Enzyme activities of FT and ST muscle fibers in heavy-resistance trained athletes

Tissue samples were obtained from the vastus lateralis muscle of elite olympic weight and power lifters (OL/PL, n = 6), bodybuilders (BB, n = 7), and sedentary men (n = 7). Enzyme activities of citrate synthase (CS), lactate dehydrogenase (LD), 3-OH-acyl-CoA-dehydrogenase (HAD), and myokinase (MK) were assayed on freeze-dried dissected pools of slow-twitch (ST) and fast-twitch (FT) fiber fragments by fluorometric means. Histochemical analyses were carried out to assess fiber type composition and fiber area. CS and HAD activities were lower (P less than 0.05), and LD and MK were higher (P less than 0.05) in FT than ST fibers in the entire subject pool (n = 20). CS of FT fibers and HAD of ST fibers were lower in athletes (P less than 0.05-0.01) compared with nonathletes, whereas LD of both fiber types was higher (P less than 0.05-0.001) in athletes. CS activity of ST fibers and MK activity of FT fibers were higher (P less than 0.05) in BB compared with OL/PL. FT and ST fiber area was greater (P less than 0.05) in athletes than in nonathletes. BB displayed greater (P less than 0.05) fiber size than OL/PL. FT/ST area was greater (P less than 0.05) in OL/PL than BB. It is suggested that long-term heavy-resistance training results in specific metabolic adaptations of FT and ST fiber types. These changes appear to be influenced by the type of resistance training.     

CK and LD isozymes in human single muscle fibers in trained athletes

Individual human muscle fibers from the vastus lateralis were isolated from age-matched endurance-trained and strength-trained athletes and untrained controls. Slow- (ST) and fast-twitch (FT) fibers were assayed for total creatine kinase (CK), CK-MB, total lactate dehydrogenase (LD), the LD isozyme that predominates in the heart muscle of most vertebrates (LD1), and citrate synthase (CS). Regardless of training of the athletes, both CK-MB and CS were higher in ST than in FT fibers. Also, irrespective of fiber type, CK-MB and CS were greatest in the endurance-trained group. A positive correlation existed between CK-MB and CS, relating oxidative capacity of individual fibers with CK-MB. Total CK varied little among the fiber types, trained groups, or controls. Total LD in FT fibers was greater than in ST fibers in all groups, with only ST fibers from the endurance-trained group containing substantial amounts of LD1. These findings suggest that specific training, endurance exercise, causes a favorable metabolic adaptation of CK and LD isozymes at the individual fiber level, allowing for the muscle to cope with increased energy demands during prolonged exercise.     

Changes in total fiber numbers of disused soleus muscle on rats

In this study, by use of technique that was modified from Morey method, we discussed the histological influence on the soleus muscle of the rats caused by disuse. This study is characterized by the calculating of total numbers of muscle fibers. ST (slow-twitch) and FT (fast-twitch) fibers in total muscular cross-sectional area were classified by their difference in intensity of staining of actomyosin adenosinetriphosphatase (myosin ATPase). During the experiment, average fiber diameter of ST and FT fibers declined when compared to control group (p less than 0.01). A 54% decrease in the total number of ST fibers was observed in the experimental group (p less than 0.01). Conversely, the total number of FT fibers increased to 362% of the control value (p less than 0.01). These results of the changes evoked in ST and FT fibers indicate 34% decrease in total muscular cross-sectional area, and showed that muscular function shifted toward a faster muscle in disused soleus muscle.     

Mitochondrial adaptations in skeletal muscle cells in mammals exposed to gravitational unloading

It is known that exposure to actual or simulated weightlessness is often accompanied by decreased muscle dynamic performance, and increased level of blood lactate accumulation. Decreased mitochondrial content found in fibers of the working muscles is considered to be one of the possible causes for those changes. Studies on oxidative potential of the muscle cell (i.e. capacity of the cell to oxidative energy production) under conditions of altered gravity have been carried out since late 70-ties. It was shown that the relatively short term spaceflight and hindlimb suspension induced significant decrease oxidative enzyme activities and mitochondrial volume density in rat fast muscle. However postural soleus muscle failed to exhibit similar changes, although the absolute mitochondrial content was found to be sufficiently lower after exposure to simulated microgravity. This phenomenon allowed to conclude that the pronounced soleus fiber atrophy masked the proportional absolute decrease in oxidative potential which failed to be revealed as subsequent changes in mitochondrial volume density and oxidative enzyme activity. It is also important, that biosatellite studies exposed considerable changes in mitochondria distribution pattern inside m. soleus fibers: volume density of mitochondria (and, correspondingly, activity of oxidative enzymes) increases (or does not change) in the center of fiber, and decreases at its periphery, in subsarcolemmal area. However the time course of mitochondrial alterations development (particularly during long-duration exposures to real or simulated microgravity) and some peculiarities of the mitochondria distribution were not described yet. Also, materials dealing with simultaneous time-course comparative analysis of mitochondrial characteristics and indices of physiological cost of submaximal exercise are very rare. The present paper is purposed to compare the data, obtained in several experimental studies, allowed to analyze the possible contribution of muscle mitochondria changes to changes in metabolic cost of submaximal exercise and the time-course dynamics of mitochondrial characteristics under conditions of actual or simulated gravitational unloading.     

Effect of long-term hypergravitation on the skeletal-muscular tissue in rats

The space flight or simulated gravitational unloading lead to the muscle atrophy, slow-to-fast transformation of muscle fibers and myofibrillar damages both in humans and animals (1, 7, 13, 17). This process could be prevented by the exercise training during space flight (1), (partly) by periodic weight support during unloading (13). It has been demonstrated in these studies that there is some level of force production necessary for the maintenance of skeletal muscle properties. It is known that adaptation to the physical training frequently induces augmentation in cross-sectional area (CSA) of muscle fibers (MF), transformation of fibers, augmentation of mitochondrial volume density, and increase in absolute volume of myofibrillas. Numerous observations suggest importance of gravitational loading in regulating muscle mass. The centrifuging is believed to be useful for preventing muscle functional and structural losses under microgravity. But there are few studies designed to investigate effect of artificial gravity on the skeletal musculature (2, 7). Our objective was to investigate structural adaptation in slow-twitch soleus muscle (percentage of connective tissue and central nuclei, fiber size, myosin heavy chain isotope, myofibrillar proteins and mitochondria volume density) after 19 and 33 days of hypergravity.     

Creatine phosphate in fiber types of skeletal muscle before and after exhaustive exercise

Percutaneous muscle biopsies were obtained from the vastus lateralis of physically active men (n = 12) 1) at rest, 2) immediately after an exercise bout consisting of 30 maximal voluntary knee extensions of constant angular velocity (3.14 rad/s), and 3) 60 s after termination of exercise. Creatine phosphate (CP) content was analyzed in pools of freeze-dried fast-twitch (FT) and slow-twitch (ST) muscle fiber fragments, and ATP, CP, creatine, and lactate content were assayed in mixed pools of FT and ST fibers. CP content at rest was 82.7 +/- 11.2 and 73.1 +/- 9.5 (SD) mmol/kg dry wt in FT and ST fibers (P less than 0.05). After exercise the corresponding values were 25.4 +/- 19.8 and 29.7 +/- 14.4 mmol/kg dry wt. After 60 s of recovery CP increased (P less than 0.01) to 41.3 +/- 12.6 and 49.6 +/- 11.7 mmol/kg dry wt in FT and ST fibers, respectively. CP content after recovery, relative to initial level, was higher in ST compared with FT fibers (P less than 0.05). ATP content decreased (P less than 0.05) and lactate content rose to 67.4 +/- 28.3 mmol/kg dry wt (P less than 0.001) in response to exercise. It is concluded that basal CP content is higher in FT fibers than in ST fibers. CP content also appears to be higher in ST fibers after a 60-s recovery period after maximal short-term exercise. These data are consistent with the different metabolic profiles of FT and ST fibers.     

Muscle fiber type effects on energetically optimal cadences in cycling

Fast-twitch (FT) and slow-twitch (ST) muscle fibers vary in their mechanical and energetic properties, and it has been suggested that muscle fiber type distribution influences energy expenditure and the energetically optimal cadence during pedaling. However, it is challenging to experimentally isolate the effects of muscle fiber type on pedaling energetics. In the present study, a modeling and computer simulation approach was used to test the dependence of muscle energy expenditure on pedaling rate during submaximal cycling. Simulations were generated using a musculoskeletal model at cadences from 40 to 120 rev min(-1), and the dynamic and energetic properties of the model muscles were scaled to represent a range of muscle fiber types. Energy expenditure and the energetically optimal cadence were found to be higher in a model with more FT fibers than a model with more ST fibers, consistent with predictions from the experimental literature. At the muscle level, mechanical efficiency was lower in the model with a greater proportion of FT fibers, but peaked at a higher cadence than in the ST model. Regardless of fiber type distribution, mechanical efficiency was low at 40 rev min(-1), increased to a broad plateau between 60 and 100 rev min(-1) , and decreased substantially at 120 rev min(-1). In conclusion, muscle fiber type distribution was confirmed as an important determinant of the energetics of pedaling.     

Influence of corticosteroids on myonuclear domain size in the rat diaphragm muscle.

Skeletal muscle fibers are multinucleated. Each myonucleus regulates gene products and protein expression in only a restricted portion of the muscle fiber, the myonuclear domain (MND). In the rat diaphragm muscle (DIAm), corticosteroid (CoS) treatment causes atrophy of fibers containing myosin heavy chain (MHC): MHC2X and/or MHC2B. We hypothesized that DIAm fiber MND size is maintained during CoS-induced atrophy. Adult male rats received methylprednisolone for 11 days at 1 (CoS-Low, n = 8) or 8 mg x kg(-1) x day(-1) (CoS-High, n = 8). Age-matched (CTL-AgeM, n = 8), sham-operated (SHAM-AgeM, n = 8), and weight-matched (CTL-WtM, n = 8) animals served as controls. In single DIAm fibers, cross-sectional area (CSA), MND size, and MHC expression were determined. Fiber CSA and MND size were similar in CTL-AgeM and SHAM-AgeM groups. Only fibers containing MHCslow or MHC2A displayed smaller CSA in CTL-WtM than in CTL-AgeM and SHAM-AgeM groups, and MND size was reduced in all fibers. Thus fibers containing MHCslow and MHC2A maintain the number of myonuclei, whereas MHC2X or MHC2B fibers show loss of myonuclei during normal muscle growth. Both CoS groups displayed smaller CSA and MND size than CTL-AgeM and SHAM-AgeM groups. However, compared with CTL-WtM DIAm fibers, only fibers containing MHC2X or MHC2B displayed reduced CSA and MND size after CoS treatment. Thus little, if any, loss of myonuclei was associated with CoS-induced atrophy of MHC2X or MHC2B DIAm fibers. In summary, MND size does not appear to be regulated during CoS-induced DIAm atrophy.     

Muscle hypertrophy in bodybuilders

Muscle biopsy samples were obtained from m. vastus lateralis and m. deltoideus of three high caliber bodybuilders. Tissue specimens were analysed with respect to relative distribution of fast twitch (FT) and slow twitch (ST) fiber types and different indices of fiber area. In comparison to a reference group of competitive power/weight-lifters the following tendencies were observed: the percentage of FT fibers was less, mean fiber area was smaller and selective FT fiber hypertrophy was not evident. Values for fiber type composition and fiber size were more similar to values reported for physical education students and non-strength trained individuals. The results suggest that weight training induced muscle hypertrophy may be regulated by different mechanisms depending upon the volume and intensity of exercise.     

Changes in muscle fiber populations and muscle enzyme activities in the primiparous lactating sow

An experiment involving 12 primiparous Large White sows was conducted to investigate changes in contractile and metabolic characteristics of skeletal muscle during the first 3 weeks of lactation. The sows lost 19.7 +/- 6.6 kg of body weight. No change in DNA concentration was observed in the longissimus dorsi (LD), a fast-twitch glycolytic muscle, and the trapezius (T), a mainly slow-twitch oxidative muscle during lactation. The percentage of type I fibers increased (P less than 0.05) in LD, but not in T. The muscle fiber cross sectional area (CSA) of IIB fibers, which represents about 78% of the total number of LD fibers, decreased by 18% (P less than 0.01) by lactation; the CSAs of I and IIA fibers were not significantly affected. Marker enzyme activities for oxidative and glycolytic metabolisms decreased in both muscles during lactation. The decrease in oxidative enzyme activities was particularly dramatic in T (P less than 0.001). No significant relationship was observed between sow weight loss and changes in muscle fiber CSA or enzyme activities. The extent to which the results could be related to a negative nutritional balance or to changes in hormonal status is discussed.     

Heart failure increases atrogin-1 and MuRF1 gene expression in skeletal muscle with fiber type-specific atrophy

Heart failure (HF) is characterized by a reduced tolerance to exercise due to early fatigue and dyspnea; this may be due in part to skeletal muscle myopathy with a shift from slow to fast fibers and loss of muscle mass. Muscle wasting does not occur similarly in all types of muscle fiber, thus we tested the hypothesis that HF induces skeletal muscle atrophy in a fiber type-specific manner altering the expression of atrogin-1 and MuRF1 in a fast muscle of rats with monocrotaline-induced heart failure. We studied extensor digitorum longus (EDL) muscle from both HF and control Wistar rats. Atrogin-1 and MuRF1 mRNA content were determined using Real-Time RT-qPCR while muscle fiber cross-sectional area (CSA) from sections stained histochemically for myofibrillar ATPase were used as an index of type-specific fiber atrophy. The measurement of gene expression by RT-qPCR revealed that EDL muscle mRNA expression of MuRF1 and atrogin-1 was significantly increased in the HF group. Muscle fiber type IIB CSA decreased in the HF group compared to the CT group; there was no significant difference in muscle fiber types I and IIA/D CSA between the HF and CT groups. In conclusion, we showed that HF induces fiber type IIB specific atrophy, up-regulating atrogin-1 and MuRF1 mRNA expression in EDL muscle of monocrotaline treated rats.     

Contrasts in muscle and myofibers of elite male and female bodybuilders

Muscle cross-sectional area (CSA), fiber area, and fiber number were determined from the biceps brachii of eight elite male bodybuilders (MB) and five elite female bodybuilders (FB) who had similar training characteristics. Biceps CSA was obtained from computer tomographic scanning and corrected for noncontractile tissue. Biceps CSA was twofold greater in MB relative to FB and strongly correlated to lean body mass (R = 0.93). Biceps CSA expressed per kilogram lean body mass (LBM) or per centimeter body height (BH) was 35% greater in MB compared with FB. Most of the gender difference in muscle CSA was because of greater absolute mean fiber areas in MB (9,607 microns2) relative to FB (5,386 microns2); however, MB also had a significantly greater population of small type II fibers (less than 2,000 microns2) compared with FB. Type II fiber area/LBM averaged 1.6-fold greater in MB compared with FB; however, type I fiber area/LBM was similar between groups. Biceps CSA was positively correlated to fiber CSA (R = 0.75) and fiber number (R = 0.55). This suggests that adaptations to resistance training may be complex and involve fiber hypertrophy and fiber number (e.g., proliferation). Alternatively, since the muscle characteristics before training are not known, these apparent adaptations might be genetically determined attributes.     

Role of afferent control in maintaining structural and metabolic characteristics of stretched soleus in rats exposed to hindlimb suspension

It is known that gravitational unloading (GU) induces atrophy of skeletal muscles and slow-to-fast muscle fiber (MF) transformation. Stretching of m. soleus prevents those changes, probably afferent information from the stretched muscle acting as triggering mechanism. It was shown that EMG of suspended animals or of stretched muscle is similar to that of control animals. Our study was aimed at revealing contribution of the afferent information from stretched m.soleus exposed to GU in maintenance of cross-sectional area (CSA) of MF and of myosine heavy chains and oxidative potential of skeletal muscles.     

Influence of weight bearing on the adaptations of rat plantaris to ablation of its synergists

The present study was designed to determine the contribution of weight bearing to the adaptations of the plantaris (PL) to synergist removal. PL from female rats were exposed to 28 days of a simultaneous condition of synergist ablation and hindlimb suspension. At 28 days, contractile responses and morphological measures were obtained and compared with muscles that either had synergists intact or were weight bearing or a combination of both. Synergist ablation prolonged PL maximum isometric twitch tension (Pt), time to peak tension (12%), and one-half relaxation time (12%); increased Pt (26%), maximum isometric tetanic tension (Po, 44%), fatigue resistance (FI, 42%), and fast fiber cross-sectional area (FT CSA, 20%); and decreased Pt/Po (13%) over nonablation counterparts. Suspension decreased PL Pt (26%), Po (26%), rest length (16%), FT CSA (31%), and slow-twitch fiber (ST) number (24%) but increased FI (75%) over weight-bearing counterparts. PL from weight-bearing animals were heavier than from suspended animals, and the extent of this response was greatest after synergist removal. Whole muscle and ST CSA and ST area contribution were greater only in weight-bearing synergist ablation muscles. Daily weight bearing (4 h) in synergist ablation hindlimb suspension groups caused PL weights and ST expressions to be halfway between 24-h suspension and 24-h weight-bearing groups. Our results suggest that weight bearing is not essential to the induction of several adaptations associated with synergist ablation but is required to cause the large muscle mass and ST expression characteristic of this model.     

Effects of simulated microgravity on immunoreactivity of conjugated-ubiquitin of muscle spindles of soleus in rats

It is well known that the muscle spindle is a receptor of muscle's tension and length, it plays an important role in maintaining the muscle's tension. The aim of the present study is to compare the cross-section area (CSA) and the immunoreactivity of conjugated-ubiquitin in soleus extrafusal and intrafusal fibers after simulated-microgravity in order to demonstrate the role of muscle spindle in muscle atrophy induced by simulated microgravity.     

Effects of laparotomy, cage type, gestation period and spaceflight on abdominal muscles of pregnant rodents.

We studied the effects of four variables on the histological properties of three body wall muscles-rectus abdominis (RA), transversus abdominis (TA), and external oblique (EO)-from pregnant rats. The variables examined were (1) gestation period; (2) cage design; (3) the effect of a midline laparotomy, performed to determine fetus numbers; and (4) exposure to a nine-day spaceflight. We measured fiber cross-sectional area (CSA), metabolic enzyme levels (succinate dehydrogenase, glycerophosphate dehydrogenase), and myosin heavy chain (MHC) immunoreactivity in samples from each muscle. A major effect of spaceflight was an increase of 42-171% in fibers double-labeled for MHC in all three muscles. Based on fiber CSA, the TA and RA muscles showed signs of stretching with increased gestation; i.e., the CSA decreased 11-12% over a nine-day period. The EO, a torso rotator, hypertrophied by 9% in rats group-housed in cages with a complex 3-D structure, compared to controls housed singly in standard flat-bottom cages. The TA and EO, whose contractions would pull on the suture line, showed signs of atrophy in laparotomized animals, exhibiting a 12% decrease in muscle fiber CSA. Exposure to weightlessness is known to induce atrophy in most skeletal muscles. Surprisingly, the EO actually hypertrophied 11% in our flight animals; however, this can be explained by the fact that those rats actively rotated their torsos seven times more often than ground controls. The flight rats also had twice as many contractions as controls. However, they were still able to give birth on time postflight.     

Throwing performance after resistance training and detraining

The purpose of the present study was to investigate the effect of short-term resistance training and detraining on shot put throwing performance. Eleven young healthy subjects with basic shot put skills participated in 14 weeks of resistance training, which was followed by 4 weeks of detraining. Shot put performance in four field tests was measured before (T1) and after (T2) resistance training and after detraining (T3). At the same time points, one repetition maximum (1RM) was measured in squat, bench press, and leg press. Fat-free mass (FFM) was determined with dual x-ray absorptiometry and muscle biopsies obtained from vastus lateralis for the determination of fiber type composition and cross-sectional area (CSA). 1RM strength increased 22-34% (p < 0.01) at T2 and decreased 4-5% (not significantly different) at T3. Shot put performance increased 6-12% (p < 0.05) after training and remained unaltered after detraining. FFM increased at T2 (p < 0.05) but remained unchanged between T2 and T3. Muscle fiber CSA increased 12-18% (p < 0.05) at T2. Type I muscle fiber CSA was not altered after detraining, but type IIa and IIx fiber CSA was reduced 10-12% (p < 0.05). The percentage of type IIx muscle fibers was reduced after training (T1 = 18.7 +/- 4, T2 = 10.4 +/- 1; p < 0.05), and it was increased at T3 compared with T2 (T3 = 13.7 +/- 1; p < 0.05). These results suggest that shot put performance remains unaltered after 4 weeks of complete detraining in moderately resistance-trained subjects. This might be linked to the concomitant reduction of muscle fiber CSA and increase in the percentage of type IIx muscle fibers.     

Effects of gender and functional overload on plantaris muscle morphology in the dwarf (HsdOla:dw-4) Lewis rat

To investigate relationships between pituitary function and gender on skeletal muscle growth and hypertrophy, fiber cross sectional area (CSA) and type were assessed in the plantaris muscle of normal and dwarf (Dw) male and female Lewis rats after 6 weeks of functional overload (FO). Serum growth hormone levels were 70-80% less in Dw rats of both genders, and body mass was 62% greater in normal rats when compared to their Dw counterparts. Muscle weight was affected by gender, dwarfism, and FO as well as a significant gender*Dw*FO interaction. FO increased Type I, IIA, and IIX/B fiber CSA 120%, 102%, and 75%, respectively. Only type 1H fibers exhibited a reduction in CSA as a function of gender or dwarfism. Both type IIA and IIX/B fibers were affected by a significant gender*Dw*FO interaction. Our results suggest that the growth of type II fibers is sensitive to gender and pituitary function, while hypertrophy of type II muscle fibers is a function of the interaction between mechanical load, gender, and pituitary function.     

Sarco(endo)plasmic reticulum calcium pump isoforms in paralyzed rat slow muscle

To assess the influence of paralysis on the expression of phenotypic protein isoforms related to muscle relaxation, the effects of spinal cord transection (ST) on sarco(endo)plasmic reticulum calcium ATPase (SERCA) pump isoform protein levels in the slow rat soleus were measured. Western blotting using SERCA isoform specific antibodies demonstrated a rapid up-regulation (7 days post ST) of the fast fiber type-specific isoform (SERCA1). In contrast, the slow fiber type-specific isoform, SERCA2, was decreased with a slower time-course. The up-regulation of SERCA1 protein preceded the up-regulation of fast myosin heavy chain (MyHC) (i.e., MyHC-II). Immunohistochemical analyses of single muscle fibers showed that 15 days after ST there was a pronounced increase in the proportion of slow MyHC fibers with SERCA1 confirming that SERCA1 was up-regulated in the slow fibers of the soleus prior to MyHC-II. These data suggest that the expression of the SERCA isoforms (particularly SERCA1) may serve as more sensitive markers of phenotypic adaptation in response to altered levels of contractile activity than the MyHC isoforms. In addition, since the expression of SERCA isoforms was dissociated from MyHC isoforms, regulation of gene expression for these two different protein systems must involve different signaling events and/or synthetic processes.