Keisuke Teramoto

Gender differences in body fat of low- and high-body-mass children: relationship with body mass index

Abstract The primary objective of this study was to determine gender differences in total body fat mass (TBFM) and body fat distribution (subcutaneous fat mass, SFM; and internal fat mass, IFM) in a cross-sectional sample of 280 children. Measurements of the body composition of 141 boys and 139 girls, all apparently healthy and aged 3–6 years were made using bioelectrical impedance. Determinations of impedance were made using a four-terminal impedance analyzer (TP-95K; Toyo Physical, Fukuoka, Japan). Lean body mass (LBM) was calculated using a previously published equation [Goran MI, Kaskoun MC, Carpenter WH, Poehlman ET, Ravussin E, Fontvieikke A-M (1993) Estimating body composition of young children by using bioelectrical resistance. J Appl Physiol 75: 1776–1780]. SFM was calculated using a modification of the equation derived by Skerjl [Skerjl B, Brozek J, Hunt EE (1953) Subcutaneous fat and age changes in body build and body form in women. Am J Phys Anthrop 11: 577–580] and Davies [Davies PSW, Jones PRM, Norgan NG (1986) The distribution of subcutaneous and internal fat in man. Ann Hum Biol 13: 189–192]. The main modifications of the equation in the present study were the introduction of: (1) mean thickness of adipose tissue over body surface/2, and (2) skin mass. IFM was calculated as the difference between TBFM and SFM. The body mass index (BMI; kg/m2) was calculated from the formula: body mass/height2. For each gender, the subjects in the lowest and highest 25th percentiles were designated as “low body mass” and “high body mass”, respectively. In the present study, no gender differences in absolute TBFM, SFM and IFM were observed in either of these groups. In contrast, gender differences in relative TBFM (%Fat) and SFM (SFM/mass) were evident in girls. However, the four subgroups were similar in terms of relative IFM (IFM/mass). The TBFM was independently related to SFM, IFM and %Fat in both genders after adjustment for BMI; however, there was no significant association of SFM with IFM after adjustment for BMI in any group. Even after adjustment for BMI, IFM was independently related to %Fat in both genders, although SFM was not independently related to %Fat in any group except low-body-mass boys. This study shows that relative TBFM and SFM are higher in high-body-mass groups and tend to be higher in girls than in boys, and that the higher %Fat in high-body-mass girls than in high-body-mass boys appears to be associated with internal adipose tissue deposits. External adipose tissue mass does not appear to be related to the higher %Fat levels in high-body-mass girls. In addition, subcutaneous fat mass appears to be higher in low-body-mass girls than in low-body-mass boys, although this observation needs confirmation using more valid measures of subcutaneous fat such as computerized tomography and magnetic resonance imaging.

MEASUREMENT OF VENTILATORY THRESHOLD BY RESPIRATORY FREQUENCY

This study was conducted to assess whether respiratory frequency can be used as a valid parameter for estimating ventilatory threshold and for examining differences in exercise modes such as a cycle ergometer and a treadmill. 24 men and 12 women performed an incremental exercise test to exhaustion on a cycle ergometer and on a treadmill. Oxygen uptake, carbon dioxide output, pulmonary ventilation, ventilatory frequency, and heart rate were measured continuously every 30 sec. during the test. Three different and independent reviewers detected the ventilatory threshold point and break point of respiratory rate, which were then compared. Analysis indicated that (1) ventilatory threshold was well correlated with break point of respiratory rate for both cycle (r = .88, p<.001) and treadmill exercise (r = .96, p<.001). However, on the average, ventilatory threshold was only 71% (cycle) or 88% (treadmill) of break point of respiratory rare. (2) The regression equation for treadmill exercise was more accurate than that for cycling, but the detected data samples were smaller. The break point of respiratory rate was more easily detected for the cycle ergometer test (33 of 36 subjects) than for the treadmill test (only 15 of 36). The cycle ergometer test identified the break point of respiratory rate more easily than did the treadmill test. (3) There was an association between physical fitness and whether the break point of respiratory rate was detectable, and the more fit the subject (above average), the more likely the break point was to be undetected. Our study demonstrates that the break point of respiratory rate is closely associated with ventilatory threshold and that the cycle ergometer test is more conducive than the treadmill test to the detectability of break point of respiratory rate.