Association among serum lipid and lipoprotein concentrations and physical activity, physical fitness, and body composition in young children.

OBJECTIVE: To examine the relationships among indicators of physical activity, physical fitness, and body composition with serum lipid and lipoprotein levels in young children. DESIGN: Cross-sectional and 1-year prospective cohort. SETTING: Studies of Child Activity and Nutrition (SCAN) program, Galveston, Tex. SUBJECTS: One hundred twenty-three 4- or 5-year-old black, Hispanic (of Mexican origin), and white children. MEASUREMENTS: Body composition, resting heart rate, and cardiovascular fitness variables and serum lipid and lipoprotein levels were measured at age 3 or 4 years (study year 1) and at age 4 or 5 years (study year 2), and day-long heart rate was measured and the Children's Activity Rating Scale was administered between study years 1 and 2. RESULTS: Year-1 waist/hip ratios were inversely correlated with total serum cholesterol (TSC) and low-density lipoprotein (LDL) levels. Mean activity level was inversely correlated with waist/hip ratios. On the basis of multiple regression analysis, the sum of seven skin-fold measurements, height, and gender explained 15.4% of the variation in triglyceride levels. The sum of seven skin-fold measurements was inversely correlated with the high-density lipoprotein (HDL) level. Resting heart rate, waist/hip ratio, and the slope of the exercise heart rate during fitness testing explained 19.5% of the variation in the concentration of an HDL subclass, HDL2. These children's levels of physical activity were associated with higher fitness levels. Year-1 waist/hip ratios and year-2 sum of seven skin-fold measurements were positively correlated with the LDL/HDL and TSC/HDL ratios. CONCLUSION: Higher levels of cardiovascular fitness and lower levels of fatness were associated with more favorable serum lipid and lipoprotein levels in these young children. Physical activity appeared to have an indirect association with serum lipid and lipoprotein values through its relationship with higher fitness levels and lower levels of fatness.

Reliability and variability of heart rate monitoring in 3-, 4-, or 5-yr-old children.

We describe the daily heart rate patterns and the between day and within day reliabilities of several heart rate variables measured in 159 Anglo-, African-, and Mexican-American children aged 3-5 yr. Heart rates were measured over 12 waking hours with a Quantum XL Telemetry heart rate monitor. There were no significant ethnic, gender, day of week, or season of the year differences in either mean resting heart rate, mean daily heart rate, mean longest duration of the heart rate sustained above 120 bpm for the day, nor percent of minutes of daily heart rate above 120 bpm. The reliabilities for these variables for 2 d of observation separated by 3-6 months ranged from 0.65 to 0.66. At this level of reliability, just over 4 d of recording are necessary to achieve a reliability of 0.80. All within-day across-hour reliabilities were greater than 0.80. However, for mean hourly heart rate and the longest duration of heart rate sustained above 120 bpm each hour, a principal components analysis revealed three distinct time components during the day. This suggests that monitoring heart rate during limited portions of the day will provide a biased estimate of overall heart rate. For the morning component, there were significant ethnic and gender differences in the children's heart rates and younger children had longer durations of heart rate sustained above 120 bpm than older children. Although daily heart rate monitoring is not a perfect indicator of children's physical activity, these data suggest that it may be a reliable measure among younger children from different ethnic and gender groups.