Stress protein induction in skeletal muscle: comparison of laboratory models to naturally occurring hypertrophy.

The purpose of the study was to compare stress protein [heat shock protein (HSP) 72] response in laboratory models of hypertrophy to naturally occurring work-induced hypertrophy. Two laboratory models of hypertrophy inducement, namely, compensatory hypertrophy and stretch hypertrophy, were compared with hypertrophy resulting from migratory flight in the blue-winged teal. We hypothesized that HSP 72 would be expressed more strongly in hypertrophied muscle than in control muscle. Furthermore, we hypothesized that changes occurring in laboratory models would also occur in work-induced enlargement. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses were used to assess HSP 72 levels in control and hypertrophied muscle. Laboratory models elicited similar responses, with increased HSP 72 content in hypertrophied muscle. Work-induced hypertrophy or disuse atrophy did not change the degree of HSP 72 expression in the blue-winged teal. The presence of HSP 72 in these conditions may indicate that stressors eliciting changes in muscle protein expression, including the loss of muscle mass, may elicit HSP 72 synthesis.

Efficiency of trained cyclists using circular and noncircular chainrings.

The purpose of this study was to determine oxygen consumption (VO2), heart rate (HR) response, and rating of perceived exertion (RPE) of trained cyclists using noncircular and circular chainrings over a range of gears and pedal cadences. The subjects included 7 male cyclists (6 USCF licensed riders, 1 national qualifying triathlete). Each subject rode his own bicycle mounted on a wind-trainer at gears of 5.92 and 7.33 meters with noncircular and circular chainrings at pedal cadences of 50, 70, and 90 rpm. VO2, HR, RPE, and respiratory exchange ratio (RER) measurements were made during each of the 12 rides. Mean percent VO2max for each condition ranged from 28.7 +/- 2.1% with the 5.92 meter gear at 50 rpm to 83.4 +/- 4.3% using the 7.33 meter gear at 90 rpm. The results indicate no significant difference in any of the parameters measured between the two chainrings for any of the experimental conditions. The data indicate that the noncircular chainrings used in this study were not more efficient than the standard circular chainring for trained cyclists.

Skeletal muscle fibre number in the rat from youth to adulthood.

The purpose of this study was to determine whether or not there was a decrease in skeletal muscle fibre number in the rat from the early postnatal period to adulthood. Twelve male Sprague-Dawley rats were used in the study. At 25 days of age the animals underwent surgical removal of the soleus and tibialis anterior muscles from one hindlimb. At 180 days of age, 6 of the animals were killed and the soleus and tibialis anterior muscles from the contralateral leg were removed. The same procedure was carried out on the remaining 6 animals at 365 days of age. Fibre number was determined by the nitric acid digestion method for the soleus muscles and the mean fibre dry weight method for the tibialis anterior muscles. There was no difference in fibre number for either muscle between 25 days of age and 180 days of age or between 25 days of age and 365 days of age. The results of this study indicate that there is no change in skeletal muscle fibre number from the early postnatal period until adulthood in the rat.

Evaluation of animal models for the study of exercise-induced muscle enlargement.

Skeletal muscle is known to enlarge in response to high-resistance training programs in humans. Study of the cellular mechanisms of muscle enlargement and the adaptations of muscle to strength-training programs has been difficult because of the need to analyze entire muscles. This precludes the use of human subjects in many experiments of this nature. Several animal models have been developed for the study of muscle enlargement; these models basically fall into three categories: 1) stretch hypertrophy, 2) compensatory hypertrophy, and 3) exercise-induced hypertrophy. This review attempts to analyze these models as models of muscle enlargement produced by strength training in humans. Three areas must be considered when evaluating animal models of human muscle enlargement produced by strength training: 1) response topography, 2) magnitude of enlargement, and 3) muscle fiber adaptations produced as a result of the enlargement. Based on these considerations, it is concluded that none of the animal models currently in use truly represents the human strength-training situation under all conditions. All three models, however, provide valuable information about the plasticity of skeletal muscle in response to a broad spectrum of muscle enlargement.

Muscle fibre size and number following immobilisation atrophy.

Muscle fibre number and cross sectional area were studied in the response to immobilisation atrophy of the long head of the triceps brachii. Following eight weeks of immobilisation, fibre number of the muscle from the immobilised limb was compared to that of the contralateral control limb in six rats. Mean fibre cross sectional area of the LHT from the immobilised limb was compared to that of the contralateral control for another six animals. Atrophy, as estimated by a decrease in wet muscle weight, was 38.0% for the group used for fibre number estimations and 45.7% for the group used for fibre area. Fibre counts revealed no difference between muscles from immobilised and control limbs. Mean fibre area was 42.1% less for the muscle from the immobilised limb compared to the control limb. The results of this study indicate that atrophy of the LHT produced by immobilisation of the forelimb is the result of atrophy of the muscle fibres without a decrease in muscle fibre number.

Changes in fiber composition of soleus muscle during rat hindlimb suspension.

Chronic reduction of gravitational load in the rear limbs of rats to simulate the influence of near-zero gravity in skeletal muscles has been shown previously to elicit atrophy in the soleus muscle. Use of this model by the present investigation indicates that soleus atrophy was characterized by a decline in the number of fibers in groups that contained the slow isoenzyme of myosin and which were classified as type I from intensity of staining to myofibrillar actomyosin adenosinetriphosphatase (ATPase) and to NADH tetrazolium reductase. Furthermore total fiber number was not changed, whereas fibers containing the intermediate isoenzyme and those classified as type IIa increased. There results could be explained by either a change in the composition within existing fibers or a simultaneous loss of slow fibers and de novo synthesis of intermediate and fast fibers. Evidence for transformation included an absence of embryonic or neonatal myosin in muscles from suspended rats and the constant fiber number that was unchanged by 4 wk of suspension. Furthermore although fiber areas of both groups of type I and IIa fibers declined during suspension, variability of the fiber areas within each group did not increase.

The effect of severe dietary protein restriction on skeletal muscle fiber number, area and composition in weanling rats.

The purpose of the present investigation was to determine the effects of severe dietary protein restriction on soleus (S) and tibialis anterior (TA) fiber number and S muscle fiber area, composition and length. The S and TA muscles were removed from one leg of 12 male Sprague-Dawley rats at 21 d of age. Six of these animals were placed on a 1% protein diet until 42 d of age, while six served as age-matched controls. Muscle fiber number was determined by the nitric acid digestion method for S muscles and the mean fiber dry-weight estimation method for the TA muscles. Mean fiber numbers for the S muscles were 2,655 +/- 42 and 2,669 +/- 71 for the treatment group at 21 and 42 d of age, respectively, and 15,989 +/- 899 and 16,067 +/- 695 at 21 and 42 d of age, respectively, for the TA muscle. For the age-matched control group, fiber numbers for the S muscle were 2,928 +/- 78 and 2,949 +/- 76 at 21 and 42 d, respectively, and 17,964 +/- 281 and 18,445 +/- 296 at 21 and 42 d, respectively, for the TA muscle. The S muscle fiber area, composition and length were studied using 12 male Sprague-Dawley rats. Six animals were placed on the 1% protein diet from 21 to 42 d of age, while six animals served as age-matched controls. The S muscle fiber area was 33.1 and 51.5% smaller for type I and type II fibers, respectively, for animals fed the 1% protein diet. The S fiber length was 27.9% less in animals fed the 1% protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Fiber number, area, and composition of mouse soleus muscle following enlargement.

Muscle fiber number, cross-sectional area, and composition were studied in response to enlargement produced by synergistic ablation in the mouse soleus muscle. The effect of the location of a histological section on the number of fibers that appear in the section was also studied using the mouse soleus muscle. Enlargement was produced in the soleus muscle of 15 male and 15 female mice by ablation of the ipsilateral gastrocnemius muscle. Fiber counts, using the nitric acid digestion method, revealed no difference between control and enlarged muscles in male and female mice. Mean fiber area, determined by planimetry, was 49.1 and 34.5% greater following enlargement in male and female mice, respectively. Increase in muscle weight could be totally accounted for by the increase in fiber area following enlargement. A transformation of type II to type I fibers occurred following enlargement for both sexes. Counts of fibers from histological sections revealed that there was a progressive decrease in the fiber number as the section was moved from the belly to the distal end of the muscle. The results of these studies indicate that muscle enlargement in the mouse soleus muscle is due to hypertrophy of the existing muscle fibers.

A brief study of within litter and within strain variation in skeletal muscle fiber number in three lines of laboratory rodents.

The purpose of this study was to describe the soleus muscle fiber number variation within litter and within strain of three lines of laboratory rodents in an effort to determine the value of these lines in muscle fiber number research. The three lines of laboratory rodents used for the study were inbred mice (18 litters, 113 animals), outbred mice (8 litters, 97 animals), and inbred rats (14 litters, 126 animals). The animals were sacrificed at approximately 7 weeks of age and the soleus muscle from the right leg was removed for fiber number determination. Fiber number was determined by the nitric acid digestion method. The mean percent difference between the animals with the highest and lowest fiber number within litters was 14.4%, 13.0%, and 18.3% for inbred mice, outbred mice, and inbred rats, respectively. This was substantially less than the 38.2%, 27.8%, and 49.1% differences, respectively, that existed within strain. The results of this study indicate that fiber number variation within litter and within strain in the three lines of laboratory rodents used in this study would make comparison of fiber number between animals difficult to interpret.

Effect of increased growth rate during the suckling period on subsequent body weight and muscle weight to body weight ratio.

The effect of increased growth rate during the suckling period on subsequent body growth rate and muscle weight to body weight (MW/BW) ratio was examined in inbred and outbred male and female mice. Growth rate during the suckling period was increased by reducing litter size to 4 pups within six hours of birth. Body weight, MW/BW ratio, and dry weight to wet weight (DW/WW) ratio for the soleus, tibialis anterior, extensor digitorum longus, biceps brachii, and heart muscles were measured at 4, 8, 16, and 24 weeks of age. The results indicate that increasing growth rate during the suckling period results in an increased body weight at 24 weeks of age in outbred male and female mice; whereas, in inbred male and female mice body weight is greater at 4 weeks of age but by 8 weeks of age the mice raised in normal litters have "caught up" with those raised in small litters. MW/BW ratio is increased in several muscles during the suckling period but returns to normal during the post weaning period.

Body composition by hydrostatic weighing at total lung capacity and residual volume.

Body density and percent fat were determined by hydro-static weighing (HW) at residual volume (RV), total lung capacity measured on land (TLCL), and total lung capacity measured in water (TLCW) in 50 male and 50 female subjects. Residual volume was measured on land by using the helium dilution method. Vital capacity was measured both on land and with the subject submerged to the neck in water. Total lung capacity was reduced during water submersion by 6.7 and 5.1% in males and females, respectively. Body density was 1.0588 +/- 0.0215, 1.0581 +/- 0.0207, and 1.0634 +/- 0.0214 for males, and 1.0246 +/- 0.0219, 1.0242 +/- 0.0233, and 1.0276 +/- 0.0238 for females at RV, TLCW, and TLCL, respectively. Percent fat was 17.7 +/- 9.7, 18.0 +/- 9.3, and 15.7 +/- 9.5 for males, and 33.4 +/- 10.3, 33.5 +/- 10.8, and 32.0 +/- 11.0 for females at RV, TLCW, and TLCL, respectively. Body density and percent fat were similar when measured by HW at RV and by HW at TLCW. Body density and percent fat measured by HW at TLCL were different than when measured by HW at RV (P less than 0.001). The subjects, using a modified 10-point Borg Scale, rated the HW procedure easier to perform at TLC than at RV (P less than 0.001). The results of this study indicate that measurement of body density and percent fat by HW at TLCW and HW at RV are similar, but if measured by HW at TLCL, body density is overestimated and percent fat is underestimated.

Estimation of skeletal muscle fiber number by mean fiber dry weight.

The purpose of this study was to determine whether skeletal muscle fiber number could be accurately estimated by the determination of mean fiber dry weight (MFD) and total muscle dry weight. The muscles studied were the soleus, plantaris, gastrocnemius, extensor digitorum longus, tibialis anterior, and biceps brachii of the rat, the anterior latissimus dorsi of the chicken, and the flexor carpi radialis of the cat. Bundles of fibers were carefully separated from the muscle following nitric acid digestion (ND) and placed in groups of similar length. MFD determined from 400 to 800 fibers from each group was used to estimate the number of fibers in the remainder of the group. Estimated fiber number was compared with the fiber number determined in the muscle from the contralateral limb by the ND method. No difference in fiber number was observed between the ND method and the MFD estimation method for any of the muscles used in the study. The results indicate that the MFD estimation method is an accurate and relatively rapid method of fiber number determination in skeletal muscle.

The effect of reduced dietary protein on the anterior latissimus dorsi muscle fibers in the Single Comb White Leghorn pullet.

Twenty-four female Single Comb White Leghorn pullets were used to investigate the effect of two levels of dietary protein on fiber number and size of the anterior latissimus dorsi muscle (ALD). The pullets were randomly assigned to a control group of 18% dietary protein or an experimental group of 14% dietary protein at 1 day of age. They were maintained on these diets until 4 weeks of age, at which time they were sacrificed by cervical dislocation. The ALD muscle was removed and analyzed for fiber number, fiber dry weight, and fiber dry weight to muscle wet weight ratio. Muscle fiber number was determined by a direct count of all the fibers following nitric acid digestion. After counting, the muscle fibers were dried to a constant weight for determination of mean fiber dry weight and fiber dry weight to muscle wet weight ratio. Muscle weight of the control group was 39.8% greater than that of the experimental group. Fiber number was not different between control and experimental groups; whereas mean fiber dry weight was 59.6% greater in the control group (P less than .05). Fiber dry weight to muscle wet weight ratio was 7.3% greater in the control group (P less than .05). The data indicate that when growth of the ALD muscle is restricted by low dietary protein content, there is a reduced growth of the individual muscle fibers with no alteration in their number.

The effect of varying postnatal growth rate on skeletal muscle fiber number in the mouse.

The present study was designed to investigate the effect of increased and decreased growth rate during the early postnatal period on skeletal muscle fiber number in the mouse. Growth rate was controlled by altering litter size shortly after birth. Three litter sizes, small (4 animals), normal (8 animals), and large (12 animals) were used for the study. The animals were sacrificed at 24 days of age and the soleus muscle from one leg was excised and used for fiber number determination. Fiber number was determined by direct counts of fibers individually teased from the muscle following HNO3 fixation. Marked differences occurred in growth rates among the three groups. The small litter animals grew more rapidly than the normal and large litter animals, and the normal litter animals grew more rapidly than the large litter animals. Fiber counts of the soleus muscle revealed no difference in fiber number among animals raised in small, normal, or large litters. These data suggest that early postnatal growth rate has no effect on soleus muscle fiber number in the mouse.

Muscular enlargement and number of fibers in skeletal muscles of rats.

The effect of muscular enlargement produced by surgical ablation of a synergist and the combination of synergist ablation and exercise on the number of fibers in the soleus (S), plantaris (P), and extensor digitorum longus (EDL) muscles of the rat was studied. The number of fibers per muscle was determined by direct counts of individual fibers dissected from HNO3-treated muscles. Ablation of a synergist produced average enlargements of about 25, 45, and 29% for the S, P, and EDL muscles, respectively. Exercise and synergist ablation produced increases in wet weight to about 44 and 88% for the S and P muscles, respectively, whereas no further increases were observed in the EDL muscles. Intra-animal comparisons revealed that no differences existed for total fiber number or the incidence of fibers with bifurcations between the enlarged and contralateral control muscles. The difference in dry weight of fibers from the enlarged as compared with control muscles was closely correlated to differences in total muscle wet weight. These data demonstrate that hypertrophy rather than hyperplasia was responsible for increases from 10 to over 100% in the weight of skeletal muscles.