior cruciate ligament.

The aim of this study is to show that the quadriceps is the primary muscular restraint to anterior tibial translation during closed kinetic chain activities such as running, jumping, walking, and standing. It is my hypothesis that the quadriceps vector is directed superiorly during open kinetic chain knee extension and inferiorly during closed kinetic chain knee extension. My methods involve vector analysis based on a lateral radiograph of the normal human knee and muscle ultrasound. My results show that the quadriceps vector is directed superiorly for open kinetic chain knee extension and inferiorly for closed kinetic chain knee extension. The inferiorly directed quadriceps vector has an anterior femoral-tibial or posterior tibial-femoral component, which protects the anterior cruciate ligament (ACL) from anterior tibial-femoral shear. Therefore during closed kinetic chain activities, the quadriceps protects the ACL regardless of the activity of the hamstrings. Given that the quadriceps is much stronger than the hamstrings, has better leverage at low knee flexion angles, and a favorable vector with regard to the ACL during closed kinetic chain activities, and since most activities of daily living, sports, and non-contact ACL injuries occur with the foot on the ground, then it can be concluded that the quadriceps is the primary ACL protagonist. My findings have the following implications: (1) weak quadriceps are a risk factor for non-contact ACL injuries, (2) strong quadriceps are important for ACL injury prevention and rehabilitation, and (3) preservation of quadriceps strength is an important surgical goal.     

Muscle exercise after anterior cruciate ligament reconstruction. Biomechanics of the simultaneous isometric contraction method of the quadriceps and the hamstrings

Biomechanical analysis of two-dimensional models composed from roentgenographic pictures and electromyographic analysis on simultaneous isometric contraction exercises of the quadriceps and hamstrings were conducted in 20 healthy adult males. During simultaneous isometric contraction at 5 degrees knee flexion, an anterior drawer force equivalent to 15% of the tension of the quadriceps was exerted to the tibia, and decreased with increased angle of flexion. The mean angle at which this force became zero was 7.4 degrees, with a standard deviation of 5.0 degrees. When the angle increased further, a posterior drawer force to the tibia occurred and gradually increased. Each tension of the quadriceps or hamstrings during maximum simultaneous isometric contraction of the quadriceps and hamstrings was estimated as 30%-60% of that during separate isometric contractions of each muscle. In the early stage of the rehabilitation after the anterior cruciate ligament reconstruction, the simultaneous isometric contraction of the quadriceps and the hamstrings is useful as one of the muscle exercise methods because it can be performed safely with the knee position near the full extension and can generate sufficient muscle force to be an effective exercise.     

Effects of isokinetic soreness-inducing exercise on blood levels of C-reactive protein and creatine kinase

This study examined whether acute inflammation was the mechanism underlying delayed muscle soreness (DMS) by assessing the effect of soreness-inducing exercise on blood levels of C-reactive protein (CRP), an acute inflammation marker. Sixteen female college students (= 20.6 +/- 2.6 years) performed three sets of 35 isokinetic contractions of the knee flexors and extensors at 120 degrees /set on a Biodex isokinetic dynamometer. Group 1 (N = 8) exercised eccentrically and Group 2 (N = 8) concentrically at an intensity of 80% of a concentric 120 degrees /set peak torque. Pre-exercise and 1, 24, 48 and 72 hours postexercise, DMS of the quadriceps femoris (QF) and hamstrings (HA) were assessed and blood samples were collected for creatine kinase (CK), an indicator of muscle damage, and CRP, which was measured by a radial immunodiffusion procedure. The mean CK values 72 hours postexercise were 14,856 and 360 IU/L for groups 1 and 2, respectively. No significant elevations of CRP occurred in either group. ANOVAs using a split plot factorial design found Group 1 to have significantly larger logarithmic CK elevations, ranked QF soreness, and ranked HA soreness than Group 2. In contrast to myocardial infarct patients and marathon runner investigations, this study did not demonstrate abnormal elevations of CRP when increases in CK were induced. With high-repetition submaximal isokinetic exercise, eccentric contractions induce higher levels of muscle damage and DMS than concentric contractions. Further, the hamstrings are more susceptible to DMS than the quadriceps femoris when eccentric isokinetic exercise is performed at the same relative intensity. J Orthop Sports Phys Ther 1992;16(5):208-214.     

Effects of Speed, Hip and Knee Angle, and Gravity-on Hamstring to Quadriceps Torque Ratios

The purpose of this study was to determine the effects of speed, hip angle, knee angle, and gravity on hamstring to quadriceps (H/Q) torque ratios. Eighteen healthy college-aged men performed three maximal-effort knee extension and flexion repetitions on a Cybex II isokinetic dynamometer at speeds of 15 and 90 degrees /sec. Hamstring and quadriceps torques were measured at 15, 30, 45, 60, 75, and 90 degrees of knee flexion and at the angles at which peak torque occurred. These torques were also measured at 5 and 120 degrees of hip flexion. H/Q torque ratios were calculated with these torques, both corrected and uncorrected for gravitational effects. Analysis of variance revealed that gravity-corrected ratios decreased with increased knee angles from 15 to 60 degrees . The higher hip angle at each speed produced higher ratios at knee angles between 30 and 90 degrees . The effect of speed on ratios was variable and interacted with hip and knee angle. Correction for gravity reduced the ratios at all knee angles except 90 degrees . H/Q torque ratios at selected knee angles ranged from 0.20 to 2.00, differed from H/Q peak torque ratios 40% of the time, and did not always correlate highly with H/Q peak torque ratios (range: r = 0.50-0.90). Thus, H/Q peak torque ratios were not indicative of H/Q torque ratios at selected knee angles. Thus, knee angle-specific H/Q torque ratios may provide different, and perhaps more useful, information about hamstring and quadriceps function than do H/Q peak torque ratios.J Orthop Sports Phys Ther 1988;9(8):287-291.     

Morphology of hamstring torque‐time curves following acl injury and reconstruction: mechanisms and implications

The purposes of this study were (i) to examine the effects of anterior cruciate ligament (ACL) status on hamstring force steadiness, peak hamstring strength, quadriceps (antagonist) activation, and physical performance, and (ii) to evaluate the associations of physical performance with hamstring steadiness and hamstring strength. Thirteen subjects with unilateral deficiency of the ACL (ACLD), 39 matched subjects with unilateral reconstructed ACL (ACLR; n = 25 with bone‐patella tendon‐bone (ACLR‐PT) graft and n = 14 with combined semitendinosus and gracilis tendon (ACLR‐STGT) graft) and 33 control subjects participated. Each subject performed maximal‐effort isokinetic knee flexion repetitions at 180° s^?1 with electromyography (EMG) electrodes attached to their medial and lateral quadriceps muscles. Physical performance was assessed using the single‐limb long hop for distance. Wavelet‐derived mean instantaneous frequency (Mif) of flexor torque‐time curves was significantly (p < 0.05) higher (i.e., less smooth) in ACLR‐STGT subjects compared to the ACLD, ACLR‐PT and control subjects. No significant differences existed for peak hamstrings strength (i.e., peak torque produced) or quadriceps antagonist EMG activity. Positive correlations were identified between hamstrings force steadiness and quadriceps antagonist activity for ACLD (r = 0.797), ACLR‐PT (r = 0.467), and ACLR‐STGT (r = 0.628) subjects. For ACLR‐STGT subjects, reduced hamstrings force steadiness associated with poorer long‐hop performance (r = ?0.695). Reduced steadiness amongst ACLR‐STGT subjects may reflect motor output variability of the antagonist (i.e., quadriceps dyskinesia) and/or agonist musculature—a maladaptive feature which potentially contributes to poorer single‐limb hop performance. Measures of hamstring force steadiness in combination with traditional measures of peak hamstring strength provide valuable clinical information regarding knee joint function following ACL injury/ACLR. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:907–914     

Specificity of training on computer obtained isokinetic measures

The purpose of this study was to examine the effects of 7 weeks of isokinetic training on knee extension and flexion peak torque, torque acceleration energy, average power, and total work, and to observe the relationship between the increases in each of the isokinetic measures. Seventeen intercollegiate lacrosse players served as subjects and were assigned to an exercise or control group. Isokinetic training consisted of 3 sets of 25 repetitions at 270 degrees /sec, 3 days per week for 7 weeks on an orthotron isokinetic dynamometer. All subjects were tested on a Cybex(R) isokinetic dynamometer at speeds of 60, 180, and 270 degrees /sec pre- and post-exercise or control condition. Results showed a significant training effect at 270 degrees /sec for knee extension peak torque, torque acceleration energy, and average power, and knee flexion torque acceleration energy. High correlations were observed between the increases in peak torque, average power, and torque acceleration energy. These findings suggest that increases in average power, peak torque and instantaneous power may be expected as a result of isokinetic exercise training in healthy athletes. J Orthop Sports Phys Ther 1989;10(12):495-498.     

Analysis of the shear force exerted on the tibia during standing on bilateral legs with knee flexion

Biomechanical analysis of the two-dimensional models composed of roentgenographic pictures and electromyographic analysis about the shear force (Fs) exerted on tibia during standing on bilateral legs was conducted in 21 young adult males. The simultaneous contraction of the quadriceps and hamstrings was observed in all electromyograms (EMGs). Amplitude observed on EMGs of the hamstrings increased as the trunk flexion angle increased. The calculated average values of Fs were negative at every knee flexion angle; Negative value means posteriorly directed force. As the trunk flexion angle increased, posterior drawer force increased at knee flexion angles of 30 degrees and 60 degrees. The simultaneous contraction of the quadriceps and the hamstrings was considered to represent the main factor that influenced these results. The standing on bilateral legs with knee and trunk flexion was considered to be applicable in the early stages after anterior cruciate ligament reconstruction.