Nonlinear relationships between weekly walking distance and adiposity in 27,596 women

A Prospective Study Comparing Distance-based vs. Time-based Exercise Prescriptions of Walking and Running in Previously Sedentary Overweight Adults

Prior work has reported that the declines observed in body mass index (BMI) and circumference measurements in their cross-sectional data were twice as large when calculated from distance energy expenditure estimations compared to energy expenditure estimations based on time and intensity. The primary purpose of this study was to compare walking/running for distance to walking/running for time as part of an exercise intervention. This study followed a between-subjects, repeated measures design. Fifteen overweight, but otherwise healthy participants completed the study. The time-based group walked/ran for self-reported time while the distance-based group walked/ran for self-reported distance. A mixed-factor repeated-measures ANOVA was used to compare all dependent variables both within-subjects and between-subjects. Weekly adherence rates to the exercise program did not exhibit a significant difference (p > 0.05). Significant interactions were shown for mean body mass loss between groups as well as mean blood glucose level (p < 0.05). Distance-based group exhibited a decline in body mass and blood glucose while the time-based group exhibited an increase in both variables. To the best of the authors' knowledge, the present study is the first to directly compare a distance-based vs. a time-based exercise program for walking and running for improvement of risk factors of cardiovascular disease. The results of this study would suggest that a distance-based exercise prescription of walking or running should provide a clinician or researcher with a closer estimation of overall accumulated exercise and resultant weight loss.

Obesity, Underweight, and Smoking Are Associated with Worse Cardiorespiratory Fitness in Finnish Healthy Young Men: A Population-Based Study

Background

Obesity and smoking are strongly associated with worse cardiorespiratory fitness (CRF). Most previous studies that have examined the association of body composition with CRF have neither assessed non-linearity nor separately examined the effects of underweight. Thus, very little is known on how underweight affects CRF. Possible joint effects of obesity and smoking on CRF have not been adequately explored.

Aims

We examined the association between body mass index (BMI) and smoking with CRF in 1,629 Finnish army conscripts. We focused on non-linear effects of BMI in order to assess the importance of underweight. We also examined whether the cooccurrence of obesity and smoking potentiates their deleterious effects on CRF.

Methods

We used the Cooper’s 12-minute run test (12MR) to measure CRF. The 12MR score was analyzed as continuous (linear, polynomial, and restricted cubic spline regression) and categorical. In categorical analyses, we used binary logistic regression with the 12MR score in two groups (low = lowest quintile vs. intermediate/high = quintiles 2–5) and multinomial logistic regression with the 12MR score in three groups (low = lowest quintile, intermediate = quintiles 2 and 3, and high = quintiles 4 and 5).

Results

Non-linearity in the spline model was statistically significant (p < 0.001). In addition, the non-linear models had a clearly better fit than the linear one in terms of Akaike Information Criterion and R-squared values. There was a statistically significant interaction between smoking and BMI (p < 0.01). In the categorical analysis, overweight/obese regular smokers were at a particularly high risk of not achieving high CRF.

Conclusion

In healthy young men, not only overweight/obesity but also underweight may be associated with worse CRF. This provides a potential mechanism for the previously reported association between underweight and increased mortality. The cooccurrence of overweight/obesity and regular smoking may have a deleterious effect on CRF.

Walking and running are associated with similar reductions in cataract risk

PURPOSE

Habitual running has been associated with reduced risk of cataract development in one prospective study. The purposes of the current analyses were to provide further evidence of this potentially important benefit of vigorous exercise and to test whether moderate exercise (e.g., walking) provides as significant and equivalent reduction in cataract risk as vigorous exercise (e.g., running).

METHODS

Cox proportional hazard analyses of self-reported, physician-diagnosed incident cataracts versus baseline energy expenditure (METs) in 32,610 runners and 14,917 walkers during a 6.2-yr follow-up. Results are reported as hazard ratios (HR), percent risk reductions (100 (HR - 1)), and 95% confidence intervals (95% CI).

RESULTS

Runners and walkers reported 733 and 1074 incident cataracts during follow-up, respectively. When adjusted for sex, race, age, education, smoking, and intakes of meat, fruit, and alcohol, lower cataract risk was significantly associated with both running (HR = 0.960 per MET·h·d, 95% CI 0.935-0.986) and walking (HR = 0.918 per MET·h·d, 95% CI = 0.881-0.956), with no significant difference in the risk reduction per MET-hours per day between running and walking or between men and women. Compared with running or walking at or below guideline levels (≤1.8 MET·h·d), incident cataract risk was significantly lower for running or walking 1.8-3.6 (16.4% lower, 95% CI = 6.4%-25.3%), 3.6-5.4 (19.0% lower, 95% CI = 5.6%-30.4%), 5.4-7.2 (26.2% lower, 95% CI = 11.2%-38.7%), 7.2-9.0 (34.1% lower, 95% CI = 10.0%-51.2%), and ≥9 MET·h·d (41.6% lower, 95% CI = 19.8%-57.4%).

CONCLUSION

Moderate (walking) and vigorous (running) exercise were both significantly associated with lower cataract risk and their effects similar. Cataract risk appears to decrease linearly with increasing exercise energy expenditure through 9 MET·h·d.

Dose-response relationship of physical activity to premature and total all-cause and cardiovascular disease mortality in walkers

Purpose

To assess the dose-response relationships between cause-specific mortality and exercise energy expenditure in a prospective epidemiological cohort of walkers.

Methods

The sample consisted of the 8,436 male and 33,586 female participants of the National Walkers' Health Study. Walking energy expenditure was calculated in metabolic equivalents (METs, 1 MET = 3.5 ml O₂/kg/min), which were used to divide the cohort into four exercise categories: category 1 (≤1.07 MET-hours/d), category 2 (1.07 to 1.8 MET-hours/d), category 3 (1.8 to 3.6 MET-hours/d), and category 4 (≥3.6 MET-hours/d). Competing risk regression analyses were use to calculate the risk of mortality for categories 2, 3 and 4 relative to category 1.

Results

22.9% of the subjects were in category 1, 16.1% in category 2, 33.3% in category 3, and 27.7% in category 4. There were 2,448 deaths during the 9.6 average years of follow-up. Total mortality was 11.2% lower in category 2 (P = 0.04), 32.4% lower in category 3 (P<10⁻¹²) and 32.9% lower in category 4 (P = 10⁻¹¹) than in category 1. For underlying causes of death, the respective risk reductions for categories 2, 3 and 4 were 23.6% (P = 0.008), 35.2% (P<10⁻⁵), and 34.9% (P = 0.0001) for cardiovascular disease mortality; 27.8% (P = 0.18), 20.6% (P = 0.07), and 31.4% (P = 0.009) for ischemic heart disease mortality; and 39.4% (P = 0.18), 63.8% (P = 0.005), and 90.6% (P = 0.002) for diabetes mortality when compared to category 1. For all related mortality (i.e., underlying and contributing causes of death combined), the respective risk reductions for categories 2, 3 and 4 were 18.7% (P = 0.22), 42.5% (P = 0.001), and 57.5% (P = 0.0001) for heart failure; 9.4% (P = 0.56), 44.3% (P = 0.0004), and 33.5% (P = 0.02) for hypertensive diseases; 11.5% (P = 0.38), 41.0% (P<10⁻⁴), and 35.5% (P = 0.001) for dysrhythmias: and 23.2% (P = 0.13), 45.8% (P = 0.0002), and 41.1% (P = 0.005) for cerebrovascular diseases when compared to category 1.

Conclusions

There are substantial health benefits to exceeding the current exercise guidelines.

The relationship of walking intensity to total and cause-specific mortality. Results from the National Walkers' Health Study

PURPOSE

Test whether: 1) walking intensity predicts mortality when adjusted for walking energy expenditure, and 2) slow walking pace (≥24-minute mile) identifies subjects at substantially elevated risk for mortality.

METHODS

Hazard ratios from Cox proportional survival analyses of all-cause and cause-specific mortality vs. usual walking pace (min/mile) in 7,374 male and 31,607 female recreational walkers. Survival times were left censored for age at entry into the study. Other causes of death were treated as a competing risk for the analyses of cause-specific mortality. All analyses were adjusted for sex, education, baseline smoking, prior heart attack, aspirin use, diet, BMI, and walking energy expenditure. Deaths within one year of baseline were excluded.

RESULTS

The National Death Index identified 1968 deaths during the average 9.4-year mortality surveillance. Each additional minute per mile in walking pace was associated with an increased risk of mortality due to all causes (1.8% increase, P=10(-5)), cardiovascular diseases (2.4% increase, P=0.001, 637 deaths), ischemic heart disease (2.8% increase, P=0.003, 336 deaths), heart failure (6.5% increase, P=0.001, 36 deaths), hypertensive heart disease (6.2% increase, P=0.01, 31 deaths), diabetes (6.3% increase, P=0.004, 32 deaths), and dementia (6.6% increase, P=0.0004, 44 deaths). Those reporting a pace slower than a 24-minute mile were at increased risk for mortality due to all-causes (44.3% increased risk, P=0.0001), cardiovascular diseases (43.9% increased risk, P=0.03), and dementia (5.0-fold increased risk, P=0.0002) even though they satisfied the current exercise recommendations by walking ≥7.5 metabolic equivalent (MET)-hours per week.

CONCLUSIONS

The risk for mortality: 1) decreases in association with walking intensity, and 2) increases substantially in association for walking pace ≥24 minute mile (equivalent to <400 m during a six-minute walk test) even among subjects who exercise regularly.

Greater weight loss from running than walking during a 6.2-yr prospective follow-up

PURPOSE

This study aimed to test whether equivalent changes in moderate (walking) and vigorous exercise (running) produce equivalent weight loss under free-living, nonexperimental conditions.

METHODS

Regression analyses of changes (Δ) in body mass index (BMI) versus exercise energy expenditure (ΔMET-hours per day, 1 MET = 3.5 mL O2·kg·min) from survey questionnaires completed at baseline and 6.2 yr thereafter in 15,237 walkers and 32,216 runners were used in this study.

RESULTS

At baseline, walkers spent less energy walking than runners spent running (mean ± SD; males = 2.22 ± 1.65 vs 5.31 ± 3.12 MET·h·d, females = 2.15 ± 1.63 vs 4.76 ± 3.03 MET·h·d), and walkers were significantly heavier than runners (males = 26.63 ± 4.04 vs 24.09 ± 2.58 kg·m, females = 25.44 ± 5.14 vs 21.61 ± 2.49 kg·m). During follow-up, energy expenditure declined less for walking in walkers than for running in runners (males = -0.19 ± 1.92 vs -1.27 ± 2.87 MET·h·d, females = -0.30 ± 1.93 vs -1.28 ± 2.85 MET·h·d). ΔBMI was inversely related to both ΔMET-hours per day run and ΔMET-hours per day walked, but more strongly to ΔMET-hours per day run than walked in men and in heavier women. Specifically, the regression coefficient for ΔBMI versus ΔMET-hours per day was significantly more negative for running than walking in men in the first quartile (differences in slope ± SE: -0.06 ± 0.03, P = 0.01), second quartile (-0.10 ± 0.03, P = 0.001), third quartile (-0.17 ± 0.03, P < 10), and fourth quartile of BMI (-0.14 ± 0.03, P < 10) and in the fourth BMI quartile of women (-0.32 ± 0.04 kg·m per MET-hours per day, P < 10). This represented 90% greater weight loss per MET-hours per day run than walked in the fourth BMI quartile for both sexes. Age-related weight gain was attenuated by running in both sexes (P < 10) and by walking in women (P = 0.005).

CONCLUSION

Although ΔBMI was significantly associated with both ΔMET-hours per day run and walked, the ΔBMI was significantly greater for Δrunning than Δwalking.

Lipid profile among Moroccan overweight women and breast cancer: a case-control study

BACKGROUND

Breast cancer has become the most common type of cancer in Morocco. In 2005, 127 new cases in women, representing 33.5% of female cancers, were added to the National Center of Oncology registry. The incidence of breast cancer is higher in Morocco than in the three other Maghreb countries, and it is significantly lower than in Western countries where it stands at over 80 cases per 100,000 people.

PURPOSE

This 2-year long case-control study was conducted to assess the causal relationship between the lipid profile of overweight Moroccan women and breast cancer risk.

PATIENTS AND METHODS

Overweight female patients with breast cancer (n = 400) were compared to 400 healthy controls at the National Institute of Oncology of Rabat. The epidemiological data on the disease and physical activity were gathered by interviewing the patients who had their lipid profile measured (total cholesterol, triglycerides, high density lipoprotein cholesterol, and low density lipoprotein cholesterol). Body mass index was used to determine if patients were overweight.

RESULTS

Univariate analysis revealed a significant association between breast cancer and high body mass index (odds ratio [OR] = 1.31; 95% confidence interval [CI] = 1.25-1.37), menopause (OR = 2.68; 95% CI = 2-3.55), lack of physical activity (OR = 0.26; 95% CI = 0.21-0.31), and triglyceridemia (OR = 3.78; 95% CI = 2.73-5.23). Multivariate analysis revealed that the statistically significant increase in breast cancer risk was associated with a higher body mass index (OR = 1.11; 95% CI = 1.04-1.18), menopause (OR = 9.11; 95% CI = 4.76-17.47), and high triglyceride levels (OR = 4.5; 95% CI = 2.94-6.88). However, a protective effect for physical activity was detected (OR = 0.35; 95% CI = 0.26-0.48).

CONCLUSION

This study suggests that there is a connection between hypertriglyceridemia, obesity, and breast cancer risk and confirms a protective role for physical activity on breast cancer risk.

Walking attenuates the relationships of high-meat, low-fruit dietary intake to total and regional adiposity in men and women

Vigorous physical activity (running) has been shown to attenuate the association between diet and body weight. Walking is the most popular physical activity, but is a moderate-intensity physical activity because it requires less than sixfold the energy expenditure of sitting at rest. We therefore examined whether reported distance walked per week affected the relationship of diet to BMI and circumferences of the waist, hip, and chest in 30,014 female and 7,133 male participants of the National Walkers' Health Study. Reported meat and fruit intakes served as indicators of high-risk diets for weight gain. The analyses showed that higher meat and lower fruit intake were significantly and consistently associated with greater BMI and waist circumference at all activity levels. Longer usual walking distance significantly attenuated the concordant relationships of diet with women's BMIs (P < 10(-8)), men's BMIs (P = 0.04), and women's waist (P < 10(-6)), hip (P = 0.0001), and chest circumferences (P < 10(-5)). Compared to walkers who averaged <1.5 km/day, the association of diet with adiposity in subjects who walked ≥1.5 km/day was reduced 21% in women and 31% in men for BMI; 20% in women and 27% in men for waist circumference; 19% for women's hip circumference; and 26% for women's chest circumference. Thus we conclude that diets characterized by high-meat/low-fruit intake were significantly associated with greater BMI, and this association was attenuated by moderate physical activity. The weaker results in men than women probably related to the smaller sample size, and reduced statistical power of the men.

Advantage of distance- versus time-based estimates of walking in predicting adiposity

PURPOSE

Physical activity recommendations are defined in terms of time spent being physically active (e.g., 30 min of brisk walking, 5 d · wk(-1)). However, walking volume may be more naturally assessed by distance than by time. Analyses were therefore performed to test whether time or distance provides the best metric for relating walking volume to estimated total and regional adiposity.

METHODS

Linear and logistic regression analyses were used to relate exercise dose to body mass index (BMI), body circumferences, and obesity in a cross-sectional sample of 12,384 female and 3434 male walkers who reported both usual distance walked and time spent walking per week on survey questionnaires. Metabolic equivalent hours per day (MET · h · d(-1), 1 MET = 3.5 mL O2 · kg(-1) · min(-1)) were calculated from the time and pace, or distance and pace, using published compendium values.

RESULTS

Average MET-hours per day walked was 37% greater when calculated from time spent walking versus usual distance in women and was 32% greater in men. Per MET-hours per day, declines in BMI and circumferences (slope ± SE) were nearly twice as great, or greater, for distance- versus time-derived estimates for kilograms per squared meter of BMI (females = -0.58 ± 0.03 vs -0.31 ± 0.02, males = -0.35 ± 0.04 vs -0.15 ± 0.02), centimeter of waist circumference (females = -1.42 ± 0.07 vs -0.72 ± 0.04, males = -0.96 ± 0.10 vs -0.45 ± 0.07), and reductions in the odds for total obesity (odds ratio: females = 0.72 vs 0.84, males = 0.84 vs 0.92) and abdominal obesity (females = 0.74 vs 0.85, males = 0.79 vs 0.91, all comparisons significant).

CONCLUSIONS

Distance walked may provide a better metric of walking volume for epidemiologic obesity research, and better public health targets for weight control, than walking duration. Additional research is required to determine whether these results, derived in a sample that regularly walks for exercise, apply more generally.

Distance walked and run as improved metrics over time-based energy estimation in epidemiological studies and prevention; evidence from medication use

PURPOSE

The guideline physical activity levels are prescribed in terms of time, frequency, and intensity (e.g., 30 minutes brisk walking, five days a week or its energy equivalence) and assume that different activities may be combined to meet targeted goals (exchangeability premise). Habitual runners and walkers may quantify exercise in terms of distance (km/day), and for them, the relationship between activity dose and health benefits may be better assessed in terms of distance rather than time. Analyses were therefore performed to test: 1) whether time-based or distance-based estimates of energy expenditure provide the best metric for relating running and walking to hypertensive, high cholesterol, and diabetes medication use (conditions known to be diminished by exercise), and 2) the exchangeability premise.

METHODS

Logistic regression analyses of medication use (dependent variable) vs. metabolic equivalent hours per day (METhr/d) of running, walking and other exercise (independent variables) using cross-sectional data from the National Runners' (17,201 male, 16,173 female) and Walkers' Health Studies (3,434 male, 12,384 female).

RESULTS

Estimated METhr/d of running and walking activity were 38% and 31% greater, respectively, when calculated from self-reported time than distance in men, and 43% and 37% greater in women, respectively. Percent reductions in the odds for hypertension and high cholesterol medication use per METhr/d run or per METhr/d walked were ≥ 2-fold greater when estimated from reported distance (km/wk) than from time (hr/wk). The per METhr/d odds reduction was significantly greater for the distance- than the time-based estimate for hypertension (runners: P<10(-5) for males and P=0.003 for females; walkers: P=0.03 for males and P<10(-4) for females), high cholesterol medication use in runners (P<10(-4) for males and P=0.02 for females) and male walkers (P=0.01 for males and P=0.08 for females) and for diabetes medication use in male runners (P<10(-3)).

CONCLUSIONS

Although causality between greater exercise and lower prevalence of hypertension, high cholesterol and diabetes cannot be inferred from these cross-sectional data, the results do suggest that distance-based estimates of METhr/d run or walked provide superior metrics for epidemiological analyses to their traditional time-based estimates.

Physical activity, walking and leanness: an analysis of the Northern Ireland Sport and Physical Activity Survey (SAPAS)

OBJECTIVE

To report on the contribution walking makes to total weekly physical activity and the relationship between the volume and intensity of walking and leanness in a representative sample of the Northern Ireland population.

METHOD

4563 adults participated in this cross-sectional survey of physical activity behaviour. Self-reported height and weight was used to determine inverse body mass index (iBMI) as a measure of leanness. Data across all domains of physical activity including self-reported volume and intensity of walking (in bouts of 10 min or more) were analysed to determine their contribution to leanness using ANCOVA, having controlled for age, gender, socio-economic and smoking status.

RESULTS

Over 68% of the participants reported walking >10 minutes during the previous week but only 24% report walking at a brisk or fast pace. Time walking at a brisk or fast pace for personal transport was identified as having the strongest positive association with being lean (F(1,4256)=10.45, β=0.051 cm(2) kg(-1) min(-1) (SE=0.016),P=0.001).

CONCLUSIONS

In addition to increasing the amount of walking and the percentage of people walking regularly, public health messages encouraging an increase in walking pace may be valuable to increase the proportion of the population meeting physical activity guidelines and gaining associated health benefits.

Quantile-specific penetrance of genes affecting lipoproteins, adiposity and height

Quantile-dependent penetrance is proposed to occur when the phenotypic expression of a SNP depends upon the population percentile of the phenotype. To illustrate the phenomenon, quantiles of height, body mass index (BMI), and plasma lipids and lipoproteins were compared to genetic risk scores (GRS) derived from single nucleotide polymorphisms (SNP)s having established genome-wide significance: 180 SNPs for height, 32 for BMI, 37 for low-density lipoprotein (LDL)-cholesterol, 47 for high-density lipoprotein (HDL)-cholesterol, 52 for total cholesterol, and 31 for triglycerides in 1930 subjects. Both phenotypes and GRSs were adjusted for sex, age, study, and smoking status. Quantile regression showed that the slope of the genotype-phenotype relationships increased with the percentile of BMI (P = 0.002), LDL-cholesterol (P = 3×10⁻⁸), HDL-cholesterol (P = 5×10⁻⁶), total cholesterol (P = 2.5×10⁻⁶), and triglyceride distribution (P = 7.5×10⁻⁶), but not height (P = 0.09). Compared to a GRS's phenotypic effect at the 10^th population percentile, its effect at the 90^th percentile was 4.2-fold greater for BMI, 4.9-fold greater for LDL-cholesterol, 1.9-fold greater for HDL-cholesterol, 3.1-fold greater for total cholesterol, and 3.3-fold greater for triglycerides. Moreover, the effect of the rs1558902 (FTO) risk allele was 6.7-fold greater at the 90^th than the 10^th percentile of the BMI distribution, and that of the rs3764261 (CETP) risk allele was 2.4-fold greater at the 90^th than the 10^th percentile of the HDL-cholesterol distribution. Conceptually, it maybe useful to distinguish environmental effects on the phenotype that in turn alters a gene's phenotypic expression (quantile-dependent penetrance) from environmental effects affecting the gene's phenotypic expression directly (gene-environment interaction).

Evidence that obesity risk factor potencies are weight dependent, a phenomenon that may explain accelerated weight gain in western societies

BACKGROUND

We have shown that individuals at the highest percentiles of the body mass index (BMI) distribution (i.e., most overweight) experience greater increases in body weight from sedentary lifestyle than those from the lowest percentiles. The purpose of the current analyses was to assess whether recent, accelerated increases in obesity could potentially be due to increased vulnerability to obesity risk factors as the population has become more overweight.

METHODOLOGY/PRINCIPAL FINDINGS

Quantile regression was used to compare BMI population percentiles to obesity risk factors (lower education, diets characterized by high-meat/low-fruit content, parental adiposity) in two independent samples of men (N(1) = 3,513, N(2) = 11,365) and women (N(1) = 15,809, N(2) = 10,159). The samples were subsets of the National Walkers' (Study 1) and Runners' (Study 2) Health Studies whose physical activities fell short of nationally recommended activity levels. The data were adjusted for age, race, and any residual effects of physical activity. The regression slopes for BMI vs. education, diet, and family history became progressively stronger from the lowest (e.g., 5(th), 6(th)…) to the highest (e.g., …, 94(th), 95(th)) BMI percentiles. Compared to the 10(th) BMI percentile, their effects on the 90(th) BMI percentile were: 1) 2.7- to 8.6-fold greater in women and 2.0- to 2.4-fold greater in men for education; 2) 3.6- to 4.8-fold greater in women and 1.7- to 2.7-fold greater in men for diet; and 3) 2.0- to 2.6-fold greater in women and 1.7-fold greater in men for family history.

CONCLUSIONS/SIGNIFICANCE

Thus we propose risk factors that produce little weight gain in lean individuals may become more potent with increasing adiposity. This leads us to hypothesize that an individual's obesity is itself a major component of their obesogenic environment, and that, the cycle of weight gain and increased sensitivity to obesity risk factors may partly explain recent increases in obesity in western societies.

Dose-response relationship between walking and the attenuation of inherited weight

OBJECTIVE

Genetic factors account for 40%-70% of the variation in body mass index (BMI). We sought to test whether moderate intensity physical activity affected parent-offspring relationships for body mass index and regional adiposity in 26,587 female and 6428 male walkers surveyed in the United States in 2000.

METHODS

Survey questionnaires provided self-reported usual walking distance, height, weight, and waist circumference, and mother's and father's adiposity (1=lean, 2=normal, 3=overweight, and 4=very overweight). Regression analyses were used to test whether the contribution of parental adiposities to the walkers' body mass indexes and waist circumferences diminished with walking.

RESULTS

In the most sedentary group (walking < 1.5 km/d), average parental adiposity was a significant determinant of the walkers' body mass indexes and waist circumferences (female: P < 10(-15); male: P < 10(-13)). Greater walking distance significantly diminished the effect of average parents' adiposity on the walkers' body mass indexes (female: P < 10(-10); male P = 0.003) and waist circumferences (female: P < 10(-6); male P = 0.01). Compared to the most sedentary female walkers, the effect of parental adiposity was reduced 36% for body mass indexes and 41% for waist circumferences (corresponding reductions in men were 36% and 46%, respectively).

CONCLUSION

These results suggest that moderate intensity physical activity attenuates inheritance of both total and regional adiposity in a dose-dependent manner.

Fifteen-year longitudinal trends in walking patterns and their impact on weight change

BACKGROUND

Although walking is the most popular leisure-time activity for adults, few long-term, longitudinal studies have examined the association between walking, an affordable and accessible form of physical activity, and weight gain.

OBJECTIVE

The objective was to evaluate the association between changes in leisure-time walking and weight gain over a 15-y period.

DESIGN

Prospective data from the Coronary Artery Risk Development in Young Adults (CARDIA) Study of 4,995 men and women aged 18-30 y at baseline (1985-1986) from 4 US cities and reexamined 2, 5, 7, 10, and 15 y later. Sex-stratified, repeated-measures, conditional regression modeling with data from all 6 examination periods (n = 23,633 observations) was used to examine associations between walking and annualized 15-y weight change, with control for 15-y nonwalking physical activity, baseline weight (and their interaction), marital status, education, smoking, calorie intake, and baseline age, race, and field center.

RESULTS

Mean (+/- SE) baseline weights were 77.0 +/- 0.3 kg (men) and 66.2 +/- 0.3 kg (women), weight gain was approximately 1 kg/y, and the mean duration of walking at baseline was <15 min/d. After accounting for nonwalking physical activity, calorie intake, and other covariates, we found a substantial association between walking and annualized weight change; the greatest association was for those with a larger baseline weight. For example, for women at the 75th percentile of baseline weight, 0.5 h of walking/d was associated with 8 kg less weight gain over 15 y compared with women with no leisure time walking.

CONCLUSION

Walking throughout adulthood may attenuate the long-term weight gain that occurs in most adults.

Reduced diabetic, hypertensive, and cholesterol medication use with walking

PURPOSE

To assess the relationships of walking distance, frequency, and intensity to the prevalence of antidiabetic, antihypertensive, and LDL cholesterol-lowering medications use.

METHODS

Cross-sectional analyses of 32,683 female and 8112 male participants of the National Walkers' Health Study, of whom 2.8% and 7.4% reported antidiabetic, 14.3% and 29.0% reported antihypertensive, and 7.3% and 21.5% reported LDL cholesterol-lowering medication use, respectively.

RESULTS

Weekly walking distance, longest walk, and walking intensity were inversely related to the prevalence of antidiabetic (males: P < 0.001, females: P < 0.0001), antihypertensive (males: P < 0.01, females: P < 0.0001), and LDL cholesterol-lowering medications (males: P < 0.01, females: P < 0.0001). Each medication remained significantly related to both walking intensity and longest weekly walk when adjusted for total weekly distance. Compared with men and women who walked at a speed of < 1.2 m.s, those who walked > 2.1 m.s had 48% and 52% lower odds for antihypertensive, 68% and 59% lower odds for antidiabetic, and 53% and 40% lower odds for LDL cholesterol-lowering medications, respectively, when adjusted for age, smoking, and diet. The longest usual weekly walk was a better discriminator of medication status than the total cumulative distance per week, particularly in men.

CONCLUSION

These results are consistent with the hypothesis that antidiabetic, antihypertensive, and LDL cholesterol-lowering medication use may be reduced substantially by walking more intensely and farther each week, and by including longer walks.

Association between walking distance and percentiles of body mass index in older and younger men

OBJECTIVE

To assess the association of weekly walking distance to body weight and waist circumference in elderly (age > or =75 years), senior (55< or = age <75 years), middle-aged (35< or = age <55 years), and younger men (18< or = age <35 years old).

DESIGN

Cross-sectional analyses of baseline questionnaires from 7082 male participants of the National Walkers' Health Study.

RESULTS

Standard regression analyses showed that body mass index (BMI) was inversely and significantly associated with walking distance (kg/m(2) per km/week) in elderly (slope (SE): -0.032 (0.008)), senior (-0.045 (0.005)) and middle-aged men (-0.037 (0.007)), as were their waist circumferences (-0.090 (0.025), -0.122 (0.012) and -0.091 (0.015) cm per km/week, respectively), and that these slopes remained significant when adjusted statistically for reported weekly servings of meat, fish, fruit and alcohol. However, percentile regression analyses showed that the declines in BMI per km/week walked were greater at the higher than the lower percentiles of the BMI distribution. In men > or =74 years old the decline per km walked was 4.9-fold greater among the heaviest men (that is, 90th BMI percentile; -0.076 kg/m(2) per km/week) than among the leanest men (that is, 10th BMI percentile; -0.015 kg/m(2) per km/week). The differences in slope at the 90th compared to the 10th BMI percentile were 5.4-fold among men 55-74 years old and sixfold among men 35-54 years old. Per km/week walked, the declines at the 90th percentile of waist circumference were also greater than at its 10th percentile, and intermediate for percentiles in between. Whereas standard regression analyses suggest that the average declines in BMI per km/week walked reported here are consistent with those reported previously per km/week run in male runners 35-54 years old (-0.036 (0.001) kg/m(2) per km/week) and > or =50 years old (-0.038 (0.001) kg/m(2) per km/week), percentile regression analyses showed that when adjusted to the leaner body weights of the runners the declines per km walked were between 49% and 59% less for walkers than runners.

CONCLUSIONS

Declines in BMI and waist circumferences with walking distance depend upon the percentile of the BMI distribution, with the decline per km walked being significantly greater among heavier men.

BMI and health-related physical fitness in Taiwanese youth 9-18 years

PURPOSE

The purpose of the study was to evaluate the cross-sectional relationship between BMI and a physical fitness index (PFI) based on four indicators of fitness in a national sample of Taiwanese youth.

METHODS

Height, weight, and four measures of physical fitness (sit-ups completed in 60 s, standing long jump, sit and reach, and 800- or 1600-m run/walk) were measured in a national sample of 102,765 Taiwanese youth 9-18 yr of age: 50,940 girls and 51,825 boys. BMI was calculated for each subject. Within each sex-specific half-year age group, students were classified into five BMI categories based on national percentiles: very low, BMI < 5th percentile; low, BMI >or= 5th but < 15th percentiles; normal, BMI >or= 15th but < 85th percentiles; high, BMI >or= 85th but < 95th percentiles; and very high, BMI >or= 95th percentiles. Z-scores based on sex- and age-specific means and standard deviations were calculated, and the sum of z-scores for the four fitness tests was used as a PFI. Differences in PFI between BMI categories within each sex-specific half-year age group were compared with ANOVA with Bonferroni adjustments. Sex-specific regressions of PFI on BMI, using a nonlinear quadratic model, were done in four broader age categories.

RESULTS

Relationships between BMI and PFI are nonlinear and vary with age from late childhood through adolescence. With increasing age during adolescence, the relationship becomes parabolic, and the peaks of the parabola are sharper in adolescent boys than girls.

CONCLUSION

PFI declines in a curvilinear manner with increasing BMI among youth 9-18 yr of age, but the slope of the relationship varies with age.

Maintaining vigorous activity attenuates 7-yr weight gain in 8340 runners

INTRODUCTION/PURPOSE

Body weight generally increases with aging in Western societies. Although training studies show that exercise produces acute weight loss, it is unclear whether the long-term maintenance of vigorous exercise attenuates the trajectory of age-related weight gain. Specifically, prior studies have not tested whether the maintenance of physical activity, in the absence of any change in activity, prevents weight gain.

METHODS

Prospective study of 6119 male and 2221 female runners whose running distances changed < 5 km x wk(-1) between baseline and follow-up surveys 7 yr later.

RESULTS

On average, men who maintained modest (0-23 km x wk(-1)), intermediate (24-47 km x wk(-1)), or prolonged running distances (> or = 48 km x wk(-1)) all gained weight through age 64; however, those who maintained > or = 48 km x wk(-1) had one half the average annual weight gain of those who maintained < 24 km x wk(-1). For example, between the ages of 35 and 44 in men and 30 and 39 yr in women, those who maintained < 24 km x wk(-1) gained, on average, 2.1 and 2.9 kg more per decade than those averaging > 48 km x wk(-1). Age-related weight gain, and its attenuation by maintained exercise, were both greater in younger than in older men. Men's gains in waist circumference with age, and its attenuation by maintaining running, were the same in older and younger men. Regardless of age, women increased their body weight, waist circumference, and hip circumference over time, and these measurements were attenuated in proportion to their maintained running distance. In both sexes, running disproportionately prevented more extreme increases in weight.

CONCLUSION

As they aged, men and women gained less weight in proportion to their levels of sustained vigorous activity. This long-term beneficial effect is in addition to the acute weight loss that occurs with increased activity.

The effect of a primary care exercise intervention for rural women

OBJECTIVE

Rural women have limited exercise opportunities and significant barriers to engaging in physical activity. This study assessed the effect of a brief primary care based walking intervention in rural women.

METHODS

The participants were recruited in March, 2003 by a primary care nurse at three locations in rural Missouri. The enrolled subjects were given a pedometer, exercise videotape and provided exercise counseling at intake and four time points over 6 months. The week 1 pedometer step counts were compared with step counts at 6-month follow-up.

RESULTS

Of the initial 75 participants, 61 completed at least one follow up encounter. The participant's mean age was 42.5 years. At intake, the majority of women (90%) exhibited one or more risk factors for cardiovascular disease; 78% were obese or overweight. Although most (62%) women reported being physically active, the mean pedometer reading was low at 6337 steps per day at week 1. Over the follow-up period, participants increased their step counts by a mean of 2573 steps per day (p<.001). Increases in step counts were seen in normal weight, overweight and obese participants.

CONCLUSIONS

A simple walking intervention through a primary care practice was effective in increasing the short term walking rates of rural women.

Self-selection contributes significantly to the lower adiposity of faster, longer-distanced, male and female walkers

OBJECTIVE

Cross-sectional studies show that active individuals are leaner than their sedentary counterparts. The purpose of this paper is to determine the extent that this is due to self-selection bias, specifically to initially leaner men and women choosing to exercise longer and more intensely.

METHODS

Walking quantity (weekly distance) and intensity (speed) were compared to current body mass index (BMI) (BMI(current)) and BMI at the start of walking (BMI(starting)) in 20,353 women and 5174 men who on average had walked regularly for exercise for 7.2 and 10.6 years, respectively.

RESULTS

The relationships of both BMI(current) and BMI(starting) to both distance and intensity were nonlinear (convex). On average, BMI(starting) explained >70% of the association between BMI(current) and intensity, and 40 and 17% of the associations between BMI(current) and distance in women and men, respectively. Although the declines in BMI(current) with distance and intensity were greater among fatter individuals than leaner individuals, the portions attributable to BMI(starting) remained relatively constant regardless of fatness. Thus, self-selection bias accounted for most of the decline in BMI with walking intensity and smaller, albeit significant, proportions of the decline with distance.

CONCLUSION

Although walking intensity and walking distance are both strongly associated with greater leanness, intensity is less likely to be causally related to leanness than is distance, and the latter should be encouraged for reversing or preventing weight gain.

Is the association between physical activity and body mass index obesity dependent?

BACKGROUND

Most studies indicate an inverse relationship between physical activity (PA) and body mass index (BMI). However, the impact of obesity on this relationship is unclear.

OBJECTIVE

To scrutinize the BMI/PA relationship by analysing multiple categories of PA from a sample with a wide BMI range.

DESIGN

PA was measured with accelerometry for 7 consecutive days during free-living conditions in 85 severely obese outpatients (mean BMI 42.7 kg/m(2) (s.d. 6.1); age 43.0 year (12.6)) and 193 control subjects (24.0 kg/m(2) (3.5); 41.6 year (13.0)). Six categories of PA were calculated from the accelerometer data (min/day of sedentary time, min/day of light PA, min/day of moderate PA, min/day of vigorous PA, activity counts/day and steps/day). Participants were stratified in obese and non-obese subgroups (BMI=30 kg/m(2) as cutoff). Associations between BMI and PA were examined in the total sample, and in subgroups. The impact of sex and age on the BMI/PA association was tested.

RESULTS

In the total sample, the association between BMI and PA was significant in all PA categories except for time spent sedentary (P=0.68). However, in subgroup analyses, the association between BMI and PA in non-obese was only significant for activity counts/day (r=-0.16, P<0.05) and vigorous intensity PA (r=-0.15, P=0.05). After adjustment for age, vigorous PA remained significantly associated with BMI in the non-obese (r=-0.17, P<0.05). In obese individuals, significant associations between BMI and PA were found for all six PA categories (age adjusted), sedentary time (r=0.26, P=0.05), light PA (r=-0.30, P<0.01), moderate PA (r=-0.35, P<0.01), vigorous PA (r=-0.39, P<0.001), activity counts/day (r=-0.50, P<0.001) and steps/day (r=-0.54, P<0.001).

CONCLUSION

The association between PA and BMI was weak in non-obese individuals. In contrast, BMI was highly significantly associated with PA in obese individuals. Longitudinal studies are needed to tease out the direction of association between PA and BMI across BMI categories, as the cross-sectional associations seem to be dependent on obesity status.