Exercise training increases lipid metabolism gene expression in human skeletal muscle

The effects of a single bout of exercise and exercise training on the expression of genes necessary for the transport and beta -oxidation of fatty acids (FA), together with the gene expression of transcription factors implicated in the regulation of FA homeostasis were investigated. Seven human subjects (3 male, 4 female, 28.9 ± 3.1 yr of age, range 20-42 yr, body mass index 22.6 kg/m², range 17-26 kg/m²) underwent a 9-day exercise training program of 60 min cycling per day at 63% peak oxygen uptake (V_{O2 peak}; 104 ± 14 W). On days 1 and 9 of the program, muscle biopsies were sampled from the vastus lateralis muscle at rest, at the completion of exercise, and again 3 h postexercise. Gene expression of key components of FA transport [FA translocase (FAT/CD36), plasma membrane-associated FA-binding protein], beta -oxidation [carntine palmitoyltransferase(CPT) I, beta -hydroxyacyl-CoA dehydrogenase] and transcriptional control [peroxisome proliferator-activated receptor (PPAR)alpha , PPARgamma , PPARgamma coactivator 1, sterol regulatory element-binding protein-1c] were unaltered by exercise when measured at the completion and at 3 h postexercise. Training increased total lipid oxidation by 24% (P < 0.05) for the 1-h cycling bout. This increased capacity for lipid oxidation was accompanied by an increased expression of FAT/CD36 and CPT I mRNA. Similarly, FAT/CD36 protein abundance was also upregulated by exercise training. We conclude that enhanced fat oxidation after exercise training is most closely associated with the genes involved in regulating FA uptake across the plasma membrane (FAT/CD36) and across the mitochondrial membrane (CPT I).

The role of puberty, media and popularity with peers on strategies to increase weight, decrease weight and increase muscle tone among adolescent boys and girls

The present study was concerned with the impact of pubertal development, relationships with peers and perceived pressure from the media on body dissatisfaction and body change behaviors among adolescent boys and girls. In particular, the study investigated the underresearched area of strategies to increase weight and muscle. The exploration of body change strategies among adolescent boys has been a neglected area of research. Methods: Respondents were 1185 adolescents (527 males, 598 females) who were enrolled in Grades 7 and 9. Participants completed measures of pubertal development, media and peer influence, body dissatisfaction and strategies to lose weight, increase weight and to increase muscle. Results: The findings demonstrated that girls were more likely than boys to adopt strategies to lose weight, whereas boys were more likely to adopt strategies to increase muscle tone (but not weight). For boys in both Years 7 and 9, the main predictors of body change strategies were puberty and, to a lesser extent, perceived popularity with peers. The major influences for Years 7 and 9 girls were puberty and the media, but these mainly focused on weight loss. For Year 9 girls, perceived popularity with opposite-sex peers also predicted body dissatisfaction and strategies to increase muscle tone. Conclusion: The implications of these findings for understanding factors related to a range of body change strategies for adolescent boys and girls are discussed.

Social comparisons and negative affect as indicators of problem eating and muscle preoccupation among children

The present study examined the utilization of social comparison practices and the role of negative affect in predicting body dissatisfaction, problem eating, and muscle preoccupation among young children. Participants were 236 children aged between 8 and 10 years. Children's eating, exercising, and muscle concerns were examined using a modified version of the Children's Eating Attitudes Test (ChEAT), which included additional items pertaining to muscle bulk and exercising. Consistent with past findings, body mass index (BMI) was found to be the sole unique indicator of body dissatisfaction for both boys and girls. Utilization of social comparison practices with adults was the main unique indicator of the modified ChEAT factors for boys, while BMI was the main unique indicator of the modified ChEAT factors for girls. In addition, negative affect was associated with binging, food preoccupation, and social pressure to eat for boys and dieting and muscle preoccupation for girls. Findings are discussed in relation to previous studies with adolescents and adults.

Exercise and skeletal muscle gene expression

1. Skeletal muscle is a complex and heterogenous tissue capable of remarkable adaptation in response to exercise training. The role of gene transcription, as an initial target to control protein synthesis, is poorly understood.
2. Mature myofibres contain several hundred nuclei, all of which maintain transcriptional competency, although the localized responsiveness of nuclei is not well known. Myofibres are capable of hypertrophy. These processes require the activation and myogenic differentiation of mononuclear satellite cells that fuse with the enlarging or repairing myofibre.
3. A single bout of exercise in human subjects is capable of activating the expression of many diverse groups of genes.
4. The impact of repeated exercise bouts, typical of exercise training, on gene expression has yet to receive systematic investigation.
5. The molecular programme elicited by resistance exercise and endurance exercise differs markedly. Muscular hypertrophy following resistance exercise is dependent on the activation of satellite cells and their subsequent myogenic maturation. Endurance exercise requires the simultaneous activation of mitochondrial and nuclear genes to enable mitochondrial biogenesis.
6. Future analysis of the regulation of genes by exercise may combine high-throughput technologies, such as gene-chips, enabling the rapid detection and analysis of changes in the expression of many thousands of genes.

Exercise increases nuclear AMPK α2 in human skeletal muscle

An acute bout of exercise increases skeletal muscle glucose uptake, improves glucose homeostasis and insulin sensitivity, and enhances muscle oxidative capacity. Recent studies have shown an association between these adaptations and the energy-sensing 5' AMP-activated protein kinase (AMPK), the activity of which is increased in response to exercise. Activation of AMPK has been associated with enhanced expression of key metabolic proteins such as GLUT-4, hexokinase II (HKII), and mitochondrial enzymes, similar to exercise. It has been hypothesized that AMPK might regulate gene and protein expression through direct interaction with the nucleus. The purpose of this study was to determine if nuclear AMPK α₂ content in human skeletal muscle was increased by exercise. Following 60 min of cycling at 72 +/- 1% of V_O2peak in six male volunteers (20.6 +/- 2.1 years; 72.9 +/- 2.1 kg; V_O2peak = 3.62 +/- 0.18 l/min), nuclear AMPK α₂ content was increased 1.9 +/- 0.4-fold (P = 0.024). There was no change in whole-cell AMPK α₂ content or AMPK α₂ mRNA abundance. These results suggest that nuclear translocation of AMPK might mediate the effects of exercise on skeletal muscle gene and protein expression.

Effect of alcohol intake on muscle glycogen storage after prolonged exercise

We studied the effects of alcohol intake on postexercise muscle glycogen restoration with samples from vastus lateralis being collected immediately after glycogen-depleting cycling and after a set recovery period. Six well-trained cyclists undertook a study of 8-h recovery (2 meals), and another nine cyclists undertook a separate 24-h protocol (4 meals). In each study, subjects completed three trials in crossover order: control (C) diet [meals providing carbohydrate (CHO) of 1.75 g/kg]; alcohol-displacement (A) diet (1.5 g/kg alcohol displacing CHO energy from C) and alcohol + CHO (AC) diet (C + 1.5 g/kg alcohol). Alcohol intake reduced postmeal glycemia especially in A trial and 24-h study, although insulin responses were maintained. Alcohol intake increased serum triglycerides, particularly in the 24-h study and AC trial. Glycogen storage was decreased in A diets compared with C at 8 h (24.4 ± 7 vs. 44.6 ± 6 mmol/kg wet wt, means ± SE, P < 0.05) and 24 h (68 ± 5 vs. 82 ± 5 mmol/kg wet wt, P < 0.05). There was a trend to reduced glycogen storage with AC in 8 h (36.2 ± 8 mmol/kg wet wt, P = 0.1) but no difference in 24 h (85 ± 9 mmol/kg wet wt). We conclude that 1) the direct effect of alcohol on postexercise glycogen synthesis is unclear, and 2) the main effect of alcohol intake is indirect, by displacing CHO intake from optimal recovery nutrition practices.

A short-term, high-fat diet up-regulates lipid metabolism and gene expression in human skeletal muscle

Background: Dietary fatty acids may be important in regulating gene expression. However, little is known about the effect of changes in dietary fatty acids on gene regulation in human skeletal muscle.
Objective: The objective was to determine the effect of altered dietary fat intake on the expression of genes encoding proteins necessary for fatty acid transport and &szlig;-oxidation in skeletal muscle.
Design: Fourteen well-trained male cyclists and triathletes with a mean (&plusmn; SE) age of 26.9 &plusmn; 1.7 y, weight of 73.7 &plusmn; 1.7 kg, and peak oxygen uptake of 67.0 &plusmn; 1.3 mL &dot; kg-1 &dot; min-1 consumed either a high-fat diet (HFat: > 65% of energy as lipids) or an isoenergetic high-carbohydrate diet (HCho: 70–75% of energy as carbohydrate) for 5 d in a crossover design. On day 1 (baseline) and again after 5 d of dietary intervention, resting muscle and blood samples were taken. Muscle samples were analyzed for gene expression [fatty acid translocase (FAT/CD36), plasma membrane fatty acid binding protein (FABPpm), carnitine palmitoyltransferase I (CPT I), &szlig;-hydroxyacyl-CoA dehydrogenase (&szlig;-HAD), and uncoupling protein 3 (UCP3)] and concentrations of the proteins FAT/CD36 and FABPpm.
Results: The gene expression of FAT/CD36 and &szlig; -HAD and the gene abundance of FAT/CD36 were greater after the HFat than after the HCho diet (P < 0.05). Messenger RNA expression of FABPpm, CPT I, and UCP-3 did not change significantly with either diet.
Conclusions: A rapid and marked capacity for changes in dietary fatty acid availability to modulate the expression of mRNA-encoding proteins is necessary for fatty acid transport and oxidative metabolism. This finding is evidence of nutrient-gene interactions in human skeletal muscle.

Motor-unit Coherence During Isometric Contractions Is Greater in a Hand Muscle of Older Adults

The purpose of this study was to quantify the strength of motor-unit coherence from the first dorsal interosseus muscle in young and old adults using data obtained in a previous study, where no differences in motor-unit synchronization between the two groups were observed.

Human skeletal muscle creatine transporter mRNA and protein expression in healthy, young males and females

The present study investigated whether there were any differences between males and females in respect to creatine transporter (CreaT) gene expression and/or total creatine (TCr) content in human vastus lateralis muscle. Skeletal muscle obtained from young healthy male (n = 13, age: 23.2 ± 5.0 years) and female subjects (n = 12, age: 21.7 ± 4.3 years) was analyzed for CreaT mRNA, CreaT protein and TCr content. Total CreaT protein content in the muscle was similar (p > 0.05) between the sexes. Two bands (~ 55 and 73 kDa) of the CreaT protein were detected in all muscle samples. Both the 55 and the 73 kDa bands were present in similar (p > 0.05) amounts in males compared with females. The 73 kDa band was in greater abundance (p < 0.05) than the 55 kDa band, irrespective of gender. In addition, CreaT mRNA expression relative to ß-actin mRNA and the TCr content (males: 117.8 ± 2.2, females: 125.3 ± 4.3 mmol.kg^–1 dry mass) were also unaffected (p > 0.05) by gender. These data demonstrate that gender does not influence skeletal muscle TCr content and CreaT gene expression in young human subjects.

Sociocultural and individual influences on muscle gain and weight loss strategies among adolescent boys and girls

The study examined the role of body dissatisfaction, body image importance, sociocultural influences (media and parent and peer encouragement), self-esteem and negative affect on body change strategies to decrease weight and increase muscles in adolescent boys and girls. Surveys were administered to 587 boys and 598 girls aged between 11 and 15 years. For both genders, parent and peer encouragement and negative affect were the primary predictors of body dissatisfaction, body image importance and strategies to decrease weight and increase muscles. In addition, body image importance was a significant factor in the development of both types of body change strategies, while the media only predicted strategies to decrease weight. Lastly, the effects of self-esteem were mediated by body dissatisfaction. For boys, a stronger focus on body importance occurred among the boys who were generally satisfied with their bodies while the reverse was the case for girls.

Body image and strategies to lose weight and increase muscle among boys and girls

This study examined factors that influence body image and strategies to either lose weight or increase muscle among children. Participants were 237 boys and 270 girls. Body mass index (BMI), body dissatisfaction, cognitions and behaviors to both lose weight and increase muscles, as well as self-esteem and positive and negative affect, were evaluated. Self-esteem was associated with body satisfaction, positive affect predicted strategies to lose weight and increase muscles, and negative affect predicted body dissatisfaction and cognitions to lose weight and increase muscles. Boys were more likely to focus on changing muscles. Respondents with higher BMIs were more focused on losing weight but not muscle. The discussion focuses on health risk behaviors related to eating and exercise among children.

Effect of creatine supplementation on housekeeping genes in human skeletal muscle using real-time RT-PCR

The present study examined the validity and reliability of measuring the expression of various genes in human skeletal muscle using quantitative real-time RT-PCR on a GeneAmp 5700 sequence detection system with SYBR Green 1 chemistry. In addition, the validity of using some of these genes as endogenous controls (i.e., housekeeping genes) when human skeletal muscle was exposed to elevated total creatine levels and exercise was also examined. For all except 28S, linear relationships between the logarithm of the starting RNA concentrations and the cycle threshold (C_T) values were established for ß-actin, ß2-microglobulin (ß₂M), cyclophilin (CYC), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). We found a linear response between C_T values and the logarithm of a given amount of starting cDNA for all the genes tested. The overall intra-assay coefficient of variance for these genes was 1.3% and 21% for raw C_T values and the linear value of 2^-C_T, respectively. Interassay variability was 2.3% for raw C_T values and 34% for the linear value of 2^-C_T. We also examined the expression of various housekeeping genes in human skeletal muscle at days 0, 1, and 5 following oral supplementation with either creatine or a placebo employing a double-blind crossover study design. Treatments were separated by a 5-wk washout period. Immediately following each muscle sampling, subjects performed two 30-s all-out bouts on a cycle ergometer. Creatine supplementation increased (P < 0.05) muscle total creatine content above placebo levels; however, there were no changes (P > 0.05) in C_T values across the supplementation periods for any of the genes. Nevertheless, 95% confidence intervals showed that GAPDH was variable, whereas ß-actin, ß₂M, and CYC were the least varying genes. Normalization of the data to these housekeeping genes revealed variable behavior for ß₂M with more stable expressions for both ß-actin and CYC. We conclude that, using real-time RT-PCR, ß-actin or CYC may be used as housekeeping genes to study gene expression in human muscle in experiments employing short-term creatine supplementation combined with high-intensity exercise.

Factors influencing creatine loading into human skeletal muscle

This review describes several factors involved in regulating skeletal muscle creatine uptake and total creatine content. Skeletal muscle total creatine content increases with oral creatine supplementation, although the response is variable. Factors that may account for this variation are carbohydrate intake, physical activity, training status, and possibly fiber type.