Publications

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Purpose: To evaluate the relationships among television viewing time (TVTIME), physical activity, and health-related fitness in youth 9–18 years of age from the Québec Family Study. Methods: The sample included 423 males and 361 females 9–18 years of age from the greater Québec city area. TVTIME, daily energy expenditure (EE), and moderate to vigorous physical activity (MVPA) were estimated. Four health-related fitness variables were tested: knee extension strength, physical work capacity at 150 beats · min−1, situps, and sum of skinfolds. The body mass index (BMI) was also included. Relationships were assessed using correlations and analysis of covariance. Results: Correlations between TVTIME and EE and MVPA were low and not significant, with no pattern by age group and gender. Those between TVTIME and fitness variables were also low and generally not significant, with no pattern by age and gender. Adolescents in the highest and lowest quartiles of TVTIME showed no consistent differences in EE, MVPA, and the four fitness items. Similarly, adolescents in the highest and lowest quartiles of EE, MVPA, and each fitness item did not consistently differ in TVTIME. Conclusions: The results indicate that time watching television has only a weak association with indicators of physical activity and health-related fitness in Québec youth. Since the data are from the early 1980s, generalizations to more current samples should be tempered with care.

We tested the hypothesis that peroxisome proliferator-activated receptor-delta (PPARdelta) gene polymorphisms are associated with cardiorespiratory fitness and plasma lipid responses to endurance training. Associations between the PPARdelta exon 4 +15 C/T and exon 7 +65 A/G polymorphisms and maximal exercise capacity and plasma lipid responses to 20 wk of endurance training were investigated in healthy white (n = 477) and black (n = 264) subjects. In black subjects, the exon 4 +15 C/C homozygotes showed a smaller training-induced increase in maximal oxygen consumption (P = 0.028) than the C/T and T/T genotypes. Similarly, a lower training response in maximal power output was observed in the exon 4 +15 C/C homozygotes (P = 0.005) compared with the heterozygotes and the T/T homozygotes in black subjects, and a similar trend was evident in white subjects (P = 0.087). In white subjects, baseline apolipoprotein A-1 (Apo A-1)levels were higher in the exon 4 +15 C/C (P = 0.011) and exon 7 +65 G/G (P = 0.05) genotypes compared with those in the other genotypes. In white subjects, exon 4 +15 C/C (P = 0.0025) and exon 7 +65 G/G (P = 0.011) genotypes showed significantly greater increases in plasma high-density lipoprotein-cholesterol (HDL-C) levels with endurance training than in the other genotypes, whereas in black subjects the exon 4 +15 CC homozygotes tended to increase (P = 0.057) their Apo A-1 levels more than the T allele carriers. DNA sequence variation in the PPARdelta locus is a potential modifier of changes in cardiorespiratory fitness and plasma HDL-C in healthy individuals in response to regular exercise.

This study assessed major gene effects for baseline HDL-C, LDL-C, TG, and their training responses (post-training minus baseline) in 527 individuals from 99 White families and 326 individuals from 113 Black families in the HERITAGE Family Study. The baseline phenotypes were adjusted for the effects of age and BMI, and the training response phenotypes were adjusted for the effects of age, BMI, and their respective baseline values, within each of the sex-by-generation-by-race groups, prior to genetic analyses. In Whites, we found that LDL-C at baseline and HDL-C training response were under influence of major recessive genes (accounting for 20 - 30 % of the variance) and multifactorial (polygenic and familial environmental) effects. Interactions of these major genes with sex, age, and BMI were tested, and found to be nonsignificant. In Blacks, we found that baseline HDL-C was influenced by a major dominant gene without a multifactorial component. This major gene effect accounted for 45 % of the variance, and exhibited no significant genotype-specific interactions with age, sex, and BMI. Evidence of major genes for the remaining phenotypes at baseline and in response to endurance training were not found in both races, though some were influenced by major effects that did not follow Mendelian expectations or were with ambiguous transmission from parents to offspring. In summary, major gene effects that influence baseline plasma HDL-C and LDL-C levels as well as changes in HDL-C levels in response to regular exercise were detected in the current study.

Introduction: Cardiorespiratory fitness and regular physical activity are inversely associated with the risk of hypertension, and exercise training has been shown to lower elevated blood pressure (BP). Genetic factors contribute significantly to the interindividual differences in endurance training-induced changes in BP. However, similar data on the genotype-by-fitness interactions on the risk of hypertension are scarce. Methods: In 2000, we started a systematic collection of blood samples from all consenting subjects of the Aerobics Center Longitudinal Study (ACLS) with a goal to generate a resource for studies addressing genotype-by-fitness interaction effects on various health-related end points. Here, we introduce the rationale and design of the first study based on the ACLS genetics resource focusing on hypertension as the health outcome (HYPGENE study), and we report the associations of cardiorespiratory fitness and body mass index (BMI) with the risk of hypertension. All HYPGENE subjects (N = 1234) were healthy and normotensive at their first clinic visit. Cases (N = 629) developed hypertension during the follow-up period (mean 8.7 yr), whereas controls (N = 605) remained normotensive (mean follow-up 10.1 yr). Results: Cardiorespiratory fitness was the strongest predictor of the hypertension risk, with each maximal metabolic equivalent unit being associated with a 19% lower risk (95% confidence interval [95% CI], 12-24%). Each baseline BMI unit was associated with a 9% higher hypertension risk (95% CI, 4-13%). However, the association of BMI was greatly attenuated (odds ratio 1.04 [95% CI, 0.99-1.09]) when fitness also was included in the model. Conclusions: The HYPGENE study will provide an excellent resource to address hypotheses regarding the genetic basis of hypertension while taking cardiorespiratory fitness level into account.

0062 In 1998, the ACSM revised its guidelines for prescribing the intensity of aerobic exercise, adding that one could lower the intensity to 40% VO2 reserve (VO2R) for “quite Unfit” people. PURPOSE: To investigate the relationship between %VO2R and the ventilatory threshold (vt) in 442 initially sedentary individuals (ages 17 to 65). METHODS: Each participant completed 2 graded cycle tests to exhaustion before and after 20 weeks of training. VO2 and heart rate data were collected at the end of each stage. The absolute (ml•kg−1•min−1) and relative (%VO2R) values for VO2vt were determined for each subject. RESULTS: The average absolute values for VO2vt were about 10–14 ml•kg−1•min−1 for 183 subjects whose VO2 max was 15.4–29.9 ml•kg−1•min−1. This is similar to the value of 15 ml•kg−1•min−1 that Shephard states is associated with activities of daily living. The range of relative values for the VO2vt of these subjects was 42–83% VO2R, with most subjects between 50% and 70% VO2R. Intensities below VO2vt are generally aerobic in nature and can be done without much distress. It should be noted that these subjects began the training program by exercising for 30 minutes at the heart rate associated with 50% VO2 max and had few problems. CONCLUSION: Because “quite Unfit” sedentary subjects are already doing enough activity in their daily lives to maintain a VO2vt at levels that are generally greater than 50% VO2R, it is not necessary to reduce the prescribed intensity to 40% VO2R, as recommended by the ACSM. Supported by multiple grants from NIH-NHLBI.

No abstract is provided for this article.

Familial aggregation and a major gene effect were assessed for baseline serum sex hormone—binding globulin (SHBG) levels and the response (post-training minus baseline) to a 20-week endurance training program in a selected sample of 428 non-obese nonhypertensive individuals from 99 white families who were sedentary at baseline in the HERITAGE Family Study. Baseline SHBG levels were not normally distributed, and were therefore logarithmically transformed prior to genetic analyses. In a sample without postmenopausal mothers, maximal (genetic and familial environmental) heritabilities were 50% averaged across sexes, 73% in men, 50% in women, and 31% in men versus women for the age-body mass index (BMI)—adjusted baseline. The estimate reached 64% when the baseline was further adjusted for the effects of estradiol, fasting insulin, and testosterone levels. For the response to training, no sex difference was found and the heritability reached about 25% to 32%. Segregation analysis was separately performed in the whole sample and in the sample without postmenopausal mothers. In addition to a multifactorial effect for both the baseline and the response to training, a major effect for the baseline appeared to be familial environmental in origin, whereas a major effect for the response to training was Mendelian in nature. The major gene effect for the response to training in the whole sample was undetectable in the sample without postmenopausal mothers, and it is therefore possible that the postmenopausal mothers, characterized by decreased sex hormones with or without estrogen replacement therapy for menopause, produced some confounding effects. In addition, the reduced sample size might also be a plausible candidate explanation. The novel finding in this study is that baseline SHBG levels and the response to training were influenced by a multifactorial effect with sex difference for the baseline. The response to training appeared to be additionally influenced by a single recessive locus that is independent of baseline SHBG levels.

The aims of this controlled experiment were to investigate the effects of short-term aerobic exercise training on plasma lipid and lipoprotein concentrations and the role of heredity in determining the individual variation observed in the lipoprotein-lipid response. Six pairs of male monozygotic (MZ) twins were subjected to an exercise training program that induced a 22,000 kcal energy deficit after 22 consecutive days of training. This program significantly reduced body weight, percent body fat, and subcutaneous fat and significantly increased maximal oxygen consumption (VO2max) (p less than 0.005). The plasma insulin response to an oral glucose challenge was markedly reduced after training (p less than 0.001). Plasma triglyceride concentration decreased and the high density lipoprotein cholesterol (HDL-CHOL)/CHOL ratio increased with training (p less than 0.05). Subjects also displayed substantial individual variation in their response to exercise training, but the changes in plasma CHOL, apolipoprotein (apo) B low density lipoprotein cholesterol (LDL-CHOL), HDL-CHOL, and the HDL-CHOL/CHOL ratio tended to be similar within MZ twin pairs (0.67 less than or equal to ri less than or equal to 0.92; 0.05 greater than p less than 0.0001) thus indicating a significant effect of heredity on the sensitivity of plasma lipids and lipoproteins to exercise training.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract is provided for this article.