Effects of position and speed on joint torques and knee shear after ACL injury.

PURPOSE: The purpose of this study was to assess the effect of joint position and movement speed on hip (HT) and knee (KT) extensor torque, HT/KT ratio (HKR), and anterior tibial shear (S) in presurgical-ACL deficient (PRE; N = 15), post-ACL reconstructed (POST; N = 15), and uninjured controls (CON; N = 15). METHODS: Measurements were recorded on a semirecumbent variable resistance, closed-chain dynamometer. Tests were conducted at 1 and 1.5 Hz and maximum speed at 33% and 50% 1RM. HT, KT, and S were recorded during the extension phase of the cycle (85 degrees -25 degrees of knee flexion). RESULTS: KT was greatest when the knee was more flexed, whereas HT dominated when it was more extended. This suggests that the hamstrings, as a component of the hip extensors, may generate considerable propulsive force during knee extension, which may help counter anterior tibial shear. S increased whereas KT decreased, suggesting that the quadriceps continue to generate shear force despite the decreasing mechanical advantage producing KT. Increasing knee extension speed significantly decreased S in the POST and CON groups. The correlations between KT and S changed from significantly negative to significantly positive as the knee extended from 85 degrees to 25 degrees in the POST and CON groups. This may be related to the orientation of the patellar tendon, relative to the tibial longitudinal axis that shifts from a posterior to anterior direction, as the knee extends. CONCLUSIONS: Joint position and movement speeds affect the magnitude of hip and knee torques and anterior tibial shear. Reducing the magnitude of S during heavy loads may be a normal phenomenon, and POST surgical subjects may retain or regain this function by 1 yr after surgery.

Differential responses to proprioceptive neuromuscular facilitation (PNF) stretch techniques.

The purpose of this study was to investigate the effects of sustained stretch and two common proprioceptive neuromuscular facilitation (PNF) stretch techniques on hamstring muscle activation and knee extension range of motion (ROM) in different athletic populations. Three stretch techniques: stretch-relax (SR), contract-relax (CR), and agonist contract-relax (ACR) were applied to 10 endurance athletes (EN), 10 high intensity athletes (HI), and 10 control subjects (C). The results revealed that ACR produced 89-110% greater hamstring EMG activity (P less than 0.05) and 9-13% more knee joint ROM than CR and SR, respectively. This same pattern was evident for the individual subject groups. Comparisons of mean data among the three subject groups revealed that the EN athletes generated 58-113% more hamstring EMG activity (P less than 0.05) than the HI and C groups, respectively, across all stretch conditions, whereas the EN group attained significantly less ROM than the HI and C groups for CR and ACR conditions. It was postulated that high intensity-short term activity training necessitates less hamstring resistance to knee extension than long term endurance training. The findings suggest that decreases in muscle activity may not be strongly related to increases in joint range of motion and that factors other than muscle relaxation are important in achieving increased ROM. Also, the differential effects of various stretch techniques between dissimilar athletic populations should be considered if stretch-induced injury is to be avoided.

Co-activation of sprinter and distance runner muscles in isokinetic exercise.

The purpose of this study was to investigate the extent of co-activation of quadriceps and hamstring musculature in sprinters and distance runners. Nine female intercollegiate track athletes performed maximal knee extensions and flexions on a modified orthotron isokinetic dynamometer at two speeds (100 degrees and 400 degrees X s-1). Simultaneous recordings of torque, joint position, and agonist/antagonist electromyographic activity from the quadriceps and hamstrings were computer-processed. The results revealed the hamstrings to be considerably more active during knee extension than the quadriceps during flexion. The integrated electromyographic activity of co-contracting hamstrings and quadriceps, throughout the joint range, averaged 33 and 6%, respectively, of the same muscle group during its agonist phase. Hamstring co-activation increased sharply during the last 25% of knee extension, generating 58% of the integrated electromyographic agonist activity. Co-activation of the sprinters' hamstrings was four times that of distance runners (57/14%), however, the faster speed of movement (400 degrees X s-1) increased hamstring coactivation of distance runners more acutely than sprinters in the final phase of extension. The data suggest that the hamstrings are used to a much greater extent than quadriceps for limb deceleration and that the distraction of antagonist muscle tension should be considered when analyzing agonist isokinetic torques. Furthermore, the relatively high co-activation of the hamstrings, particularly during the last 25% of extension, may induce hamstring soreness or strain in vulnerable subjects.

Contralateral hamstring (biceps femoris) coactivation patterns and anterior cruciate ligament dysfunction.

It has been postulated that coactivation of antagonist hamstring musculature during active knee extension aids the anterior cruciate ligament (ACL) in maintaining joint stability by exerting an opposing torque to anterior tibial displacement induced by the quadriceps. It was the purpose of this study to compare contralateral patterns of hamstring coactivation in subjects who have suffered ACL dysfunction with subjects who have normal knees. Five subjects who had suffered ACL dysfunction (INJ) and five uninjured (UNI) subjects performed maximal flexions and extensions of the knee on a modified isokinetic dynamometer at 100 degrees and 300 degrees.s-1. Simultaneous recordings of torque, angular displacement, and electromyographic (EMG) activity from the hamstring musculature were computer processed. No significant differences (P < 0.05) in torque were found between ACL/normal and right/left limbs for the INJ and UNI groups, respectively. For the INJ subjects, mean coactivation of the normal limb hamstrings during extension averaged twice that of the ACL limb. In contrast, no significant difference was found for the same comparison between right and left limbs in the UNI group. The results of this study suggest that asymmetry in hamstring coactivation during knee extension may result from ACL dysfunction.

Eccentric knee flexor torque following anterior cruciate ligament surgery.

The purposes of this study were to compare eccentric knee flexor torque and muscle activation in the limbs of normal (NOR) subjects and in subjects who had undergone unilateral ACI, autograft surgical reconstruction (INJ) and to assess the effect of movement speed on EMG/ torque ratios and eccentric-concentric actions. Fourteen subjects (7 NOR and 7 INJ) were tested for knee eccentric flexor torque and EMG activity at four isokinetic speeds (15 degrees, 30 degrees, 45 degrees and 60 degrees.s-1). Results revealed that post-surgical limbs (ACL) produced significantly less (P < 0.05) eccentric torque and flexor EMG activity at 60 degrees.s-1 than uninjured (UNI) contralateral limbs. Eccentric torque rose significantly as speed increased from 45 degrees to 60 degrees.s-1 for surgical group uninjured limbs and NOR group left and right limbs. Eccentric flexor torque increased with speed for both groups and approximated equality with concentric extensor torque at 60 degrees.s-1 for INJ group ACL and UNI limbs. Concentric flexor muscle EMG/torque ratios were 30-191% greater than eccentric muscle actions across groups and speeds. The results suggest that ACL dysfunction may result in reduced eccentric flexor torque at rapid movement speeds, that eccentric flexor torque increases with movement speed and may have the capacity to counter forceful extensor concentric torque, and that eccentric muscle actions produce less muscle activation per unit force than concentric actions which may reflect reduced energy cost.

Medial tibial stress syndrome. The location of muscles in the leg in relation to symptoms.

The legs of fifty cadavera were dissected to identify accurately the structures that attach to the tibia at the site of symptoms of medial tibial stress syndrome and that could potentially contribute to this condition. The origins of the soleus, the flexor digitorum longus, and the tibialis posterior muscles as well as that of the deep crural fascia were measured. The average sites of attachment and the ranges of attachment were determined for each structure. The soleus, the flexor digitorum longus, and the deep crural fascia were found to attach most frequently at the site where symptoms of medial tibial stress syndrome occur, while in no specimen was the tibialis posterior found to attach at this site. The data support recent reports that the soleus is probably the major contributor to traction-induced medial tibial stress syndrome. The data also contradict the contention that the tibialis posterior may contribute to this particular condition.

Instrumented Lachman tests for the evaluation of anterior laxity after reconstruction of the anterior cruciate ligament.

Using a KT-1000 arthrometer, in fifty subjects were measured the anterior ligamentous laxity in a knee in which the anterior cruciate ligament had been reconstructed and in the normal, contralateral knee. We also determined the anterior tibial displacement and anterior compliance, using the Lachman test. The subjects were divided into groups according to the type of autogenous intra-articular substitute (either the central one-third of the patellar tendon or the semitendinosus tendon) that had been used for the anterior cruciate ligament and according to the duration of follow-up (range, twenty-four to 101 months). Lachman tests were performed, applying sixty-eight and ninety newtons of force, and indices for anterior compliance were calculated. Although significantly more anterior laxity was demonstrated with both sixty-eight and ninety newtons of force in the reconstructed knees than in the contralateral, normal knees (p less than 0.001), thirteen subjects, of whom eight lacked full extension of the reconstructed knee, had more anterior laxity in the normal knee. Analyses of variance showed no significant differences in the results of the Lachman tests as related to either the type of reconstruction or the length of postoperative follow-up. The results suggested that the two types of ligamentous substitute that were used in this study were equally efficient in limiting anterior tibial displacement, as demonstrated by the Lachman test. The study also demonstrated that the substitutes did not elongate significantly during the period of the study.

An assessment of subject variability, subject-shoe interaction, and the evaluation of running shoes using ground reaction force data.

Several aspects of dynamic foot function were investigated using ground reaction forces obtained from five runners performing in five different shoes. A minimum of eight trials were necessary in order to obtain stable subject-condition values. Statistically significant subject-shoe interactions occurred for all parameters. It was therefore concluded that a knowledge of shoe characteristics independent of subject characteristics provided little useful information regarding the effects of the shoes tested on selected foot mechanics of the runners. The various subject-conditions were evaluated in an attempt to determine which was the best shoe. Selected descriptive data are presented and the 'best' shoe concept discussed.

Effects of prophylactic knee bracing on lower extremity joint position and muscle activation during running.

The primary purpose of a prophylactic knee brace is to decrease injury potential without compromising joint function; however, the extent that these devices can alter knee muscle function is not clear. This study investigated effects of nonprescription prophylactic knee bracing on lower extremity joint position and muscle activation during running. Six healthy male college-aged recreational runners used a motor-driven treadmill under 6 conditions: fast or slow speeds, with and without wearing a prophylactic knee brace, and with and without wearing a weighted vest. Changes in hip, knee, and ankle joint position and electromyographic activity from 9 lower extremity muscles were monitored during the running cycle weightbearing phase. Results revealed significant changes (P < 0.05) in joint position and electromyographic activity for comparisons of slow versus fast, braced versus nonbraced, and weighted versus nonweighted conditions. From 83% to 89% of the braced and nonbraced comparisons generated significant differences in knee joint position while significant hip and ankle joint position changes occurred in 50% to 58% of comparisons. From 67% to 83% of braced and nonbraced comparisons for the 9 muscles produced significant differences in electromyographic activity. Findings suggest that neuromuscular control is altered when external prophylactic devices are applied.

Foot orthotic devices to modify selected aspects of lower extremity mechanics.

Excessive foot pronation has been speculated to be a cause of leg and foot problems among runners. Foot orthotic devices are often used to modify this condition. Examination of the records of 180 patients treated for various running injuries showed that 83 individuals (46%) were prescribed orthotic devices and that 65 of these runners (78%) were able to return to their previous running programs. In order to assess further the effects of this type of orthotic device, six runners were selected from this group and filmed using two cameras (200 frames/sec) under three conditions: (1) barefoot, (2) regular shoe, and (3) regular shoe plus orthotic device. Both the period of pronation and the amount of maximum pronation were significantly reduced by using the foot orthotic device. The data support the conclusion that foot orthotic devices can be successfully used to modify selected aspects of lower extremity mechanics during the support phase of running.

Long-term evaluation of knee stability and function following surgical reconstruction for anterior cruciate ligament insufficiency.

Currently used measures of knee stability and function for ACL reconstructed knees have not gained universal acceptance. Clinical test results often are given more value than the patient's subjective evaluation of the surgical outcome. This study was designed to identify specific knee stability and function variables that were most predictive of the patient's rating of knee function following one of two types of combined (intraarticular and extraarticular) ACL reconstruction procedures. Individual measures of knee stability and function were also evaluated for differences between contralateral operated and nonoperated limbs. Postoperative and healthy contralateral knees of 51 male and female patients aged 18 to 49 years (mean, 23.7 years) were evaluated on a battery of tests at an average of 48.0 months after surgery (range, 24 to 101 months). All subjects possessed a normal contralateral knee for comparative purposes. The results of this retrospective study indicated that the variables selected were not highly correlated with, nor could they effectively predict, the patients' perceptions of postoperative knee status as measured by the Knee Function Rating Form (KFR). Statistically significant differences (P less than 0.001) between operated and nonoperated knees were found for 9 of 11 variables analyzed. The data suggest that patients' perceptions of postoperative knee status were independent of the results of static and dynamic clinical tests commonly used to assess knee stability and function. Postoperative deficits of up to 30% between the surgically reconstructed and normal contralateral knees on specific measures of knee stability and function did not greatly influence the patients' perceptions of knee function. Development of new, more specific dynamic tests may be necessary before stronger relationships between clinical test results and patients' perceptions of knee status in the ACL reconstructed knee can be realized.

Effects of electromyographic feedback training on motor control in spastic cerebral palsy.

Electromyographic feedback training may play a special role in increasing active range of motion in spastic cerebral palsied individuals. The effects of electromyographic feedback training were documented on four persons with spastic diplegic cerebral palsy within a single subject design. Subjects received immediate auditory and visual feedback twice daily during ten consecutive days. Electromyographic feedback training resulted in increases in the active range of motion of the ankle joint of from 20 percent to 500 percent in the limbs trained during the first five days with electromyographic feedback and of from 33 percent to 450 percent in the limbs trained in the last five days. The acquired active range of motion was maintained by two of the subjects over intervals of from four to nine weeks.

Fatigue effects in running.

Effects of fatigue were assessed on 12 female subjects who were filmed at two stages of a maximal-effort, gross physical performance task (running). Comparisons were then made between selected temporal and kinematic parameters describing the activity: The results appear to support the concept that fatigue does not simply produce a uniform reduction in the components of a movement pattern but, rather, changes their relationship completely.

Attentional deficits in concussion.

PRIMARY OBJECTIVE: The purpose of the present study was to examine deficits in the alerting, orienting and executive components of attention in individuals who have recently suffered a concussion. RESEARCH DESIGN: A group design was used in which the performance by individuals with concussion was compared to control subjects matched for age, height, weight and activity level. METHODS AND PROCEDURES: Participants completed the Attentional Network Test (ANT) that breaks down attention into alerting, orienting and executive components. Reaction time and response accuracy were the dependent variables. MAIN OUTCOMES AND RESULTS: It was found that only the orienting and executive components of attention were affected by concussion, whereas the alerting component was normal. Furthermore, participants with concussion required a significantly longer time than controls to initiate correct responses. CONCLUSIONS: These results suggest that the orienting and executive components of attention are most susceptible to the effects of concussion.

Optimal isokinetic loads and velocities producing muscular power in human subjects.

The torque values of the quadriceps muscles of 16 college football players were tested by means of an isokinetic dynamometer in order to determine the optimal loads and velocities producing muscular power. The men were tested at velocities ranging from 5 to 25 rpm and throughout a range of knee extension between the positions of 85 degrees to 50 degrees of knee flexion. Isometric measures were also recorded at corresponding angles. The muscular torque values recorded isokinetically at the various velocities were then compared to the isometric forces at the corresponding angles of knee extension to ascertain the arithemtic proportion of isokinetic to isometric torque which produced maximum muscular power. The results indicated that the proportionate values of isokinetic to isometric torque and isokinetic velocities which produced maximum power were not directly comparable to similar loads and velocities found in vitro. The weight of the leg may have contributed to submaximal isometric recordings, thus resulting in higher proportionate values of isokinetic to isometric force. Changes in these values as the knee was extended were deemed to be a result of variance in the isometric torque since the isokinetic torque stayed relatively constant throughout the range of movement. The data suggested that a plateau of isokinetic torque may have been reached in the production of maximum power. Maximum isokinetic torque values tended to shift to more extended joint positions as the speed of knee extension increased. This shift may have been due to the momentum of the leg during the faster isokinetic speeds overcoming some of the inertia of the weight of the leg as it was extended.

Isokinetic dynamometry: implications for muscle testing and rehabilitation.

Isokinetic exercise has become an increasingly popular modality in rehabilitative medicine during the past decade. The facility by which isokinetic dynamometers provide information about dynamic muscle contractions has, no doubt, been a major factor in this popularity. Isokinetic dynamometers are passive devices which resist applied forces and control the speed of exercise at a predetermined rate. Such dynamometers generally provide a record of applied force throughout a joint range of motion. Some of the postulated advantages of isokinetic exercise include safety, accommodating resistance and the facility for muscle force analysis. In spite of the advantages that isokinetic dynamometry provides, there are a number of considerations that are important in the interpretation of force recordings. While the term "isokinetics" generally denotes a type of muscular contraction which accompanies a constant rate of limb movement, periods of acceleration and deceleration exist in the context of isokinetic exercise. The acceleration and subsequent oscillatory and deceleration periods of "isokinetic" exercise limit the duration of the period of constant velocity in exercises with isokinetic dynamometry. Impact artifacts on torque records result from the compliance of the dynamometer system as it adjusts the accelerating limb to the present speed. The position at which peak torque occurs in a joint range varies with speed of motion. Therefore, analysis of maximal values at specific joint angles across speeds should be made in addition to the peak values generated throughout a joint range. The shape of the isokinetic force-velocity curve differs from the classic curve derived from prepared muscle specimens. As speed approaches zero, the isokinetic muscular force tends to rise much less steeply than that of the in vitro curve. Because measurements of absolute maximal force or velocity are subject to constraints in human studies, the direct comparison of in vivo to in vitro force-velocity curves is not justified. Neural inhibition of the force generated in intact muscle as tension rises has been postulated as a possible mechanism retarding the force curve at slow speeds. The reliability of specific types of isokinetic dynamometers appears to be quite high when test-retest analyses are performed with inert weights. Whether submaximal or maximal warm-ups are essential to ensure stable measures is still questionable at this time. It seems prudent to recommend submaximal warm-ups prior to maximal testing in order to reduce the possibility of muscle strain.(ABSTRACT TRUNCATED AT 400 WORDS)

Isokinetic evaluation of quadriceps and hamstrings symmetry following anterior cruciate ligament reconstruction.

After anterior cruciate ligament (ACL) reconstruction, isokinetic muscle parameters are commonly measured to assess the dynamic status of the knee and to monitor progress in rehabilitation. This study evaluated the symmetry of the quadriceps and hamstrings musculature in postsurgical and contralateral normal limbs of subjects who had undergone one of two types of ACL reconstruction. Subjects were also evaluated for differences on selected isokinetic parameters between types of surgery and lengths of postoperative periods. Postsurgical and normal contralateral limbs of 46 subjects aged 18 to 49 years (mean, 23.7 years) were divided into groups according to type of autogenous intraarticular ACL substitute and length of postoperative period. Results of paired t-tests and analyses of variance indicated significant asymmetries between limbs for all measures of quadriceps and hamstrings musculature strength and endurance (p less than .001) irrespective of the type of reconstruction technique. Average surgical knee deficits in hamstrings endurance were significantly less for the long-term (41 to 101 months) follow-up group (1.9%) than for the intermediate (24 to 40 months) group (12.1%). The results suggest that extended periods of time are required to approximate hamstrings endurance symmetry after ACL reconstruction. Asymmetries between postsurgical and contralateral normal limbs in these subjects may reflect either incomplete rehabilitation or an inability to regain full isokinetic strength and endurance after ACL reconstruction.