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Background: Fat distribution, rather than total body fat, has been identified as a significant risk factor for chronic disease. Patterning of subcutaneous fat, in particular, may play a pervasive role in shaping the metabolic milieu that is critical for disease development. Several studies have shown that early-life nutrition may influence later body composition. The effect of breastfeeding and formula feeding on early patterns of subcutaneous fat deposition, however, are uncertain. Objective: At a time when early infant growth is emerging as a predictor for later chronic disease, it is the aim of the present analysis to investigate whether feeding style (breastfeeding versus formula feeding) modifies subcutaneous fat growth rates and trajectories in the first year of life with a focus on the historical iterations of WHO infant feeding recommendations (0 to 4 months, 4 to 6 months, and 6 to 12 months of age). Methods: This is an ex post-facto design that utilizes data collected as part of a longitudinal growth study in the first year of life. Subcutaneous fat mass was anthropometrically assessed weekly by skinfold thickness (triceps, quadriceps, calf, subscapular, suprailiac, midaxillary, and abdominal) in 21 infants. Feeding data were collected through daily parental records and are entered here as a categorical variable (predominantly breast fed and predominantly formula fed). Multi-level mixed effects models for repeated measures were used (STATA 14) adjusting for age, sex, weight, birthweight, and number of feeding episodes per day. Statistical significance was accepted at p Results:Infants experienced fat accretion only during the first four months, and this was limited to peripheral skinfolds. Thereafter, subcutaneous skinfolds followed a trend of declining rates. Breastfed and formula fed infants, however, demonstrated different patterns of subcutaneous fat deposition in both the sum of skinfolds and in each skinfold site. During the first four months, formula fed infants experienced greater rates for the subscapular, abdominal, suprailiac, trunk, quadriceps, sum of skinfolds (p Conclusion: Weekly skinfold assessments of seven subcutaneous sites have identified that feeding style predicts differences in deposition patterns in the first year of life. Breastfed infants demonstrated both slower rates of accretion and decline by comparison with their formula fed peers. This analysis further suggests that the first four months may be a critical period for subcutaneous fat deposition. Feeding specific effects were identified for truncal deposition and utilization, which suggests that future studies may benefit from depot-specific inquiries.

Objective: The purposes of this study were to 1) quantify trunk endurance times according to subjects’ age and sex; and 2) identify factors affecting the endurance times. Material and Method: Endurance times of sedentary workers aged 20-49 years were determined by an extensor endurance, a flexor endurance, and right and left side bridge (trunk lateral flexor) tests. Each test was performed once in random order with a resting period of 10 minutes between tests. Results: Of 137 workers, Two-way analysis of variance indicated that age had no effect on these 4 isometric trunk endurance tests. Sex had an effect on the extensor endurance test, and right and left side bridge tests. Females had longer endurance times than males for the trunk extensor muscle, whereas males had longer endurance times than females for right and left lateral flexor trunk muscles. Low negative but significant Pearson’s correlations (r = -0.233 to -0.377, p = 0.047 to 0.001) were found between extensor endurance times vs. body weight and abdominal skinfold thickness in both sexes. Only in males, both right and left side bridge endurance times correlated with abdominal skinfold thickness (r = -0.296 and r = -0.382, respectively, p < 0.05 both). Conclusion: Sex, weight and abdominal skinfold thickness factors should be considered when trunk muscle endurance is evaluated.

Skinfold thickness has long been found to be highly correlated with total body fat. Yet it remains largely underutilized in comparison to other anthropometric measures. The ability of skinfold thickness to characterize adiposity-related health outcomes should contribute to its utility in studying these outcomes. Objective: To determine comparability of skinfold thickness with whole body total fat, measured by dual energy X-ray absorptiometry (DXA), and their relationships with insulin resistance and serum triglyceride levels in a large sample of US adolescents. The utility of skinfold thickness was evaluated by determining optimum subscapular percentile-cut points for identifying adolescents who are at risk of elevated insulin resistance. Methods: Pooled serial cross-sectional data from the continuous National Health and Nutrition Examination Survey (NHANES) cycles 2001-04 were analyzed. Primary data used included skinfold thicknesses, DXA-based total body fat (DXF), serum insulin and fasting glucose (for homeostasis model assessment of insulin resistance; HOMA-IR), and serum triglycerides. Data from a total of approximately 1500 US youths aged 12-18 years were used in this work. Findings from manuscript one demonstrated that skinfold thickness is comparably associated with both continuous HOMA and the upper quintile of elevated insulin resistance in adolescents as total body fat weight measured with DXA. Similarly, in manuscript two skinfold thickness was comparable to DXA in associations with variation in serum triglycerides, and in predicting adolescents who have elevated serum triglyceride levels. Additionally, subscapular skinfold was found to be better at identifying adolescent girls at risk of elevated serum triglyceride levels than DXA whole-body fat weight. In manuscript three, subscapular skinfold thickness was found to be sufficiently correlated with HOMA-IR to justify identification of age- and sex-specific percentile cut-offs for identifying elevated insulin resistance in adolescents. These new subscapular skinfold percentile cut-offs can be used as a screening tool for identifying US adolescents at risk of elevated insulin resistance, who can then be referred for subsequent follow-up and diagnostic studies. Findings from this dissertation have demonstrated that skinfolds are amply correlated with insulin resistance and serum triglyceride levels, thus supporting their wider use in anthropometric assessment of obesity and its related health outcomes in adolescents.