Electrical stimulation of human muscle studied using 31P-nuclear magnetic resonance spectroscopy.

This study used phosphorous nuclear magnetic resonance (31P-NMR) spectroscopy to examine the metabolic demand resulting from electrical muscle stimulation (EMS) applied to human skeletal muscle. For each of six subjects, the forearm flexor muscle group was monitored with 31P-NMR during both maximum voluntary and 6-s EMS-induced contractions. A simple protocol using a tourniquet was added in one subject to assess the role of blood flow in this model. Eight hertz (nontetanic) EMS showed less (p less than 0.025) depletion of phosphocreatine (36%) than did tetanic 70-Hz EMS (60%), voluntary isometric (66%), and voluntary isokinetic (68%). The results of the tourniquet studies suggested that the nontetanic EMS allowed relatively increased muscle blood flow and oxygen supply during contraction. Tetanic EMS provided a similar metabolic demand to that of conventional resistive exercise, as measured by 31P-NMR spectroscopy.

The nature of torque "overshoot" in Cybex isokinetic dynamometry.

Transient peaks or "spikes" frequently appear in the initial segments of torque curves recorded with the Cybex isokinetic dynamometer. The purpose of this investigation was to determine whether these spikes represent artifact or transient initial surges of true muscular force output. Cinematographic analysis using both inert weights and a human subject as the source of torque input to the Cybex revealed that the dynamometer's input lever initially exceeded the pre-set angular velocity by an amount ranging from 11% (inert weight; pre-set Cybex velocity = 180 degrees/s) to 200% (human hip abduction; pre-set velocity = 30 degrees/s). The majority of this "overspeeding" occurred in the latter part of the free acceleration period, prior to the engagement of the dynamometer's resistance mechanism. The remainder occurred in the initial part of the elastic loading phase, just after resistance had engaged. A sharp deceleration of the overspeeding lever and the affixed weight or limb then followed in response to the dynamometer's continuing build-up of resistance. Simultaneous with this deceleration, a prominent torque spike was recorded that superseded the correct (mechanical equilibrium) torque value. Within our error of measurement, the deceleration observed in the film quantitatively accounted for all of the "overshoot" torque, i.e., that amount of the spike that exceeded the correct value. It was concluded that such prominent, initial torque spikes represent inertial forces and should not be confused with true muscular tension development.

Phosphorus nuclear magnetic resonance: a non-invasive technique for the study of muscle bioenergetics during exercise.

Phosphorus nuclear magnetic resonance (31P NMR) spectroscopy is a non-destructive analytical laboratory technique that, due to recent technical advances, has become applicable to the study of high-energy phosphate metabolism in both animal and human extremity muscles (in vivo). 31P NMR can assay cellular phosphocreatine, ATP, inorganic phosphate, the phosphorylated glycolytic intermediates, and intra-cellular pH in either resting or exercising muscle, in a non-invasive manner. NMR uses non-perturbing levels of radio-frequency energy as its biophysical probe and can therefore safely study intact muscle in a repeated fashion while exerting no artifactual influence on ongoing metabolic processes. Compared with standard tissue biopsy and biochemical assay techniques, NMR possesses the advantages of being non-invasive, allowing serial in situ studies of the same tissue sample, and providing measurements of only active (unbound) metabolites. NMR studies of exercising muscle have yielded information regarding fatigue mechanisms at the cellular level and are helping resolve long-standing questions regarding the metabolic control of glycolysis, oxidative phosphorylation, and post-exercise phosphocreatine re-synthesis. NMR is also being utilized to measure enzymatic reaction rates in vivo. In the near future, other forms of NMR spectroscopy may also permit the non-invasive measurement of tissue glycogen and lactate content.

Phosphorus nuclear magnetic resonance: a non-invasive technique for the study of muscle bioenergetics during exercise.

Phosphorus nuclear magnetic resonance (31P NMR) spectroscopy is a non-destructive analytical laboratory technique that, due to recent technical advances, has become applicable to the study of high-energy phosphate metabolism in both animal and human extremity muscles (in vivo). 31P NMR can assay cellular phosphocreatine, ATP, inorganic phosphate, the phosphorylated glycolytic intermediates, and intra-cellular pH in either resting or exercising muscle, in a non-invasive manner. NMR uses non-perturbing levels of radio-frequency energy as its biophysical probe and can therefore safely study intact muscle in a repeated fashion while exerting no artifactual influence on ongoing metabolic processes. Compared with standard tissue biopsy and biochemical assay techniques, NMR possesses the advantages of being non-invasive, allowing serial in situ studies of the same tissue sample, and providing measurements of only active (unbound) metabolites. NMR studies of exercising muscle have yielded information regarding fatigue mechanisms at the cellular level and are helping resolve long-standing questions regarding the metabolic control of glycolysis, oxidative phosphorylation, and post-exercise phosphocreatine re-synthesis. NMR is also being utilized to measure enzymatic reaction rates in vivo. In the near future, other forms of NMR spectroscopy may also permit the non-invasive measurement of tissue glycogen and lactate content.

Testing for isometry during reconstruction of the anterior cruciate ligament. Anatomical and biomechanical considerations.

Instrumented tibiofemoral (bone-to-bone) excursion wires were implanted in the mid-substance of the anteromedial, central, and posterior fiber-regions of the anterior cruciate ligament through limited anterior and posterior arthrotomies in eight fresh knees from cadavera. The change in the distance of linear separation between each pair of osseous fiber-insertion sites was measured and was plotted against the angle of flexion of the knee as the knee was cycled through a 120-degree range of motion. Testing conditions likely to be present during intraoperative testing for isometry were used (anterior cruciate fibers transected, quadriceps relaxed, femur stabilized with the patient in the supine position and the leg freely dependent, and motion of the knee induced in neutral rotation by force applied at the level of the foot). In no instance did the insertion-site centers of any fiber-region exhibit isometric behavior (change in the distance of linear separation of 1.0 millimeter or less). The least deviations from isometry (range, 1.4 to 3.1 millimeters) were observed for the anteromedial sites, under conditions when the gravitational dependency of the lower leg was constrained. When the leg hung in a dependent manner during passive motion, the deviation from isometry of the anteromedial sites of insertion increased significantly (range, 2.8 to 5.6 millimeters). The central sites of insertion were generally less isometric than the anteromedial sites, and the posterior sites were the least isometric, regardless of testing conditions.

Optimizing tourniquet application and release times in extremity surgery. A biochemical and ultrastructural study.

Despite numerous studies investigating the pathophysiology of tourniquet ischemia, definitive data at the cellular level have been lacking and no consensus regarding safe tourniquet-application times in extremity surgery has emerged. In light of the particular vulnerability of skeletal muscle to ischemic injury, we determined the degree of muscular metabolic derangement and cell damage produced by seven different protocols of tourniquet application and release, each providing three hours of total tourniquet time. We performed thirty-six experiments on canine hind limbs, comparing the following time-patterns of tourniquet application: I--three sequential one-hour periods, II--two sequential one and one-half-hour periods, III--two hours followed by one hour, and IV--a single continuous three-hour application. Five and fifteen-minute reperfusion intervals between ischemic periods were compared for the first three time-patterns, creating a total of seven different tourniquet protocols. Muscular metabolic derangement and cell injury were evaluated by monitoring changes in the cellular bioenergetic state (high-energy phosphate profile), cell pH, post-ischemic leakage of creatine phosphokinase, and ultrastructural cell degeneration. At the intracellular level, the metabolic recovery of muscle during reperfusion was much faster than previous studies focusing on extracellular parameters have indicated. In all instances complete intracellular bioenergetic recovery occurred within five minutes after tourniquet release. The use of one or more five-minute reperfusion intervals significantly reduced the degree of ischemic cell injury, as indicated by a decrease in creatine phosphokinase leakage and myofibrillar destruction. No additional benefit was derived by extending the reperfusion periods to fifteen minutes. The longest period of continuous ischemia in each tourniquet-application protocol bore the closest relationship with the amount of cell damage produced. Within the spectrum of observed pathological changes, time-patterns I and II produced comparatively little muscle damage.

The bioenergetics of preservation of limbs before replantation. The rationale for intermediate hypothermia.

Of all tissues of the extremities, muscle is the least tolerant of ischemia. Hypothermia of tissue is considered beneficial for the maintenance of viability of muscle in amputated limbs before surgical replantation, but it has never been established that conventional cooling in an ice bath or its equivalent (temperature of tissue, approximately 1 degree Celsius) is the optimum level of hypothermia for minimizing metabolic derangement in ischemic muscle. In this study, we first defined the time course and level of metabolic derangement of muscle in twenty-eight ischemic hind limbs in cats at 22, 15, 10, 5, and 1 degree Celsius. The levels of adenosine triphosphate and phosphocreatine and the mean intracellular pH of the muscles in the lateral aspect of the thigh in each limb were monitored with phosphorus nuclear magnetic-resonance spectroscopy over time. The excised muscles from six freshly amputated legs of live humans were then similarly studied to determine whether muscles from cats and from humans exhibit comparable bioenergetic responses to hypothermic ischemia. A final series of ten ischemic hind limbs from cats was studied by nuclear magnetic resonance and muscle biopsy for direct biochemical assay of tissue energy metabolites to compare the metabolic benefits of two different methods of preserving limbs: continuous cooling in an ice bath, and a newly devised protocol for the rapid induction and maintenance of so-called intermediate (10 +/- 5 degrees Celsius) hypothermia of tissue. Ischemic skeletal muscle in cats exhibited a paradoxical metabolic response to extreme cold (1 degree Celsius). The rate of metabolic deterioration progressively declined with decreasing temperature of tissue to 10 degrees Celsius. However, at 5 degrees Celsius, no additional benefit was detected, and at 1 degree Celsius, there was a significant acceleration in the rates of degradation of adenosine triphosphate and phosphocreatine and in the production of lactate. The rate of degradation of adenosine triphosphate in human ischemic muscle was also faster at 1 degree Celsius than at 10 degrees Celsius. This paradoxical response is apparently due to a severe inhibition of the calcium pump of the sarcoplasmic reticulum of the muscle cell at temperatures of less than 5 degrees Celsius. The inhibition permits an efflux of calcium to the myofibrils, which stimulates both glycolysis and the degradation of adenosine triphosphate by myofibrillar adenosine triphosphatase.

Sport-specific performance factor profiling: fencing as a prototype.

A musculoskeletal profiling study was done on 24 members of the U. S. Pan American and Olympic fencing squads. This was presented as a methodological prototype for future, more comprehensive sport profiling studies. It is proposed that sport-specific profiling data have practical application in the following areas: 1. The identification of physical deficiencies in an athlete, using his or her sport profile as a comparative standard. This would apply to general pre- and postseason screening as well as to medical complaint-related examinations. 2. Providing objective, sport-specific criteria for determining when an injured athlete has recovered to the extent that he or she is adequately prepared to return to play. Rehabilitation goals for full recovery can also be defined. 3. Increasing the efficacy and efficiency of training techniques. 4. The prospective identification of superior performance potential in athletes at early competitive levels. If sport profiles were developed for the major participant sports at several competitive levels, the profiling system as described here could have significant application to a large number of athletes in a variety of playing situations.

Testing for isometry during reconstruction of the posterior cruciate ligament. Anatomic and biomechanical considerations.

The change in the distance of linear separation between each pair of osseous fiber attachment sites of the posterior cruciate ligaments was measured and plotted as a function of the knee flexion angle from 0 degree to 120 degrees. Data were collected under four sequential test conditions that had in common quadriceps relaxation, absence of tibial rotation forces, and horizontal femoral stabilization. The posterior cruciate ligament fibers were intact or transected (excursion wires left intact) with gravitational joint distraction of the lower leg unconstrained or constrained. The small, posterior oblique fiber region was the most isometric of the four tested fiber regions. Progressively increasing deviations from isometry were seen in the posterior longitudinal, central, and anterior fiber regions, in that order. Transection of the posterior cruciate ligament, combined with unconstrained gravitational distraction of the knee joint, further increased the magnitude of deviation from isometry of the anterior and central fibers, but only changed the pattern of deviation for the more nearly isometric posterior fibers. Under simulated operative conditions, most of the posterior cruciate ligament's anatomic attachment sites exhibit nonisometric behavior, with near isometry demonstrated only by the relatively small posterior fiber attachment sites. If isometry alone is used for bone tunnel placement, the large anterior and central fiber regions will be left largely unreconstructed. Because the normal behavior of most of the fibers of the posterior cruciate ligament involves 4 to 6 mm of end-to-end length increase with progressive knee flexion, this pattern and degree of deviation from isometry should be sought to approximate an anatomic reconstruction of the anterocentral bulk of the ligament.

Magnetic resonance imaging of knee disorders. Clinical value and cost-effectiveness in a sports medicine practice.

To prospectively evaluate the clinical value of magnetic resonance imaging of the knee in a referral sports medicine practice, we performed a three-part study. First, we asked 72 consecutive patients a series of clinically relevant questions regarding the ordering of their magnetic resonance imaging scans. Second, we asked the treating physicians at our center if the magnetic resonance imaging findings changed the diagnosis or treatment. Third, we compared the clinical evaluation with the findings on magnetic resonance imaging scans for 37 patients who had arthroscopic confirmation. From the physician's perspective, in only three cases would the results of the scan have changed the diagnosis. Information from the scans was judged to contribute to patient treatment in only 14 of 72 patients. Finally, comparison of clinical evaluation and magnetic resonance imaging findings with findings during arthroscopic procedures showed that clinical evaluation had a sensitivity and specificity of 100% for diagnosis of anterior cruciate ligament injuries, whereas magnetic resonance imaging was 95% sensitive and 88% specific. For isolated meniscal lesions, the clinical assessment had a sensitivity and specificity of 91% compared with 82% and 87%, respectively, for magnetic resonance imaging. For evaluation of articular surface damage, the predictive value of a positive test was 100% for clinical assessment and 33% for the magnetic resonance imaging. We conclude that magnetic resonance imaging is overused in the evaluation of knee disorders and not a cost-effective method for evaluating injuries when compared with a skilled examiner. Clinical assessment equals or surpasses the magnetic resonance imaging in accuracy.

The effect of early versus late return to vigorous activities on the outcome of anterior cruciate ligament reconstruction.

The effect of early (mean, 5 months) versus late (mean, 9 months) return to vigorous cutting activity on the long-term outcome of anterior cruciate ligament reconstruction was evaluated retrospectively. Sixty-four reconstructions, using a distally attached medial one-third patellar tendon, were reviewed on an average of 46 months postoperatively. After surgery, the timing of return to vigorous activity was based on biologic fixation of the graft, a negative Lachman test, absence of effusion, and the patient's desire to return to previous activity. The 64 patients were retrospectively separated into two groups. The early group consisted of 31 patients who returned to activity 2 to 6 months after reconstruction, and the late group consisted of 33 patients who returned to activity 7 to 14 months after reconstruction. By clinical examination, KT-1000 arthrometer measurements, subjective evaluation, and Cybex testing, there were no differences between the early and late return groups except for reestablishment of final range of motion. At an average followup of 46 months, this study indicates that an early return to vigorous physical cutting activities after ACL reconstruction does not predispose patients to reinjury or a less satisfactory longterm result.

The definition and assessment of muscular power.

Considerable confusion still exists in the sports medicine literature concerning the measurement of muscular power and what it represents. Measures of muscular performance cannot be conveniently categorized as "strength " or ''power" on the basis of the contractile velocity employed in the performance task. Given the proper physical definitions and formulations involved in muscular power measurement, it is concluded that although strength (force output) and power (work/time) are quantitatively related, they remain separate physical parameters that can be measured in all dynamic muscular contractions, whether fast or slow. J Orthop Sports Phys Ther 1983;5(1):7-9.

Anatomy and function of the posterior cruciate ligament.

At the present time, our understanding of the PCL still lags behind that of the ACL. This knowledge gap has narrowed over the past few years, however, as more basic research has shed new light on the complex anatomy and functional mechanical behavior of the PCL and the nearby capsuloligamentous structures. Recent insights have included recognition that the PCL is composed of a fiber continuum rather than morphologically separate bands or bundles, a better appreciation of the predominantly nonisometric behavior of the intact PCL, and a greater awareness of the PCLs importance in preserving normal articular kinematics. Continued advances in the basic science of the PCL are a prerequisite for improvements in the treatment and rehabilitation of its injury.

The biomechanics of femoral and tibial posterior cruciate ligament graft placement.

Parameters for ideal posterior cruciate ligament graft placement have yet to be convincingly defined. Both anatomic and biomechanical data are reviewed and analyzed with respect to the concepts of isometric and physiometric graft placement. Perhaps elements of both may represent the ultimate solution.

Musculoskeletal performance testing and profiling of elite competitive fencers.

Twenty-four male members of the 1976 United States Olympic Fencing Squad were profiled. Data were collected on anthropometry; flexibility; and muscular strength, endurance, and power. Five of the physical variables measured in the laboratory were shown to have a significant relationship to competitive success.

The Clinical Use of Musculoskeletal Profiling in Orthopedic Sportsmedicine.

In brief: The accurate assessment of muscular strength, endurance, power, and flexibility through quantitative testing is important in the evaluation and rehabilitation of injured athletes. Test results must be compared to normal values to be properly interpreted. If healthy baseline data on an individual athlete is not available, the next most specific set of data would be a profile derived from athletes of the same sport, competitive level, and playing position. Inter-extremity comparisons are useful, but may be misleading even with unilateral involvement.

Modifications for Enhanced Data Collection and Analysis With the Cybex Isokinetic Dynamometer.

In brief: Two modifications of the standard Cybex II isokinetic dynamometry system permit a more complete evaluation of muscular strength, endurance, and power output, while minimizing manual data analysis. The addition of an X-Y plotter to the Cybex system provides a graphic display that combines torque and joint position on a single graph. Strength data need not be limited to "peak torque" values, because the plotter permits muscular torque output to be analyzed bilaterally through the full range of motion without the need for manually transposing data from strip-chart records. The second modification is a dual-channel reciprocal work integration system that separately measures the muscular work output performed in each rotational direction of joint movement. This allows individual assessments of endurance or power output for each muscle group of a reciprocal pair in a bout of continuous reciprocal exercise.

Biophysical Factors in Range-of-Motion Exercise.

In brief: Studies of the physical properties of connective tissue have helped determine improved techniques for therapeutic range-of-motion exercise. Laboratory studies indicate that the best way to permanently lengthen connective tissue structures without compromising their structural integrity is prolonged, low-intensity stretching at elevated tissue temperatures and cooling the tissue before releasing the tension. This article provides some practical therapeutic guidelines for physicians, trainers, and therapists who prescribe range-of-motion exercise for both rehabilitation and physical conditioning.