Short-time recovery skeletal muscle from dexamethasone-induced atrophy and weakness in old female rats.

BACKGROUND: Several pathological conditions (atrophy, dystrophy, spasticity, inflammation) can change muscle biomechanical parameters. Our previous works have shown that dexamethasone treatment changes skeletal muscle tone, stiffness, elasticity. Exercise training may oppose the side effects observed during dexamethasone treatment. The purpose of this study was to examine the changes in biomechanical parameters (tone, stiffness, elasticity) of skeletal muscle occurring during dexamethasone treatment and subsequent short-time recovery from glucocorticoid-induced muscle atrophy and weakness, as well as the effect of mild therapeutic exercise. METHODS: 17 old female rats, aged 22 months were used in this study. The hand-held and non-invasive device (MyotonPRO, Myoton Ltd., Tallinn, Estonia) was used to study changes in biomechanical properties of muscle. Additionally, body and muscle mass, hind limb grip strength were assessed. FINDINGS: Results showed that dexamethasone treatment alters muscle tone, stiffness and elasticity. During 20-day recovery period all measured parameters gradually improved towards the average baseline, however, remaining significantly lower than these values. The body and muscle mass, hind limb grip strength of the rats decreased considerably in the groups that received glucocorticoids. After 20 days of recovery, hind limb grip strength of the animals was slightly lower than the baseline value and mild therapeutic exercise had a slight but not significant effect on hind limb grip strength. Biomechanical parameters improved during the recovery period, but only dynamic stiffness and decrement retuned to baseline value. INTERPRETATION: The study results show that monitoring muscle biomechanical parameters allows to assess the recovery of atrophied muscle from steroid myopathy.

The Effect of Different Periodization and Modes of Concurrent Strength and Endurance Training on Double Poling Performance and Body Composition in Adolescent Cross-Country Skiers.

The aim of the study was to compare the effects of different types and periodization of strength training on body composition and maximal aerobic performance in 10-week training period in adolescent XC skiers. Twenty-eight adolescent competitive cross-country skiers, including 10 females (age 17.9 ± 1.8 years; body mass 69.6 ± 9.7 kg; height 1.77 ± 0.1 m; training experience 8.6 ± 3.2 years) took part in this study. Pre-and post-intervention performance was measured with the incremental exercise test (Pmax) on a double poling ski ergometer. Changes in body composition were measured with DXA. In addition to regular endurance training, experimental group one (EXP1) performed maximal and explosive strength training two times per week, experimental group two (EXP2) performed maximal and explosive strength training 1-3 times per week, and the traditional (TRAD) group performed low intensity-high volume strength training 2 times per week. Increases in arm, trunk, and overall lean mass were found in TRAD (p < 0.05). Increases in arm lean-mass was found in EXP1 (p < 0.05), while no changes in body composition occurred in EXP2 (p ≥ 0.05). Pmax improved significantly in all groups (p < 0.05). Changes in body mass, overall and arm lean mass was related to changes in absolute performance (W; p < 0.05), while no relationships were found between changes in body composition parameters and relative performance (W/kg; p ≥ 0.05). In conclusion, different periodization of strength training led to similar improvements in double poling ergometer performance, but resulted in different changes in body composition (lean mass) in adolescent cross-country skiers.

Vitamin C and E Treatment Blunts Sprint Interval Training-Induced Changes in Inflammatory Mediator-, Calcium-, and Mitochondria-Related Signaling in Recreationally Active Elderly Humans.

Sprint interval training (SIT) has emerged as a time-efficient training regimen for young individuals. Here, we studied whether SIT is effective also in elderly individuals and whether the training response was affected by treatment with the antioxidants vitamin C and E. Recreationally active elderly (mean age 65) men received either vitamin C (1 g/day) and vitamin E (235 mg/day) or placebo. Training consisted of nine SIT sessions (three sessions/week for three weeks of 4-6 repetitions of 30-s all-out cycling sprints) interposed by 4 min rest. Vastus lateralis muscle biopsies were taken before, 1 h after, and 24 h after the first and last SIT sessions. At the end of the three weeks of training, SIT-induced changes in relative mRNA expression of reactive oxygen/nitrogen species (ROS)- and mitochondria-related proteins, inflammatory mediators, and the sarcoplasmic reticulum Ca2+ channel, the ryanodine receptor 1 (RyR1), were blunted in the vitamin treated group. Western blots frequently showed a major (>50%) decrease in the full-length expression of RyR1 24 h after SIT sessions; in the trained state, vitamin treatment seemed to provide protection against this severe RyR1 modification. Power at exhaustion during an incremental cycling test was increased by ~5% at the end of the training period, whereas maximal oxygen uptake remained unchanged; vitamin treatment did not affect these measures. In conclusion, treatment with the antioxidants vitamin C and E blunts SIT-induced cellular signaling in skeletal muscle of elderly individuals, while the present training regimen was too short or too intense for the changes in signaling to be translated into a clear-cut change in physical performance.

Better Economy on Indoor Track Compared to Treadmill Running With 1% Inclination.

Purpose: The purpose of this study was to investigate the differences in metabolic responses between the track and the treadmill (1% inclination) running. The latter is recommended for use in laboratory settings to mimic outdoor running. Method: Seventeen male endurance athletes (mean 25.8, s = 3.8 years) performed 4-min running bouts on an indoor track and the treadmill. Results: At all speeds (11, 13, and 15 km·h-1) athletes showed better economy on the track running compared to the treadmill expressed as oxygen (7.9%, 5.2%, and 2.8%) and caloric (7.0%, 5.3%, and 2.6%) unit cost. Rating of perceived exertion was evaluated substantially higher at all speeds on the treadmill (F(1,16) = 31.45, p < .001, η2p = .663) compared to running on the track. Participants presented lower heart rate (F(1,16) = 13.74, p = .002, η2p = .462) on the track at the speed of 11 and 13 km·h-1 compared to the treadmill, but not at 15 km·h-1 (p = .021). Conclusions: We conclude that constant inclination (i.e.. 1%) during the treadmill test might not be suitable to reproduce comparable effort to running on the track; rather, there is an optimal treadmill inclination for different intensities to reproduce similar effort compared to the track running.

Changes in Body Composition of Old Rats at Different Time Points After Dexamethasone Administration.

BACKGROUND: Aging leads to changes in skeletal muscle quantity and quality and is accompanied with increase in body mass and fat mass, whereas fat-free mass either decreases or remains unchanged. The body composition of rodents has been an important factor for clinical trials in the laboratory. Glucocorticoids such as dexamethasone are widely used in clinical medicine, but may induce myopathy, characterized by muscle weakness, atrophy, and fatigue. In animals treated with glucocorticoids, a dose-dependent reduction of body weight has been observed. This weight loss is usually followed by muscle atrophy and a reduction of several muscle proteins, contributing to impaired muscle function. This study was designed to describe changes in body composition and BMC of 22-month-old rats during 10- and 20-day recovery period after 10-day dexamethasone administration. METHOD: Data on body mass, lean body mass, fat mass and bone mineral content of the rats were obtained with dual energy X-ray absorptiometry scan. RESULT: Significant reduction in body mass, lean body mass, fat mass and fast-twitch muscle mass was observed after dexamethasone treatment. Body mass, fat mass and fast-twitch muscle mass stayed decreased during 20 days after terminating the hormone administration; lean body mass reached the preadministration level after 20-day recovery period. There were no significant changes in bone mineral density during the recovery period. Dexamethasone treatment gradually reduced hindlimb grip strength that also stayed decreased during the 20-day recovery period. CONCLUSION: This study demonstrated that a 10-day period of overexprosure to glycocorticoids induced longlasting changes in old rats' body composition and these values did not attain the baseline level even after 20-day recovery period.

Glucocorticoid-Induced Changes in Rat Skeletal Muscle Biomechanical and Viscoelastic Properties: Aspects of Aging.

OBJECTIVES: The purpose of this study was to estimate the state of tension (tone) and the biomechanical and viscoelastic properties of skeletal muscle in aging rats during the administration of different doses of dexamethasone and to find the relationships among the state of muscle atrophy, muscle strength, and the abovementioned muscle properties. METHODS: Muscle state of tension, biomechanical (elasticity, dynamic stiffness) and viscoelastic (mechanical stress relaxation time, Deborah number) properties (using MyotonPRO, Myoton Ltd, Tallinn, Estonia), lean body mass (BM), and hind limb grip strength were measured before and after the administration of a 10-day treatment with dexamethasone 100 µg/100 g BM (young and old group) and 50 µg/100 g BM (old group). RESULTS: Muscle elasticity (logarithmic decrement) was lower in old animals (1.86 ± 0.03) in comparison with young adult rats (1.38 ± 0.04) (P < .01). After the 10-day treatment with dexamethasone 100 µg/100 g BM, young adult rats had 10% lower muscle elasticity (P < .01). The same dose of dexamethasone in old rats increased tone (frequency of natural oscillation) from 29.13 ± 0.51 Hz to 38.50 ± 0.95 Hz (P < .001). There were dose-dependent differences in dynamic stiffness and tone of muscle; changes in elasticity were independent of the dose in old animals. In old rats, the muscle's viscoelastic properties decreased after dexamethasone administration. Significant correlation was found between changes in muscle logarithmic decrement and stiffness (rs = 0.90; P < .05) in old animals. CONCLUSIONS: Biomechanical and viscoelastic properties of skeletal muscle indicate changes in the main function of muscle during glucocorticoid-induced muscle atrophy and are in agreement with changes in hind limb strength. The myometric measurements indicate the direction and magnitude of change in muscle tissue after different doses of dexamethasone administration easily and quickly.

Morphological peculiarities of neuromuscular junctions among different fiber types: Effect of exercise.

The aim of our research was to examine whether there are differences in the morphology of neuromuscular junctions of different types of muscle fibers in rodents, and after their adaptation to six weeks endurance exercise training. After 5-day acclimation, Wistar rats were subjected to run with the speed 35 m/min during 6 week, 5 days per week and the training volume reached 60 min per day. Muscle samples for ultrastructural studies were fixed, dehydrated and embedded in Epon-812. Ultra-thin sections were cut from longitudinally and transversely oriented blocs, using 4 blocks from each animal. The area of axon terminals on fast- twitch fibers is 1.5 time large (p<0.001) and the perimeter of terminals is 1.7 time large in comparison with slow- twitch oxidative fibers (p<0.001) in control group. There are correlation between cross-sectional area of different muscle fibers and length of axon terminals (r=0.72), between cross-sectional area and with of axon terminal (r=-0.62), and between turnover rate of contractile proteins and length of axon terminal (r=0.75). Fast remodeling of synapse on oxidative and oxidative-glycolytic muscle fibers during endurance training seems to guarantees the intensive renewal of the structures of muscle fibers with higher oxidative capacity.

Physical Education Increases Daily Moderate to Vigorous Physical Activity and Reduces Sedentary Time.

BACKGROUND: Physical activity (PA) is important to mental and physical health. Physical education (PE) lessons have the potential to increase daily moderate to vigorous PA (MVPA) and reduce sedentary time (SED). We measured MVPA and SED in primary school PE, determined the contribution of PE to daily MVPA and SED, and compared PA on days with and without PE. METHODS: PA was measured in 504 first (ages 7-9) and second (ages 10-12) school level children for 1 school week, with inclusion criteria of at least 10 hours of valid data. Linear mixed methods were used for data analysis. RESULTS: In PE, students spent 28.6 ± 16.5% in MVPA and 29.3 ± 19.8% in SED. Each additional MVPA minute in PE was associated with 1.4 more daily MVPA minutes. On days with PE, students had 12.8 (95% CI 10.5; 15.0) minutes more MVPA and 9.7 (95% CI 16.3; 3.1) minutes less SED compared with days without PE. CONCLUSIONS: Although MVPA in PE was relatively low and SED high, PE significantly increased daily MVPA and reduced SED, confirming the important role of PE in supporting the healthy development of children.

Lower Leg Length is Associated with Running Economy in High Level Caucasian Distance Runners.

The aim of the present study was to investigate lower limb anthropometric and composition variables related to running economy (RE) and running performance in a homogeneous group of high level European distance runners. RE at the speeds of 14, 16 and 18 km·h-1 (189 ± 12; 188 ± 11; 187 ± 11 O2 ml·kg-1·km-1) and maximal oxygen uptake (VO2max) (67.3 ± 2.9 ml·kg-1·min-1) of 13 high level distance runners were determined on a motorised treadmill. Anthropometric variables and body composition were measured. The BMI was related to RE at the speed of 14 (r2 = 0.434; p = 0.014), 16 (r2 = 0.436; p = 0.014) and 18 km·h-1 (r2 = 0.389; p = 0.023). Lower leg length was negatively related to RE at the speed of 16 and showed such a tendency at the speed of 14 and 18 km·h-1. VO2max indicated a moderate relationship with RE at the speeds of 14, 16 and 18 km·h-1 (r2 = 0.372, p = 0.030; r2 = 0.350, p = 0.033; r2 = 0.376, p = 0.026, respectively) which was confirmed by subsequent partial correlation analysis. While lower leg length and the BMI presented a relationship with RE, none of the calculated body composition and anthropometric proportions were related to RE or performance. The relationship between RE and VO2max would confirm the notion that RE could be at least partly compensated by VO2max to achieve high performance results.

Objectively measured sedentary behaviour and moderate and vigorous physical activity in different school subjects: a cross-sectional study.

BACKGROUND: Evidence shows the positive influence of moderate and vigorous physical activity (MVPA) and negative influence of sedentary time on health and academic achievement. Although schools can significantly contribute to overall physical activity, little is known about MVPA and sedentary behaviour in different school subjects in different grades. METHODS: Physical activity of 646 students from 18 schools (94 classes) and from three school stages (grades 1-9, aged 7-16) was measured with accelerometry for 5 school days. Time and proportion of MVPA and sedentary time, also average sedentary bout length was calculated for native language (Estonian), mathematics, science, foreign language, music and crafts lessons. RESULTS: A total of 6363 lessons were measured, with lesson duration of 45 min. The average lesson time MVPA remained below 2.2 min in all school stages and in all subjects. Students in grades 4-6 had greatest decline in the proportion of lesson time MVPA in science (ß = -1.9, 95%CI -3.1- -0.6) and music (-1.2, -2.1- -0.4) and in grades 7-9 in music (-1.7, -3.1- -0.3) lessons compared to grades 1-3. In grades 1-3 students spent on average 76% of lesson time (34.0 ± 7.0 min) as sedentary, whereas in grades 7-9 the average proportion of sedentary time was 87% (38.9 ± 5.7 min). An average sedentary bout length increased from 13 min in grades 1-3 to 20 min in grades 7-9. An increase in sedentary bout length from grades 1-3 compared to grades 7-9 was present in most subjects, except crafts, with smallest increase in foreign language (6 min, 3.5-8.9) and greatest in music lessons (16.6 min, 11.9-21.3). Lessons with prolonged sedentary bouts formed a maximum 36% of all lessons in grades 1-3 and 73% in grades 7-9. CONCLUSION: The long sedentary time, bout length and low MVPA in most subjects were unfavourable in respect of both health and academic achievement. Significantly increasing sedentary time and sedentary bout length in older school stages highlights the need for interventions in all subjects and especially in older grades in order to combat the inactivity of children.

Role of Myofibrillar Protein Catabolism in Development of Glucocorticoid Myopathy: Aging and Functional Activity Aspects.

Muscle weakness in corticosteroid myopathy is mainly the result of the destruction and atrophy of the myofibrillar compartment of fast-twitch muscle fibers. Decrease of titin and myosin, and the ratio of nebulin and MyHC in myopathic muscle, shows that these changes of contractile and elastic proteins are the result of increased catabolism of the abovementioned proteins in skeletal muscle. Slow regeneration of skeletal muscle is in good correlation with a decreased number of satellite cells under the basal lamina of muscle fibers. Aging causes a reduction of AMP-activated protein kinase (AMPK) activity as the result of the reduced function of the mitochondrial compartment. AMPK activity increases as a result of increased functional activity. Resistance exercise causes anabolic and anticatabolic effects in skeletal muscle: muscle fibers experience hypertrophy while higher myofibrillar proteins turn over. These changes are leading to the qualitative remodeling of muscle fibers. As a result of these changes, possible maximal muscle strength is increasing. Endurance exercise improves capillary blood supply, increases mitochondrial biogenesis and muscle oxidative capacity, and causes a faster turnover rate of sarcoplasmic proteins as well as qualitative remodeling of type I and IIA muscle fibers. The combination of resistance and endurance exercise may be the fastest way to prevent or decelerate muscle atrophy due to the anabolic and anticatabolic effects of exercise combined with an increase in oxidative capacity. The aim of the present short review is to assess the role of myofibrillar protein catabolism in the development of glucocorticoid-caused myopathy from aging and physical activity aspects.

Different Methods Yielded Two-Fold Difference in Compliance with Physical Activity Guidelines on School Days.

INTRODUCTION: The aim was to compare the average and the days method in exploring the compliance of children with physical activity guidelines and describe their physical activity patterns in different school day segments. METHODS: Physical activity was objectively measured in 472 children aged 6-13 for one school week. Children were compliant when fulfilling PA recommendations 1) on average over all measured days (average method) or 2) on at least four measured days (days method). To explore the difference in moderate to vigorous physical activity (MVPA) minutes between compliant and non-complaint children (using both the average and days method) in various day segments, linear mixed models was used. RESULTS: Compliance with physical activity guidelines was significantly higher with the average compared to the days method (51.7% and 23.7%, respectively). In segmented-day analysis, compliant children accrued more MVPA minutes in all day segments, especially during after-school. Gender differences appeared only during the in-school segments, where girls spent less time in MVPA (average method: -4.39 min, 95% CI = -5.36,-3.42, days method: -4.45 min, 95%CI = -5.46,-3.44). Older children accrued more MVPA minutes during physical education classes, but less during breaks, compared to younger children. CONCLUSIONS: The used methods yielded remarkably different prevalence estimates for compliance to physical activity recommendations. To ensure comparability between studies, interventions and reports, there is a need for internationally agreed operationalization and assessment methods of physical activity guidelines. As non-compliant children had lower MVPA during all day segments, greater efforts should be made to provide physical activity opportunities both during and after school.

Letter to the editor.

Santos-Concejero and Tucker argued in their letter to the editor that in our study the running economy in achieving superior performance was overlooked due to some methodological aspects. Having given the remarks of Santos-Concejero and Tucker appropriate consideration, in this letter to the editor, we argue that our paper does not downplay the influence of running economy on the determinants of the East African running phenomenon, but rather adds novel insights into the interaction between running economy, maximal oxygen uptake and performance.

Dissociation between running economy and running performance in elite Kenyan distance runners.

The purpose of this study was to investigate the relationship between running economy (RE) and performance in a homogenous group of competitive Kenyan distance runners. Maximal aerobic capacity (VO2max) (68.8 ± 3.8 ml∙kg(-1)∙min(-1)) was determined on a motorised treadmill in 32 Kenyan (25.3 ± 5.0 years; IAAF performance score: 993 ± 77 p) distance runners. Leg anthropometry was assessed and moment arm of the Achilles tendon determined. While Achilles moment arm was associated with better RE (r(2) = 0.30, P = 0.003) and upper leg length, total leg length and total leg length to body height ratio were correlated with running performance (r = 0.42, P = 0.025; r = 0.40, P = 0.030 and r = 0.38, P = 0.043, respectively), RE and maximal time on treadmill (t(max)) were not associated with running performance (r = -0.01, P = 0.965; r = 0.27; P = 0.189, respectively) in competitive Kenyan distance runners. The dissociation between RE and running performance in this homogenous group of runners would suggest that RE can be compensated by other factors to maintain high performance levels and is in line with the idea that RE is only one of many factors explaining elite running performance.

Aging and regenerative capacity of skeletal muscle in rats.

The objective of the study was to examine skeletal muscle regeneration capacity of young and very old rats during autotransplantation. In 3.5 and 30 month-old Wistar rats, gastrocnemius muscle was removed and grafted back to its original bed. Incorporation of 3H leucine into myofibrillar and sarcoplasmic protein fractions, their relative contents in autografts and synthesis rate of MyHC and actin were recorded. The relative muscle mass of old rats was about 67% of that of young rats; the absolute mass of autografted muscle was 61% intact in the young rat group and 51% in the old rat group. Content of myofibrillar protein in the autografts of young rats was 46% of the intact muscle content, and 39% in the old rat group. In conclusion, the difference in skeletal muscle regeneration capacity of young and very old rats is about ten percent. In the autografts of both young and old rats, the regeneration of the contractile apparatus is less effective in comparison with the sarcoplasmic compartment.

Role of exercise therapy in prevention of decline in aging muscle function: glucocorticoid myopathy and unloading.

Changes in skeletal muscle quantity and quality lead to disability in the aging population. Physiological changes in aging skeletal muscle are associated with a decline in mass, strength, and inability to maintain balance. Glucocorticoids, which are in wide exploitation in various clinical scenarios, lead to the loss of the myofibrillar apparatus, changes in the extracellular matrix, and a decrease in muscle strength and motor activity, particularly in the elderly. Exercise therapy has shown to be a useful tool for the prevention of different diseases, including glucocorticoid myopathy and muscle unloading in the elderly. The purpose of the paper is to discuss the possibilities of using exercise therapy in the prevention of glucocorticoid caused myopathy and unloading in the elderly and to describe relationships between the muscle contractile apparatus and the extracellular matrix in different types of aging muscles.

Review on aging, unloading and reloading: changes in skeletal muscle quantity and quality.

Aging and muscle unloading are associated with a decline in muscle mass, structure, force and changes in the mechanical properties of skeletal muscle. There is a perception that reloading restores muscle architecture and function but differences in the regeneration capacity of intra- and extra-cellular compartments, age dependent susceptibility to muscle damage, particularly in the contractile machinery, make it difficult to attribute the main role of the above mentioned components. This review briefly summarizes studies that examine aging skeletal muscle during unloading and reloading. The article highlights changes in muscle mass, structure, extra-cellular matrix (ECM) components, strength, locomotion, adaptability to exercise, peculiarities of protein metabolism, susceptibility to glucocorticoids and recovery of muscle from injury.

Impaired oxidative phosphorylation in overtrained rat myocardium.

The present study was undertaken to characterize and review the changes in energy metabolism in rat myocardium in response to chronic exhaustive exercise. It was shown that a treadmill exercise program applied for six weeks led the rats into a state characterized by decreased performance, loss of body weight and enhanced muscle catabolism, indicating development of overtraining syndrome. Electron microscopy revealed disintegration of the cardiomyocyte structure, cellular swelling and appearance of peroxisomes. Respirometric assessment of mitochondria in saponin-permeabilized cells in situ revealed a decreased rate of oxidative phosphorylation (OXPHOS) due to diminished control over it by ADP and impaired functional coupling of adenylate kinase to OXPHOS. In parallel, reduced tissue content of cytochrome c was observed, which could limit the maximal rate of OXPHOS. The results are discussed with respect to relationships between the volume of work and corresponding energy metabolism. It is concluded that overtraining syndrome is not restricted to skeletal muscle but can affect cardiac muscle as well.

Relationship between extracellular matrix, contractile apparatus, muscle mass and strength in case of glucocorticoid myopathy.

The purpose of this study was to evaluate the effect of dexamethasone on the contractile apparatus and extracellular matrix (ECM) components of slow-twitch (ST) soleus (Sol) and fast-twitch (FT) extensor digitorum longus (EDL) muscle. The specific aim was to assess the development of glucocorticoid-induced myopathy on the level of contractile apparatus and ECM, paying attention to the expression of fibrillar forming collagen types I and III and nonfibrillar type IV collagen expression in extracellular compartment of muscle. Degradation of myofibrillar proteins increased from 2.62+/-0.28 to 5.58+/-0.49% per day during glucocorticoids excess. Both fibril- and network-forming collagen-specific mRNA levels decreased at the same time in both types of skeletal muscle. Specific mRNA level for MMP-2 did not change significantly during dexamethasone administration. Hindlimb grip strength simultaneously decreased. The effect of excessive glucocorticoids on the extracellular compartment did not differ significantly in skeletal muscles with different twitch characteristics.

Ageing and dexamethasone associated sarcopenia: peculiarities of regeneration.

The purpose of this study was to assess the development of ageing- and glucocorticoid-related sarcopenia on the level of myofibrillar apparatus, paying attention to the synthesis (SR) and degradation rate (DR) of contractile proteins, muscle strength, and daily motor activity. We also wanted to test the effect of ageing and dexamethasone (Dex) excess on the regeneration peculiarities of skeletal muscle autografts. Four and 30-month-old male rats of the Wistar strain were used. Ageing associated sarcopenia was calculated from gastrocnemius muscle relative mass decrease (from 5.6 +/- 0.08 to 3.35 +/- 0.04; p < 0.001). The SR of MyHC in old rats was approximately 30% and actin approximately 23% lower than in young rats. Dex treatment decreased SR of two main contractile proteins significantly in both age groups (p < 0.001) and increased DR during ageing from 2.11 +/- 0.15 to 4.09 +/- 0.29%/day (p < 0.001). Hindlimb grip strength in young rats was 5.90 +/- 0.35 N/100 g bw and 2.64 +/- 0.2 N/100 g bw (p < 0.001) in old rats. Autografts of old rats have a higher content of adipose tissue 14.9 +/- 1.1% in comparison with young rats 6.8 +/- 0.51% (p < 0.001) and less muscle tissue 39.8 +/- 2.6% and 48.3 +/- 2.8%, respectively (p < 0.05). Both, ageing and dex-caused sarcopenic muscles have diminished capacity for regeneration.