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Carbohydrate (CHO) metabolism is crucial for short-duration, high-intensity exercise performance, but the effects of variations in glycogen availability have not been investigated in field trials of trained athletes. This study was designed to test how 1500 m time trial (TT) performance is affected by the manipulation of pre-race glycogen reserves. Competitive middle-distance runners (n = 11 (4 females)) completed a 1500 m individually paced indoor TT after abundant (high, >5 g/kg/d) or restricted (low, <1.5 g/kg/d) dietary CHO intake for 2 days after a glycogen-depleting session. Stride pattern, heart rate (HR), capillary blood lactate, and glucose and plasma malondialdehyde (MDA) response were determined. The TT was slower in low vs. high condition by 4.5 (4.5) s (~2%; p < 0.01), with a tendency toward shorter stride length. Blood lactate and glucose were lower before the TT in low vs. high condition (1.8 (0.5) vs. 2.2 (0.7) mmol/L and 5.4 (0.7) vs. 5.9 (0.8) mmol/L, p = 0.022 and 0.007, respectively), and peak lactate was higher in high vs. low condition (16.8 (3.1) vs. 14.5 (4.2) mmol/L, p = 0.039). Plasma MDA was the same before the TT, and 15 min after the TT, it increased similarly by 15% in low (p = 0.032) and high (p = 0.005) conditions. The restriction of pre-test CHO intake impaired 1500 m TT performance and reduced baseline and peak blood lactate concentrations but not blood glucose or MDA response. [ABSTRACT FROM AUTHOR]

Caloric restriction (CR) induces weight loss, but is associated with rapid weight regain upon return to ad libitum feeding. Our aim was to investigate effects of the macronutrient composition of the diet on weight loss and regain in elderly mice. Males, 18 months old, of the C57BL/6J strain were subjected to 4-week 30% CR followed by 4 weeks of ad libitum refeeding on either high-carb (HC), high-fat (HF) or high-protein (HP) diets (n = 22 each). Mice (n = 11) fed a chow diet ad libitum served as a control group (CON). Body mass and food intake were monitored daily. Twenty-four-hour indirect calorimetry was used to assess energy expenditure and substrate oxidation. Muscle and fat mass were evaluated with dissection of the tissues. Serum leptin and ghrelin levels were also measured. CR-induced weight loss did not differ between the diets. Weight regain was particularly fast for HF as mice overshot their initial weight by 12.8 ± 5.7% after 4-week refeeding when HC and HP mice reached the weight of the CON group. Weight regain strongly correlated with energy intake across the groups. The respiratory exchange ratio was lower in HF mice (0.81 ± 0.03) compared to HC (0.94 ± 0.06, p < 0.001), HP (0.89 ± 0.04, p < 0.001) and CON mice (0.91 ± 0.06, p < 0.01) during the refeeding. Serum leptin levels were higher in HF mice (1.03 ± 0.50 ng/mL) compared to HC (0.46 ± 0.14, p < 0.001), HP (0.63 ± 0.28, p < 0.05) or CON mice (0.41 ± 0.14, p < 0.001). Thus, CR induces similar weight loss in aging mice irrespective of the diet's macronutrient composition. An HF diet leads to excessive energy intake and pronounced gain in body fat in spite of increased fat oxidation and serum leptin during the refeeding after CR. [ABSTRACT FROM AUTHOR]

Objective: It is controversial whether low-carbohydrate diets are better suited for weight control and metabolic health than high-carbohydrate diets. This study examined whether these diets induce different improvements in body composition and glucose tolerance in obese mice during caloric restriction (CR).Methods: Male C57BL/6J mice were fed an obesogenic diet ad libitum for 18 weeks and then subjected to 6-week progressive CR of up to 40%, using either a low-fat or low-carbohydrate diet with equal protein content. Mice fed a regular chow diet ad libitum served as controls. Body mass, hindlimb muscle mass, fat mass, energy expenditure, and glucose tolerance were compared between the groups.Results: Initially low-fat and low-carbohydrate groups had similar body mass, which was 30% greater compared with controls. CR induced similar weight loss in low-fat and low-carbohydrate groups. This weight loss was mainly due to fat loss in both groups. Energy expenditure of freely moving mice did not differ between the groups. Glucose tolerance improved compared with the values before CR and in controls but did not differ between the diets.Conclusions: Dietary carbohydrate or fat content does not affect improvements in body composition and metabolic health in obese mice exposed to CR with fixed energy and protein intake. [ABSTRACT FROM AUTHOR]

Background. Both fasting and ageing processes lead to muscle wasting. We studied the effect of single 48 h fasting on soleus skeletal muscle mass and force in young and old mice. Methods. The study involved 18 young and 13 old mice. Body and soleus (SOL) muscle mass were measured followed by assessment of peak and specific SOL force under ex vivo conditions. SOL muscle half-relaxation time and 20 Hz to 100 Hz force ratio were also measured. Results. After fasting, weight loss was greater (p < .05) in young mice compared to old mice (17.0 ± 2.6 versus 12.0 ± 1.7%, respectively). Fasted young, but not old mice showed reduction (p < .05) in SOL mass compared to the control values. On the other hand, specific SOL force was reduced (p < .05) only in old mice, while 20 Hz to 100 Hz force ratio decreased (p < .05) only in young mice after fasting. Conclusions. Our results showed that 48 h fasting caused lower SOL muscle peak and specific force in old but not young mice. [ABSTRACT FROM AUTHOR]

Background. Citrate synthase (CS) plays an important role in the regulation of carbohydrate oxidation. Variation in citrate synthase activity has an influence on metabolic changes. We tested the hypothesis that reduced mitochondrial CS activity could affect energy expenditure (EE) and respiratory quotient (RQ) in mouse model with an emphasizing on gender differences between tested strains. Methods. 16-week of age wild-type C57Bl/6J (B6) mouse strain, B6.A-(rs3676616-D10Utsw1)/Kjn (B6.A) and C57BL/6J-Chr 10A/J/NaJ (B6.A10) strains with reduced CS activity were studied in physiocage by the "Panlab" metabolism analysing equipment. The following parameters were calculated: EE (ml/min/kg^0.75), RQ, physical activity and rearing. Results. In female mice EE values were lower in B6.A10 strain compared to wild-type B6 strain. RQ values were similar in all tested mouse strains. In B6 mice EE was higher in females compared to males. Rearing was elevated in females of B6 mice compared to males. Conclusions. EE was lower in B6.A10 compared to B6 mice. Gender differences were noticed only in B6 mice: EE and rearing were significantly higher in female compared to male mice. Current study did not reveal any other association between reduced CS activity and EE or RQ variation in male and female mice. [ABSTRACT FROM AUTHOR]

Phenotypic diversity between laboratory mouse strains provides a model for studying the underlying genetic mechanisms. The A/J strain performs poorly in various endurance exercise models. The aim of the study was to test if endurance capacity and contractility of the fast- and slow-twitch muscles are affected by the genes on mouse chromosome 10. The C57BL/6J (B6) strain and C57BL/6J-Chr 10A/J/NaJ (B6.A10) consomic strain which carries the A/J chromosome 10 on a B6 strain background were compared. The B6.A10 mice compared to B6 were larger in body weight (p < 0.02): 27.2 ± 1.9 vs. 23.8 ± 2.7 and 23.4 ± 1.9 vs. 22.9 ± 2.3 g, for males and females, respectively, and in male soleus weight (p < 0.02): 9.7 ± 0.4 vs. 8.6 ± 0.9 mg. In the forced running test the B6.A10 mice completed only 64% of the B6 covered distance (p < 0.0001). However, there was no difference in voluntary wheel running (p = 0.6) or in fatigability of isolated soleus (p = 0.24) or extensor digitorum longus (EDL, p = 0.7) muscles. We conclude that chromosome 10 of the A/J strain contributes to reduced endurance performance. We also discuss physiological mechanisms and methodological aspects relevant to interpretation of these findings. [ABSTRACT FROM AUTHOR]

Background. Genetic factors play an important role in determining muscle mass. Indeed, myostatin dysfunction is associated with a pronounced muscle hypertrophy. The aim of our study was to test the hypothesis that starvation induced muscle wasting differs between BEH+/+ and C57BL/6J strains of mice and myostatin dysfunction prevents muscle wasting in BEH strain. Methods. 18-week-old males of C57BL/6J, BEH+/+ and BEH were subjected to 48 h food deprivation (FD). C57BL/6J mice were representatives of classic mouse strain. BEH mice which differ from BEH+/+ mice by Compact mutation in the Mstn gene represented a model for myostatin dysfunction. All mice were divided into experimental and control groups. The control groups consisted of mice fed ad libitum. Seven mice were studied in each group. Mice were weighed before as well as 24 h and 48 h after FD which was followed by dissection and weighing of the hindlimb skeletal muscle. Results. BEH and BEH+/+ mice showed a similar (16.9 ± 1.4% vs. 19.3 ± 2.4%, p > .05) loss of body mass while loss of body mass in C57BL/6J mice was the greatest (24.8 ± 1.9%, p < .001) after FD. The loss of muscle mass was significant in both BEH (p < .001) and C57BL/6J (p < .01) mice, but it was below the level of significance (p > .05) in BEH+/+ mice. Conclusions. Myostatin dysfunction promotes muscle atrophy after FD. During short periods of FD, BEH+/+ mice are more resistant to body and muscle loss compared to C57BL/6J mice. [ABSTRACT FROM AUTHOR]

Background. Mouse strains differ in body and skeletal muscle mass. It is commonly believed that specific force is a constant value irrespective of muscle mass. We hypothesised that excessive muscle hypertrophy might compromise force output. Methods. We studied force generating capacity and muscle mass of isolated soleus (SOL) and extensor digitorum longus (EDL) muscles in 14-15-week-old males of C57BL/6J, BEH+/+ and DUH mice (n = 7 per strain). In addition, muscles of young (4-5 weeks old, n = 7 per strain) BEH+/+ and DUH mice were also studied. Specific forces were calculated as isometric tetanic force divided by the estimated physiological cross-section area (PCSA) of the muscles. Results. DUH strain generated lower specific force (p < .01- .001) than both C57BL/6J and BEH+/+ strains in SOL (110 ± 20 vs. 146 ± 28 and 164 ± 8 mN/mm², respectively) and EDL muscles (74 ± 18 vs. 101 ± 19 and 95 ± 11 mN/mm², respectively). There were no differences between muscles of young and adult mice (p > .05). C57BL/6J and BEH+/+ generated similar specific force. Conclusions. Our results show that body mass is not associated with reduction in specific force of skeletal muscles in mice. It seems that age did not affect specific force either. However, the heaviest DUH mice had lower specific force in both slow twitch SOL and fast twitch EDL compared to BEH+/+ and C57BL/6J mice. It appears that DUH strain could be a useful model in studying factors limiting specific force of skeletal muscle. [ABSTRACT FROM AUTHOR]

Fasting improves metabolic health, but is also associated with loss of lean body mass. We investigated if old mice are less resistant to fasting-induce muscle wasting than adult mice. We compared changes in skeletal muscles and fat distribution in C57BL/6J mice subjected to 48-hour fasting at adult (6-month old) or old (24-month old) age. Old mice lost less weight (11.9 ± 1.5 vs 16.9 ± 2.8%, p < 0.001) and showed less (p < 0.01) pronounced muscle wasting than adult mice. Extensor digitorum longus (EDL) muscle force decreased only in adult mice after fasting. Serum IGF-1 levels were higher (p < 0.01) and showed greater (p < 0.01) decline in adult mice compared to old mice. Phosphorylation of 4EBP1 was reduced in the gastrocnemius muscles of adult mice only. Energy expenditure was slower in old mice and showed smaller fasting-induced decline than in adult mice when adjusted for variations in physical activity. There was a loss of fat mass in both age groups, but it was more pronounced in adult mice than old mice. Our results suggest that ageing-related decrease in metabolic rate protects old mice from skeletal muscle wasting during fasting. • We investigated effects of fasting on body composition of adult and old C57BL/6J mice. • 48-hour fasting was associated with low physical activity and greater decrease serum IGF-1 in adult compared to old mice. • Fasting induced significant muscle wasting and force loss only in adult mice. • Reduced metabolic rate protects old mice from excessive muscle wasting during fasting. [ABSTRACT FROM AUTHOR]

Caloric restriction (CR) is of key importance in combating obesity and its associated diseases. We aimed to examine effects of dietary macronutrient distribution on weight loss and metabolic health in obese mice exposed to CR. Male C57BL/6J mice underwent diet-induced obesity for 18 weeks. Thereafter mice were exposed to a 6-week CR for up to 40% on either low-fat diet (LFD; 20, 60, 20% kcal from protein, carbohydrate, fat), low-carb diet (LCD; 20, 20, 60% kcal, respectively) or high-pro diet (HPD; 35, 35, 30% kcal, respectively) (n = 16 each). Ten mice on the obesogenic diet served as age-matched controls. Body composition was evaluated by tissue dissections. Glucose tolerance, bloods lipids and energy metabolism were measured. CR-induced weight loss was similar for LFD and LCD while HPD was associated with a greater weight loss than LCD. The diet groups did not differ from obese controls in hindlimb muscle mass, but showed a substantial decrease in body fat without differences between them. Glucose tolerance and blood total cholesterol were weight-loss dependent and mostly improved in LFD and HPD groups during CR. Blood triacylglycerol was lowered only in LCD group compared to obese controls. Thus, CR rather than macronutrient distribution in the diet plays the major role for improvements in body composition and glucose control in obese mice. Low-carbohydrate-high-fat diet more successfully reduces triacylglycerol but not cholesterol levels compared to isocaloric high-carbohydrate-low-fat weight loss diets. [ABSTRACT FROM AUTHOR]

Myostatin is an inhibitor of skeletal muscle growth and might be involved in adaptations to caloric restriction (CR). We compared responses to 12-week 30% CR in male mice of Berlin high strain with myostatin dysfunction (BEH) and wild-type myostatin (BEH+/+). BEH mice were heavier than BEH+/+ mice (58.8 ± 2.0 versus 53.1 ± 2.7 g, p < 0.001), had 1.8-fold greater hind limb muscle mass and were less (p < 0.05) physically active when fed ad libitum. After CR, BEH and BEH+/+ strains experienced similar weight loss (24.7 ± 5.7 versus 20.6 ± 6.5%, p > 0.05, respectively) and decreases (p < 0.001) in plasma IGF-1 and total cholesterol, but loss of hind limb muscle mass was greater (p < 0.001) in BEH mice than BEH+/+ mice. BEH mice had better (p < 0.001) glucose tolerance and showed smaller (p < 0.05) improvements of it than BEH+/+ mice after CR (1038.2 ± 174.7 versus 744.4 ± 95.8 glucose mM× 120 min, p < 0.01 for BEH; 1365.8 ± 218.5 versus 831.5 ± 134.4 glucose mM ×120 min, p < 0.001, for BEH+/+, respectively). In summary, myostatin dysfunction is associated with muscle hypertrophy and high glucose tolerance, but greater muscle wasting and smaller improvements in glucose tolerance in response to CR. • We investigated effects of myostatin dysfunction and caloric restriction in Berlin high mouse strain. • 12 weeks of 30% caloric restriction induced loss of fat and muscle mass, lowered plasma triacylglycerol and cholesterol. • Myostatin dysfunction was associated with greater loss of hind limb muscle mass and attenuated improvements in glucose tolerance of mice • Myostatin dysfunction does not protect from muscle wasting during caloric restrriction. [ABSTRACT FROM AUTHOR]