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Biomedical subjects

R L Lieber

Publications and source records attributed to R L Lieber.

At least 91 records · Page 5Linked to original sources
PubMed1991

Frog semitendinosis tendon load-strain and stress-strain properties during passive loading.

The mechanical properties of the frog semitendinosis (ST) tendon, bone-tendon junction, and aponeurosis were measured during passive loading to a tension equal to maximum isometric tension (Po). Stiffness and strain in these regions continuously increased as load increased. Tendon stiffness was approximately four times the aponeurosis stiffness. Tendon Young's modulus at Po was only 188 MPa, which is approximately 10 times less than the modulus reported for most mammalian tendons. Similarly, tendon stress at Po was only approximately 3 MPa, which is also less than that predicted for many tendons. Tendon strain at Po was approximately 2% after passive loading. We conclude that different regions of the frog ST tendon have different mechanical properties and that the frog ST tendon operates physiologically in the "toe" region of the stress-strain curve with a variable stiffness that increases with load. Taken together, these results have significant implications in understanding muscle-tendon design and neuromotor control strategies.

Animals↗
PubMed1991

Muscle damage induced by eccentric contractions of 25% strain.

Contractile and morphological properties were measured in the rabbit tibialis anterior muscle 1 h after isometric contraction (IC), passive stretch (PS), or eccentric contraction (EC). Maximal tetanic tension (Po) was reduced after 30 min of PS (P less than 0.001), IC (P less than 0.001), or EC (P less than 0.0001). However, the magnitude of the force deficit was a function of the treatment method. After 30 min of cyclic PS, Po decreased by 13%, whereas after IC or EC, Po decreased by 31 and 69%, respectively. The time course of tension decline in the various groups suggested that the EC-induced injury occurred during the first few minutes of treatment. Although the morphology of samples from the PS and IC groups appeared normal, eccentrically exercised muscles exhibited portions of abnormally large fibers (diam greater than or equal to 110 microns) when viewed in cross section. Examination of 231 such fibers from 6 muscles revealed that all enlarged fibers were exclusively of the fast-twitch glycolytic fiber type. Although no ultrastructural abnormalities were observed in any of the muscles from the IC or PS groups, a significant portion of the fibers in the EC group displayed various degrees of disorganization of the sarcomeric band pattern. Taken together, these studies highlight the importance of fiber oxidative capacity in EC-induced injury, which may be related to the damage mechanism.

Animals↗
PubMed1990

Statistical significance and statistical power in hypothesis testing.

Experimental design requires estimation of the sample size required to produce a meaningful conclusion. Often, experimental results are performed with sample sizes which are inappropriate to adequately support the conclusions made. In this paper, two factors which are involved in sample size estimation are detailed--namely type I (alpha) and type II (beta) error. Type I error can be considered a "false positive" result while type II error can be considered a "false negative" result. Obviously, both types of error should be avoided. The choice of values for alpha and beta is based on an investigator's understanding of the experimental system, not on arbitrary statistical rules. Examples relating to the choice of alpha and beta are presented, along with a series of suggestions for use in experimental design.

Research Design↗
PubMed1990

A model of semitendinosus muscle sarcomere length, knee and hip joint interaction in the frog hindlimb.

The interaction between the semitendinosus muscle and both hip and knee joint angles was examined in the frog (Rana pipiens) hindlimb. Sarcomere length was measured by laser diffraction in passive muscle during hip and knee rotation. A model was then developed to predict semitendinosus sarcomere length as a function of both hip and knee flexion angle. Based on published frog muscle fiber length-tension [Gordon, A. M. et al., J. Physiol. 184, 170-192 (1966)] and force-velocity [Edman, K. A. P., J. Physiol. 291, 143-159 (1979)] properties, and published joint angles during hopping [Calow, L. J. and Alexander, R. McN., J. Zool. (Lond.) 171, 293-321 (1973)], muscle sarcomere length, force and hip and knee torque during a hop were predicted. The semitendinosus muscle generally operated on the descending limb of the length-tension curve at normal joint angle combinations. The model predicted that, during a single coordinated movement, a period of sarcomere shortening (concentric) was followed by a period of sarcomere lengthening (eccentric). Based on calculated torque profiles at the hip and knee joints, this study suggested that the semitendinosus muscle probably functions more as a hip extensor than a knee flexor. In addition, based on the nature of the shortening-lengthening cycle, the semitendinosus may act to mechanically link the force of knee extension to hip extension.

Animals↗
PubMed1990

Architecture of selected wrist flexor and extensor muscles.

The architectural features of 25 wrist flexor and extensor muscles were studied. Muscles included the flexor carpi ulnaris, the flexor carpi radialis, the extensor carpi ulnaris, the extensor capri radialis brevis, and the extensor carpi radialis longus. Muscle length, mass, fiber pennation angle, fiber length, and sarcomere length (by use of laser diffraction techniques) were determined. In addition, physiological cross-sectional area and fiber length/muscle length ratio were calculated. The muscles were found to be highly specialized, with architectural features of same muscles very similar. The fiber length/muscle length ratio, muscle length, and pennation angle represented the major differences between muscles. Thus using these parameters in discriminant analysis permitted correct identification of each of the 25 muscles. In terms of size and intrinsic design, these individual muscles were highly specialized for their function.

Forearm↗
PubMed1989

Skeletal muscle architecture of the rabbit hindlimb: functional implications of muscle design.

The muscle-fiber architecture of 29 muscles from six rabbits (Oryctolagus cuniculus) was measured in order to describe the muscular properties of this cursorial animal, which possesses several specific skeletal adaptations. Several muscles were placed into one of four functional groups: hamstrings, quadriceps, dorsiflexors, or plantarflexors, for statistical comparison of properties between groups. Antagonistic groups (i.e., hamstrings vs. quadriceps or dorsiflexors vs. plantarflexors) demonstrated significant differences in fiber length, fiber length/muscle length ratio, muscle mass, pinnation angle, and number of sarcomeres in series (P less than .02). Discriminant analysis permitted characterization of the "typical" muscle belonging to one of the four groups. The quadriceps were characterized by their large pinnation angles and low fiber length/mass ratios, suggesting a design for force production. Conversely, the hamstrings, with small pinnation angles, appeared to be designed to permit large excursions. Similar differences were observed between plantarflexors and dorsiflexors, which have architectural features that suit them for force production and excursion respectively. Although these differences were not absolute, they represented clear morphological distinctions that have functional consequences.

Animals↗
PubMed1989

Recovery of the dog quadriceps after 10 weeks of immobilization followed by 4 weeks of remobilization.

Skeletal muscle fiber areas were measured in three heads of the dog quadriceps after 10 weeks of immobilization followed by 4 weeks of remobilization. Two-way analysis of variance demonstrated a significant decrease in both type 1 (p less than 0.005) and type 2 (p less than 0.001) fiber area. However, there was no significant difference among the three heads of the quadriceps (p less than 0.2). Although muscle fiber areas had not returned to control levels following remobilization, the area fraction of perimysial and epimysial connective tissue was not significantly different from control values (p greater than 0.15). These data suggest that although the degree of muscle atrophy following 10 weeks of immobilization is severe and muscle specific, following 4 weeks of remobilization, muscles uniformly recover to about 70% of control values.

Analysis of Variance↗
PubMed1989

Kappa Delta Award paper. Tissue fluid pressures: from basic research tools to clinical applications.

The two basic research tools developed to measure tissue fluid pressure (wick catheter) and osmotic pressure (colloid osmometer) have undergone extensive validation and refinement over the past 20 years. Using these techniques, basic science investigations were undertaken of edema in Amazon reptiles, pressure-volume relations in animals and plants, adaptive physiology of Antarctic penguins and fishes, edema in spawning salmon, tissue fluid balance in humans under normal conditions and during simulated weightlessness, and orthostatic adaptation in a mammal with high and variable blood pressures--the giraffe. Following and sometimes paralleling this basic research have been several clinical applications related to use of our colloid osmometer and wick technique. Applications of the osmometer have included insights into (a) reduced osmotic pressure of sickle-cell hemoglobin with deoxygenation and (b) reduced swelling pressure of human nucleus pulposus with hydration or certain enzymes. Clinical uses of the wick technique have included (a) improvement of diagnosis and treatment of acute and chronic compartment syndromes, (b) elucidation of tissue pressure thresholds for neuromuscular dysfunction, and (c) development of a better tourniquet design for orthopaedics. This article demonstrates that basic research tools open up areas of basic, applied, and clinical research.

Animals↗
PubMed1989

Myoneural necrosis following high-frequency electrical stimulation of the cast-immobilized rabbit hindlimb.

The morphological and physiological effects of 4 weeks of high-frequency electrical stimulation (1 h/day, 5 days/week) on cast-immobilized rabbit hindlimbs were investigated in the tibialis anterior muscle and peroneal nerve. In 2 out of 6 animals, high-frequency stimulation with immobilization caused muscle fiber death, internalization of muscle fiber nuclei, connective tissue proliferation, inflammatory response, altered fiber size distribution and variable staining intensities. The fast-twitch fibers were predominantly affected. Two of six peripheral nerves subjected to immobilization and stimulation showed severe damage. Tetanic forces were significantly reduced in the affected muscles. Therefore, the immobilization and high-frequency stimulation may be detrimental to myoneural structure and function and, thus, this combination of therapies should be applied conservatively.

Animals↗
PubMed1989

Effects of run-training and swim-training at similar absolute intensities on treadmill VO2max.

Thirty-seven sedentary males, aged 28-35 yr, were either run-trained, swim-trained, or served as controls in an 11 1/2-wk training study. Runners and swimmers exercised once a d, 3 d.wk, at a heart rate (HR) intensity equivalent to 75% of their treadmill VO2max. Treadmill maximal oxygen consumption (VO2max), submaximal cardiorespiratory response, and body composition parameters were measured before and following the training period. Runners, swimmers, and controls experienced a significant increase in treadmill VO2max over the 11 1/2-wk study period. The 28 and 25% increases observed for the runners and swimmers, respectively, were significantly greater than the 5% increase observed for the controls (P less than 0.0001). Runners and swimmers did not differ significantly from each other with respect to this increase in VO2max; nor did they demonstrate significant changes in respiratory exchange ratio (RER) at VO2max between tests. The run-trained and swim-trained groups both experienced a decrease in HR at a standard submaximal walking workload but did not differ significantly from each other. Controls showed no significant change in submaximal exercise response. A significant difference was observed among groups (P less than 0.01) for change in percent body fat. Changes in lean and fat weight over the training period were significant for both the runners (P less than 0.002) and swimmers (P less than 0.03) but not for the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Corrective shoes and inserts as treatment for flexible flatfoot in infants and children.

We performed a prospective study to determine whether flexible flatfoot in children can be influenced by treatment. One hundred and twenty-nine children who had been referred by pediatricians, and for whom the radiographic findings met the criteria for flatfoot, were randomly assigned to one of four groups: Group I, controls; Group II, treatment with corrective orthopaedic shoes; Group III, treatment with a Helfet heel-cup; or Group IV, treatment with a custom-molded plastic insert. All of the patients in Groups II, III, and IV had a minimum of three years of treatment, and ninety-eight patients whose compliance with the protocol was documented completed the study. Analysis of radiographs before treatment and at the most recent follow-up demonstrated a significant improvement in all groups (p less than 0.01), including the controls, and no significant difference between the controls and the treated patients (p greater than 0.4). We concluded that wearing corrective shoes or inserts for three years does not influence the course of flexible flatfoot in children.

Child↗
PubMed1988

Differential response of the dog quadriceps muscle to external skeletal fixation of the knee.

The change in muscle fiber size and fiber percentage was studied in three heads of the dog quadriceps following 10 weeks of immobilization using an external skeletal fixator. Muscle biopsy morphometric analysis revealed that muscle fiber atrophy was greatest for the vastus medialis and least for the rectus femoris. The atrophic response for type 1 fibers was, in order from most to least atrophied: VM greater than VL greater than RF, whereas for type 2 fibers the corresponding order was VM = VL greater than RF. An increase in connective tissue was also observed for all muscles. These results are discussed in terms of skeletal muscle architecture, initial fiber-type distribution, and level of use. As a result, predictions are made as to the muscles that are most vulnerable to disuse atrophy, namely the postural muscles that contain a relatively large proportion of slow muscle fibers and cross a single joint. Conversely, those that are least susceptible to atrophy are those that are not used as postural muscles, that cross multiple joints, and that are predominantly composed of fast muscle fibers.

Animals↗
PubMed1988

Differential effects of 10-Hz and 50 Hz-stimulation of the tibialis anterior on the ipsilateral, unstimulated soleus muscle.

Twelve rabbits were cast-immobilized for 4 weeks during which either 10- or 50-Hz stimulation was applied transcutaneously to the anterior compartment muscles. After the treatment period, tibialis anterior and soleus muscle contractile and histochemical properties were measured. Tibialis anterior stimulation at either 10 or 50 Hz had significantly different effects on the ipsilateral, unstimulated soleus muscles. Whereas soleus muscles of both groups demonstrated significant atrophy relative to nonstimulated, nonimmobilized soleus muscles, the soleus muscles from the 50-Hz group demonstrated significantly less atrophy than did the soleus muscles from the 10-Hz group as indicated by significantly greater muscle mass, maximum tetanic tension, and fast fiber area. The results indicate that muscle stimulation may have beneficial effects on ipsilateral muscles that are passively stretched secondary to stimulation. In addition, passive tension, not just muscle activation, appears to have an important role in regulating muscle size.

Animals↗
PubMed1988

Sarcomere length and joint kinematics during torque production in frog hindlimb.

The relationship between semitendinosus muscle force and knee joint kinematics during isometric torque production was examined in the frog (Rana pipiens) hindlimb. Passive muscle sarcomere length was monitored by laser diffraction during knee rotation, and joint center of rotation was determined later using principles of rigid body kinematics. Contractile force at the distal tibia, resulting from semitendinosus contraction, was also measured, and, using the kinematic data, a torque vs. joint angle curve constructed. Muscle sarcomere length varied from 3.6 micron at full knee extension to 2.0 micron at full knee flexion. Effective lever arm varied almost as a sine function, with optimal lever arm at 90 degrees of flexion. Joint torque increased linearly from 0 to 140 degrees of flexion and then sharply decreased to 160 degrees of flexion. Thus the optimal joint angle occurred at an angle (140 degrees) that was neither the angle at which muscle force was maximum (160 degrees) nor the angle at which the effective lever arm was maximum (90 degrees). These data indicate that knee torque production in the frog results from the interaction between muscular and joint properties and not either property alone.

Analysis of Variance↗
PubMed1988

Muscle force and moment arm contributions to torque production in frog hindlimb.

The relative contribution of maximum muscle tetanic tension (Po) and muscle moment arm to maximum knee flexion torque was investigated in the frog hindlimb. Isometric torque was measured in frog semitendinosus muscle-bone complexes throughout the range of 0-160 degrees of flexion. Optimal joint angle (the angle at which isometric torque was maximum) was observed at 140 degrees of flexion. After torque measurements, the muscle was excised and the muscle length-tension relationship measured for determination of Po and optimal muscle length. In addition, the kinematics of the knee joint and therefore, the muscle moment arm was measured as a function of joint angle using principles of rigid body kinematics. Stepwise linear regression indicated that maximum torque was most highly correlated with Po (r = +0.77, P less than 0.01) and accounted for approximately 75% of the measured torque. In addition, there was no significant correlation between maximum torque and maximum muscle moment arm (r = +0.11, P greater than 0.7) suggesting that muscle force, not musculoskeletal anatomy, represents the major determinant of maximum torque production in the frog hindlimb.

Animals↗
PubMed1988

Comparison between animal and human studies of skeletal muscle adaptation to chronic stimulation.

Functional electrical stimulation (FES) has recently emerged as a clinical tool for treatment of neuromuscular disorders. Chronic muscle stimulation, however, has long been used by basic scientists studying the details of the muscular adaptation process. Biochemical, morphological, and functional changes occur in skeletal muscle secondary to chronic stimulation. Chronic stimulation (12-24 hours per day for six weeks) results in a well-defined progression of changes in which a "fast" muscle becomes a typical "slow" muscle with a large decrease in force-generating capacity. On the other hand, clinical studies of FES have demonstrated muscle strengthening following treatment. An attempt is made to reconcile the results obtained in the two fields.

Adaptation, Physiological↗