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Dietos kompozicijos poveikis vyresnio amžiaus pelių medžiagų apykaitai ir aktyvumui svorio metimo metu ir jam pasibaigus.
No full textIntroduction: Weight regains after weight loss is a frequent problem that people with obesity or athletes of weight-making sports face (Fothergill et al. 2016). It is suggested that diets high in carbohydrates or protein decrease or increase energy expenditure, respectively, and thus affect energy balance and the success of weight maintenance (Oliveira et al. 2021; Ebbeling et al. 2018). Our goal is to examine the role of diet composition on weight maintenance and energy metabolism in aged mice during caloric restriction (CR) and post-caloric restriction (P-CR). Methods: Males of C57BL/6J mice strain were grown until 18-month-old and then mice with overweight were selected and divided into 4 groups matched by body mass: low-fat (LFD; 20, 20, 60% of kcal from fat, protein, carbohydrate), low-carbohydrate (LCD; 60, 20, 20%, respectively), high-protein (HPD; 30, 35, 35%, respectively) and control (regular chow diet) (n=9-11 each). Mice were subjected to 30% CR for 4 weeks followed by ad libitum P-CR feeding for 4 weeks using the same diets. Controls were fed chow diet ad libitum all the time. Body mass and 23-h indirect calorimetry in the metabolic cage (energy expenditure, respiratory quotient, physical activity levels) were assessed during CR and P-CR. Results: Weight reduction was similar between the diet groups during CR (P > 0.05) but only LCD group regained more weight in P-CR than had initially prior CR. Energy expenditure did not change between diet groups neither during CR nor P-CR (P > 0.05) but was lower in CR and higher in P-CR compared to controls. Energy expenditure normalized to body mass was similar between diet groups during CR but lower in LCD group during P-CR compared to HPD and especially LFD group (P 0.05). Respiratory quotient was significantly lower in LCD group compared to all groups during both CR and P-CR (P < 0.001). Conclusion: Low-carb but high-fat diet is associated with greater weight regain and lower relative energy expenditure after previous weight loss compared to other types of diets in aged mice. Low respiratory quotient during this diet indicates overall fat metabolism and oxidation but is not a good predictor of burned body fat
Effects of diets with different macronutrient distribution on body composition during caloric restriction followed by ad libitum feeding in aged mice.
No full textWeight loss and body composition improvements pursued by overweight persons and athletes can be achieved with caloric restriction (CR) using different dietary macronutrient distribution (Ge et al. 2020, Aragon et al. 2017). However, a post-diet period is less studied and it is not clear how selected dietary macronutrient distribution sustains these achievements particularly when return to ad libitum feeding (Muhammad et al. 2017). The aim of the study was to examine this issue using the mouse model. 18-month-old naturally overweight males of the C57BL/6J mouse strain were examined. They were matched by body mass into three groups (n = 23 each) and subjected to 30% CR for 4 weeks with either low-fat (LFD; 20, 60, 20% of total kcal for protein, carbohydrate, fat, respectively), low-carbohydrate diet (LCD; 20, 20, 60%) or high-protein (HPD; 35, 35, 30%) followed by 4 weeks of refeeding period (RFD) on the same diets ad libitum. Body mass was monitored daily and hindlimb muscles as well as major body fat sites were dissected and precisely weighted at the end of CR or RFD. Eleven mice on ad libitum chow diet served as controls throughout the experiment. CR resulted in more than 30% weight loss with no differences between diet groups (P > 0.05). Majority of it was contributed to body fat loss while muscle mass loss was much less but still significant compared to controls (P 0.05). However, LCD overshot controls and both other diet groups in body and fat mass by 18-21% and 100-118%, respectively (P < 0.001). In conclusion, the low-carb-high-fat diet leads to similar improvements in body composition during CR compared to other types of diets but much greater body fat recovery and overshoot during ad libitum post-diet period in aged mice
The effect of different macronutrient composition hypocaloric diets on metabolism and activity in obese individuals: mouse model.
No full textThe aim of research: To determine the effect of different macronutrient composition in hypocaloric diets on metabolism and activity in obese mice (C57BL/6J). The research problem: It is not clear whether a different macronutrient composition in hypocaloric diets with the same energy content can affect metabolic and activity processes. There is a hypothesis that lower consumption of dietary carbohydrate stimulates metabolism (i.e. increases energy expenditure) and so has a positive effect on the energy balance in obese individuals (Ludwig & Ebbeling, 2018). Methods: 28 weeks old diet-induced obese C57BL/6J mice were fed different macronutrient composition hypocaloric diets with the same calorie content: high protein, high carbohydrate or high fat diet. Age-matched obese mice fed ad libitum high fat and high sugar diet served as controls. Metabolism and activity were assessed after 6 weeks of hypocaloric dietary intervention. The following paremeters were calculated: oxygen consumption (VO2), carbon dioxide (CO2) production, energy expenditure (EE), respiratory quotient (RQ), locomotor activity and rearing. These parameters were measured by the \"Panlab\" metabolism analysing equipment. The research questions: 1. Will different macronutrient composition diets with the same energy content have a similar effect on metabolism and activity in obese mice? 2. Which hypocaloric diet will be the most effective in reducing body mass and will have the highest metabolic rate in obese mice? Hypothesis: 1. Different macronutrient composition in hypocaloric diets with the same protein and energy content will have a similar effect on metabolism and activity in obese mice. The metabolic contribution of fat (based on the respiratory quotient) will be higher in high-fat diet (Martinez et al., 2014). 2. Hypocaloric high protein diet will be the most effective in reducing body mass in obese mice and will have the highest metabolic rate due to its higher thermogenic effect compared to isocaloric high carbohydrate and high fat diets (Hall & Guo, 2017). Results: There was a significant difference in absolute energy expenditure (EE) between high fat and high protein diets.. There were no statistically significant differences in body mass, activity and relative energy expenditure between all three diets. High protein and high carbohydrate diet groups showed a strong relationship between relative EE and activity. Conclusions: 1. The most important determinant of successful weight loss is caloric intake but not the macronutrient composition of the diet. Different macronutrient composition diets with the same energy content have a similar effect on body mass in obese mice. 2. Different macronutrient composition diets with the same energy content have a similar effect on the main metabolic parameters in obese mice. Relative energy expenditure does not indicate the metabolic advantage of any diet. 3. Different macronutrient composition diets with the same energy content have a similar effect on activity in obese mice which tends to increase slightly during dieting. Same activity levels between different diet groups allowed for a more reliable assessment of metabolic parameters such as energy expenditure that shows a significant dependence on mice activity
Effects of obesity with and without exercise training on the functional properties of isolated mouse hindlimb muscles.
No full textResearch Problem: Obesity causes deterioration in health and function of many tissues through multiple metabolic changes. However, force generation of locomotory muscles may also improve due to increased weight-bearing functional overload. Research Aim: To identify effects of obesity on the functional properties of mouse hindlimb muscles and determine whether observed effects are modified with exercise training. Research Tasks: 1. Identify the impact of obesity on contractility of isolated mouse muscles. 2. Determine the effects of exercise training on contractile properties of isolated obese mouse muscles. Hypothesis: Obesity will negatively affect the functional properties of isolated mouse muscles, but regular exercise will mitigate this effect. Methodology: Twenty-four male C57BL/6J mice were divided into three groups (n=8 per group): control (CON), obese (OB), and obese with exercise training (OB-EX). Both obese groups were ~70% heavier than the CON group due to a feeding of a high-fat diet. OB-EX also underwent standardized 30 min daily training regimen on treadmill 5 times/week for 6 weeks while CON and OB were left sedentary during that time. After the training, the mice were euthanized, and the slowtwitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles were extracted for ex vivo contractility assessments (1200A-LR Muscle Test System, Aurora Scientific Inc., Canada). Results: Exercise did not affect the body mass of the OB-EX group compared to OB. SOL and EDL force did not significantly differ between the groups at any point on the force-frequency curve. Force normalized to muscle mass did not differ between groups either. While no differences were observed in contraction and relaxation time of EDL between groups, obesity led to a shortened twitch halfrelaxation time in SOL muscles of OB compared to CON (136±30 vs. 218 ± 86 ms, p0.05). Conclusions: Obesity does not affect the force generation capacity of isolated mouse SOL and EDL muscles. However, it does alter SOL contractility, leading to faster relaxation
Hipokalorinės dietos riebalų ir angliavandenių kiekio poveikis pagyvenusių pelių kūno masei ir sudėčiai.
No full textObesity is a medical condition with an excess of accumulated body fat which prevalence is constantly increasing worldwide NCD Risk Factor Collaboration, 2016. Caloric restriction (CR) is essential for non-invasive obesity treatment and weight-making practices in some sports. It is still controversial about the role of carbohydrate and fat content in weight-loss diets on body mass and composition (Ludwig & Ebbeling 2018, Hall et al. 2018). The aim of the study was to examine the effect of carbohydrate and fat content in the hypocaloric diet on body mass and composition in aged and naturally overweight mice. We hypothesize that old mice might respond differently to isocaloric weight-loss diets with contrasting dietary carbohydrate and fat content due to the age-related inclination to glucose intolerance (Testa et al., 2014). 18-month-old males of the C57BL/6J mouse strain were matched by body mass into two groups (n = 6 each) and then randomly subjected to 30% CR for 4 weeks with either low-fat (Low-Fat; 20 and 60% of total kcal from fat and carbohydrate, respectively) or low-carbohydrate diet (Low-Carb; 60 and 20%). Body mass was monitored daily and hindlimb muscles as well as major body fat sites were dissected and precisely weighted at the end of CR. The results of this study indicated that the dynamics of the daily changes in body mass were similar between Low-Fat and Low-Carb at each time point during CR (P > 0.05). Overall, Low-Fat and Low-Carb groups decreased their body mass by 27.5 ± 3.0 and 25.6 ± 2.6%, respectively. There were no differences between groups in the mass of any single muscle or fat site at the end of CR. Combined muscle mass was 391.7 ± 34.5 and 406.3 ± 20.4 mg and combined fat mass was 1137.2 ± 660.3 and 1170.2 ± 344.2 mg for Low-Fat and Low-Carb (P > 0.05). To conclude, dietary carbohydrate and fat content do not affect body mass and composition improvements in elderly mice during caloric restriction with fixed energy and protein intake
Placebo effect in women's training with resistance.
No full textOften, due to a lack of knowledge or subjective beliefs, women who exercise with resistance feel unable to lift heavy weights, are afraid, and do not even try to do exercises with a ‘to do exercises near to their potential limit’. It is important to follow the rule of progressive overload for the muscles to grow – to use such resistance, which increases with time and training experience. Therefore, two important aspects of hypertrophy need to be noted: the perception of effort (how close we are to not being able to carry more load) and the intensity of the load (how much weight of the tool that is being used for training). The aim of the research: is to determine whether there is a positive effect of placebo in resistance training in women. Exercises involving the entire body muscles will be performed on: chest press machine, vertical/lat pulldown machine and on leg press machine. After the first meeting, the ability of the subjects to perform the exercises was assessed. During the second meeting, the intensity of 80% of the exercises performed from 1 repetition maximum (1 RM) will be tested. The weight of the exercises performed during the third meeting will be increased to 85% from 1 RM without the subject's knowledge, and the subject will be informed that the exercises are performed with the same resistance that was used during the second meeting. Hypothesis of research: it is likely that subjects will not experience a change in weight if it is stated that it is the same lifting weight that was used at the previous meeting. In other words, a positive effect of placebo will be demonstrated. Research tasks: 1. To determine how women’s strength results change during exercises with resistance for the main muscle groups, when the intensity of resistance is increased without revealing it to the women under the study (using placebo); 2. To determine how strength results relate using such a placebo “cheating” method to women’s perceived effort. Conclusions: There was a positive effect of placebo in training with resistance among women. All women did not feel an increase in the intensity of their latent resistance load and performed the same or greater number of repetitions as in the exercises indicated a week ago with a known submaximal intensity. In two exercises (leg press and pulldown machines), this improvement was statistically significant.
Due to lack of knowledge or subjective beliefs, women who exercise with resistance are often afraid and do not even try to do exercises with heavy weight that they can overcome. Muscle strengthening and hypertrophy must follow the progressive overload rule - use such resistance, which increases with time and training experience. Perception of efforts (how close we are to no longer being able to carry exercise) and load intensity (how heavy weight of the tool in exercise) are important components of training in the development of muscle hypertrophy. The aim of the study was to determine whether there is a positive effect of placebo on training with resistance among women who regularly attend sports clubs. The study involves exercises that cover the major muscle groups in the body (machine bench press, vertical pulldown, and leg press). By indirectly estimating the womens' maximum single repetition (1RM) in all exercises, the women had to perform as many repetitions with “the same” weight as possible in subsequent meetings. During the first test, they loaded with 80% of the RM, and a week later during the second test, with 85% of the RM. Women were not informed of a 5% increase in exercise intensity. Perceived magnitude of load effort was also assessed using the RPE scale in both tests. Changes in women body composition were observed throughout the study. Among women, a positive effect of placebo on training with resistance has been found. Women in the study did not feel an increase in the intensity of hidden from them resistance load and caried out a higher number of repetitions with less perceived effort. In two exercises (leg press and vertical pulldown), this improvement was statistically significant. Changes in body composition are not responsible for improving results
Dietos sudėties poveikis energijos suvartojimui, alkio ir sotumo hormonams kalorijų apribojimo metu ir po jo: pelės modelis.
No full textThe aim: to examine the role of diet composition on weight maintenance and appetite control mechanisms in the post-dieting period when energy intake is not controlled. The problem: Caloric restriction (CR) has been proven as a successful strategy for obesity treatment and management of weight (Minderis et al. 2020). However, the majority of individuals do not maintain their weight loss for longer periods (Kraschnewski et al. 2010). It is suggested that diet composition affects hunger and food cravings leading to increase energy intake (Ludwig & Ebbeling, 2018). Methods: Mouse model, caloric restriction, ad libitum feeding, dynamic weighing for body mass, blood sample gathering, ELISA method for hormone assessments, statistical analysis. Objectives: 1. To compare the weight gain and energy intake on the low carbohydrate, low fat and high protein diets in ad libitum feeding conditions; 2. To compare leptin and ghrelin hormones on the low carbohydrate, low fat and high protein diets after caloric restriction and refeeding periods. Hypothesis: the high protein diet will result in the most satiety-promoting leptin and ghrelin concentrations after the 4-week weight loss and 4-week ad libitum feeding periods in mice. High protein diet will also induce the lowest weight regain during ad libitum eating period due to lower energy intake compared to other diets. Results: our findings showed that low-carb group regained the biggest amount of weight and significantly exceeded the low fat and high protein groups in post-diet period (P 0.001) but neither leptin nor ghrelin caused the weight gain in low-carb group as the hormones were not different between groups at the start of refeeding period (P > 0.05). Conclusions: low-carb diet has the least favourable effects on body composition when energy intake is not controlled in aged and overweight mice. It seems to be caused by the caloric density of the diet rather than hormonal changes in satiety and hunger
Griaučių raumenų masė ir specifinė jėga: genetinio fono ir miostatino disfunkcijos, esant hipertrofijos ir atrofijos stimulams, poveikis pelėms.
No full textSkeletal muscle is an abundant tissue compromising 40–50 % of the body mass in humans (Sakuma et al., 2014). Its main role is to generate force for posture maintenance and performance of daily movements, but it also acts as a metabolically active organ. Muscle mass and function are of particular importance for health and well-being as well as for the athletic performance in sports (Wolfe, 2006). On the contrary, muscle loss is undesired process characterising the consenquence of various diseases and/or catabolic conditions and leads to weakness, frailty and even death (Schiaffino et al., 2013). Thus, investigations of physiological and genetic factors underlying muscle mass and force is crucial for solving and improving health issues of society. Mouse is the most widely used mammalian species in biomedical research. There are several reasons for its popularity. Firstly, analysis of mouse genome has shown that about 99 % of mouse genes have a homolog in the human genome (Guénet, 2005). Secondly, distinct mouse strains show significant variation in phenotypic traits facilitating identification of genes responsible for those traits. Thirdly, contrary to the inbred mice, humans present an outbred population complicating analysis of association between genes and phenotypic traits. Moreover, genetically engineered mice with mutations of specific genes, as in case of myostatin knockout (KO) mice (McPherron et al., 1997), provide a useful tool in identifying functions of those genes. Finally, studies of mice are cost effective due to small body size and relatively short lifespan which is 30 times shorter than in humans (Chang, 2013). Physiological factors that influence the relationship between skeletal muscle mass and force are of large interest. Both these traits to a large extent are determined by genetic factors (Pescatello et al., 2013). Mice of distinct genetic backgrounds (strains) vary substantially in body and skeletal muscle mass (Lionikas et al., 2013a). Large body and skeletal muscle mass in the Berlin High (BEH) and Dummerstorf High (DUH) strains compared to other mouse strains, including a “classic” C57BL/6J strain, is a result of the selective breeding for large body mass and/or carcass protein accretion (Bünger et al., 2004). It is, however, unclear how these enlarged skeletal muscles differ from skeletal muscles of other strains. It is often believed that muscle force is proportional to muscle mass and muscle force per cross-sectional area (CSA) or specific force is a constant value with the exception of pathological conditions as Duchenne muscular dystrophy (Gregorevic et al., 2004). However, this is an oversimplified view. There might be an optimal range of skeletal muscle mass for force production. Beyond this range muscle force might be compromised (Amthor et al., 2007). For instance, changes in an architecture or concentration of contractile proteins in hypertrophied muscles might affect force generation (Degens et al., 2009; Van der Meer et al., 2011; Qaisar et al., 2012). In vivo studies on humans do not allow us to examine these factors comprehensively. Methodological limitations such as difficulties in evaluating the actual muscle mass, influences of neural activation and coactivation of antagonistic muscles complicate assessment of specific muscle force (Erskine et al., 2010). Mouse model permits ex vivo experimentation where skeletal muscle can be isolated and stimulated electrically, thus avoiding most of those issues. Therefore, an identification of mouse strains that differ in specific force could be an important initial step, which would facilitate search for the relevant genetic factors and physiological mechanisms responsible for variation in specific muscle force. Myostatin dysfunction, which was a main focus of this thesis, is the one of the known genetic factors affecting skeletal muscle mass and force. After myostatin discovery by Se-Jin Lee and colleagues it quickly attracted the attention of scientists from various fields including pharmacologists, physiotherapists and even sport scientists (McPherron et al., 1997). Myostatin is a natural inhibitor of muscle growth and protein synthesis. Mice with a deleted function of the myostatin gene (Mstn) display a striking increase in skeletal muscle mass which results a double-muscle phenotype (McPherron et al., 1997). On the other hand, muscle-specific overexpression of myostatin induces a significant reduction in skeletal muscle mass in mice (Reisz-Porszasz et al., 2003). In addition to the prominant muscularity, myostatin-deficient mice show improved bone formation, reduced adiposity as well as increased resistance to weight gain and insulin sensitivity when fed high fat diet (McPherron, Lee, 2002; Hamrick et al., 2006; Wilkes et al., 2009; Elkasrawy, Hamrick, 2010). Altogether, this suggests that myostatin inhibition might be an effective treatment against various muscle wasting conditions including aging-related sarcopenia as well as metabolic dysfunctions such as obesity and diabetes. Indeed myostatin blocking antibodies have a positive effect on muscle mass and function on mdx mice representing a model of Duchenne muscular dystrophy (Bogdanovich et al., 2002; Wagner et al., 2002). There is also some interest in the myostatin inhibition effect on skeletal muscle mass and function of otherwise-normal individuals (e.g. athletes). Large muscles and fast glycolytic fibre profile in myostatin-deficient animals might be beneficial in strength and power events in sports (Girgenrath et al., 2005). Indeed, whippets which are heterozygotes for myostatin mutation are excellent performers in dog races (Mosher et al., 2007). Moreover, the woman who is heterozygous for myostatin mutation and gave birth to the homozygous child is a former sprinter (Schuelke et al., 2004). However, before considering myostatin inhibition as a performance enhancing strategy, more research should be done on physiological effects of myostatin dysfunction using animal models. In fact, studies of myostatin-deficient mice demonstrate that force in isolated skeletal muscles of these animals might be compromised compared to the wild type (WT) animals with the normal myostatin function (Amthor et al., 2007; Qaisar et al., 2012). There is also a gap in knowledge about a plasticity of skeletal muscles in myostatin-deficient animals, because little research has been carried out on adaptability to exercise training of these animals. Several studies examined effect of endurance training on skeletal muscle of myostatin-deficient mice (Savage, McPherron, 2010; Matsakas et al., 2010; Matsakas et al., 2012) but there is a lack of research about adaptations to high resistance training. Thus we carried out a study on compensatory hypertrophy of skeletal muscles in myostatin-deficient animals. Indeed athletes involved in strength training but not endurance training might be those who could benefit from myostatin inhibition. It is well established that an increase of myostatin expression is a key factor in every type of skeletal muscle atrophy examined to date (Allen et al., 2010). Most of the studies are focused on myostatin inhibition in pathological conditions such as Duchenne muscular dystrophy (Bogdanovich et al., 2002; Wagner et al., 2002). However, the otherwise normal individuals might be subjected to catabolic stimuli as well. For instance, they might undergo skeletal muscle wasting either involuntary due to starvation, bed rest and/or space flight (Hegarty, Kim, 1981; Fitts et al., 2010; Sandonà et al., 2012). Various dietary regimes often involve intermittent fasting which reduces lean body mass (Varady, 2011). Thus, muscle wasting can be a result of conscious manipulations involving caloric restriction in order to achieve cosmetic goals which are associated with body shape and appearance. However, caloric restriction is also associated with improved health and longevity biomarkers in rodents and humans (Heilbronn et al., 2006; Ingram et al., 2006). It seems that caloric restriction will be popular in near future as new dietary interventions are being developed (Varady et al., 2015). In this scenario myostatin inhibition might be a useful strategy to preserve skeletal muscle mass during caloric restriction. Moreover, myostatin inhibition is a promising target for an enhanced fat loss as well (McPherron, Lee, 2002). To date, few attempts have been made to investigate effects of myostatin deficiency on skeletal muscle mass after food deprivation (FD) (Allen et al., 2010; Collins-Hooper et al., 2015). These studies have produced contradictory results and more research is needed. Effects of FD on contractile properties of skeletal muscle also need to be examined in this regard. It appears that FD causes reduction in muscle mass which is associated with an increase in specific force of fast-twitch skeletal muscles of myostatin-deficient mice (Collins-Hooper et al., 2015). Similar findings have been reported after 5 week caloric restriction study (Matsakas et al., 2013). Based on these evidences, we carried out a study in which we examined effects of myostatin dysfunction on skeletal muscle mass and force in both predominantly slow-twitch and fast-twitch muscles following FD. Slow- and fast-twitch muscles are showing different metabolic and functional properties as well as a content of myostatin-binding ActRIIB receptors (Mendias et al., 2006). Therefore effects of myostatin dysfunction and FD might be muscle specific. Moreover, we also examined how a genetic background affects these parameters following FD. THE AIM OF THE RESEARCH was to examine effects of genetic background and myostatin dysfunction on specific force and mass of skeletal muscles after muscle hypertrophy and atrophy. RESEARCH OBJECTIVES: 1. To investigate effects of genetic background on skeletal muscle mass and force. 2. To investigate effects of myostatin dysfunction on skeletal muscle mass and force before and after functional overload. 3. To investigate effects of myostatin dysfunction and genetic background on skeletal muscle atrophy and muscle force during food deprivation. RESEARCH HYPOTHESES: 1. We studied skeletal muscles in mouse strains which differ significantly in body size. On the basis that larger muscle hypertrophy might lead to unfavourable for force production changes in muscle architecture and/or contractile material maintainence (Kawakami et al., 1995; Amthor et al., 2007; Ikegawa et al., 2008), our hypothesis was that specific muscle force will be dependent on muscle size and it will decrease with increase in body and muscles mass of the studied mouse strains. 2. Myostatin-deficient mice have increased glycolytic type II fibre content in muscles (Girgenrath et al., 2005; Gentry et al., 2011) which are more prone to hypertrophy (Verdijk et al., 2009). It appears that only muscle mass reduction toward wild type phenotype could restore force production in myostatin-deficient mice (Matsakas et al., 2013; Collins-Hooper et al., 2015). Thus, we hypothesized that ablation of the gastrocnemius muscle will be associated with greater compensatory hypertrophy of soleus and its function deterioration in BEH mice with dysfunctional myostatin compared to BEH+/+ mice carrying the wild type myostatin. 3. We studied mass and force of the hindlimb muscles in BEH and BEH+/+ mice as well as in the C57BL/6J background. Our hypothesis was that myostatin dysfunction which positively affects a net muscle protein turnover by enhanced protein synthesis (Morrisete et al., 2009; Lipina et al., 2010) will prevent loss of muscle mass and improve force during food deprivation. We also hypothesized that there might be differences in loss of muscle mass between genetic backgrounds due to possible changes in a body composition and/or metabolic peculiarities (Konarzewski, Diamond, 1995). CONCLUSIONS Study 1: 1. Skeletal muscles of mouse strains vary significantly in muscle mass and force generation capacity. Specific muscle force, however, does not change with increase in body size and as a result of muscle growth during maturation. 2. DUH background shows lower specific muscle force compared to both BEH+/+ and C57BL/6J backgrounds. Study 2: 1. Myostatin dysfunction is associated with increased muscle mass, but reduced specific muscle force. 2. Myostatin dysfunction is also associated with reduction in hypertrophy and impairment in force generation capacity of soleus muscle after functional overload. Study 3: 1. Skeletal muscle atrophy after food deprivation is dependant on myostatin dysfunction, genetic background and muscle properties. Myostatin dysfunction is associated with a greater loss of muscle mass. C57BL/6J background is more susceptible to muscle atrophy than BEH+/+ background under these conditions. 2. After food deprivation, the slower contracting soleus shows less severe muscle atrophy, but greater loss of specific muscle force compared to a faster contracting extensor digitorum longus
Effect of cold acclimation on the neuromuscular function.
No full textHuman can adapt to cold in terms of thermal responses (Young et al., 1986; Jansky et al., 1996). Although it is established that cold exposure produces a decrease in physical performance, especially due to the effects of impaired peripheral (muscular) function (Giesbrecht et al., 1995), there are only a few studies regarding effect of repeated cold exposures on the neuromuscular function. 2-3 weeks repeated local cold water immersion failed to show any adaptation in the neuromascular function (Geurts et al., 2005, 2006), but after 3 months of whole body cryotherapy was established that neuromuscular function can adapt to cold due to increased activity of agonist and decreased activity of antagonist (Westerlund et al., 2009). According to this study, the effect on the core temperature seems to be minimal, but in our study it was controlled strictly (reaching 35,5±0,1 0C core temperature). It was also different methodology of testing neuromuscular function in our study, where using isometric contractions of plantar flexors we focused on effect of cold acclimation on peripheral and central function. The object of our study – neuromuscular function affected by cold acclimation. The purpose of our study is to investigate the effect of cold acclimation on the neuromuscular function. Objectives: 1. To observe and evaluate the changes of physiological responses (rectal, skin temperature, heart rate, physiologic stress) during the acclimation period. 2. To establish the effect of cold acclimation on peripheral (muscular) function. 3. To establish the effect of cold acclimation on central (neural) function. Hypothesis: 1. According to Jansky et al. (1996) study which showed lower central and peripheral (skin) body temperature after 4-6 weeks whole-body cooling in water (14 0C, 1 hr, 3 times per week) and referred it to as hypothermic adaptation, it was hypothesized that similar results would recur in our study and hypothermic or insulative-hypothermic adaptation to cold would occur. 2. According to Geurts et al. (2005) study of repeated (3 weeks) local cooling where muscle temperature and electrically evoked twitch didn’t increase at the end of acclimation, it was hypothesized that after 16 days of passive cooling muscle temperature wouldn’t change drastically, suggesting no changes in contractile properties, and peripheral (muscle) adaptation to cold wouldn’t occur. 3. According to Westerlund et al. (2009) study which showed that acute repeated whole-body cold exposure induces neuromuscular adaptation by decreasing co-activation, it was also hypothesized that chronic mild hypothermia is sufficient stimulus to induce central (neural) adaptation and increase central activation, agonist activity and decrease antagonist activity, thereby improve performance of 2 min sustained maximal voluntary contraction (MVC-2min). Conclusions: 1. After 16 days of passive cooling there was more rapid decrease in rectal temperature and more pronounced decrease in skin temperature, suggesting that insulative-hypothermic adaptation to cold occurred. 2. Cold acclimation didn’t result in significant changes of electrically evoked twitch torque and contractile properties of plantar flexors, suggesting that peripheral (muscular) adaptation didn’t occur. 3. Cold acclimation increased central activation ratio, muscle agonist and decreased muscle antagonist activity of plantar flexors, suggesting that central (neural) adaptation occurred
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