Genetic factors in physical activity levels: a twin study

Moderate-to-vigorous intensity physical activity levels of children with intellectual disability during physical education classes

Background

Physical education (PE) class is an excellent way to improve moderate-to-vigorous intensity physical activity (MVPA). Increasing number of research has explored the children's PA based on movement during PE classes, but data for children with intellectual disability (ID) is still lacking.

Purpose

The purpose of this study was to investigate the current status of MVPA levels of children with ID during PE classes in China, as well as differences of MVPA levels according to gender and grade.

Methods

Accelerometers were used to record MVPA levels of fifty-three children with severe ID from 9 to 16 years of age (mean age: 12.60 ± 1.66 years) during standard PE classes.

Results

The mean time spent in MVPA during PE classes was 8.00 ± 2.10 min, meaning only 22.88% of PE class time was spent in MVPA. As grade levels progresses, time spent in MVPA during PE classes tended to decrease; the fourth-grade children tended to spend more time in MVPA during PE classes compared with the fifth-grade and the sixth-grade (9.15 vs. 7.61 vs. 7.25 min, all p < 0.05). Boys spend significantly more time in MVPA during PE classes than girls; both in the entire sample (9.20 vs. 5.70 min) as well as in each grade (9.76 vs. 6.09 min, 9.35 vs. 5.68 min, 8.31 vs. 5.59 min, all p < 0.05).

Conclusion

Findings from this study indicate that the proportion of PE class spent in the MVPA of children with ID was lower than the 50% recommended by the U.S. Department of Health and Human Services (DHHS) and U.K. Association for Physical Education (AfPE). And the amount of MVPA participation varied by the grade and gender as well as by the activity performed. Therefore, in order to help children with ID achieve MVPA goals, educators need to reevaluate the PE curriculum as well as take due consideration of grade and gender when devising new content.

Studies of twin responses to understand exercise THerapy (STRUETH): Cerebrovascular function

KEY POINTS

Characterising individual responses to resistance and endurance exercise training can inform optimal strategies for exercise prescription. This study utilised monozygotic and dizygotic twins in a randomised cross-over study to determine individual responsiveness to different modalities of exercise training. The influence of environment versus genetics in cerebrovascular responses to training was determined. It is apparent that individuals respond differently to distinct exercise stimuli and that switching modality may be a beneficial way to obtain positive responses in cerebrovascular function. This study has implications for improving individualised exercise prescription to maintain or improve cerebral structure and function.

ABSTRACT

Introduction We studied monozygotic (MZ) and dizygotic (DZ) twin pairs following resistance (RES) and endurance (END) training to assess genetic and environmental contributions to cerebrovascular function. Methods Cerebrovascular function (rest, autoregulation, hypercapnia, exercise) was assessed in 86 healthy same-sex MZ (30 pairs) and DZ (13 pairs) twins, who underwent three-months of END and RES. Carbon dioxide (P_ET CO₂ ), mean arterial pressure (MAP) and middle cerebral artery velocity (MCAv) were measured and MCAv resistance (MCA_CVRi ) was calculated. Results Resting MCAv reduced by -2.8 cm/s following RES (P = 0.024), with no change following END (-0.3 cm/s, P = 0.758). Change in MCA_CVRi following RES was +0.11 mmHg/cm/s (P < 0.001), which was significantly greater than END (+0.02 mmHg/cm/s, P = 0.030). MAP also increased following RES (+4 mmHg, P = 0.010), but not END (+1 mmHg, P = 0.518). No changes were apparent in P_ET CO₂ . At rest, positive response rates following RES ranged from 27-71% and 40-64% following END. Intraclass correlations between twins were moderate for most variables at baseline. In response to training, only MZ pairs were significantly correlated for change in MCAv (P = 0.005) and low frequency phase (P = 0.047) following RES. Conclusion This study is the first to compare cerebrovascular function following RES and END in MZ and DZ twins. Most individuals who did not respond to one modality were able to respond by switching modality and baseline heritability estimates were higher than training response. Exercise professionals should therefore consider modality and environmental factors when optimising interventions. Abstract figure legend Schematic summary of the assessment battery of cerebrovascular measures of function and health developed by Ainslie and Green. Transcranial Doppler (TCD) measures are complemented by contemporaneous assessment of whole brain blood flow, derived from simultaneous high-resolution ultrasound via insonation of the internal carotid and vertebral arteries. Results show that group response does not always reflect individual responses, and that switching exercise modality can increase individual responsiveness to exercise training. Low twin correlations in response to exercise training indicate nurture has a larger contribution to training response than nature. This article is protected by copyright. All rights reserved.

Affective response to physical activity as a deep phenotype in a non-randomized pilot study

Large-scale genomic studies are beginning to identify genetic predictors of physical activity (PA). For those genetically predisposed to engage in low PA, a behavioral intervention may target a malleable factor that mediates genetic predisposition to low PA (i.e., intermediate phenotype) to mitigate the genetic influences. In a non-randomized exercise promotion pilot study, we test the feasibility of examining affective response to PA (how one feels during PA) as an intermediate phenotype between genetic variation and PA adherence. We hypothesized that three single nucleotide polymorphisms (SNPs; rs8044769 and rs3751812 in FTO; rs6265 in BDNF), identified from a prior systematic review, would be predictive of affective response to PA, and that affective response to PA would mediate the SNP-PA link. Forty five healthy, low-active adults received a 12-week print-based PA promotion program. Baseline affective response to PA was assessed using the Feeling Scale, a single-item measure of affective valence. Moderate to vigorous PA (MVPA) was assessed using accelerometers pre- and post-intervention. We examined the three SNPs in a weighted genetic score. Age, sex, body mass index, race, and neighborhood walkability were potential covariates. Affective response to PA and MVPA at follow-up (minutes/day over 4-7 days) were regressed on variation in SNPs, controlling for covariates. One unit increase in genetic score was associated with a 0.14 higher mean Feeling Scale, though was not statistically significant (p = 0.13). Among individual SNPs, having an additional FTO rs8044769 C allele was associated with a mean Feeling Scale score of 0.53 units higher (p = 0.015), which was statistically significant after applying the corrected p-value of 0.016. The genetic score or individual SNPs were not predictive of MVPA 12 weeks later, thereby mediation analyses were not performed. The preliminary findings demonstrate the promise of the intermediate phenotype approach.

Leveraging Genomic Associations in Precision Digital Care for Weight Loss: Cohort Study

BACKGROUND

The COVID-19 pandemic has highlighted the urgency of addressing an epidemic of obesity and associated inflammatory illnesses. Previous studies have demonstrated that interactions between single-nucleotide polymorphisms (SNPs) and lifestyle interventions such as food and exercise may vary metabolic outcomes, contributing to obesity. However, there is a paucity of research relating outcomes from digital therapeutics to the inclusion of genetic data in care interventions.

OBJECTIVE

This study aims to describe and model the weight loss of participants enrolled in a precision digital weight loss program informed by the machine learning analysis of their data, including genomic data. It was hypothesized that weight loss models would exhibit a better fit when incorporating genomic data versus demographic and engagement variables alone.

METHODS

A cohort of 393 participants enrolled in Digbi Health's personalized digital care program for 120 days was analyzed retrospectively. The care protocol used participant data to inform precision coaching by mobile app and personal coach. Linear regression models were fit of weight loss (pounds lost and percentage lost) as a function of demographic and behavioral engagement variables. Genomic-enhanced models were built by adding 197 SNPs from participant genomic data as predictors and refitted using Lasso regression on SNPs for variable selection. Success or failure logistic regression models were also fit with and without genomic data.

RESULTS

Overall, 72.0% (n=283) of the 393 participants in this cohort lost weight, whereas 17.3% (n=68) maintained stable weight. A total of 142 participants lost 5% bodyweight within 120 days. Models described the impact of demographic and clinical factors, behavioral engagement, and genomic risk on weight loss. Incorporating genomic predictors improved the mean squared error of weight loss models (pounds lost and percent) from 70 to 60 and 16 to 13, respectively. The logistic model improved the pseudo R2 value from 0.193 to 0.285. Gender, engagement, and specific SNPs were significantly associated with weight loss. SNPs within genes involved in metabolic pathways processing food and regulating fat storage were associated with weight loss in this cohort: rs17300539_G (insulin resistance and monounsaturated fat metabolism), rs2016520_C (BMI, waist circumference, and cholesterol metabolism), and rs4074995_A (calcium-potassium transport and serum calcium levels). The models described greater average weight loss for participants with more risk alleles. Notably, coaching for dietary modification was personalized to these genetic risks.

CONCLUSIONS

Including genomic information when modeling outcomes of a digital precision weight loss program greatly enhanced the model accuracy. Interpretable weight loss models indicated the efficacy of coaching informed by participants' genomic risk, accompanied by active engagement of participants in their own success. Although large-scale validation is needed, our study preliminarily supports precision dietary interventions for weight loss using genetic risk, with digitally delivered recommendations alongside health coaching to improve intervention efficacy.

Genetic and Environmental Influences on Vigorous Exercise in South Korean Adolescent and Young Adult Twins

Twin studies of physical exercise for Asian twins are sparse. This study aimed to examine genetic and environmental influences on frequency of vigorous exercise (FVE) in South Korean twins, with a special emphasis on sex effects. Telephone interviews on FVE were administered to 1757 twins (mean age = 19.05 years, SD = 3.01 years). Tetrachoric correlations were significantly different between monozygotic (MZ) and dizygotic (DZ) twins in males (.40 vs. .12), but they were similar in females (.44 vs. .45), suggesting the importance of genetic factors in FVE in males and that of common environmental factors in females. A scalar sex-limitation model incorporating age as a modifier was applied to data. The results revealed that genetic, common and individual environmental influences did not vary significantly with age, but differed across two sexes, confirming twin correlational analyses. In the best-fitting model, additive genetic and individual environmental influences on FVE were, respectively, .35 (95% CI [.26, .39]) and .65 (95% CI [.61, .74]) in males, and common and individual environmental influences were, respectively, .45 (95% CI [.35, .53]) and .55 (95% CI [.47, .65]) in females. These results contrasted starkly with recent findings from a large sample of Chinese adult twins (age >18 years), in which most variance (≥95%) of vigorous physical activity was attributable to common environmental influences in both sexes. Replications in other Asian samples are clearly needed.

Factors That Influence Participation in Physical Activity in School-Aged Children and Adolescents: A Systematic Review from the Social Ecological Model Perspective

High prevalence of physical inactivity and obesity in children and adolescents has become a global problem. This systematic review aimed to examine the existing literature regarding the factors that influence participation in physical activity (PA) in children and adolescents with reference to the social ecological model (SEM) proposed by McLeroy et al. (1988). The SEM provides a framework under which the influencing factors are categorized into five levels: intrapersonal, interpersonal, organizational, community, and public policy. A systematic search of relevant literature published before July 2020 was conducted through Ebsco, ProQuest, PubMed Central, Scopus, and Web of Science. A total of fourteen studies met the inclusion criteria. The selected articles were all of high quality as assessed using the Mixed Methods Appraisal Tool (2018). The results indicated that gender, age, ethnicity, and self-concept were the most common influencing factors at the intrapersonal level. At the interpersonal and organization levels, supports from friends, parents, and teachers were positive predictors of students' PA participation. Accessibility of facilities and safe neighborhoods was a crucial factor that influenced children and adolescents' participation in PA at the community level. Future studies on the effective types of policies or practices that could successfully promote facilities' accessibility and improve neighborhood safety are required. The outcomes of this systematic review are expected to inform practice and support the development and implementation of sound policies for the promotion of PA participation in children or adolescents from a comprehensive social ecological viewpoint.

The Role of Dopamine Receptor D2 in Bridging the Intention-Behavior Gap in Sport Participation

Previous studies have identified that a behavior can occur through the strongest predictor intention, but there is a gap between intention and behavior. Dopamine receptor D2 (DRD2) is known to account for a variance in sporting behaviors in human and animal subjects. However, the relationship between DRD2 and sport participation has been poorly studied, and the limited available reports are inconsistent. The present study was performed to examine the impact of DRD2 on sport participation among Korean university students based on the integrated behavioral model (IBM). Data were collected from enrolled university students in Seoul (N = 45). Participants answered survey questions first, and then they gave investigators their hair to provide DNA information (i.e., the A1 allele of DRD2). DRD2 had a significant effect on sport participation, but only in male students. Male students who carried the A1 allele of DRD2 significantly participated in 105.10 min more sporting activities than male students who did not. Moreover, the effect of intention on sport participation was significantly decreased when considering DRD2. Despite the small sample size, the results of this study could be a preliminary case for a larger study and indicate the direction of future research. Our results suggest that DRD2 may have played an important role as the “actual skill” shown in the IBM.

Affective response to physical activity as an intermediate phenotype

Over the past seventy years, biomedical and epidemiological research has shown that regular physical activity (PA) is critical for physical and mental health. Despite this knowledge, physical inactivity is the fourth leading risk factor for global mortality, accounting for 9% (5.3 million) of premature deaths annually. We suggest this mismatch between knowing about the risks of PA and engaging in regular PA can be reconciled by focusing less on expected health benefits of PA and more on how people feel during PA. Specifically, in this position paper, we argue that affective response (feeling good versus bad) to PA is an intermediate phenotype that can explain significant variance in PA behavior and is, in turn, a function of genetic variability. In making this argument, we first review empirical evidence showing that affective response to PA predicts future physical activity behavior. Second, we systematically review research on single nucleotide morphisms (SNPs) that are associated with affective response to PA. Investigating affective response to PA as an intermediate phenotype will allow future researchers to move beyond asking "What SNPs are associated with PA?", and begin asking "How do these SNPs influence PA?", thus ultimately optimizing the translation of knowledge gained from genomic data to intervention development.

Exploring human trainability: Design and rationale of Studies of Twin Responses to Understand Exercise as a Therapy (STRUETH) study

Background

Exercise confers myriad health benefits and physical inactivity is a modifiable risk factor for many non-communicable chronic diseases. However, individual responsiveness to guideline-based exercise programs is idiosyncratic for health and fitness outcomes. It is not known whether the response of individuals to distinct exercise modalities tend to be concordant or whether there is a genetic contribution to variation in exercise responsiveness.

Methods/design

Healthy, young adult (16-40yrs) monozygotic (MZ) and dizygotic (DZ) twin pairs were recruited and randomly assigned to 3 months of endurance or resistance exercise training. Twin pairs trained together. After 3 months of training in their randomly assigned mode, a washout period of 3 months was observed before twin pairs crossed over to complete 3 months of the alternate exercise intervention. Measures of cardiac morphology and function, cerebrovascular function, cognitive performance, peripheral artery function, biochemistry, blood pressure, body composition, skeletal muscle strength and cardiopulmonary fitness were collected before and after each exercise intervention (i.e. at weeks 0, 12, 24 and 36).

Discussion

We adopted exercise modalities that produce distinct haemodynamic and physiological stimuli for physiological adaptation and recruited MZ and DZ twin pairs to address questions such as; do individuals exhibit concordant responses to distinct exercise modalities? and what is the genetic contribution to adaptation resulting from distinct training modalities? The results of this study will provide insight into the genetic and environmental contribution to exercise response to distinct modes of training, with implications for determining the optimal approaches to exercise prescription.

The effects of dopamine receptor genes on the trajectories of sport participation from adolescence through young adulthood

Background: Although previous studies suggest that dopamine receptor genes partially affect physical activity-related behaviours, all of these studies were cross-sectional studies that examined the effects of dopamine receptor genes on physical activity-related behaviours at some point in time. Therefore, the nature and extent of this relationship across the lifespan are even more uncertain.Aim: The purpose of this study is to examine the effects of dopamine receptor genes (i.e. DRD2, DRD4 and DRD5) on sport participation trajectories from adolescence to young adulthood.Subjects and methods: This study used the National Longitudinal Study of Adolescent Health data (wave 1-4). Group-based trajectory modelling was used to investigate the effect of dopamine receptor genes on the probability of being in each sport participation trajectory group.Results: A three-group model was the best fitting model for men whereas a two-group model was the best fitting model for women. The more participants possess the A1 allele of the DRD2, the less likely they are to be in the "high-decreasing group" rather than the "low-stable group" in both men and women. In male participants, the more participants carry the A1 allele of the DRD2, the more likely they are to be in the "high-stable group" rather than the "high-decreasing group" (coefficient = 0.206, p<.05).Conclusions: These results can contribute to the literature by providing important information on the effects of dopamine receptor genes on sport participation trajectories from adolescence through young adulthood.

Active behaviors and screen time in offspring of parents with major depressive disorder, bipolar disorder and schizophrenia

Activities may be modifiable factors that moderate the risk and resilience in the development of mental health and illness. Youth who spend more time using screens are more likely to have poor mental health. Conversely, time spent engaged in active behaviors (i.e., physical activity, socializing and reading) is associated with better mental health. The choice of activities may be important in offspring of parents with mental illness, who are at increased risk for developing mental disorders. Among 357 youth of the FORBOW (Families Overcoming Risks and Building Opportunities for Well-being) cohort aged 6-21, we examined whether parental diagnosis of mental illness (i.e., major depressive disorder, schizophrenia and bipolar disorder) and current levels of depression influenced the amount of time their offspring spent using screens and engaging in active behaviors. Parental history of mental illness and higher levels of current depression in mothers were associated with less time spent engaged in active behaviors and more time spent using screens. Creating opportunities and incentives for active behaviors may redress the balance between youth with and without a familial history of mental illness.

Familial aggregation and heritability of markers of metabolic risk, physical activity, and physical fitness in nuclear families from Muzambinho (Minas Gerais, Brazil)

OBJECTIVE

This study investigated the familial aggregation and heritability of markers of metabolic risk, physical activity, and physical fitness in nuclear families from Muzambinho (Minas Gerais, Brazil).

SUBJECTS AND METHODS

The study included members of 139 families, comprising 97 fathers (aged 40 ± 7 years), 129 mothers (35 ± 6 years), 136 sons (12 ± 4 years), and 121 daughters (12 ± 5 years). Evaluated markers included (A) body mass index, waist circumference, glycemia, and cholesterolemia, as metabolic risk markers; (B) total weekly volume of physical activity, as a physical activity marker; and (C) relative muscle strength, as a physical fitness marker. Correlations between family members and heritability (h2) were estimated using the software S.A.G.E.

RESULTS

Significant familial correlations were obtained between parents-offspring for glycemia and cholesterolemia (both ρ = 0.21, p < 0.05) and relative muscle strength (ρ = 0.23, p < 0.05), and between siblings for waist circumference, glycemia, total weekly volume of physical activity, and relative muscle strength (ρ variation 0.25 to 0.36, p < 0.05). Heritability values were significant for almost all variables (h2 variations: 20% to 57% for metabolic risk markers, 22% for the total weekly volume of physical activity, and 50% for relative muscle strength), except for waist circumference (h2 = 15%, p = 0.059).

CONCLUSION

The presence of significant correlations between family members and/or significant heritability strengthens the possible genetic and/or common familial environment influence on metabolic risk markers, total weekly volume of physical activity, and relative muscle strength.

Perspectives of adolescents, parents, and teachers on barriers and facilitators of physical activity among school-age adolescents: a qualitative analysis

Background

Physical activity levels are low among adolescents in Morocco; however, the influences on physical activity behavior of adolescents have not yet been explored in a qualitative study. Here, we explored potential social-ecological barriers and facilitators of physical activity in Moroccan adolescents with the goal of developing a successful intervention program aimed at improving their physical activity level.

Methods

For this study, we conducted 17 focus group discussions (100 participants, composed of 56 adolescents, 26 parents, and 18 teachers from two middle schools in Taza city, Morocco). Discussions during focus groups were facilitated by a semi-structured interview guide. Guide questions were underpinned by the social-ecological model as a theoretical framework. Data analysis was carried out by two coders using thematic analysis.

Results

We found that barriers and facilitators of physical activity in adolescents are organized into six themes that belong to different levels of the social-ecological model. Three themes belonged to the intrapersonal level (perceived motivating and limiting factors, physical activity awareness, and time constraints), two themes were classified into the interpersonal/cultural level (social support and gender and cultural norms), and one theme belonged to the environmental level (access to opportunities). Most of the themes were at the individual level, with each theme including both barriers and facilitators.

Conclusions

Adolescent participation in physical activity can be facilitated or hampered by many factors. Results from the focus group discussions showed that these factors belonged to different levels of the social-ecological model, but most were at the individual level. Our findings have several implications. First, they may offer suggestions for a tailored intervention program aimed at improving adolescent physical activity. Second, they can improve quantitative research by enriching the battery of questions of physical activity instruments (e.g., a question related to physical disability). Third, the proposed thematic map can contribute to understanding interactions and causal pathways in the social-ecological model.

Genetic Factors Associated With Human Physical Activity: Are Your Genes Too Tight To Prevent You Exercising?

The benefits of physical activity (PA) on health and fitness are well known. It has become apparent from studies of heritability that there is a considerable genetic component to PA. However, PA is such a complex phenotype that the measurement and quantification of it provide a challenge to a clearer understanding of its genetic basis. In this review, we assessed available evidence from family and twin studies that have estimated the heritability of PA. Heritability is greater when evaluated by accelerometry compared with questionnaires, and for questionnaires higher in twin than family studies. Accelerometry studies suggest heritability of PA is 51% to 56%. There have been many genome-wide linkage studies, candidate gene studies, and four genome-wide association studies that have highlighted specific genetic factors linked to different PA levels. These studies have generally failed to replicate identified loci, with the exception of the melanocortin 4 receptor, and this may be because of the variability in the measurement techniques used to characterize the behavior. Future work should aim to standardize the procedures used to measure PA in the context of trying to identify genetic causes. The link of genetics to physical exercise is not so tight that it prevents voluntary interventions.

Biological/Genetic Regulation of Physical Activity Level: Consensus from GenBioPAC

PURPOSE

Physical activity unquestionably maintains and improves health; however, physical activity levels globally are low and not rising despite all the resources devoted to this goal. Attention in both the research literature and the public policy domain has focused on social-behavioral factors; however, a growing body of literature suggests that biological determinants play a significant role in regulating physical activity levels. For instance, physical activity level, measured in various manners, has a genetic component in both humans and nonhuman animal models. This consensus article, developed as a result of an American College of Sports Medicine-sponsored round table, provides a brief review of the theoretical concepts and existing literature that supports a significant role of genetic and other biological factors in the regulation of physical activity.

CONCLUSIONS

Future research on physical activity regulation should incorporate genetics and other biological determinants of physical activity instead of a sole reliance on social and other environmental determinants.

How Consistent are Genetic Factors in Explaining Leisure-Time Physical Activity and Sport Participation? The Portuguese Healthy Families Study

This study investigates how consistent genetic factors are, as measured by heritability estimates (h2), in the leisure-time physical activity index (LTPAI) and sport participation index (SPI) from early (10-14 yrs) to late adolescence (15-19 yrs). The sample comprises 12,385 subjects from 3,378 Portuguese nuclear families. Height and weight were measured and body mass index (BMI) was calculated, and the LTPAI and SPI were estimated by questionnaire. Socioeconomic status (SES) was assessed by parental occupation. Analyses were done using S.A.G.E. software. Our results showed that h2 estimates for the LTPAI and SPI in the two age groups (10-14 yrs and 15-19 yrs) were stable: for the LTPAI, h2 = 0.297 and 0.322, respectively; and for the SPI, h2 = 0.413 and 0.428, respectively. Sibling correlations and environmental correlations are higher in the younger age group for both the LTPAI and the SPI. Spousal correlations are higher in the younger age group for the LTPAI and lower for the SPI than the older group. Parent-offspring correlations are similar in both age groups for the LTPAI and SPI. In conclusion, the influence of genetic factors on physical activity and sport participation remains stable across age in adolescence. However, variation in sibling correlations - in particular, environmental correlations - was observed. These findings suggest that shared/non-shared environmental factors express different degrees of importance across age. Future intervention programs aiming to promote change in behaviors need to consider these results to bring about positive changes in physical activity and sport participation behaviors within the family setting.

Resemblance in physical activity levels: The Portuguese sibling study on growth, fitness, lifestyle, and health

OBJECTIVES

To investigate the relationships of biological, behavioral, familial, and environmental characteristics with siblings´ physical activity (PA) levels as well as the intrapair resemblance in PA.

METHODS

The sample comprises 834 (390 females) biological siblings [brother-brother (BB), sister-sister (SS), brother-sister (BS)] aged 9 to 20 years. Total PA index (TPAI) was estimated by questionnaire. Information on potential behavioral, familial, and environmental correlates was obtained by self-report; body mass index (BMI), biological maturation, and physical fitness were measured. Multilevel models were used to analyze siblings´ clustered data, and sibling resemblance was estimated with the intraclass correlation (ρ).

RESULTS

On average, younger sibs, those more physically fit, and those with more parental support had greater TPAI. Further, BB pairs had higher TPAI levels than SS or BS pairs, but also had greater within-pair variance. When adjusted for all covariates, SS pairs demonstrated greater resemblance in TPAI (ρ = 0.53, 95%CI = 0.38-0.68) than BS (ρ = 0.26, 95%CI = 0.14-0.43) or BB pairs (ρ = 0.18, 95%CI = 0.06-0.44).

CONCLUSIONS

Age, physical fitness, and parental support were the best predictors of TPAI levels. A moderate level of resemblance in TPAI was observed in SS pairs, while lower resemblance was found for BS and BB pairs. These findings may be due to differences in the roles of shared genetic factors, familial, and environmental characteristics across different sibling types.

Multilevel modelling of somatotype components: the Portuguese sibling study on growth, fitness, lifestyle and health

BACKGROUND

Somatotype is a complex trait influenced by different genetic and environmental factors as well as by other covariates whose effects are still unclear.

AIMS

To (1) estimate siblings' resemblance in their general somatotype; (2) identify sib-pair (brother-brother (BB), sister-sister (SS), brother-sister (BS)) similarities in individual somatotype components; (3) examine the degree to which between and within variances differ among sib-ships; and (4) investigate the effects of physical activity (PA) and family socioeconomic status (SES) on these relationships.

SUBJECTS AND METHODS

The sample comprises 1058 Portuguese siblings (538 females) aged 9-20 years. Somatotype was calculated using the Health-Carter method, while PA and SES information was obtained by questionnaire. Multi-level modelling was done in SuperMix software.

RESULTS

Older subjects showed the lowest values for endomorphy and mesomorphy, but the highest values for ectomorphy; and more physically active subjects showed the highest values for mesomorphy. In general, the familiality of somatotype was moderate (ρ = 0.35). Same-sex siblings had the strongest resemblance (endomorphy: ρ_SS > ρ_BB > ρ_BS; mesomorphy: ρ_BB = ρ_SS > ρ_BS; ectomorphy: ρ_BB > ρ_SS > ρ_BS). For the ectomorphy and mesomorphy components, BS pairs showed the highest between sib-ship variance, but the lowest within sib-ship variance; while for endomorphy BS showed the lowest between and within sib-ship variances.

CONCLUSIONS

These results highlight the significant familial effects on somatotype and the complexity of the role of familial resemblance in explaining variance in somatotypes.

NIH working group report-using genomic information to guide weight management: From universal to precision treatment

OBJECTIVE

Precision medicine utilizes genomic and other data to optimize and personalize treatment. Although more than 2,500 genetic tests are currently available, largely for extreme and/or rare phenotypes, the question remains whether this approach can be used for the treatment of common, complex conditions like obesity, inflammation, and insulin resistance, which underlie a host of metabolic diseases.

METHODS

This review, developed from a Trans-NIH Conference titled "Genes, Behaviors, and Response to Weight Loss Interventions," provides an overview of the state of genetic and genomic research in the area of weight change and identifies key areas for future research.

RESULTS

Although many loci have been identified that are associated with cross-sectional measures of obesity/body size, relatively little is known regarding the genes/loci that influence dynamic measures of weight change over time. Although successful short-term weight loss has been achieved using many different strategies, sustainable weight loss has proven elusive for many, and there are important gaps in our understanding of energy balance regulation.

CONCLUSIONS

Elucidating the molecular basis of variability in weight change has the potential to improve treatment outcomes and inform innovative approaches that can simultaneously take into account information from genomic and other sources in devising individualized treatment plans.

Variability and Stability in Daily Moderate-to-Vigorous Physical Activity among 10 Year Old Children

Day-to-day variability and stability of children's physical activity levels across days of the week are not well understood. Our aims were to examine the day-to-day variability of moderate-to-vigorous physical activity (MVPA), to determine factors influencing the day-to-day variability of MVPA and to estimate stability of MVPA in children. The sample comprises 686 Portuguese children (10 years of age). MVPA was assessed with an accelerometer, and BMI was computed from measured height and weight. Daily changes in MVPA and their correlates (gender, BMI, and maturity) were modeled with a multilevel approach, and tracking was calculated using Foulkes &amp; Davies γ. A total of 51.3% of boys and 26.2% of girls achieved 60 min/day of MVPA on average. Daily MVPA was lower during the weekend (23.6% of boys and 13.6% of girls comply with the recommended 60 min/day of MVPA) compared to weekdays (60.8% and 35.4%, boys and girls, respectively). Normal weight children were more active than obese children and no effect was found for biological maturation. Tracking is low in both boys (γ = 0.59 ± 0.01) and girls (γ = 0.56 ± 0.01). Children's MVPA levels during a week are highly unstable. In summary, boys are more active than girls, maturation does not affect their MVPA, and obese children are less likely to meet 60 min/day of MVPA. These results highlight the importance of providing opportunities for increasing children's daily MVPA on all days of week, especially on the weekend.

Sex-specific genetic effects in physical activity: results from a quantitative genetic analysis

BACKGROUND

The objective of this study is to present a model to estimate sex-specific genetic effects on physical activity (PA) levels and sedentary behaviour (SB) using three generation families.

METHODS

The sample consisted of 100 families covering three generations from Portugal. PA and SB were assessed via the International Physical Activity Questionnaire short form (IPAQ-SF). Sex-specific effects were assessed by genotype-by-sex interaction (GSI) models and sex-specific heritabilities. GSI effects and heterogeneity were tested in the residual environmental variance. SPSS 17 and SOLAR v. 4.1 were used in all computations.

RESULTS

The genetic component for PA and SB domains varied from low to moderate (11% to 46%), when analyzing both genders combined. We found GSI effects for vigorous PA (p = 0.02) and time spent watching television (WT) (p < 0.001) that showed significantly higher additive genetic variance estimates in males. The heterogeneity in the residual environmental variance was significant for moderate PA (p = 0.02), vigorous PA (p = 0.006) and total PA (p = 0.001). Sex-specific heritability estimates were significantly higher in males only for WT, with a male-to-female difference in heritability of 42.5 (95% confidence interval: 6.4, 70.4).

CONCLUSIONS

Low to moderate genetic effects on PA and SB traits were found. Results from the GSI model show that there are sex-specific effects in two phenotypes, VPA and WT with a stronger genetic influence in males.

Quasi-causal associations of physical activity and neighborhood walkability with body mass index: a twin study

OBJECTIVE

Physical activity, neighborhood walkability, and body mass index (BMI, kg/m(2)) associations were tested using quasi-experimental twin methods. We hypothesized that physical activity and walkability were independently associated with BMI within twin pairs, controlling for genetic and environmental background shared between them.

METHODS

Data were from 6376 (64% female; 58% identical) same-sex pairs, University of Washington Twin Registry, 2008-2013. Neighborhood walking, moderate-to-vigorous physical activity (MVPA), and BMI were self-reported. Residential address was used to calculate walkability. Phenotypic (non-genetically informed) and biometric (genetically informed) regression was employed, controlling for age, sex, and race.

RESULTS

Walking and MVPA were associated with BMI in phenotypic analyses; associations were attenuated but significant in biometric analyses (Ps<0.05). Walkability was not associated with BMI, however, was associated with walking (but not MVPA) in both phenotypic and biometric analyses (Ps<0.05), with no attenuation accounting for shared genetic and environmental background.

CONCLUSIONS

The association between activity and BMI is largely due to shared genetic and environmental factors, but a significant causal relationship remains accounting for shared background. Although walkability is not associated with BMI, it is associated with neighborhood walking (but not MVPA) accounting for shared background, suggesting a causal relationship between them.

Child-caregivers' body weight and habitual physical activity status is associated with overweight in kindergartners

Background

The aim of this study was to examine whether child-caregivers’, both parents and kindergarten teachers, health parameters (age, weight status, habitual physical activity score) are significantly associated with the risk of overweight in young children.

Methods

We assessed the individual body mass index standard deviation score in a regional cross-sectional health study and matched a representative sample of 434 kindergartners aged 3 to 6-years with their caregivers’ weight and habitual physical activity status. Furthermore, we identified factors associated with the general ability of child-caregivers to identify overweight in children, and the awareness to classify a child within the correct weight category.

Results

Our study confirmed most of the known associations between parental anthropometrics and psychosocial factors with childhood overweight and obesity. A significantly higher proportion of boys tended to be overweight or obese (p = 0.027) and parents were more likely to misclassified boys overweight as normal weight (OR: 1.86; 95% CI 1.21-2.86). Adjusted for confounders, logistic regression analysis revealed that kindergarten teachers’ weight status (OR: 1.97; 95%-CI: 1.01-3.83) and habitual physical activity scores (OR: 2.32; 95%-CI: 1.10-4.92) were associated with children’s weight status.

Conclusions

Kindergarten teachers’ weight and habitual physical activity score seem to be new independent risk factors for overweight in kindergartners 3 to 6-years of age. Our results suggest that the psychosocial, non-genetic association of non-parental child-caregivers on children’s weight is relatively high and that the association of non-parental child-caregivers warrants further investigation.

Factors behind leisure-time physical activity behavior based on Finnish twin studies: the role of genetic and environmental influences and the role of motives

Different approaches are being taken to clarify the role of various factors in the development of physical activity behaviors. Genetic studies are a new area of physical activity research and also the motives for physical activity have been widely studied. The purpose of this paper is to review the findings emerging from the longitudinal genetic studies on leisure-time physical activity and to evaluate the associations between motivational factors and leisure-time physical activity. The focus is to review recent findings of longitudinal Finnish twin studies. The results of the latest longitudinal Finnish twin studies point to the existence of age-specific genetic and environmental influences on leisure-time physical activity. Variations in environmental factors seem to explain the observed deterioration in leisure-time physical activity levels. A decline in genetic influences is seen first from adolescence to young adulthood and again from the age of thirty to the mid-thirties. In the Finnish twin participants, mastery, physical fitness, and psychological state were the major motivation factors associated with consistent leisure-time physical activity behavior. The results also indicate that intrinsic motivation factors may be important for engagement in leisure-time physical activity.

Genetic factors in exercise adoption, adherence and obesity

Physical activity and exercise play critical roles in energy balance. While many interventions targeted at increasing physical activity have demonstrated efficacy in promoting weight loss or maintenance in the short term, long term adherence to such programmes is not frequently observed. Numerous factors have been examined for their ability to predict and/or influence physical activity and exercise adherence. Although physical activity has been demonstrated to have a strong genetic component in both animals and humans, few studies have examined the association between genetic variation and exercise adherence. In this review, we provide a detailed overview of the non-genetic and genetic predictors of physical activity and adherence to exercise. In addition, we report the results of analysis of 26 single nucleotide polymorphisms in six candidate genes examined for association to exercise adherence, duration, intensity and total exercise dose in young adults from the Training Interventions and Genetics of Exercise Response (TIGER) Study. Based on both animal and human research, neural signalling and pleasure/reward systems in the brain may drive in large part the propensity to be physically active and to adhere to an exercise programme. Adherence/compliance research in other fields may inform future investigation of the genetics of exercise adherence.

Sex differences in genetic and environmental influences on percent body fatness and physical activity

BACKGROUND

Knowing the extent to which genetic and environmental factors influence percent body fatness (%Fat) and physical activity (PA) would be beneficial, since both are tightly correlated with future health outcomes. Thus, the purpose was to evaluate sex differences in genetic and environmental influences on %Fat and physical activity behavior in male and female adolescent twins.

METHODS

Subjects were adolescent (age range 8.3 to 16.6 yr) twins. %Fat (n = 518 twins) was assessed by bioelectrical impedance analysis (BIA) and PA (n = 296 twins) was measured using 3-Day PA Recall. Each activity was converted to total MET-minutes. Univariate twin models were used to examine sex differences in genetic and environmental factors influencing %Fat and PA.

RESULTS

%Fat was influenced by genetic effects in both boys and girls (88% and 90%, respectively), with slightly higher heritability estimates for girls. PA was influenced solely by environmental effects for both sexes with higher shared environmental influences in boys (66%) and higher nonshared effects in girls (67%).

CONCLUSIONS

When developing interventions to increase PA in adolescents, it is important to consider the environment in which it takes place as it is the primary contributor to PA levels.

Heritability of objectively assessed daily physical activity and sedentary behavior

BACKGROUND

Twin and family studies that estimated the heritability of daily physical activity have been limited by poor measurement quality and a small sample size.

OBJECTIVE

We examined the heritability of daily physical activity and sedentary behavior assessed objectively by using combined heart rate and movement sensing in a large twin study.

DESIGN

Physical activity traits were assessed in daily life for a mean (± SD) 6.7 ± 1.1 d in 1654 twins from 420 monozygotic and 352 dizygotic same-sex twin pairs aged 56.3 ± 10.4 y with body mass index (in kg/m(2)) of 26.1 ± 4.8. We estimated the average daily movement, physical activity energy expenditure, and time spent in moderate-to-vigorous intensity physical activity and sedentary behavior from heart rate and acceleration data. We used structural equation modeling to examine the contribution of additive genetic, shared environmental, and unique environmental factors to between-individual variation in traits.

RESULTS

Additive genetic factors (ie, heritability) explained 47% of the variance in physical activity energy expenditure (95% CI: 23%, 53%) and time spent in moderate-to-vigorous intensity physical activity (95% CI: 29%, 54%), 35% of the variance in acceleration of the trunk (95% CI: 0%, 44%), and 31% of the variance in the time spent in sedentary behavior (95% CI: 9%, 51%). The remaining variance was predominantly explained by unique environmental factors and random error, whereas shared environmental factors played only a marginal role for all traits with a range of 0-15%.

CONCLUSIONS

The between-individual variation in daily physical activity and sedentary behavior is mainly a result of environmental influences. Nevertheless, genetic factors explain up to one-half of the variance, suggesting that innate biological processes may be driving some of our daily physical activity.

Multi-level modelling of physical activity in nuclear families

BACKGROUND

Few studies focus on the different dyadic relations among family members to study physical activity (PA) levels.

AIM

The aim was to investigate predictors and sources of variance of PA levels in nuclear families using multi-level modelling.

SUBJECTS AND METHODS

The sample consisted of 2661 Portuguese four-member nuclear families (10 644 subjects). PA was measured using a questionnaire and socioeconomic status (SES) was assessed by parental occupation. Height and weight were measured in children, while parents self-reported their values.

RESULTS

The results showed that intra-generational similarities were higher than inter-generational, with correlation values of 0.26 and 0.10, respectively. SES was unrelated to any family members' PA level. Being male (β = 0.26, t = 21.77), being older (β = -0.36, t = -4.73) and greater BMI for mothers (β = 0.02, t = 2.55) had effects on individuals' PA.

CONCLUSION

These results suggest a strong dyadic resemblance in PA, showed different effects of gender, age and BMI on individuals' PA and demonstrated that multi-level modelling is a useful strategy to study PA in families.

What psychiatric genetics has taught us about the nature of psychiatric illness and what is left to learn

Psychiatric genetics has taught us a great deal about the nature of psychiatric disorders. Traditional family, twin and adoption studies have demonstrated the substantial role of genetic factors in their etiology, clarified the role of genetic factors in comorbidity, elucidated development pathways, and documented the importance of gene-environment correlation and interaction. We have also received some hard lessons when we were unable to detect replicable genes of large effect size and found that our much-valued candidate genes did not live up to their expected promise. With more mature molecular and statistical methods, we are entering now a different era. Statistical analyses of aggregate molecular signals are validating earlier heritability estimates. Replicated findings from genome-wide association studies are beginning to emerge, as are discoveries of large-effect size rare genomic variants. The number of such findings is likely to soon grow dramatically. The most pressing question facing the field is what biological picture these results will reveal. I articulate four possible scenarios that reflect (i) no, (ii) minimal, (iii) moderate and (iv) high biological coherence in the replicated molecular variant findings, which are soon likely to emerge. I discuss the factors that will likely influence these patterns, including the problems of etiological heterogeneity and multiple realizability. These findings could provide critical insights into the underlying biology of our psychiatric syndromes and potentially permit us to perceive, 'through a glass darkly,' the levels of the mind-brain system that are disordered.

Genetic influences of sports participation in Portuguese families

To estimate familial aggregation and quantify the genetic and environmental contribution to the phenotypic variation on sports participation (SP) among Portuguese families. The sample consisted of 2375 nuclear families (parents and two offspring each) from different regions of Portugal with a total of 9500 subjects. SP assessment was based on a psychometrically established questionnaire. Phenotypes used were based on the participation in sports (yes/no), intensity of sport, weekly amount of time in SP and the proportion of the year in which a sport was regularly played. Familial correlations were calculated using family correlations (FCOR) in the SAGE software. Heritability was estimated using variance-components methods implemented in Sequential Oligogenic Linkage Analysis Routines (SOLAR) software. Subjects of the same generation tend to be more similar in their SP habits than the subjects of different generations. In all SP phenotypes studied, adjusted for the effects of multiple covariates, the proportion of phenotypic variance due to additive genetic factors ranged between 40% and 50%. The proportion of variance attributable to environmental factors ranged from 50% for the participation in sports to 60% for intensity of sport. In this large population-based family study, there was significant familial aggregation on SP. These results highlight that the variation on SP phenotypes have a significant genetic contribution although environmental factors are also important in the familial resemblance of SP.

Gene-environment correlation: difficulties and a natural experiment-based strategy

OBJECTIVES

We explored how gene-environment correlations can result in endogenous models, how natural experiments can protect against this threat, and if unbiased estimates from natural experiments are generalizable to other contexts.

METHODS

We compared a natural experiment, the College Roommate Study, which measured genes and behaviors of college students and their randomly assigned roommates in a southern public university, with observational data from the National Longitudinal Study of Adolescent Health in 2008. We predicted exposure to exercising peers using genetic markers and estimated environmental effects on alcohol consumption. A mixed-linear model estimated an alcohol consumption variance that was attributable to genetic markers and across peer environments.

RESULTS

Peer exercise environment was associated with respondent genotype in observational data, but not in the natural experiment. The effects of peer drinking and presence of a general gene-environment interaction were similar between data sets.

CONCLUSIONS

Natural experiments, like random roommate assignment, could protect against potential bias introduced by gene-environment correlations. When combined with representative observational data, unbiased and generalizable causal effects could be estimated.

Genetic and Environmental Influences on Longitudinal Changes in Leisure-Time Physical Activity From Adolescence to Young Adulthood

The aim of this study was to estimate genetic and environmental influences on the longitudinal evolution of leisure-time physical activity habits from adolescence to young adulthood. Data were gathered at four time points, at mean ages 16.2, 17.1, 18.6, and 24.5 years. At baseline, the sample comprised 5,216 monozygotic and dizygotic twins, born 1975–1979, and, at the last follow-up point, of 4,531 monozygotic and dizygotic twins. Physical activity volume was assessed as frequency of leisure-time physical activity and participants were categorized into three groups: inactive, moderately active, and active. Genetic and environmental influences were estimated using a multivariate, longitudinal Cholesky decomposition with a ‘multifactorial liability threshold’ approach. The results suggest that, in both sexes the heritability of leisure-time physical activity remained moderate (~43–52%) during adolescence, declining to ~30% in young adulthood. Shared environmental influences increased from adolescence (~18–26%) to young adulthood (43% in men and 49% in women). Specific environmental influences remained relatively stable during the total follow-up (~20–30%). New genetic, shared, and specific environmental influences at every follow-up point were suggested by the low correlations across occasions. In conclusion, the study demonstrated gender differences in genetic influences in the evolution of leisure-time physical activity habits from adolescence to young adulthood. However, shared environmental influences, especially in women, were crucial in explaining longitudinal changes in leisure-time physical activity. These outcomes emphasize the need of gender-specific measures to promote physical activity habits during young adulthood.

Physical activity, physical fitness, gross motor coordination, and metabolic syndrome: focus of twin research in Portugal

A very brief history of Portuguese twin research in sport and human movement sciences is presented. Recruitment procedures, zygosity determination, and phenotypes are given for twins and their parents from the mainland, and Azores and Madeira archipelagos. Preliminary findings are mostly related to physical activity, health-related physical fitness, gross motor coordination, neuromotor development, and metabolic syndrome traits.

Genetic inheritance effects on endurance and muscle strength: an update

Top-level sport seems to play a natural Darwinian stage. The most outstanding athletes appear to emerge as a result of exogenous influences of nature and/or coincidence, namely, the contingency of practicing certain sport for which their talents best fit. This coincidence arises because certain individuals possess anatomical, metabolic, functional and behavioural characteristics that are precisely those required to excel in a given sport. Apart from the effects of training, there is strong evidence of genetic influence upon athletic performance. This article reviews the current state of knowledge regarding heritable genetic effects upon endurance and muscle strength, as reported by several twin and family studies. Due, probably, to the inaccuracy of the measurement procedures and sampling error, heritability estimates differ widely between studies. Even so, the genetic inheritence effects seem incontrovertible in most physical traits: ~40-70% for peak oxygen uptake and cardiac mass and structure, and ~30-90% for anaerobic power and capacity, ranging according to the metabolic category. Studies in development by several researchers at this present time seem to guarantee that future reviews will include twins and family studies concerning genes associated with the adaptive processes against hormetic agents, such as exercise, heat and oxidative stress.

Correlates of physical activity: why are some people physically active and others not?

Physical inactivity is an important contributor to non-communicable diseases in countries of high income, and increasingly so in those of low and middle income. Understanding why people are physically active or inactive contributes to evidence-based planning of public health interventions, because effective programmes will target factors known to cause inactivity. Research into correlates (factors associated with activity) or determinants (those with a causal relationship) has burgeoned in the past two decades, but has mostly focused on individual-level factors in high-income countries. It has shown that age, sex, health status, self-efficacy, and motivation are associated with physical activity. Ecological models take a broad view of health behaviour causation, with the social and physical environment included as contributors to physical inactivity, particularly those outside the health sector, such as urban planning, transportation systems, and parks and trails. New areas of determinants research have identified genetic factors contributing to the propensity to be physically active, and evolutionary factors and obesity that might predispose to inactivity, and have explored the longitudinal tracking of physical activity throughout life. An understanding of correlates and determinants, especially in countries of low and middle income, could reduce the eff ect of future epidemics of inactivity and contribute to effective global prevention of non-communicable diseases.

A Longitudinal Study on Genetic and Environmental Influences on Leisure Time Physical Activity in the Finnish Twin Cohort

The purpose of this study was to examine changes in the contribution of genetic and environmental influences to leisure time physical activity among male and female twins over a 6-year follow-up. At baseline the sample comprised 4,280 monozygotic and 9,276 dizygotic twin individuals, and at follow-up 4,383 monozygotic and 9,439 dizygotic twin individuals. Participants were aged 18–54 years at baseline. Genetic modeling results showed that genetic influences on leisure time physical activity declined from baseline (44%) to follow-up (34%). Most of the genetic influences identified at baseline were present at followup (rg= 0.72). Specific environmental influences increased from baseline (56%) to follow-up (66%) while at follow-up new environmental time-specific influences were observed (re= 0.23). The model with sex differences showed a higher estimate of genetic influences for men than women both at baseline (men 47% vs. women 42%) and at follow-up (men 38% vs. women 31%). The additive genetic correlation for this phenotype was greater for men (rg= 0.79) than women (rg= 0.64). The specific environmental influences were corresponding; at baseline men 53% and women 56% and at follow-up men 62 % and women 69%. The environmental correlations between the two time points were similar for men (re= 0.21) and for women (re= 0.24). In conclusion, in a sample of healthy twins most of the genetic influences on leisure time physical activity expressed at baseline were present at 6 years of follow-up. New specific environmental factors underlying follow-up leisure time physical activity were observed.

Regular exercise, subjective wellbeing, and internalizing problems in adolescence: causality or genetic pleiotropy?

This study tests in a genetically informative design whether exercise behavior causally influences subjective wellbeing (SWB) and internalizing problems (INT). If exercise causally influences SWB and INT, genetic and environmental factors influencing exercise behavior will also influence SWB and INT. Furthermore, within genetically identical (MZ) twin pairs, the twin who exercises more should also show higher levels of SWB and lower levels of INT, than the co-twin who exercises less, because genetic confounding is excluded. Data on these phenotypes were available in a sample of 6317 adolescent twins and 1180 non-twin-siblings. Most participants had longitudinal data with 2-year follow-up. Exercise behavior was cross-sectionally and longitudinally associated with fewer internalizing problems and increased SWB (correlations ranged from 0.12 to 0.16). Cross-sectional and longitudinal associations were mainly accounted for by genetic factors, whereas the contribution of environmental factors was negligible. Within MZ twin pairs, the twin who exercised more did not show fewer internalizing problems and increased SWB. This was found cross-sectionally and longitudinally. We conclude that exercise behavior is associated with fewer internalizing problems and higher levels of SWB. The association largely reflects the effects of common genetic factors on these traits.

Contribution of physical education to overall physical activity

For many children, physical activity (PA) during physical education (PE) lessons provides an important opportunity for being physically active. Although PA during PE has been shown to be low, little is known about the contribution of PA during PE to overall PA. The aim was therefore to assess children's PA during PE and to determine the contribution of PE to overall PA with special focus on overweight children. Accelerometer measurements were done in 676 children (9.3 ± 2.1 years) over 4-7 days in 59 randomly selected classes. Moderate-and-vigorous PA (MVPA; ≥ 2000 counts/min) during PE (MVPAPE), overall MVPA per day (MVPADAY), and a comparison of days with and without PE were calculated by a regression model with gender, grade, and weight status (normal vs overweight) as fixed factors and class as a random factor. Children spent 32.8 ± 15.1% of PE time in MVPA. Weight status was not associated to MVPAPE . MVPAPE accounted for 16.8 ± 8.5% of MVPADAY, and 17.5 ± 8.2% in overweight children. All children were more active on days with PE than on days without PE (differences: 16.1 ± 29.0 min of MVPADAY; P ≤ 0.001; 13.7 ± 28.0 min for overweight children). Although MVPAPE was low, PE played a considerable role in providing PA and was not compensated by reducing extracurricular MVPA.

Heritability of physical activity traits in Brazilian families: the Baependi Heart Study

Background

It is commonly recognized that physical activity has familial aggregation; however, the genetic influences on physical activity phenotypes are not well characterized. This study aimed to (1) estimate the heritability of physical activity traits in Brazilian families; and (2) investigate whether genetic and environmental variance components contribute differently to the expression of these phenotypes in males and females.

Methods

The sample that constitutes the Baependi Heart Study is comprised of 1,693 individuals in 95 Brazilian families. The phenotypes were self-reported in a questionnaire based on the WHO-MONICA instrument. Variance component approaches, implemented in the SOLAR (Sequential Oligogenic Linkage Analysis Routines) computer package, were applied to estimate the heritability and to evaluate the heterogeneity of variance components by gender on the studied phenotypes.

Results

The heritability estimates were intermediate (35%) for weekly physical activity among non-sedentary subjects (weekly PA_NS), and low (9-14%) for sedentarism, weekly physical activity (weekly PA), and level of daily physical activity (daily PA). Significant evidence for heterogeneity in variance components by gender was observed for the sedentarism and weekly PA phenotypes. No significant gender differences in genetic or environmental variance components were observed for the weekly PA_NS trait. The daily PA phenotype was predominantly influenced by environmental factors, with larger effects in males than in females.

Conclusions

Heritability estimates for physical activity phenotypes in this sample of the Brazilian population were significant in both males and females, and varied from low to intermediate magnitude. Significant evidence for heterogeneity in variance components by gender was observed. These data add to the knowledge of the physical activity traits in the Brazilian study population, and are concordant with the notion of significant biological determination in active behavior.

Effects of exercise training and a hypocaloric diet on female monozygotic twins in free-living conditions

This paper aims to examine the similarities in effects of exercise training and a hypocaloric diet within overweight female monozygotic twin pairs and to assess differences in twin partners' responses depending on the timing of exercise bouts and main meals. Six previously untrained twin pairs (aged 20-37 years, body fat 35.8±6.3%) performed an identical exercise program (12 bouts endurance and 8 bouts resistance training) and took part in a nutrition counseling program for a period of 28 days. They pursued one identical goal: to lose body weight and fat. Each twin partner was randomly assigned to one of the two intervention groups: "exercise after dinner" (A) and "exercise before dinner" (B). Subjects followed a hypocaloric diet, supervised by a nutritionist, in free-living conditions. Reductions in body weight, waist and hip circumference, glucose tolerance, mean daily %fat intake, changes in morning resting energy rate and resting metabolic rate showed great variation between twin pairs, but only small variation within twin pairs. Thus, the genetic influence on the changes in most of the examined anthropometric and physiological variables was high. There was no influence of the specific timing on the dependent variables.

Impact of exercise training on endothelial function and body composition in young people: a study of mono- and di-zygotic twins

Flow mediated dilation (FMD) is a surrogate marker of arterial function which can be improved by exercise training. To date, no study has assessed the magnitude of FMD changes in response to exercise training between groups of mono- (MZ) and di-zygotic (DZ) twins. The purpose of this study was therefore to compare FMD in MZ- and DZ twins before and after identical exercise training interventions. At baseline, FMD was assessed using high resolution Duplex ultrasound in 12 twin pairs (6 MZ pairs 13.5 ± 0.8 years, 6 DZ pairs 13.4 ± 0.8 years). Twins completed 8 weeks of exercise training (65-85% HR(max)), consisting of three 45-min sessions per week. Change (Δ) scores were entered into twin versus twin intraclass correlation analyses by group. Change in %body fat (r = 0.63, P = 0.05) was significantly correlated in the MZ, but not the DZ group (r = 0.31, P = 0.23). Change in FMD was also highly correlated in MZ (r = 0.74, P = 0.02) but not in the DZ group (r = 0.37, P = 0.18). Heritability of ΔFMD was estimated at 0.74. Exercise induced changes in FMD were similar within sets of monozygotic twins but not dizygotic twins. These data suggest that a significant portion of the arterial function response to exercise training may be genetically determined.

Heritability of arterial function, fitness, and physical activity in youth: a study of monozygotic and dizygotic twins

OBJECTIVES

To examine the role of heredity in determining flow-mediated dilation in young people by comparing conduit artery endothelial function in monozygotic and dizygotic twins. We also determined relationships between physical activity and fitness in each twin subset.

STUDY DESIGN

Flow-mediated dilation was assessed with high-resolution ultrasonography of the brachial artery in 22 twin pairs (11 monozygotic pairs 13.3 ± 1.6 years, 11 dizygotic pairs 13.6 ± 1.6 years). Fitness was assessed as peak oxygen uptake during an incremental treadmill test. Physical activity was measured with accelerometry. Twin versus twin intraclass correlations were performed for both groups.

RESULTS

Flow-mediated dilation was significantly correlated in monozygotic twins only (r = 0.60, P = .02). Heritability of flow-mediated dilation was estimated at 0.44. Total PA time (monozygotic r = 0.77, dizygotic r = 0.60, P < .05) and light physical activity time (monozygotic r = 0.67, dizygotic r = 0.63, P < .05) correlated significantly in both groups. The peak oxygen uptake (r = 0.84, P < .01) was correlated only in monozygotic twins.

CONCLUSION

Genetic factors appear to be responsible for a modest portion of the flow-mediated dilation response, suggesting that flow-mediated dilation can be influenced by environmental factors.

Exercise participation in adolescents and their parents: evidence for genetic and generation specific environmental effects

Individual differences in adolescent exercise behavior are to a large extent explained by shared environmental factors. The aim of this study was to explore to what extent this shared environment represents effects of cultural transmission of parents to their offspring, generation specific environmental effects or assortative mating. Survey data on leisure-time exercise behavior were available from 3,525 adolescent twins and their siblings (13-18 years) and 3,138 parents from 1,736 families registered at the Netherlands Twin Registry. Data were also available from 5,471 adult twins, their siblings and spouses similar in age to the parents. Exercise participation (No/Yes, using a cut-off criterion of 4 metabolic equivalents and 60 min weekly) was based on questions on type, frequency and duration of exercise. A model to analyze dichotomous data from twins, siblings and parents including differences in variance decomposition across sex and generation was developed. Data from adult twins and their spouses were used to investigate the causes of assortative mating (correlation between spouses = 0.41, due to phenotypic assortment). The heritability of exercise in the adult generation was estimated at 42%. The shared environment for exercise behavior in adolescents mainly represents generation specific shared environmental influences that seem somewhat more important in explaining familial clustering in girls than in boys (52 versus 41%). A small effect of vertical cultural transmission was found for boys only (3%). The remaining familial clustering for exercise behavior was explained by additive genetic factors (42% in boys and 36% in girls). Future studies on adolescent exercise behavior should focus on identification of the generation specific environmental factors.