A longitudinal investigation of the development of weight and muscle concerns among preadolescent boys

The study examined the impact of body mass index (BMI), negative affect, self-esteem, and sociocultural influences in the development of weight and muscle concerns among preadolescent boys. Body dissatisfaction, importance placed on weight and muscles, weight loss strategies, and strategies to increase muscles were evaluated. Participants were 237 boys aged between 8 and 11 years who were tested at three assessment periods 8 months apart. The main predictor of boys’ body change strategies was their perceived pressures to modify weight and muscles from parents, peers, and the media. The other main predictor of boys’ body change strategies and the sole predictor of body dissatisfaction was BMI. Self-esteem and negative affect were found to be weak and generally nonsignificant predictors of boys’ body image concerns and body change strategies. Additional studies that examine the risk and protective factors associated with boys’ weight and muscle concerns are needed to assist in the development of prevention programs for preadolescent boys.

A prospective study of individual factors in the development of weight and muscle concerns among preadolescent children

The present study was designed to assess body mass index (BMI), self-esteem, parent and peer relations, negative affect, and perfectionism, as predictors of dieting, food preoccupation, and muscle preoccupation, in 326 preadolescent children (150 girls and 176 boys) aged between 8 and 10 years. Preadolescents were tested twice over a 10-month period. BMI was found to be the main predictor of girls' and boys' dieting, both cross-sectionally and longitudinally. Perfectionism was an important predictor of boys' dieting and muscle preoccupation, while self-esteem, peer relations and negative affect predicted girls' muscle preoccupation. The findings are discussed in relation to past research with both preadolescents and adolescents.

Preventing weight and muscle concerns among preadolescents

The high level of weight and shape concerns amongst preadolescent children has prompted interest in the development of prevention programs for this age group. In the 1990s weight and shape concerns were considered primarily an adolescent phenomenon. However, prevention programs which have been designed with adolescent and adult populations have been found to show limited success. Some researchers have argued that programs which target preadolescent children are more likely to be effective than programs that target adolescents, as by adolescence many attitudes and behaviours have become entrenched so they may be more difficult to modify. On the other hand, children's weight and shape concerns are believed to be more malleable and amenable to change. To date there have been limited controlled studies implementing prevention programs designed to reduce weight and shape concerns with preadolescent populations. The new study conducted as part of this thesis involves the development and implementation of the ‘Everybody’ s Different, Nobody Else Is Me’ preadolescent prevention program. The program was designed to address some of the methodological biases of past research and incorporate three risk factors, social comparisons, negative affect, and self-esteem, to reduce and/or prevent the development of weight and muscle concerns among children. These three risk factors have been found to be associated with weight and shape concerns of adolescents and adults, and there is also increasing evidence that they are important factors among children. Research also suggests that social comparisons, negative affect, and self-esteem are interrelated, which highlights the importance of targeting the variables in one program. The new five session prevention initiative was implemented with 156 grade four children. Both the treatment and control conditions consisted of 78 children. Preliminary evidence from the new prevention initiative indicated that the program reduced muscle bulk and exercise (ie. An over-emphasis on exercise to lose weight rather than health promotion), and negative affect in the long term as assessed by the six month follow-up. At the six month follow-up, children in both the treatment and control conditions reported reduced negative affect, dieting, and muscle bulk and exercise scores and increased positive affect. Consistent with short term follow-up results, boys reported greater muscle bulk and exercise scores than girls at the six month follow-up. Girls, in both conditions, were also found to report greater positive affect than boys. These findings are discussed in relation to past research, and suggestions for future prevention initiatives are highlighted.

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.

Weight concerns among elementary school children : a review of prevention programs

There is increasing evidence that children display high levels of weight and muscle concerns, which include body dissatisfaction and problem eating. In order to address these issues, researchers have designed and implemented prevention programs for this age group. Thirteen published studies were located and reviewed, with children aged 8–12 years from elementary schools, or equivalent. Overall, the programs were shown to be effective in improving children's knowledge at post-test and at follow-up assessments. However, there is limited evidence to show that the programs reduced or prevented body image concerns and/or problem eating. Too few studies have examined muscle concerns so no conclusions can yet be drawn about this domain. Limitations of the studies and suggestions for future prevention efforts are discussed.

A biopsychosocial model for understanding body image and body change strategies among children

The present study was designed to assess the role of biopsychosocial factors in understanding body image concerns and cognitions and behaviors related to losing weight or increasing muscles among 507 children (270 girls and 237 boys) aged between 8 and 11 years. Biological, psychological, and sociocultural factors have been found to be relevant in understanding the development of body image concerns and weight loss strategies among children. However, these factors have not been examined together in a single study; thus, the relative influence of each factors and how these factors may interact is not known. In the current study, body mass index (BMI) was found to be a good indicator of girls' and boys' body dissatisfaction, while the main indicator of children's body change strategies was perceived pressure from parents, peers, and the media. Overall, there were more similarities than differences between girls and boys. The age between 8 and 11 years is a significant period to commence studying body image concerns and body change strategies, as it can be used to help us understand the emergence of gender differences in children's weight and muscle concerns.

Where is all the pressure coming from? Messages from mothers and teachers about preschool children's appearance, diet and exercise

This study used interviews and qualitative analyses to investigate the nature of the messages that preschool children receive from mothers and teachers about their bodies, general appearance, exercise and eating practices. Participants were 10 female teachers and 53 mothers. The behaviours of the 53 children (24 boys, 29 girls) were also observed to determine the nature of their eating and exercise behaviours. The results demonstrated that both mothers and teachers expressed concerns about their own bodies. Mothers also communicated messages to their daughters about losing weight and messages to their sons about increasing their muscles. Both girls and boys were concerned about their appearance, particularly their clothes and hair. Girls also demonstrated some concerns about losing weight, and boys with increasing muscles. Implications of these results are discussed in terms of designing education programs for mothers, teachers and children to prevent the development of body image concerns and disordered eating among children. Copyright © 2006 John Wiley & Sons, Ltd and Eating Disorders Association.

Longitudinal study of children's disordered eating and muscle preoccupation

This thesis examined the role of individual factors in the development of dieting and muscal preoccupation in children. The main factor associated with these weight and shape concerns was perfectionism. It is important to identify risk factors in order to design intervention programs to decrease these behaviours in children.

Brief report : maltreatment in childhood and body concerns in adulthood

Objective: We examined the relationship between maltreatment in childhood and body concerns in adulthood.

Method: A community sample of 156 women and 143 men completed measures of maltreatment – frequency of sexual abuse, physical abuse, physical neglect, emotional abuse and emotional neglect – in childhood. They also reported current dissatisfaction with body weight and shape and drive for thinness and drive for muscle.

Results and conclusions: Childhood maltreatment was associated with drive for muscle in women and body dissatisfaction and drive for thinness in men. The results provide some evidence that adverse conditions in childhood can be associated with gender-atypical body concerns in adulthood.

Adrenaline increases skeletal muscle glycogenolysis, pyruvate dehydrogenase activation and carbohydrate oxidation during moderate exercise in humans

# 1.
To evaluate the role of adrenaline in regulating carbohydrate metabolism during moderate exercise, 10 moderately trained men completed two 20 min exercise bouts at 58 ± 2 % peak pulmonary oxygen uptake (̇V_o2,peak). On one occasion saline was infused (CON), and on the other adrenaline was infused intravenously for 5 min prior to and throughout exercise (ADR). Glucose kinetics were measured by a primed, continuous infusion of 6,6-[2H]glucose and muscle samples were obtained prior to and at 1 and 20 min of exercise.

# 2.
The infusion of adrenaline elevated (P < 0.01) plasma adrenaline concentrations at rest (pre-infusion, 0.28 ± 0.09; post-infusion, 1.70 ± 0.45 nmol l−1; means ±s.e.m.) and this effect was maintained throughout exercise. Total carbohydrate oxidation increased by 18 % and this effect was due to greater skeletal muscle glycogenolysis (P < 0.05) and pyruvate dehydrogenase (PDH) activation (P < 0.05, treatment effect). Glucose rate of appearance was not different between trials, but the infusion of adrenaline decreased (P < 0.05, treatment effect) skeletal muscle glucose uptake in ADR.

# 3.
During exercise muscle glucose 6-phosphate (G-6-P) (P = 0.055, treatment effect) and lactate (P < 0.05) were elevated in ADR compared with CON and no changes were observed for pyruvate, creatine, phosphocreatine, ATP and the calculated free concentrations of ADP and AMP.

# 4.
The data demonstrate that elevated plasma adrenaline levels during moderate exercise in untrained men increase skeletal muscle glycogen breakdown and PDH activation, which results in greater carbohydrate oxidation. The greater muscle glycogenolysis appears to be due to increased glycogen phosphorylase transformation whilst the increased PDH activity cannot be readily explained. Finally, the decreased glucose uptake observed during exercise in ADR is likely to be due to the increased intracellular G-6-P and a subsequent decrease in glucose phosphorylation.

Differential effects of exercise on insulin-signaling gene expression in human skeletal muscle.

Skeletal muscle insulin sensitivity is enhanced after acute exercise and short-term endurance training. We investigated the impact of exercise on the gene expression of key insulin-signaling proteins in humans. Seven untrained subjects (4 women and 3 men) completed 9 days of cycling at 63 ± 2% of peak O₂ uptake for 60 min/day. Muscle biopsies were taken before, immediately after, and 3 h after the exercise bouts (on days 1 and 9). The gene expression of insulin receptor substrate-2 and the p85α subunit of phosphatidylinositol 3-kinase was significantly higher 3 h after a single exercise bout, although short-term training ameliorated this effect. Gene expression of insulin receptor and insulin receptor substrate-1 was not significantly altered at any time point. These results suggest that exercise may have a transitory impact on the expression of insulin receptor substrate-2 and phosphatidylinositol 3-kinase; however, the predominant actions of exercise on insulin sensitivity appear not to reside in the transcriptional activation of the genes encoding major insulin-signaling proteins.

Creatine transporter protein content, localization, and gene expression in rat skeletal muscle

The present study examined the gene expression and cellular localization of the creatine transporter (CreaT) protein in rat skeletal muscle. Soleus (SOL) and red (RG) and white gastrocnemius (WG) muscles were analyzed for CreaT mRNA, CreaT protein, and total creatine (TCr) content. Cellular location of the CreaT protein was visualized with immunohistochemical analysis of muscle cross sections. TCr was higher (P <= 0.05) in WG than in both RG and SOL, and was higher in RG than in SOL. Total CreaT protein content was greater (P <= 0.05) in SOL and RG than in WG. Two bands (55 and 70 kDa) of the CreaT protein were found in all muscle types. Both the 55-kDa (CreaT-55) and the 70-kDa (CreaT-70) bands were present in greater (P <= 0.05) amounts in SOL and RG than in WG. SOL and RG had a greater amount (P <= 0.05) of CreaT-55 than CreaT-70. Immunohistochemical analysis revealed that the CreaT was mainly associated with the sarcolemmal membrane in all muscle types. CreaT mRNA expression per microgram of total RNA was similar across the three muscle types. These data indicate that rat SOL and RG have an enhanced potential to transport Cr compared with WG, despite a higher TCr in the latter.