Isometric Quadriceps Contractions Research Articles

Physiologic parameters and perceived exertion with local muscle fatigue in postpolio subjects.

Fifty postpolio patients, 34 with and 16 without complaints of progressive loss of muscle strength, and 41 control subjects were studied to compare physiologic measures of the fatiguing process and to determine whether there is a significant interaction between the rating of perceived exertion (RPE) and physiologic measures. Statistical analyses were by ANOVA and repeated-measures ANOVA. The RPE was obtained every 20 seconds during an isometric contraction of the quadriceps at 40% of maximal torque; median frequency (Fm) of the power spectrum of the surface electromyographic signal and neuromuscular efficiency (NME) were constantly monitored. The RPE increased similarly (p greater than .05), whereas Fm and NME decreased similarly (p greater than .05) during endurance exercise at 40% of maximal torque in all three groups. A significant (p less than .05) interaction was found between RPE and both Fm and NME. We conclude that physiologic measures of the fatiguing process (Fm and NME) occur in a similar manner in postpolio and control subjects and that there is a significant interaction between subjective RPE and physiologic measures of the fatiguing process.

Anterior tibial translation during a maximum quadriceps contraction: Is it clinically significant?

Quadriceps exercises are used sparingly in the early rehabilitation of ACL reconstructions because of concern about prematurely stretching the ACL graft. The aim of this study was to determine if a maximum isometric quadriceps contraction significantly translates the tibia anteriorly at 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 75 degrees of flexion. Secondly, the role of the ACL in knee stability was analyzed by comparing the amount of tibial translation in normal, ACL deficient, and reconstructed knees. Thirdly, the location in the motion arc where a quadriceps contraction produces anterior tibial translation was determined. Anterior tibial translation was measured using an arthrometer (KT-1000) during an 89 N and manual maximum translation applied to the knee at rest. The manual maximum translation test determines the magnitude of anterior tibial translation produced by a high anterior force applied directly to the proximal calf. These translations were compared to the tibial translation intrinsically induced by a quadriceps contraction. Testing was performed in normal (N = 22), ACL deficient (N = 10), and reconstructed (N = 10) knees. Anterior tibial translation produced by a maximum quadriceps contraction was measured at 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 75 degrees of flexion. The extension exercise resulted in less anterior tibial displacement than an 89 N drawer and half the translation produced by a manual maximum translation (P less than 0.001). Instrumented laxity testing produced greater anterior translation of the tibia than a maximum isometric quadriceps contraction. Anterior tibial translation was the same during maximum isometric knee extension in all tested knees.(ABSTRACT TRUNCATED AT 250 WORDS)

Arthroscopic strain gauge measurement of the normal anterior cruciate ligament

This article describes a new arthroscopic technique to study the anterior cruciate ligament (ACL) in vivo. A Hall effect strain transducer (HEST) is inserted arthroscopically into the anterior medial band (AMB) of the ACL. The strain is calculated from HEST displacement data. This method determines a reference length of the AMB when it becomes taut and load bearing. Data from HEST implantation in five patients with normal ACLs are reported. The HEST was implanted in the AMB with patients under local anesthesia. Strain was calculated during anterior-posterior shear testing and isometric quadriceps contractions at 30 and 90° of knee flexion. The results demonstrate that this technique is safe and reliable. Lachman testing (anterior shear testing at 30°) caused significantly higher strain in comparison to the drawer tests (anterior shear testing at 90°). A significant increase in strain occurred during isometric quadriceps contraction when the knee was flexed at 30°. No significant change in strain was measured, however, during isometric quadriceps contraction at 90° of flexion. These results confirm previous studies showing that the Lachman test is a more sensitive clinical method for evaluating the AMB. They suggest that isometric quadriceps activity at 90° of knee flexion can be prescribed for rehabilitation without risk of increased strain of the AMB.

Gradual increase in leg oxygen uptake during repeated submaximal contractions in humans

We examine whether muscle oxygen consumption (VO2) increases gradually during repeated submaximal isometric contractions. Six subjects made two-legged isometric quadriceps contractions at 30% maximal voluntary contraction for 6 s with 4 s of rest between until exhaustion (58 +/- 8 min). Blood samples were taken from the femoral vein and artery, and blood velocity was recorded by ultrasound-Doppler technique in the femoral artery. Blood flow was calculated from velocity and artery diameter values. Leg VO2 increased sixfold within the 1st min of exercise. A further doubling of the VO2 was seen during the remainder of the exercise, reaching 307 +/- 22 ml/min at exhaustion. This latter increase was due to a 54% increase in blood flow and a 34% increase in oxygen extraction. After 20 min of recovery VO2 was still 75% higher than preexercise values. The results show a twofold increase in energy demand of the working muscle during repeated constant-force isometric contractions. The increased energy cost of contraction is probably localized at the cellular level, and it parallels fatigue determined as decreased force-generating capacity.

Pressures in normal and acutely distended human knee joints and effects on quadriceps maximal voluntary contractions.

Pressures were recorded in ten knees from five subjects with informed consent. Resting intra-articular pressures were found to be sub-atmospheric with a mean value of -5 +/- 1.5 mmHg (S.E. of mean). There was little variation in intra-articular pressure with changing joint angle in the normal joint. Infusion of as small a volume as 5 ml of sterile saline into the joint cavity caused the intra-articular pressure to increase to supra-atmospheric levels. Changing joint angle now produced clear modulations in intra-articular pressure. Pressure increased as the limb was moved out to extension and back to flexion with a minimum occurring in the mid-range. These modulations were more pronounced with active positioning of the joint than with passive positioning. Successive increases in intra-articular volume produced increases in intra-articular pressure as well as the degree of modulation of intra-articular pressure with joint angle. Cyclical flexion-extension movements caused a progressive decrease in the maximum pressure observed in extension. Non-noxious distension of the knee joint caused substantial reductions in the magnitude of isometric and isokinetic maximal voluntary contractions of quadriceps due to a reflex inhibition from joint mechanoreceptor afferents.

Fatigue of intermittent submaximal voluntary contractions: central and peripheral factors.

Central and peripheral factors were studied in fatigue of submaximal intermittent isometric contractions of the human quadriceps and soleus muscles. Subjects made repeated 6 s, 50% maximal voluntary contractions (MVC) followed by 4 s rest until the limit of endurance (Tlim). Periodically, a fatigue test was performed. This included a brief MVC, either a single shock or 8 pulses at 50 Hz during a rest period and a shock superimposed on a target force voluntary contraction. At Tlim, the MVC force had declined by 50%, usually in parallel with the force from stimulation at 50 Hz. The twitches superimposed on the target forces declined more rapidly, disappearing entirely at Tlim. In similar experiments on adductor pollicis, no reduction of the evoked M wave was seen. The results suggest that, during fatigue of quadriceps and adductor pollicis induced by this protocol, no central fatigue was apparent, but some was seen in soleus. Thus the reduced force-generating capacity could result mainly or entirely from failure of the muscle contractile apparatus.

Current trends in repair and rehabilitation of complete (acute) anterior cruciate ligament injuries. Analysis of 1984 questionnaire completed by ACL Study Group.

Results of a 21 question survey, taken at the ACL Study Group meeting in 1984, present a composite picture of current practices in ACL reconstruction and rehabilitation. Forty-four of the 50 questionnaires were returned. Responses represented views from knee surgeons in the United States, Canada, Australia, Sweden, and Switzerland. These results were compared with a report of a 1980 international survey in which views of 40 knee experts from the United States, Canada, England, France, and Sweden were summarized. Questions on the two surveys were similar, particularly about rehabilitation. Although the time span between the two surveys was only 4 years, we can see both consistencies and changes. Responses about length of time between ACL repair and full range of motion (by 6 months) were essentially the same (88% in 1980, and 86.4% in 1984). However, changes were evident in length of immobilization (longer in 1980) and prescribing isometric contractions of quadriceps 1st week postoperatively (more frequently in 1980). Surgeons allowed patients to return to full activity sooner in 1980 than in 1984. Electrical stimulation was being used more frequently in 1984, and apparently the practice of simultaneous hamstring and quadriceps contraction has come into prominence since 1980 as it was not mentioned in the first survey. In 1984, 50% of the respondents indicated they prescribed it. Since standardized reporting systems are not established, we cannot do reliable statistical analyses on large samples. At the present time, making surveys with responses from similar groups every few years is the best available way to capture trends in treatment of ACL injuries.

EMG Biofeedback as Treatment for Patellofemoral Pain Syndrome

Patellofemoral pain syndrome may be classified as a dysfunction of the patella's ability to track in the femoral groove. This study identifies an effective treatment approach for patellofemoral pain syndrome. The approach integrates the concept of improved patellar tracking through selective enhancement of the vastus medialis oblique muscle with conventional exercise regimens for patellofemoral pain syndrome. Six patellofemoral pain syndrome patients were enrolled in a three-phase electromyographic biofeedback and exercise program: 1) biofeedback orientation and instruction in isometric quadriceps contractions, straight leg raises, and a home program; 2) biofeedback training for vastus medialis oblique enhancement with isometric quadriceps contractions, straight leg raises, terminal knee extensions, and progressive resistive exercises; and 3) incorporation of increased vastus medialis oblique activity in functional patterns of movement. All six patients learned to alter their vastus medialis oblique activity through the use of this treatment approach. The alteration of vastus medialis oblique activity resulted in an apparent change in the patellofemoral forces and a concomitant decrease in the patients' complaints of pain. These patients were able to return to pain-free functional activities in only six to nine treatment sessions within a 4- to 6-week period. The use of electromyographic biofeedback coupled with a graded exercise program is an efficient and effective treatment approach for patellofemoral pain syndrome patients.J Orthop Sports Phys Ther 1984;6(2):95-103.

The biomechanics of anterior cruciate ligament rehabilitation and reconstruction.

The rehabilitation of knee injuries involving the anterior cruciate ligament (ACL) is controversial. This paper describes strain in the normal and reconstructed ACL during a series of passive and active tests of knee flexion with and without varus, valgus, and axial rotation torques on the tibia. Strain in the human knee ACL was significantly different depending on whether the knee flexion angle was changed passively or via simulated quadriceps contraction. The knee joint capsule was found to be important for strain protection of the ACL. Quadriceps activity did not strain the normal or reconstructed ACL when the knee was flexed beyond 60 degrees, but significantly strained the tissue from 0 to 45 degrees of knee flexion. Immobilization may not protect the ACL if isometric quadriceps contractions are allowed to occur. Properly placed reconstructions exhibited strain behavior which closely followed the anteromedial band of the ACL.

Relaxation Rate of Constituent Muscle-Fibre Types in Human Quadriceps

1. Muscle fibres may be subdivided into type I (with slow-twitch contractile properties) and type II (fast-twitch) depending on their myosin adenosine triphosphatase activity. In voluntary isometric contractions type I fibres are utilized at low forces (less than 20% of maximum) whereas type II fibres are recruited in addition at high forces. This physiological recruitment order has enabled us to measure the relaxtion rate of type I and II fibres in vivo in normal human subjects. 2. Relaxation rate was measured in 16 subjects from low (10% of maximum) and maximum isometric quadriceps contractions and the muscle-fibre type composition determined from needle-biopsy specimens in 10 subjects. The relaxation rate of type II fibres was calculated to be twice as fast as that of type I. 3. It was not possible to estimate, from studies in 33 quadriceps muscles (25 normal subjects), the contribution of type II fibres to overall fibre area from the relaxation rate as determined from electrically stimulated isometric contractions.