Unit Cross-sectional Area Of Muscle Research Articles

Estimation of capillary density in human skeletal muscle based on maximal oxygen consumption rates.

A previously developed Krogh-type theoretical model was used to estimate capillary density in human skeletal muscle based on published measurements of oxygen consumption, arterial partial pressure of oxygen, and blood flow during maximal exercise. The model assumes that oxygen consumption in maximal exercise is limited by the ability of capillaries to deliver oxygen to tissue and is therefore strongly dependent on capillary density, defined as the number of capillaries per unit cross-sectional area of muscle. Based on an analysis of oxygen transport processes occurring at the microvascular level, the model allows estimation of the minimum number of straight, evenly spaced capillaries required to achieve a given oxygen consumption rate. Estimated capillary density values were determined from measurements of maximal oxygen consumption during knee extensor exercise and during whole body cycling, and they range from 459 to 1,468 capillaries/mm2. Measured capillary densities, obtained with either histochemical staining techniques or electron microscopy on quadriceps muscle biopsies from healthy subjects, are generally lower, ranging from 123 to 515 capillaries/mm2. This discrepancy is partly accounted for by the fact that capillary density decreases with muscle contraction and muscle biopsy samples typically are strongly contracted. The results imply that estimates of maximal oxygen transport rates based on capillary density values obtained from biopsy samples do not fully reflect the oxygen transport capacity of the capillaries in skeletal muscle.

Normalization of force generated by canine airway smooth muscles

A variety of normalizations have been employed to compare maximal isometric force (Po) produced by smooth muscles at different locations and stages of maturation. Because these procedures have not always been based on rigorous principles, confusion has resulted. To obtain a less ambiguous index of force production, we measured in vitro Po from mongrel canine tracheal (TSM) and bronchial (BSM) smooth muscle with an electromagnetic lever and normalized it to force per unit cross-sectional area of whole tissue (tissue stress), to force per unit cross-sectional area of muscle in the cross section of total tissue (muscle stress), and to force per fractional unit of myosin in the tissue cross section (myosin stress). Proportion of myosin in cross-sectional area of tissue was deduced from data obtained by sodium dodecyl sulfate gel electrophoresis of crude muscle extracts. For TSM, tissue stress was 1.499 X 10(5) N/m2 +/- 0.1 (SE), whereas it was only 0.351 X 10(5) N/m2 +/- 0.05 (SE) for BSM, representing a 4.27-fold difference (P less than 0.01). There was a 1.60-fold difference (P less than 0.05) in muscle stress, which was correlated to the morphometric finding that 79 +/- 1.4% (SE) of the tracheal strip cross section was muscle, whereas only 30 +/- 1.0% (SE) of bronchial tissue was occupied by muscle. Average myosin content was the same in smooth muscle cells of TSM and BSM, indicating that total amount of myosin in tissue cross sections was essentially a function of proportional area of muscle cells in total tissue cross sections.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Aging on Diaphragm Contractile Function in Golden Hamsters

The present study investigated the effects of aging on the contractile properties of the adult diaphragm in 42 Golden Syrian hamsters. Experiments were performed on isolated diaphragm strips from three groups of animals 4.9 +/- 0.4 (SE), 12.8 +/- 0.2, and 18.8 +/- 0.3 months of age. Aging was associated with a decrease in the maximal isometric tension generated per unit cross-sectional area of muscle and slowing in the time-to-peak tension and rate of muscle relaxation. The velocity of muscle shortening at a given load was also significantly less in older than in younger animals, and the force-velocity curve became flatter with advancing age as reflected by increases in the Hill coefficient (a/P0). Changes in maximal active tension and maximal velocity of unloaded shortening with aging correlated weakly (r greater than 0.3; p less than 0.05) and were of similar magnitude (-17 to -21%), suggesting that aging affects these two indices of muscle function in similar fashion. Finally, the diaphragm fatigued more rapidly in older than in younger animals. We conclude that aging depresses the ability of the adult diaphragm to generate tension and to shorten and resist fatigue.

Changes in strength and cross sectional area of the elbow flexors as a result of isometric strength training.

Changes in strength and size of the elbow flexor muscles have been compared during six weeks of isometric strength training in six male and six female subjects. Isometric training of one arm resulted in a significant increase in isometric force (14.5 +/- 5.1%, mean +/- SD, n = 12). No differences were seen in the response of male and female subjects. The extent of the change was similar to that reported for training studies of other muscles, thus refuting the suggestion that the elbow flexors may be especially amenable to training. Biceps and brachialis cross-sectional area (CSA) was measured from mid-upper arm X-ray computerized tomography before and after training. Muscles increased in area (5.4 +/- 3.8%) but this was smaller than, and not correlated with, the increase in strength. The main change in the first six weeks of strength training was therefore an increase in the force generated per unit cross-sectional area of muscle. The arrangement of fibres in the biceps is nearly parallel to the action of the muscle and it is argued that the increase in force per unit cross-sectional area is unlikely to be due to changes in the pennation of the muscle fibres as has been suggested for other muscles.

Human muscle strength training: the effects of three different regimens and the nature of the resultant changes.

1. Increases in strength and size of the quadriceps muscle have been compared during 12 weeks of either isometric or dynamic strength training. 2. Isometric training of one leg resulted in a significant increase in force (35 +/- 19%, mean +/- S.D., n = 6) with no change in the contralateral untrained control leg. 3. Quadriceps cross-sectional area was measured from mid-thigh X-ray computerized tomography (c.t.) scans before and after training. The increase in area (5 +/- 4.6%, mean +/- S.D., n = 6) was smaller than, and not correlated with, the increase in strength. 4. The possibility that the stimulus for gain in strength is the high force developed in the muscle was examined by comparing two training regimes, one where the muscle shortened (concentric) and the other where the muscle was stretched (eccentric) during the training exercise. Forces generated during eccentric training were 45% higher than during concentric training. 5. Similar changes in strength and muscle cross-sectional area were found after the two forms of exercise. Eccentric exercise increased isometric force by 11 +/- 3.6% (mean +/- S.D., n = 6), and concentric training by 15 +/- 8.0% (mean +/- S.D., n = 6). In both cases there was an approximate 5% increase in cross-sectional area. 6. It is concluded that as a result of strength training the main change in the first 12 weeks is an increase in the force generated per unit cross-sectional area of muscle. The stimulus for this is unknown but comparison of the effects of eccentric and concentric training suggest it is unlikely to be solely mechanical stress or metabolic fluxes in the muscle.

Maximal voluntary isometric strength in Danish adolescents 16-19 years of age.

The force in maximal voluntary isometric contraction of elbow flexors, knee extensors, trunk flexors, and trunk extensors was measured in a representative sample of Danish school children 16-19 years of age (128 boys and 165 girls). The 16 year old boys were 177.8 cm in height, with a mean increase of 1.4 cm per year up to 19 years, and they weighed 66.0 kg, with a mean increase of 1.8 kg per year up to age 19. The girls were 168.0 cm in height with no increase up to age 19, and their mean weight was 59.6 kg, which increased by 1.8 kg per year up to age 19 (p greater than 0.05). The strength in the four muscle groups for boys a girls respectively was 281 N and 182 N for elbow flexors, 574 N and 419 N for knee extensors, 601 N and 404 N for trunk flexors and 664 N and 499 N for trunk extensors. An increase in strength in the elbow and trunk flexors and a decrease in strength in the trunk extensors in relation to values obtained in 1956 was seen, and a difference in strength per kg lean body mass between the boys and the girls was also observed. The estimated strength per unit cross-sectional area of muscle was 38 N X cm-2 in both boys and girls.

Effect of bilateral sacral decentralization on detrusor contractility and passive properties in dog

AbstractA series of five dogs underwent complete parasympathetic decentralization through a lumbosacral laminectomy. A full‐thickness biopsy was taken from the anterior wall of the bladder before and 12 weeks after surgery. Both mucosa and adventitia were dissected out and muscle layer was cut into several consecutive longitudinal strips. Each strip was mounted in a muscle chamber and frequencyresponse curves were obtained at different pulse duration. Activelpassive force‐length relationships were then obtained under condi tions of maximal electrical stimulation (100 V, 2 msec, 40 cps), by stretching the strips in successive increments until length of maximal active force development was reached. Curves were normalized per unit cross‐sectional area of muscle. The maximum active stress of the specimens was taken as a measure of bladder contractility, and the rate of exponential increase in passive stress with strain (ratio of deformed to undeformed length) as a measure of detrusor stiffness.Twelve weeks after detrusor decentralization the following changes were found: (1) The frequency that yielded maximum contraction was 10 cps at 2‐ and 5‐;msec pulse duration as compared to 40 cps in controls at every pulse duration. (2) The maximum active stress was 123.9 ± 13.8 vs 244.7 ± 24.7 gm/cm2 in controls (p<.001). (3) The level of strain corresponding to the maximal active stress was significantly reduced. (4) The stiffness of the bladder wall was markedly increased; the rate of exponential increase was 4.47 ± 0.63 vs 2.19 ± 0.42 in controls (p<.001). (5) Thickness of the bladder wall was significantly increased (7 ± 1 vs 4 ± 1 mm; p<.001). (6) Histology sections of the specimens demonstrated collagen infiltration in all layers as well as smooth muscle hyperplasia.In summary, the effects of parasympathetic decentralization of the bladder wall are collagen infiltration, increased thickness, increased stiffness, and decreased contractility.

Isokinetic作業時のpeak torqueに及ぼす筋線維比率および筋断面積の影響

The purpose of this study was to investigate the effects of muscle fiber composition and muscle cross-sectional area on muscle strength in isokinetic contractions. Muscle biopsies were taken from the right vastus lateralis of 9 healthy untrained men. Using staining for myofibrillar adenosinetriphosphatase after preincubation at pH 4.3 and 4.6, muscle fibers were classified as ST, FTa, FTb, and FTc. But, FTc fibers were not calculated. Cross-sectional area of the leg extensor muscles were measured by ultrasonic measurements. Maximum strength for the leg extensor muscles were determined as peak torques with constant angular velocity using an isokinetic dynamometer (Cybex II, Lumex, New York). The peak torque values at various angular velocities (30°, 60°, 120°, and 180°/s) indicated significant positive correlation to %FTa fibers, % Area FTa fibers and Total area of FTa fibers. Other fiber types such as ST or FTb, however, were not related significantly to the peak torque values at all angular velocities. Significant positive correlation was observed between peak torque values per unit cross-sectional area of muscle (absolute strength) and % FTa fibers. These results suggest that in untrained men, %FTa fibers play more important role in producing high peak torques thah %FTb and % ST fibers, and that even if muscle cross-sectional areas are equal, muscles with high % FTa fibers can exert high isokinetic strength.

The relations between sarcomere length and characteristics of isometric twitch contractions of frog sartorius muscle.

1. Relations between sarcomere length, tension and time course of isometric twitches at 20 degrees C were determined for thirty-two sartorius muscles from Rana temporaria.2. The maximum isometric twitch tension per unit cross-sectional area of muscle ranged from 0.56 to 2.2 kg/cm(2) at 20 degrees C and initial sarcomere length about 2.1 mu. This variation was not correlated with the corresponding measure of tetanic tension.3. The maximum isometric twitch tension per unit cross-sectional area of muscle at 2.1 mu sarcomere length was directly correlated with twitch contraction time and inversely correlated with the cross-sectional area of the muscle.4. The isometric twitch contraction was potentiated with increase in initial sarcomere length from about 2.1 to about 2.8 mu at 20 degrees C, and the degree of potentiation was inversely correlated with the maximum isometric twitch tension per unit cross-sectional area of muscle at 2.1 mu sarcomere length.5. The sarcomere length: twitch tension relation is labile and may be altered by changes in temperature and the after-effects of repetitive stimulation.6. Variation in twitch contractions at different sarcomere lengths are discussed in connexion with excitation-contraction coupling and the degree of activation of muscle fibres during twitch contractions at 20 degrees C.

A study on training effect on strength per unit cross-sectional area of muscle by means of ultrasonic measurement.

The training effect on the human arm flexor was studied by subjecting 5 healthy males. The training was made by isometric maximum contraction, 3 times (10 seconds/bout) a day, every day except Sunday for 100 days. Ultrasonic photography was employed to estimate the cross-sectional area of the muscle.

Force:velocity properties of kitten muscles

1. The characteristics of isometric contractions and force:velocity properties of the extensor digitorum longus (EDL) and soleus (SOL) muscles of neonatal kittens were determined in situ.2. The mean contraction time is 51 msec for EDL and 70 msec for SOL and the half-relaxation time is 51 msec for EDL and 109 msec for SOL.3. The average maximum isometric tetanic tension per unit cross-sectional area of muscle is 1.27 kg/cm(2) for EDL and 1.17 kg/cm(2) for SOL.4. The average twitch:tetanus ratio is 0.28 for EDL and 0.119 for SOL; the low value for SOL was found for both indirect and direct stimulation.5. The average maximum speed of shortening of a sarcomere is 22.8 mu/sec for EDL and 12.7 mu/sec for SOL.6. These properties of neonatal muscles are compared with those of adult cat muscles and discussed in connexion with differentiation of mammalian muscles into fast and slow types.