Bone mineral and calcium accretion during puberty

We measured bone mineral content (BMC) and estimated calcium accretion in children to provide insight into dietary calcium requirements during growth. Anthropometric measurements were done semiannually and whole-body BMC was measured annually by dual-energy X-ray absorptiometry for 4 y in 228 children (471 scans in 113 boys and 507 scans in 115 girls). Mean values for BMC, skeletal area, and height were calculated for 1-y age groups from 9.5 to 19.5 y of age. Cross-sectional analysis of the pooled data gave peak height velocity and peak BMC velocity (PBMCV) and the ages at which these occurred (13.3 y in boys and 11.4 y in girls). PBMCV did not peak until 1.2 y after peak height velocity in boys and 1.6 y after peak height velocity in girls. Within 3 y on either side of PBMCV, boys had consistently higher BMC and BMC velocity compared with girls and the discrepancy increased steadily through puberty. Three years before PBMCV, BMC values in girls were 69% of those in boys; 3 y after peak height velocity this proportion fell to 51%. PBMCV was 320 g/y in boys and 240 g/y in girls. Under the assumption that bone mineral is 32.2% calcium, these values corresponded to a daily calcium retention of 282 mg in boys and 212 mg in girls. Individual values could be much greater. In one boy in a group of six subjects for whom there were enough data for individual analysis through puberty, PBMCV was 555 g Ca/y or 490 mg Ca/d. Such high skeletal demands for calcium require large dietary calcium intakes and such requirements may not be met immediately in some children.

Effects of group- versus home-based exercise in the treatment of obesity

This study examined the effects of 2 aerobic exercise regimens on exercise participation, fitness, eating patterns, treatment adherence, and weight change in 49 obese women undergoing a year-long behavioral weight loss program. Participants were assigned randomly to weight loss treatment plus either group- or home-based exercise. All participants were instructed to complete a moderate-intensity walking program (30 min/day, 5 days/week). Group exercise participants were provided with 3 supervised group exercise sessions per week for the first 26 weeks and with 2 sessions per week thereafter. Home exercise participants were instructed to complete all exercise in their home environment. After 6 months, both conditions displayed significant improvements in exercise participation, fitness, eating patterns, and weight loss. At 12 months, the home-based program showed superior performance to the group condition in exercise participation and treatment adherence; at 15 months, participants in the home program demonstrated significantly greater weight losses than those in the group program.

Effects of group- versus home-based exercise in the treatment of obesity

This study examined the effects of 2 aerobic exercise regimens on exercise participation, fitness, eating patterns, treatment adherence, and weight change in 49 obese women undergoing a year-long behavioral weight loss program. Participants were assigned randomly to weight loss treatment plus either group- or home-based exercise. All participants were instructed to complete a moderate-intensity walking program (30 min/day, 5 days/week). Group exercise participants were provided with 3 supervised group exercise sessions per week for the first 26 weeks and with 2 sessions per week thereafter. Home exercise participants were instructed to complete all exercise in their home environment. After 6 months, both conditions displayed significant improvements in exercise participation, fitness, eating patterns, and weight loss. At 12 months, the home-based program showed superior performance to the group condition in exercise participation and treatment adherence; at 15 months, participants in the home program demonstrated significantly greater weight losses than those in the group program.

Exercise for the older woman: choosing the right prescription

Many elderly women in industrially developed countries are at, or near to, functionally important strength related thresholds and so have either lost, or are in danger of losing, the ability to perform some important everyday tasks. The increased rate of healthcare expenditure due to loss of physical function is a major economic issue. Even though women make up most of the senior population, little current research on the impact of physical activity on strength and function in elderly people has included women. Elderly women typically have more barriers to participation in physical activity than do other groups and because of decreased participation, may possibly experience higher disability rates. Physical activity in old age may delay the progression of osteoporosis and is of paramount importance for maintaining the functional abilities needed to carry out daily tasks. Current research on exercise and the elderly population suggests that strength training may be the exercise mode of choice for maintenance of strength, physical function, bone integrity, and psychosocial health. This review summarises recent research on the impact of strength training on the fitness and health of elderly women and highlights considerations and potential barriers to physical activity that must be taken into account when planning exercise programmes for them.

Bone mineral density and adipose tissue distribution in young women: relationship to smoking status

Interrelationships between anthropometric variables and bone mineral density (BMD) may allow simple and inexpensive identification of those at risk for low bone density and osteoporosis. Risk appraisal is particularly important in young women, as lifestyle modifications may slow the rate of bone loss through adulthood and decrease the risk of osteoporosis later in life. Though weight, height and body mass index are frequently assessed in relation to bone, adipose tissue distribution has rarely been considered. Smoking is associated with low bone density and abdominally localized adipose tissue. The relationship between smoking, adipose tissue distribution and BMD in women has not been examined. Regional and whole-body BMD were assessed by dual-energy X-ray absorptiometry, and adipose tissue distribution using the anthropometric indicator, waist-to-hip girth ratio (WHR), in 52 women (25 smokers, and 27 nonsmokers) aged 20-35 years. There were significant (p < 0.05) positive correlations between WHR and BMD for smokers and nonsmokers separately (r = 0.44-0.57), and for the sample overall (r = 0.30-0.51). Most relationships remained significant after adjustment for weight. Smokers did not differ significantly from nonsmokers in relationships between WHR and BMD. The results indicate a positive relationship between BMD and abdominal relative to gluteal-femoral adiposity. This relationship is independent of smoking status. The biological determinants underlying a relationship between BMD and WHR require consideration before inferences regarding BMD can reasonably be considered on the basis of WHR.

Calculated thermal conductivities and heat flux in man

Using data compiled by the Brussels Cadaver Analysis Study on 13 unembalmed cadavers, this study examined the validity of assumptions often made concerning the role of the skin and adipose tissue layers in thermal insulation in vivo. Skin thickness was previously reported to vary from 0.35 to 2.55 mm, depending on the site of measurement and gender of the subject. Assuming a thermal conductivity of 0.70 x 10(-3) kcal/(cm.s-1.degree C-1) for the skin, heat flux across the skin would vary between site and gender in the order of 7.5 times, ranging from 0.16 to 1.20 kcal.min-1.degree C-1.m-2. Due to the negligible thermal gradient across the skin layer, however, this would be of little physiologic significance. Assumptions concerning the homogeneity of skin thickness across gender and measurement site when investigating thermal insulation of the peripheral tissues would not, therefore, influence the reported results significantly. However, it has recently been shown that the calculated lipid fraction of the adipose tissue layer varies according to a person's level of adiposity. Using a two-component model of adipose tissue, the predicted thermal conductivity (k) of the adipose tissue in the present sample was found to range from 0.50 to 0.97 x 10(-3) kcal/(cm.s-1.degree C-1), being significantly lower (P = 0.005) in the five most obese cadavers [6.66 +/- 0.45 x 10(-4) kcal/(cm.s-1.degree C-1)] than in the five most lean cadavers [8.22 +/- 0.93 x 10(-4) kcal/(cm.s-1.degree C-1)]. Adiposity level correlated significantly (r = 0.80; P < 0.01) with calculated k values, suggesting caution must be taken when assuming a single k for the adipose tissue layer when examining divergent populations (i.e., obese vs. thin).

Adipose tissue density, estimated adipose lipid fraction and whole body adiposity in male cadavers

Lipid and water together typically make up more than 90% of the body's adipose tissue mass. Although some reports have shown that the fraction of lipid in adipose tissue is greater in obese people than in lean ones, the quantitative relationship between adipose lipid fraction and overall adiposity of the body has never been investigated. We dissected six male unembalmed cadavers and weighed all adipose tissue (range 9.7-25.7 kg), allowing the calculation of percentage adiposity as 100 x total adipose mass/body mass (range 17.8-43.9%). Adipose tissue volume was determined by hydrostatic weighing of all portions of the dissected adipose tissue. For the six cadavers, whole body adipose tissue density ranged from 0.925-0.970 g/ml. Based on a three-component model of adipose tissue (lipid, water and dry fat-free solids), an expression for lipid fraction, F, was derived. After assuming densities for adipose lipid (0.905 g/ml), water at 36 degrees C (0.997 g/ml) and the dry fat-free component (1.38 g/ml), the equation simplified to F = 6.256/D-5.912, where D is adipose tissue density (g/ml). Lipid fraction was then calculated for each of the six cadavers: the range (0.54-0.85) was in excellent agreement with published data. There was a significant correlation (r = 0.95, P < 0.005) between calculated lipid fraction and percentage adiposity. The regression equation predicting lipid fraction from percentage adiposity was y = 0.327 + 0.0124x. We conclude that the estimated fraction of lipid in human adipose tissue shows both a wide range and a strong positive linear relationship with overall body fatness.

Oxygen cost of treadmill running in 24-month-old Fischer-344 rats

The oxygen cost of treadmill running is well documented in young adult rats. However, to our knowledge there are no detailed reports concerning the oxygen cost of treadmill running in senescent rats. Young adult (4 months; N = 8) and senescent (24 months; N = 8) female Fischer-344 rats were tested for O2 cost of treadmill running. One-half of the animals tested in each age group had completed 10 wk of endurance training. Oxygen cost of treadmill running, using a flow-through system, was measured on a per minute basis from 7-10 min of each work bout and averaged. Separate work bouts were performed at 0%, 5%, and 10% grade at 15, 20, 25, and 30 m.min-1. Oxygen cost of treadmill running for trained rats for all speeds and grades were not significantly different (P = 0.77) from untrained animals; thus, data were pooled for oxygen cost of running. Results revealed significantly lower (P < 0.05) VO2 (expressed as ml.kg-1.min-1) for senescent rats vs young adult rats rest and at all comparable treadmill grades and speeds except for 5% grade, 25 m.min-1 and 10% grade, 20 m.min-1. In addition, resting VO2 was significantly lower (P < 0.05) in old rats when compared with young rats. Thus, we conclude that the oxygen cost of treadmill running is lower for 24-month-old rats than in 4-month-old rats except at higher work levels.