Adaptation to a standardized training program and changes in fitness in a large, heterogeneous population: the HERITAGE Family Study

The Impact of Personalized versus Standardized Cardiorespiratory and Muscular Training on Health-Related Outcomes and Rate of Responders

Recent research has shown more favorable training adaptations for inactive adults when cardiorespiratory fitness (CRF) exercise is prescribed with the use of ventilatory thresholds compared to percentages of heart rate reserve (HRR). However, there is limited research on changes in health-related outcomes with the use of these CRF methods in combination with muscular fitness exercises. The objective of this study was to compare the effectiveness of two training programs for improving CRF, muscular fitness, and cardiometabolic risk factors. Inactive men and women (n=109, aged 49.3±15.5 years) were randomized to a non-exercise control group or one of two exercise training groups. The exercise training groups consisted of 13 weeks of structured exercise with progression using either CRF exercise prescribed with the use of ventilatory thresholds and functional training for muscular fitness (THRESH group) or HRR and traditional muscular fitness training (STND group). After the 13-week protocol, there were significant differences in body weight, body composition, systolic blood pressure, high-density lipoprotein cholesterol (HDL-c), VO2max, 5-repetition maximum (RM) bench press, and 5-RM leg press for both treatment groups compared to the control group after controlling for baseline values. However, the THRESH group had significantly more desirable outcomes for VO2max, 5-RM bench press, 5-RM leg press, body composition, and HDL-c when compared to both the STND and control group. Additionally, the proportion of individuals estimated as likely to respond above 3.5 mL·kg-1·min-1 in VO2max (i.e., the minimal clinically important difference) was 76.4%, 20.8%, and 0.13% for the THRESH, STND, and control groups, respectively. While both exercise programs elicited favorable health-related adaptations after 13 weeks, these results suggest that a personalized program with exercise prescribed based on ventilatory threshold and with the use of functional muscular fitness training may yield greater training adaptations.

Omics-driven investigation of the biology underlying intrinsic submaximal working capacity and its trainability

Submaximal exercise capacity is an indicator of cardiorespiratory fitness with clinical and public health implications. Submaximal exercise capacity and its response to exercise programs are characterized by heritability levels of about 40%. Using physical working capacity (power output) at a heart rate of 150 beats/min (PWC150) as an indicator of submaximal exercise capacity in subjects of the HERITAGE Family Study, we have undertaken multi-omics and in silico explorations of the underlying biology of PWC150 and its response to 20 wk of endurance training. Our goal was to illuminate the biological processes and identify panels of genes associated with human variability in intrinsic PWC150 (iPWC150) and its trainability (dPWC150). Our bioinformatics approach was based on a combination of genome-wide association, skeletal muscle gene expression, and plasma proteomics and metabolomics experiments. Genes, proteins, and metabolites showing significant associations with iPWC150 or dPWC150 were further queried for the enrichment of biological pathways. We compared genotype-phenotype associations of emerging candidate genes with reported functional consequences of gene knockouts in mouse models. We investigated the associations between DNA variants and multiple muscle and cardiovascular phenotypes measured in HERITAGE subjects. Two panels of prioritized genes of biological relevance to iPWC150 (13 genes) and dPWC150 (6 genes) were identified, supporting the hypothesis that genes and pathways associated with iPWC150 are different from those underlying dPWC150. Finally, the functions of these genes and pathways suggested that human variation in submaximal exercise capacity is mainly driven by skeletal muscle morphology and metabolism and red blood cell oxygen-carrying capacity.NEW & NOTEWORTHY Multi-omics and in silico explorations of the genes and underlying biology of submaximal exercise capacity and its response to 20 wk of endurance training were undertaken. Prioritized genes were identified: 13 genes for variation in submaximal exercise capacity in the sedentary state and 5 genes for the response level to endurance training, with no overlap between them. Genes and pathways associated with submaximal exercise capacity in the sedentary state are different from those underlying trainability.

Association between estimated cardiorespiratory fitness and breast cancer: a prospective cohort study

OBJECTIVE

To examine the association between cardiorespiratory fitness (CRF) and the risk of breast cancer in postmenopausal women.

METHODS

This study used data from 17 840 cancer-free postmenopausal women with a CRF assessment from the UK Biobank. High estimated CRF (eCRF) was categorised as being >80th percentile within 10-year age bands. Fine and Gray regression was used to examine the association between eCRF and breast cancer risk, accounting for both non-breast cancer diagnoses and all-cause mortality as competing risks. Age was used as the time scale. Several different models were produced, including those adjusting for known breast cancer risk factors, and stratified by measures of body fat (body mass index and per cent body fat).

RESULTS

Over a median follow-up of 11.0 years there were 529 cases of invasive breast cancer, 1623 cases of non-breast cancer disease and 241 deaths. With adjustment for breast cancer risk factors, high eCRF was associated with a 24% (subdistribution HR (SDHR) 0.76, 95% CI 0.60 to 0.97) lower risk of breast cancer. When stratified by measures of body fat, we found evidence of effect measure modification. Mainly, having high eCRF was only associated with a lower risk of breast cancer among those classified as having overweight/obesity (SDHR 0.33, 95% CI 0.11 to 1.01) or percentage body fat above the 1st quintile (SDHR 0.65, 95% CI 0.45 to 0.94).

CONCLUSION

Having higher CRF may be a protective factor against breast cancer in postmenopausal women but only for women with elevated body fat.

Energetic Cost of Walking and Brain Atrophy in Mid-to-Late Life

BACKGROUND

Higher energetic costs for mobility are associated with declining gait speed, and slow gait is linked to cognitive decline and Alzheimer's disease. However, the physiological underpinnings of gait and brain health have not been well explored. We examined the associations of the energetic cost of walking with brain volume in cognitively unimpaired adults from the Baltimore Longitudinal Study of Aging.

METHODS

We used brain magnetic resonance imaging (MRI) data from 850 participants (mean baseline age 66.3 ± 14.5 years), of whom 451 had longitudinal MRI data (2.8 ± 1.0 MRI scans over 4.0 ± 2.0 years). The energetic cost of walking was assessed as the average energy expended (V̇O2) during 2.5 minutes of customary-paced overground walking. Multivariable linear mixed-effects models examined the associations between baseline energetic cost of walking and regional brain volumes adjusting for covariates.

RESULTS

At baseline, higher energetic cost of walking was cross-sectionally associated with lower gray and white matter volumes within the frontal, parietal, and temporal lobes, as well as hippocampal, total brain, and larger ventricular volumes (all false-discovery rate [FDR] p < .05). A baseline energetic cost of walking × time interaction demonstrated that participants with higher energetic cost of walking had faster annual decline in hippocampal volume (FDR p = .02) and accelerated annual increase in ventricular volumes (FDR p = .02).

CONCLUSIONS

The energetic cost of walking is associated with gray and white matter volumes and subsequent hippocampal atrophy and ventricular enlargement. Collectively, these data suggest the energetic cost of walking may be an early marker of neurodegeneration that contributes to the gait brain connection.

The association of cardiorespiratory fitness and the risk of hypertension: a systematic review and dose-response meta-analysis

Established evidence has indicated a negative correlation between cardiorespiratory fitness (CRF) and hypertension risk. In this study, we performed a meta-analysis to investigate the categorical and dose-response relationship between CRF and hypertension risk and the effects of CRF changes on hypertension risk reduction. The PubMed, Web of Science, and Embase databases were searched for relevant studies. The summarized relative risk (RR) and 95% confidence interval (95% CI) were estimated using the DerSimonian and Laird random effect model, and the dose-response relationship between CRF and hypertension risk was characterized using generalized least-squares regression and restricted cubic splines. Nine cohorts describing 110,638 incident hypertension events among 1,618,067 participants were included in this study. Compared with the lowest category of CRF, the RR of hypertension was 0.63 (95% CI: 0.56-0.70) for the highest CRF category and 0.85 (95% CI: 0.80-0.91) for the moderate category of CRF. For a 1-metabolic equivalent increment in CRF, the pooled RR of hypertension was 0.92 (95% CI: 0.90-0.94) in the total population. The RR of hypertension was 0.71 (95% CI: 0.64-0.79) for participants with CRF increased compared with those whose CRF was decreased over time. In conclusion, our meta-analysis supports the widely held notion of a negative dose-dependent relationship between CRF and hypertension risk.

The HERITAGE Family Study: A Review of the Effects of Exercise Training on Cardiometabolic Health, with Insights into Molecular Transducers

The aim of the HERITAGE Family Study was to investigate individual differences in response to a standardized endurance exercise program, the role of familial aggregation, and the genetics of response levels of cardiorespiratory fitness and cardiovascular disease and diabetes risk factors. Here we summarize the findings and their potential implications for cardiometabolic health and cardiorespiratory fitness. It begins with overviews of background and planning, recruitment, testing and exercise program protocol, quality control measures, and other relevant organizational issues. A summary of findings is then provided on cardiorespiratory fitness, exercise hemodynamics, insulin and glucose metabolism, lipid and lipoprotein profiles, adiposity and abdominal visceral fat, blood levels of steroids and other hormones, markers of oxidative stress, skeletal muscle morphology and metabolic indicators, and resting metabolic rate. These summaries document the extent of the individual differences in response to a standardized and fully monitored endurance exercise program and document the importance of familial aggregation and heritability level for exercise response traits. Findings from genomic markers, muscle gene expression studies, and proteomic and metabolomics explorations are reviewed, along with lessons learned from a bioinformatics-driven analysis pipeline. The new opportunities being pursued in integrative -omics and physiology have extended considerably the expected life of HERITAGE and are being discussed in relation to the original conceptual model of the study.

Regular exercise and patterns of response across multiple cardiometabolic traits: the HERITAGE family study

OBJECTIVES

We investigated whether high responsiveness or low responsiveness to exercise training aggregates in the same individuals across seven cardiometabolic traits.

METHODS

A total of 564 adults (29.2% black, 53.7% female) from the HERITAGE family study completed a 20-week endurance training programme (at 55%-75% of participants' maximal oxygen uptake (VO₂max)) with VO₂max, per cent body fat, visceral adipose tissue, fasting levels of insulin, high-density lipoprotein cholesterol, small low-density lipoprotein particles and inflammatory marker GlycA measured before and after training. For each exercise response trait, we created ethnicity-specific, sex-specific and generation-specific quintiles. High responses were defined as those within the 20th percentile representing the favourable end of the response trait distribution, low responses were defined as the 20th percentile from the least favourable end, and the remaining were labelled as average responses.

RESULTS

Only one individual had universally high or low responses for all seven cardiometabolic traits. Almost half (49%) of the cohort had at least one high response and one low response across the seven traits. About 24% had at least one high response but no low responses, 24% had one or more low responses but no high responses, and 2.5% had average responses across all traits.

CONCLUSIONS

Interindividual variation in exercise responses was evident in all the traits we investigated, and responsiveness did not aggregate consistently in the same individuals. While adherence to an exercise prescription is known to produce health benefits, targeted risk factors may not improve.

Monitoring and adapting endurance training on the basis of heart rate variability monitored by wearable technologies: A systematic review with meta-analysis

OBJECTIVES

To systematically perform a meta-analysis of the scientific literature to determine whether the outcomes of endurance training based on heart rate variability (HRV) are more favorable than those of predefined training.

DESIGN

Systematic review and meta-analysis.

METHODS

PubMed and Web of Science were searched systematically in March of 2020 using keywords related to endurance, the ANS, and training. To compare the outcomes of HRV-guided and predefined training, Hedges' g effect size and associated 95% confidence intervals were calculated.

RESULTS

A total of 8 studies (198 participants) were identified comprising 9 interventions involving a variety of approaches. Compared to predefined training, most HRV-guided interventions included fewer moderate- and/or high-intensity training sessions. Fixed effects meta-analysis revealed a significant medium-sized positive effect of HRV-guided training on submaximal physiological parameters (g = 0.296, 95% CI 0.031 to 0.562, p = 0.028), but its effects on performance (g = 0.079, 95% CI -0.050 to 0.393, p = 0.597) and V̇O2peak (g = 0.171, 95% CI -0.213 to 0.371, p = 0.130) were small and not statistically significant. Moreover, with regards to performance, HRV-guided training was associated with fewer non-responders and more positive responders.

CONCLUSIONS

In comparison to predefined training, HRV-guided endurance training had a medium-sized effect on submaximal physiological parameters, but only a small and non-significant influence on performance and V̇O_2peak. There were fewer non-responders regarding performance with HRV-based training.

Association between Cardiorespiratory Fitness and Circulating Proteins in 50-Year-Old Swedish Men and Women: a Cross-Sectional Study

BACKGROUND AND AIMS

A strong cardiorespiratory fitness is suggested to have beneficial effects on cardiovascular risk; the exact mechanisms underlying the cardioprotective effects of fitness remain uncertain. Our aim was to investigate associations between cardiorespiratory fitness and multiple plasma proteins, in order to obtain insights about physiological pathways associated with the effects of exercise on cardiovascular health.

METHODS

In the Prospective investigation of Obesity, Energy and Metabolism (POEM) study (n=444 adults aged 50 years, 50% women), cardiorespiratory fitness was measured by a maximal exercise test on bicycle ergometer with gas exchange (VO₂peak) normalized for body lean mass (dual-energy X-ray absorptiometry (DXA)). We measured 82 cardiovascular proteins associated with cardiovascular pathology and inflammation in plasma samples with a proximity extension assay.

RESULTS

In sex-adjusted linear regression, VO₂peak was associated with 18 proteins after Bonferroni correction for multiple testing (p<0.0006). Following additional adjustment for fat mass (DXA), fasting glucose (mmol/L), low-density lipoprotein (LDL, mmol/L), smoking status, waist/hip ratio, blood pressure (mmHg), education level, and lpnr (lab sequence number), higher VO₂peak was significantly associated with lower levels of 6 proteins: fatty-acid binding protein-4 (FABP4), interleukin-6 (IL-6), leptin, cystatin-B (CSTB), interleukin-1 receptor antagonist (IL-1RA), and growth differentiation factor 15 (GDF-15), and higher levels of 3 proteins: galanin, kallikrein-6 (KLK6), and heparin-binding EGF-like growth factor (HB-EGF), at nominal p-values (p<0.05).

CONCLUSIONS

We identified multiple novel associations between cardiorespiratory fitness and plasma proteins involved in several atherosclerotic processes and key cellular mechanisms such as inflammation, energy homeostasis, and protease activity, which shed new light on how exercise asserts its beneficial effects on cardiovascular health. Our findings encourage additional studies in order to understand the underlying causal mechanisms for these associations.

Nonresponders of Physical Activity on Prescription (PAP) Can Increase Their Exercise Capacity with Enhanced Physiotherapist Support

Swedish physical activity on prescription (PAP) is an evidence-based method to promote physical activity. However, few studies have investigated the effect of Swedish PAP on physical fitness, in which better cardiorespiratory fitness is associated with lower risks of all-cause mortality and diagnose-specific mortality. Direct measures of cardiorespiratory fitness, usually expressed as maximal oxygen uptake, are difficult to obtain. Hence, exercise capacity can be assessed from a submaximal cycle ergometer test, taking the linear relationship between heart rate, work rate, and oxygen uptake into account. The aim of this study was to evaluate exercise capacity in the long term, following PAP treatment with enhanced physiotherapist support in a nonresponding patient cohort. In total, 98 patients (48 women) with insufficient physical activity levels, with at least one component of the metabolic syndrome and nonresponding to a previous six-month PAP treatment, were randomized to PAP treatment with enhanced support from a physiotherapist and additional exercise capacity tests during a two-year period. A significant increase in exercise capacity was observed for the whole cohort at two-year follow-up (7.6 W, p ≤ 0.001), with a medium effect size (r = 0.34). Females (7.3 W, p = 0.025), males (8.0 W, p = 0.018) and patients ≥58 years old (7.7 W, p = 0.002) improved significantly, whereas a nonsignificant increase was observed for patients <58 years old (7.6 W, p = 0.085). Patients with insufficient physical activity levels who did not respond to a previous six-month PAP treatment can improve their exercise capacity following PAP treatment with enhanced support from a physiotherapist during a two-year period. Future studies should include larger cohorts with a control group to ensure valid estimations of exercise capacity and PAP.

Predefined vs data-guided training prescription based on autonomic nervous system variation: A systematic review

Monitoring variations in the functioning of the autonomic nervous system may help personalize training of runners and provide more pronounced physiological adaptations and performance improvements. We systematically reviewed the scientific literature comparing physiological adaptations and/or improvements in performance following training based on responses of the autonomic nervous system (ie, changes in heart rate variability) and predefined training. PubMed, SPORTDiscus, and Web of Science were searched systematically in July 2019. Keywords related to endurance, running, autonomic nervous system, and training. Studies were included if they (a) involved interventions consisting predominantly of running training; (b) lasted at least 3 weeks; (c) reported pre- and post-intervention assessment of running performance and/or physiological parameters; (d) included an experimental group performing training adjusted continuously on the basis of alterations in HRV and a control group; and (e) involved healthy runners. Five studies involving six interventions and 166 participants fulfilled our inclusion criteria. Four HRV-based interventions reduced the amount of moderate- and/or high-intensity training significantly. In five interventions, improvements in performance parameters (3000 m, 5000 m, Loadmax, Tlim) were more pronounced following HRV-based training. Peak oxygen uptake ( V ˙ O 2 peak ) and submaximal running parameters (eg, LT1, LT2) improved following both HRV-based and predefined training, with no clear difference in the extent of improvement in V ˙ O 2 peak . Submaximal running parameters tended to improve more following HRV-based training. Research findings to date have been limited and inconsistent. Both HRV-based and predefined training improve running performance and certain submaximal physiological adaptations, with effects of the former training tending to be greater.

Fitness, independent of physical activity is associated with cerebral blood flow in adults at risk for Alzheimer's disease

Patterns of decreased resting cerebral blood flow (CBF) within the inferior temporal gyri, angular gyri, and posterior cingulate are a feature of aging and Alzheimer's disease (AD) and have shown to be predictive of cognitive decline among older adults. Fitness and physical activity are both associated with many indices of brain health and may positively influence CBF, however, the majority of research to date has examined these measures in isolation, leaving the potential independent associations unknown. The purpose of this study was to determine the unique contributions of fitness and physical activity when predicting CBF in cognitively healthy adults at risk for AD. One hundred participants (63% female) from the Wisconsin Registry for Alzheimer's Prevention underwent a maximal exercise test, physical activity monitoring, and a 3-D arterial spin labeling magnetic resonance imaging scan. For the entire sample, fitness was significantly associated with CBF while accounting for physical activity, age, gender, APOE ε4, family history of AD, education, and handedness (p = .026). Further, fitness explained significantly more variance than the combined effect of the covariates on CBF (R2 change = .059; p = .047). These results appear to be gender dependent, our data suggest fitness level, independent of physical activity, is associated with greater CBF in regions that are known to decline with age and AD for female (p = .011), but not male participants.

Adaptations to exercise in compensators and noncompensators in the E-MECHANIC Trial

Rating of perceived exertion (RPE) and respiratory exchange ratio (RER) have previously been associated with acute exercise compensation. This study examined adaptations in the RPE and RER with long-term exercise training in individuals who did (noncompensators) and did not (compensators) lose the expected amount of weight. Participants (n = 110, 71.8% women, means ± SD; age 49 ± 12 yr) completed 24 wk of supervised exercise training at 65-85% V̇o_2peak to achieve a prescribed dose of 8 kcal·kg body wt^-1·wk^-1 (8 KKW) or 20 KKW. Participants were categorized as noncompensators (n = 55) or compensators (n = 55) based on the percent of expected weight loss (%EWL) achieved. Changes in RPE and RER during exercise over time (baseline, week 12, week 24) were compared by weight compensation category. Individual %EWL in relation to RPE, RER, and training intensity (%V̇o_2peak) was evaluated over the same time period. RPE and RER for a given workload decreased from baseline to week 12 and stabilized through week 24, regardless of weight compensation (time P < 0.0001). Noncompensators had a higher RPE relative to heart rate, which was partly explained by higher %V̇o_2peak. RPE and %V̇o_2peak both positively predicted %EWL, independent of age, sex, and exercise dose. Training intensity and RPE were positively associated with weight loss on the individual level, warranting further investigation into self-selection in exercise-based programs. Understanding individual heterogeneity in training intensity and behavioral responses may improve future weight management efforts that involve exercise.NEW & NOTEWORTHY In sedentary individuals with overweight and obesity, achievement of expected weight loss from long-term exercise training was associated with individual adaptations in perceived exertion. Contrary to our hypothesis, those with higher relative perceived exertion achieved a larger proportion of their expected weight loss, which was partly explained by a higher self-selected exercise training intensity.

Prevention of Long-term Adverse Health Outcomes With Cardiorespiratory Fitness and Physical Activity in Childhood Acute Lymphoblastic Leukemia Survivors

BACKGROUND

Most childhood acute lymphoblastic leukemia (ALL) survivors develop chronic treatment-related adverse effects several years after the end of therapy. A regular practice of physical activity and a good cardiorespiratory fitness have the potential to reduce the risk of chronic disease and improve quality of life. The aim of this study was to evaluate in a cohort of ALL survivors, the association between a good cardiorespiratory fitness or the respect of physical activity guidelines and major long-term health outcomes.

METHODS

In total, 247 ALL survivors underwent a cardiopulmonary exercise test, completed a physical activity questionnaire and a battery of clinical examinations. We calculated the odds ratio to obtain the preventive fraction (PF) to evaluate the effects of the cardiorespiratory fitness and physical activity levels on health outcomes (ie, obesity, metabolic health, cardiac health, cognitive health and mood, bone health).

RESULTS

Despite their young age, 88% of the participants presented at least one adverse health outcome, and 46% presented ≥3. Their cardiorespiratory fitness was also lower than expected with a median VO2 peak reaching 84% of the predicted value. In the analyses using cardiorespiratory fitness, statistically significant PFs were observed for obesity (0.30), low-high-density lipoprotein-cholesterol (0.21) and depression (0.26). In the physical activity level analyses, statistically significant PFs were observed for obesity, depression, and low bone mineral density, with a PF of 0.55, 0.81, and 0.60, respectively.

CONCLUSIONS

Our results indicate that a good cardiorespiratory fitness and physical activity level induced a preventive action for most health outcomes studied and was associated with a lower late adverse effects prevalence in ALL survivors.

Exploring the underlying biology of intrinsic cardiorespiratory fitness through integrative analysis of genomic variants and muscle gene expression profiling

Intrinsic cardiorespiratory fitness (CRF) is defined as the level of CRF in the sedentary state. There are large individual differences in intrinsic CRF among sedentary adults. The physiology of variability in CRF has received much attention, but little is known about the genetic and molecular mechanisms that impact intrinsic CRF. These issues were explored in the present study by interrogating intrinsic CRF-associated DNA sequence variation and skeletal muscle gene expression data from the HERITAGE Family Study through an integrative bioinformatics guided approach. A combined analytic strategy involving genetic association, pathway enrichment, tissue-specific network structure, cis-regulatory genome effects, and expression quantitative trait loci was used to select and rank genes through a variation-adjusted weighted ranking scheme. Prioritized genes were further interrogated for corroborative evidence from knockout mouse phenotypes and relevant physiological traits from the HERITAGE cohort. The mean intrinsic V̇o2max was 33.1 ml O2·kg-1·min-1 (SD = 8.8) for the sample of 493 sedentary adults. Suggestive evidence was found for gene loci related to cardiovascular physiology (ATE1, CASQ2, NOTO, and SGCG), hematopoiesis (PICALM, SSB, CA9, and CASQ2), skeletal muscle phenotypes (SGCG, DMRT2, ADARB1, and CASQ2), and metabolism (ATE1, PICALM, RAB11FIP5, GBA2, SGCG, PRADC1, ARL6IP5, and CASQ2). Supportive evidence for a role of several of these loci was uncovered via association between DNA variants and muscle gene expression levels with exercise cardiovascular and muscle physiological traits. This initial effort to define the underlying molecular substrates of intrinsic CRF warrants further studies based on appropriate cohorts and study designs, complemented by functional investigations. NEW & NOTEWORTHY Intrinsic cardiorespiratory fitness (CRF) is measured in the sedentary state and is highly variable among sedentary adults. The physiology of variability in intrinsic cardiorespiratory fitness has received much attention, but little is known about the genetic and molecular mechanisms that impact intrinsic CRF. These issues were explored computationally in the present study, with further corroborative evidence obtained from analysis of phenotype data from knockout mouse models and human cardiovascular and skeletal muscle measurements.

Integrated Framework of Load Monitoring by a Combination of Smartphone Applications, Wearables and Point-of-Care Testing Provides Feedback that Allows Individual Responsive Adjustments to Activities of Daily Living

Athletes schedule their training and recovery in periods, often utilizing a pre-defined strategy. To avoid underperformance and/or compromised health, the external load during training should take into account the individual's physiological and perceptual responses. No single variable provides an adequate basis for planning, but continuous monitoring of a combination of several indicators of internal and external load during training, recovery and off-training as well may allow individual responsive adjustments of a training program in an effective manner. From a practical perspective, including that of coaches, monitoring of potential changes in health and performance should ideally be valid, reliable and sensitive, as well as time-efficient, easily applicable, non-fatiguing and as non-invasive as possible. Accordingly, smartphone applications, wearable sensors and point-of-care testing appear to offer a suitable monitoring framework allowing responsive adjustments to exercise prescription. Here, we outline 24-h monitoring of selected parameters by these technologies that (i) allows responsive adjustments of exercise programs, (ii) enhances performance and/or (iii) reduces the risk for overuse, injury and/or illness.

Oxygen uptake at aerobic threshold is inversely associated with fatal cardiovascular and all-cause mortality events

PURPOSE

We aimed to assess the associations of oxygen uptake at aerobic threshold (VO₂ at AT) with cardiovascular and all-cause mortality.

DESIGN

VO₂ at AT was assessed in 1663 middle-aged men in a cohort study. Hazard ratios (HRs) were calculated for sudden cardiac death (SCD), fatal coronary heart disease (CHD) and cardiovascular disease (CVD) and all-cause mortality.

RESULTS

During a median follow-up of 25.6 years, 138 SCDs, 209 fatal CHDs, 333 fatal CVDs and 719 all-cause mortality events occurred. On adjustment for established risk factors, the HRs (95% CIs) for SCD, fatal CHD, fatal CVD and all-cause mortality were 0.48 (0.28-0.82), 0.48 (0.31-0.74), 0.57 (0.41-0.79) and 0.66 (0.53-0.82), respectively comparing extreme quartiles of VO₂ at AT. On further adjustment for peak VO₂, the HRs were 0.87 (0.48-1.56), 0.83 (0.52-1.34), 0.91 (0.63-1.30) and 0.88 (0.69-1.12), respectively. Addition of VO₂ at AT to a standard CVD mortality risk prediction model was associated with a C-index change of 0.0085 (95% CI: -0.0002-0.0172; p = .05) at 25 years.

CONCLUSIONS

VO₂ at AT is inversely associated with cardiovascular and all-cause mortality events, but the associations are partly dependent on peak VO₂. VO₂ at AT may improve the prediction of the long-term risk for CVD mortality. KEY MESSAGES Oxygen uptake at aerobic threshold (VO₂ at AT), a cardiopulmonary exercise testing parameter, may be a useful prognostic tool for adverse clinical outcomes in the general population. In a population-based prospective cohort study of men, VO₂ at AT was inversely associated with cardiovascular and all-cause mortality events and improved the prediction of cardiovascular mortality. In populations who cannot achieve maximal VO₂, VO₂ at AT may serve as a useful prognostic tool; however, further studies are warranted.

The Beneficial Effects of Physical Activity: Is It Down to Your Genes? A Systematic Review and Meta-Analysis of Twin and Family Studies

Background

There is evidence for considerable heterogeneity in the responsiveness to regular physical activity (PA) which might reflect the influence of genetic factors. The aim of this systematic review was to assess whether the response to a PA intervention for measures of body composition and cardiorespiratory fitness is (i) correlated within twin pairs and/or families and (ii) more correlated in monozygotic twins (MZ) compared to dizygotic twins (DZ), which would be consistent with genetic effects.

Methods

We performed electronic database searches, combining key words relating to “physical activity” and “genetics”, in MEDLINE, CINAHL, EMBASE, SPORTS Discuss, AMED, PsycINFO, WEB OF SCIENCE, and SCOPUS from the earliest records to March 2016.

Twin and family studies were included if they assessed body composition and/or cardiorespiratory fitness following a PA intervention, and provided a heritability estimate, maximal heritability estimate, or within MZ twin pair correlation (r_MZ).

Data on heritability (twin studies), maximal heritability (family studies), and the r_MZ were extracted from included studies, although heritability estimates were not reported as small sample sizes made them uninformative.

Results

After screening 224 full texts, nine twin and five family studies were included in this review. The pooled r_MZ in response to PA was significant for body mass index (r_MZ = 0.69, n = 58), fat mass (r_MZ = 0.58, n = 48), body fat percentage (r_MZ = 0.55, n = 72), waist circumference (r_MZ = 0.50, n = 27), and VO₂max (r_MZ = 0.39, n = 48), where “n” represents the total number of twin pairs from all studies. Maximal heritability estimates ranged from 0–21% for measures of body composition, and 22–57% for cardiorespiratory fitness.

Twin studies differed in sample age, baseline values, and PA intervention, although the exclusion of any one study did not affect the results.

Conclusions

Shared familial factors, including genetics, are likely to be a significant contributor to the response of body composition and cardiorespiratory fitness following PA.

Genetic factors may explain individual variation in the response to PA.

Trial Registrations

PROSPERO Registration No CRD42015020056.

Electronic supplementary material

The online version of this article (doi:10.1186/s40798-016-0073-9) contains supplementary material, which is available to authorized users.

Aerobic exercise increases resistance to oxidative stress in sedentary older middle-aged adults. A pilot study

Older individuals who exercise regularly exhibit greater resistance to oxidative stress than their sedentary peers, suggesting that exercise can modify age-associated loss of resistance to oxidative stress. However, we recently demonstrated that a single bout of exercise confers protection against a subsequent oxidative challenge in young, but not older adults. We therefore hypothesized that repeated bouts of exercise would be needed to increase resistance to an oxidative challenge in sedentary older middle-aged adults. Sedentary older middle-aged men and women (50-63 years, n = 11) participated in an 8-week exercise intervention. Maximal oxygen consumption was measured before and after the intervention. The exercise intervention consisted of three sessions per week, for 45 min at an intensity corresponding to 70-85 % maximal heart rate (HR_max). Resistance to oxidative stress was measured by F₂-isoprostane response to a forearm ischemia/reperfusion (I/R) trial. Each participant underwent the I/R trial before and after the exercise intervention. The intervention elicited a significant increase in maximal oxygen consumption (VO_2max) (P < 0.0001). Baseline levels of F₂-isoprostanes pre- and post-intervention did not differ, but the F₂-isoprostane response to the I/R trial was significantly lower following the exercise intervention (time-by-trial interaction, P = 0.043). Individual improvements in aerobic fitness were associated with greater improvements in the F₂-isoprostane response (r = -0.761, P = 0.011), further supporting the role of aerobic fitness in resistance to oxidative stress. These data demonstrate that regular exercise with improved fitness leads to increased resistance to oxidative stress in older middle-aged adults and that this measure is modifiable in previously sedentary individuals.

Importance of Assessing Cardiorespiratory Fitness in Clinical Practice: A Case for Fitness as a Clinical Vital Sign: A Scientific Statement From the American Heart Association

Mounting evidence has firmly established that low levels of cardiorespiratory fitness (CRF) are associated with a high risk of cardiovascular disease, all-cause mortality, and mortality rates attributable to various cancers. A growing body of epidemiological and clinical evidence demonstrates not only that CRF is a potentially stronger predictor of mortality than established risk factors such as smoking, hypertension, high cholesterol, and type 2 diabetes mellitus, but that the addition of CRF to traditional risk factors significantly improves the reclassification of risk for adverse outcomes. The purpose of this statement is to review current knowledge related to the association between CRF and health outcomes, increase awareness of the added value of CRF to improve risk prediction, and suggest future directions in research. Although the statement is not intended to be a comprehensive review, critical references that address important advances in the field are highlighted. The underlying premise of this statement is that the addition of CRF for risk classification presents health professionals with unique opportunities to improve patient management and to encourage lifestyle-based strategies designed to reduce cardiovascular risk. These opportunities must be realized to optimize the prevention and treatment of cardiovascular disease and hence meet the American Heart Association's 2020 goals.

Beneficial effects of dark chocolate on exercise capacity in sedentary subjects: underlying mechanisms. A double blind, randomized, placebo controlled trial

In heart failure patients the consumption of (-)-epicatechin ((-)-Epi)-rich cocoa can restore skeletal muscle (SkM) mitochondrial structure and decrease biomarkers of oxidative stress. However, nothing is known about its effects on exercise capacity and underlying mechanisms in normal, sedentary subjects. Twenty normal, sedentary subjects (∼50 years old) were randomized to placebo or dark chocolate (DC) groups and consumed 20 g of the products for 3 months. Subjects underwent before and after treatment, bicycle ergometry to assess VO2 max and work, SkM biopsy to assess changes in mitochondrial density, function and oxidative stress and blood sampling to assess metabolic endpoints. Seventeen subjects completed the trial. In the DC group (n = 9), VO2 max increased (17% increase, p = 0.056) as well as maximum work (watts) achieved (p = 0.026) with no changes with placebo (n = 8). The DC group evidenced increases in HDL levels (p = 0.005) and decreased triglycerides (p = 0.07). With DC, SkM evidenced significant increases in protein levels for LKB1, AMPK and PGC1α and in their active forms (phosphorylated AMPK and LKB1) as well as in citrate synthase activity while no changes were observed in mitochondrial density. With DC, significant increases in SkM reduced glutathione levels and decreases in protein carbonylation were observed. Improvements in maximum work achieved and VO2 max may be due to DC activation of upstream control systems and enhancement of SkM mitochondria efficiency. Larger clinical studies are warranted to confirm these observations.

Less Sitting, More Physical Activity, or Higher Fitness?

Epidemiological studies have found that time spent in sedentary behaviors, levels of physical activity, and cardiorespiratory fitness are all associated with mortality rates. They are also related to the risks of obesity, type 2 diabetes mellitus, hypertension, cardiovascular disease, aging-associated frailty, and cancer. The evidence is such that the National Institutes of Health recently launched a new Common Fund initiative aimed at identifying the molecular transducers of adaptation to physical activity in various tissues and organs. It has been estimated that 9.4% of all 57 million deaths in the world in 2008 could be attributed to physical inactivity, which translates into more than 5 million deaths worldwide. Physical inactivity has a deleterious effect that is comparable to smoking and obesity. Importantly, this global estimate relates to levels of physical activity and does not take into account sedentary behavior and cardiorespiratory fitness. Currently, there are national and international guidelines for physical activity level that are highly concordant. The weekly recommendations include 150 minutes of moderate-intensity activity, 75 minutes of vigorous-intensity activity, or some combination of moderate and vigorous activity with 2 days of resistance exercise. However, these guidelines offer no recommendations regarding sedentary time or goals for cardiorespiratory fitness levels. It will be increasingly important for disease prevention, successful aging, and reduction of premature mortality to broaden the focus of the public health message to include not only more physical activity but also less sitting and higher cardiorespiratory fitness. We briefly review the evidence and discuss key issues to be addressed to make this approach a reality.

Is a threshold-based model a superior method to the relative percent concept for establishing individual exercise intensity? a randomized controlled trial

BACKGROUND

Exercise intensity is arguably the most critical component of the exercise prescription model. It has been suggested that a threshold based model for establishing exercise intensity might better identify the lowest effective training stimulus for all individuals with varying fitness levels; however, experimental evidence is lacking. The purpose of this study was to compare the effectiveness of two exercise training programs for improving cardiorespiratory fitness: threshold based model vs. relative percent concept (i.e., % heart rate reserve - HRR).

METHODS

Apparently healthy, but sedentary men and women (n = 42) were randomized to a non-exercise control group or one of two exercise training groups. Exercise training was performed 30 min/day on 5 days/week for 12weeks according to one of two exercise intensity regimens: 1) a relative percent method was used in which intensity was prescribed according to percentages of heart rate reserve (HRR group), or 2) a threshold based method (ACE-3ZM) was used in which intensity was prescribed according to the first ventilatory threshold (VT1) and second ventilatory threshold (VT2).

RESULTS

Thirty-six men and women completed the study. After 12weeks, VO2max increased significantly (p < 0.05 vs. controls) in both HRR (1.76 ± 1.93 mL/kg/min) and ACE-3ZM (3.93 ± 0.96 mL/kg/min) groups. Repeated measures ANOVA identified a significant interaction between exercise intensity method and change in VO2max values (F = 9.06, p < 0.05) indicating that VO2max responded differently to the method of exercise intensity prescription. In the HRR group 41.7 % (5/12) of individuals experienced a favorable change in relative VO2max (Δ > 5.9 %) and were categorized as responders. Alternatively, exercise training in the ACE-3ZM group elicited a positive improvement in relative VO2max (Δ > 5.9 %) in 100 % (12/12) of the individuals.

CONCLUSIONS

A threshold based exercise intensity prescription: 1). elicited significantly (p < 0.05) greater improvements in VO2max, and 2). attenuated the individual variation in VO2max training responses when compared to relative percent exercise training. These novel findings are encouraging and provide important preliminary data for the design of individualized exercise prescriptions that will enhance training efficacy and limit training unresponsiveness.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: ID NCT02351713 Registered 30 January 2015.

High responders and low responders: factors associated with individual variation in response to standardized training

The response to an exercise intervention is often described in general terms, with the assumption that the group average represents a typical response for most individuals. In reality, however, it is more common for individuals to show a wide range of responses to an intervention rather than a similar response. This phenomenon of 'high responders' and 'low responders' following a standardized training intervention may provide helpful insights into mechanisms of training adaptation and methods of training prescription. Therefore, the aim of this review was to discuss factors associated with inter-individual variation in response to standardized, endurance-type training. It is well-known that genetic influences make an important contribution to individual variation in certain training responses. The association between genotype and training response has often been supported using heritability estimates; however, recent studies have been able to link variation in some training responses to specific single nucleotide polymorphisms. It would appear that hereditary influences are often expressed through hereditary influences on the pre-training phenotype, with some parameters showing a hereditary influence in the pre-training phenotype but not in the subsequent training response. In most cases, the pre-training phenotype appears to predict only a small amount of variation in the subsequent training response of that phenotype. However, the relationship between pre-training autonomic activity and subsequent maximal oxygen uptake response appears to show relatively stronger predictive potential. Individual variation in response to standardized training that cannot be explained by genetic influences may be related to the characteristics of the training program or lifestyle factors. Although standardized programs usually involve training prescribed by relative intensity and duration, some methods of relative exercise intensity prescription may be more successful in creating an equivalent homeostatic stress between individuals than other methods. Individual variation in the homeostatic stress associated with each training session would result in individuals experiencing a different exercise 'stimulus' and contribute to individual variation in the adaptive responses incurred over the course of the training program. Furthermore, recovery between the sessions of a standardized training program may vary amongst individuals due to factors such as training status, sleep, psychological stress, and habitual physical activity. If there is an imbalance between overall stress and recovery, some individuals may develop fatigue and even maladaptation, contributing to variation in pre-post training responses. There is some evidence that training response can be modulated by the timing and composition of dietary intake, and hence nutritional factors could also potentially contribute to individual variation in training responses. Finally, a certain amount of individual variation in responses may also be attributed to measurement error, a factor that should be accounted for wherever possible in future studies. In conclusion, there are several factors that could contribute to individual variation in response to standardized training. However, more studies are required to help clarify and quantify the role of these factors. Future studies addressing such topics may aid in the early prediction of high or low training responses and provide further insight into the mechanisms of training adaptation.

Physical activity versus cardiorespiratory fitness: two (partly) distinct components of cardiovascular health?

Physical activity (PA) and cardiorespiratory fitness (CRF) both have inverse relationships to cardiovascular (CV) morbidity and mortality. Recent position papers and guidelines have identified the important role of both of these factors in CV health. The benefits of PA and CRF in the prevention of CV disease and risk factors are reviewed. In addition, assessment methodology and utilization in the research and clinical arenas are discussed. Finally, the benefits, methodology, and utilization are compared and contrasted to better understand the two (partly) distinct components and their impact on CV health.

Personalized preventive medicine: genetics and the response to regular exercise in preventive interventions

Regular exercise and a physically active lifestyle have favorable effects on health. Several issues related to this theme are addressed in this report. A comment on the requirements of personalized exercise medicine and in-depth biological profiling along with the opportunities that they offer is presented. This is followed by a brief overview of the evidence for the contributions of genetic differences to the ability to benefit from regular exercise. Subsequently, studies showing that mutations in TP53 influence exercise capacity in mice and humans are succinctly described. The evidence for effects of exercise on endothelial function in health and disease also is covered. Finally, changes in cardiac and skeletal muscle in response to exercise and their implications for patients with cardiac disease are summarized. Innovative research strategies are needed to define the molecular mechanisms involved in adaptation to exercise and to translate them into useful clinical and public health applications.

Physical activity, genes for physical fitness, and risk of coronary heart disease

PURPOSE

Both physical activity and physical fitness are associated with decreased coronary heart disease (CHD) risk. Our objective was to determine whether genes associated with physical fitness modify the association between physical activity and CHD.

METHODS

We conducted a prospective cohort study among 23,016 initially healthy women in the Women's Genome Health Study. Leisure time physical activity was reported at entry and during follow-up. A total of 58 single nucleotide polymorphisms associated with physical fitness were identified from published literature and summed to create four separate genetic scores related to phenotypes of endurance, muscle strength, V˙O2max, and overall fitness.

RESULTS

During a median of 14.4 yr, 320 incident CHD events occurred. Increased physical activity was associated with lower CHD risk in multivariable-adjusted models (P = 0.0008). Independent of physical activity, only muscle strength genetic score was inversely associated with CHD risk (P = 0.05). There was no evidence that the inverse relation between physical activity and CHD was modified by any of the genetic scores for physical fitness. For overall fitness genetic score, the hazard ratio (HR) per 500 kcal·wk of physical activity was 0.85 (95% confidence interval [CI] = 0.72-1.00) in the highest quartile of genetic score and 0.79 (95% CI = 0.67-0.92) in the lowest quartile (P, interaction = 0.50). For V˙O2max genetic score, the HR was 0.86 (95% CI = 0.72-1.02) and 0.84 (95% CI = 0.72-0.98), respectively (P, interaction = 0.59).

CONCLUSIONS

In this large prospective cohort of women, genes associated with physical fitness did not modify the inverse association between physical activity and CHD risk.

Objectively measured physical activity, cardiorespiratory fitness and cardiometabolic risk factors in the Health Survey for England

OBJECTIVES

The study aims to test the hypothesis that physical activity (PA) and cardiorespiratory fitness (CRF) are associated with cardiometabolic risk factors; and to test the hypothesis that CRF modifies (changes the direction and/or strength of) the associations between PA and cardiometabolic risk factors.

METHODS

PA and CRF were objectively measured in the 2008 Health Survey for England and the present study included 536 adults who completed at least 4 min of the eight-minute sub-maximal step test and wore an accelerometer for at least 10 h on at least four days. Linear regression models were fitted to examine the relationship between PA and cardiometabolic risk factors and between CRF and cardiometabolic risk factors. A test of interaction was performed to examine whether CRF modifies the associations between PA and cardiometabolic risk factors.

RESULTS

PA and CRF were associated with HDL cholesterol, the ratio of total to HDL cholesterol, glycated haemoglobin and BMI after adjustment for potential confounders. There was little evidence that CRF changed the direction or strength of associations between PA and cardiometabolic risk factors.

CONCLUSIONS

PA and CRF are associated with cardiometabolic risk factors. A larger sample is required to determine if CRF modifies associations between PA and cardiometabolic risk factors.

Integrative pathway analysis of a genome-wide association study of (V)O(2max) response to exercise training

We previously reported the findings from a genome-wide association study of the response of maximal oxygen uptake (Vo2max) to an exercise program. Here we follow up on these results to generate hypotheses on genes, pathways, and systems involved in the ability to respond to exercise training. A systems biology approach can help us better establish a comprehensive physiological description of what underlies Vo2maxtrainability. The primary material for this exploration was the individual single-nucleotide polymorphism (SNP), SNP-gene mapping, and statistical significance levels. We aimed to generate novel hypotheses through analyses that go beyond statistical association of single-locus markers. This was accomplished through three complementary approaches: 1) building de novo evidence of gene candidacy through informatics-driven literature mining; 2) aggregating evidence from statistical associations to link variant enrichment in biological pathways to Vo2max trainability; and 3) predicting possible consequences of variants residing in the pathways of interest. We started with candidate gene prioritization followed by pathway analysis focused on overrepresentation analysis and gene set enrichment analysis. Subsequently, leads were followed using in silico analysis of predicted SNP functions. Pathways related to cellular energetics (pantothenate and CoA biosynthesis; PPAR signaling) and immune functions (complement and coagulation cascades) had the highest levels of SNP burden. In particular, long-chain fatty acid transport and fatty acid oxidation genes and sequence variants were found to influence differences in Vo2max trainability. Together, these methods allow for the hypothesis-driven ranking and prioritization of genes and pathways for future experimental testing and validation.

Heritability of submaximal exercise heart rate response to exercise training is accounted for by nine SNPs

Endurance training-induced changes in hemodynamic traits are heritable. However, few genes associated with heart rate training responses have been identified. The purpose of our study was to perform a genome-wide association study to uncover DNA sequence variants associated with submaximal exercise heart rate training responses in the HERITAGE Family Study. Heart rate was measured during steady-state exercise at 50 W (HR50) on 2 separate days before and after a 20-wk endurance training program in 483 white subjects from 99 families. Illumina HumanCNV370-Quad v3.0 BeadChips were genotyped using the Illumina BeadStation 500GX platform. After quality control procedures, 320,000 single-nucleotide polymorphisms (SNPs) were available for the genome-wide association study analyses, which were performed using the MERLIN software package (single-SNP analyses and conditional heritability tests) and standard regression models (multivariate analyses). The strongest associations for HR50 training response adjusted for age, sex, body mass index, and baseline HR50 were detected with SNPs at the YWHAQ locus on chromosome 2p25 (P = 8.1 × 10(-7)), the RBPMS locus on chromosome 8p12 (P = 3.8 × 10(-6)), and the CREB1 locus on chromosome 2q34 (P = 1.6 × 10(-5)). In addition, 37 other SNPs showed P values <9.9 × 10(-5). After removal of redundant SNPs, the 10 most significant SNPs explained 35.9% of the ΔHR50 variance in a multivariate regression model. Conditional heritability tests showed that nine of these SNPs (all intragenic) accounted for 100% of the ΔHR50 heritability. Our results indicate that SNPs in nine genes related to cardiomyocyte and neuronal functions, as well as cardiac memory formation, fully account for the heritability of the submaximal heart rate training response.

Fine mapping of a QTL on chromosome 13 for submaximal exercise capacity training response: the HERITAGE Family Study

Although regular exercise improves submaximal aerobic capacity, there is large variability in its response to exercise training. While this variation is thought to be partly due to genetic differences, relatively little is known about the causal genes. Submaximal aerobic capacity traits in the current report include the responses of oxygen consumption (ΔVO(2)60), power output (ΔWORK60), and cardiac output (ΔQ60) at 60% of VO2max to a standardized 20-week endurance exercise training program. Genome-wide linkage analysis in 475 HERITAGE Family Study Caucasians identified a locus on chromosome 13q for ΔVO(2)60 (LOD = 3.11). Follow-up fine mapping involved a dense marker panel of over 1,800 single-nucleotide polymorphisms (SNPs) in a 7.9-Mb region (21.1-29.1 Mb from p-terminus). Single-SNP analyses found 14 SNPs moderately associated with both ΔVO(2)60 at P ≤ 0.005 and the correlated traits of ΔWORK60 and ΔQ60 at P < 0.05. Haplotype analyses provided several strong signals (P < 1.0 × 10(-5)) for ΔVO(2)60. Overall, association analyses narrowed the target region and included potential biological candidate genes (MIPEP and SGCG). Consistent with maximal heritability estimates of 23%, up to 20% of the phenotypic variance in ΔVO(2)60 was accounted for by these SNPs. These results implicate candidate genes on chromosome 13q12 for the ability to improve submaximal exercise capacity in response to regular exercise. Submaximal exercise at 60% of maximal capacity is an exercise intensity that falls well within the range recommended in the Physical Activity Guidelines for Americans and thus has potential public health relevance.

Influence of electrically assisted cycling on physiological parameters in untrained subjects

Electrically assisted bicycles (EAB) as a form of transport not only offer the potential to reduce energy use and environmental impact but could also be an effective way of encouraging active living. The purpose of this study is to assess the influence of physical active commuting to work using an EAB, on physiological parameters in 20 untrained men and women. Tests were performed at three different time points over a 10-week period, including four weeks of passive (control period) and six weeks of active commuting (intervention period). ANOVA for repeated measures was used to test differences between the testing series for the most important physiological parameters: Pmax·kg(-1), V˙O2peak·kg(-1), fixed blood lactate concentration (2, 4 mmol·l(-1)). The subjects performed over a 6-week period a mean total cycling distance of 405.1±156.0 km with a weekly frequency of 4.1±1.7 days·week(-1) for men and 246.0±116.3 km with a frequency of 2.9±1.0 days·week(-1) for women. Pmax·kg(-1) significantly increased in men and women after 6 weeks of active commuting. Power output at 2 mmol·l(-1) significantly increased in women (P=0.001) but not in men (P=0.0604). Power output at 4 mmol·l(-1) significantly increased for men and women. V˙O2peak·kg(-1) did not differ. With respect to the study limitations, it is concluded that cycling to work on an EAB was effective in increasing the maximal power output and power output at 4 mmol·l(-1) in these untrained subjects. Cycling on an EAB seems to be a promising tool as a health enhancing physical activity, for those who will benefit the most in terms of health related fitness, namely the physically inactive, unfit and older people.

Genomic predictors of the maximal O₂ uptake response to standardized exercise training programs

Low cardiorespiratory fitness is a powerful predictor of morbidity and cardiovascular mortality. In 473 sedentary adults, all whites, from 99 families of the Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study, the heritability of gains in maximal O(2) uptake (VO(2max)) after exposure to a standardized 20-wk exercise program was estimated at 47%. A genome-wide association study based on 324,611 single-nucleotide polymorphisms (SNPs) was undertaken to identify SNPs associated with improvements in VO(2max) Based on single-SNP analysis, 39 SNPs were associated with the gains with P < 1.5 × 10(-4). Stepwise multiple regression analysis of the 39 SNPs identified a panel of 21 SNPs that accounted for 49% of the variance in VO(2max) trainability. Subjects who carried ≤9 favorable alleles at these 21 SNPs improved their VO(2max) by 221 ml/min, whereas those who carried ≥19 of these alleles gained, on average, 604 ml/min. The strongest association was with rs6552828, located in the acyl-CoA synthase long-chain member 1 (ACSL1) gene, which accounted by itself for ~6% of the training response of VO(2max). The genes nearest to the SNPs that were the strongest predictors were PR domain-containing 1 with ZNF domain (PRDM1); glutamate receptor, ionotropic, N-methyl-D-aspartate 3A (GRIN3A); K(+) channel, voltage gated, subfamily H, member 8 (KCNH8); and zinc finger protein of the cerebellum 4 (ZIC4). The association with the SNP nearest to ZIC4 was replicated in 40- to 65-yr-old, sedentary, overweight, and dyslipidemic subjects trained in Studies of a Targeted Risk Reduction Intervention Through Defined Exercise (STRRIDE; n = 183). Two SNPs were replicated in sedentary obese white women exercise trained in the Dose Response to Exercise (DREW) study (n = 112): rs1956197 near dishevelled associated activator of morphogenesis 1 (DAAM1) and rs17117533 in the vicinity of necdin (NDN). The association of SNPs rs884736 in the calmodulin-binding transcription activator 1 (CAMTA1) locus and rs17581162 ~68 kb upstream from regulator of G protein signaling 18 (RGS18) with the gains in VO(2max) in HERITAGE whites were replicated in HERITAGE blacks (n = 247). These genomic predictors of the response of Vo(2max) to regular exercise provide new targets for the study of the biology of fitness and its adaptation to regular exercise. Large-scale replication studies are warranted.

The "fit but fat" concept revisited: population-based estimates using NHANES

Low cardiovascular fitness is an independent risk factor for type 2 diabetes and cardiovascular disease in adults. The "fit but fat" concept suggests that cardiovascular fitness attenuates risk of metabolic and cardiovascular disease independent of body mass index (BMI), even among the obese. However, the proportion of U.S. adults considered both fit and obese is unknown. Thus, the purposes of this short paper were to estimate the proportion of U.S. adults who are obese yet have a high cardiovascular fitness level (fit but fat), and determine the independent effect of obesity on cardiovascular fitness. The study was a secondary data analysis of 4,675 adults (20-49 years) who completed a submaximal exercise test, from the National Health and Nutrition Examination Survey (1999-2002). Cardiovascular fitness and body weight were expressed as continuous (estimated VO_2max [ml.kg^-1.min^-1] and BMI [kg/m²]) and categorical variables (low, moderate, and high cardiovascular fitness level; normal weight, overweight, and obese), the later using sex and age-specific criteria from the Aerobics Center Longitudinal Study and standard BMI cut-points, respectively. Using these methods, the prevalence of meeting the fit but fat definition among U.S. adults was 8.9% (95% C.I. = 6.9 - 10.9%), whereas 17.4% were overweight and high fit, and 30% were normal weight and high fit. Importantly, the proportion of low, moderate, and high cardiovascular fitness differed significantly (p < 0.05) by BMI level. Using multiple regression, being obese was associated with a 9.2% lower estimated VO_2max compared to being normal weight, even after controlling for age, sex, race/ethnicity, and income. These results suggest that a small percentage of U.S. adults can be considered fit but fat, and that obesity is independently associated with reduced cardiovascular fitness. The likely explanation for the low proportion of U.S. adults who can be considered fit but fat is a low level of physical activity, which constributes to both a positive energy balance and low fitness. Thus, engaging obese adults in physical activity that is sufficient to improve cardiovascular fitness may help to reduce not only body weight, but the excess health burden in this population.

CREB1 is a strong genetic predictor of the variation in exercise heart rate response to regular exercise: the HERITAGE Family Study

BACKGROUND

A genome-wide linkage scan identified a quantitative trait locus for exercise training-induced changes in submaximal exercise (50 W) heart rate (DeltaHR50) on chromosome 2q33.3-q34 in the HERITAGE Family Study (n=472).

METHODS AND RESULTS

To fine-map the region, 1450 tag SNPs were genotyped between 205 and 215 Mb on chromosome 2. The strongest evidence of association with DeltaHR50 was observed with 2 single-nucleotide polymorphisms (SNPs) located in the 5' region of the cAMP-responsive element-binding protein 1 (CREB1) gene (rs2253206: P=1.6x10(-5) and rs2360969: P=4.3x10(-5)). The associations remained significant (P=0.01 and P=0.023, respectively) after accounting for multiple testing. Regression modeling of the 39 most significant SNPs in the single-SNP analysis identified 9 SNPs that collectively explained 20% of the DeltaHR50 variance. CREB1 SNP rs2253206 had the strongest effect (5.45% of variance), followed by SNPs in the FASTKD2 (3.1%), MAP2 (2.6%), SPAG16 (2.1%), ERBB4 (3 SNPs approximately 1.4% each), IKZF2 (1.4%), and PARD3B (1.0%) loci. In conditional linkage analysis, 6 SNPs from the final regression model (CREB1, FASTKD2, MAP2, ERBB4, IKZF2, and PARD3B) accounted for the original linkage signal: The log of the odds score dropped from 2.10 to 0.41 after adjusting for all 6 SNPs. Functional studies revealed that the common allele of rs2253206 exhibits significantly (P<0.05) lower promoter activity than the minor allele.

CONCLUSIONS

Our data suggest that functional DNA sequence variation in the CREB1 locus is strongly associated with DeltaHR50 and explains a considerable proportion of the quantitative trait locus variance. However, at least 5 additional SNPs seem to be required to fully account for the original linkage signal.

FTO genotype is associated with exercise training-induced changes in body composition

The fat mass (FM) and obesity-associated (FTO) gene is the first obesity-susceptibility gene identified by genome-wide association scans and confirmed in several follow-up studies. Homozygotes for the risk allele (A/A) have 1.67 times greater risk of obesity than those who do not have the allele. However, it is not known whether regular exercise-induced changes in body composition are influenced by the FTO genotype. The purpose of our study was to test whether the FTO genotype is associated with exercise-induced changes in adiposity. Body composition was derived from underwater weighing before and after a 20-week endurance training program in 481 previously sedentary white subjects of the HERITAGE Family Study. FTO single-nucleotide polymorphism (SNP) rs8050136 was genotyped using Illumina GoldenGate assay. In the sedentary state, the A/A homozygotes were significantly heavier and fatter than the heterozygotes and the C/C homozygotes in men (P = 0.004) but not in women (P = 0.331; gene-by-sex interaction P = 0.0053). The FTO genotype was associated with body fat responses to regular exercise (P < 0.005; adjusted for age, sex, and baseline value of response trait): carriers of the C allele showed three times greater FM and %body fat losses than the A/A homozygotes. The FTO genotype explained 2% of the variance in adiposity changes. Our data suggest that the FTO obesity-susceptibility genotype influences the body fat responses to regular exercise. Resistance to exercise-induced reduction in total adiposity may represent one mechanism by which the FTO A allele promotes overweight and obesity.

Quantifying training load: a comparison of subjective and objective methods

PURPOSE

To establish the relationship between a subjective (session rating of perceived exertion [RPE]) and 2 objective (training impulse [TRIMP]) and summatedheart- rate-zone (SHRZ) methods of quantifying training load and explain characteristics of the variance not accounted for in these relationships.

METHODS

Thirty-three participants trained ad libitum for 2 wk, and their heart rate (HR) and RPE were recorded to calculate training load. Subjects were divided into groups based on whether the regression equations over- (OVER), under- (UNDER), or accurately predicted (ACCURATE) the relationship between objective and subjective methods.

RESULTS

A correlation of r = .76 (95% CI: .56 to .88) occurred between TRIMP and session-RPE training load. OVER spent a greater percentage of training time in zone 4 of SHRZ (ie, 80% to 90% HRmax) than UNDER (46% +/- 8% vs 25% +/- 10% [mean +/- SD], P = .008). UNDER spent a greater percentage of training time in zone 1 of SHRZ (ie, 50% to 60% HRmax) than OVER (15%+/- 8% vs 3% +/- 3%, P = .005) and ACCURATE (5% +/- 3%, P = .020) and more time in zone 2 of SHRZ (ie, 60% to 70%HRmax) than OVER (17% +/- 6% vs 7% +/- 6%, P = .039). A correlation of r = .84 (.70 to .92) occurred between SHRZ and session-RPE training load. OVER spent proportionally more time in Zone 4 than UNDER (45% +/- 8% vs 25% +/- 10%, P = .018). UNDER had a lower training HR than ACCURATE (132 +/- 10 vs 148 +/- 12 beats/min, P = .048) and spent more time in zone 1 than OVER (15% +/- 8% vs 4% +/- 3%, P = .013) and ACCURATE (5% +/- 3%, P = .015).

CONCLUSIONS

The session-RPE method provides reasonably accurate assessments of training load compared with HR-based methods, but they deviate in accuracy when proportionally more time is spent training at low or high intensity.

Walking: a matter of quantity and quality physical activity for type 2 diabetes management

Walking is often prescribed as a mode of physical activity for people with type 2 diabetes (T2D). We and others have found that although people with T2D may increase the amount that they walk (e.g., more steps per day), improvements in key health outcomes are rarely achieved. We agree that walking is an acceptable approach for people with T2D to meet current clinical practice guidelines, but consideration of both the total number of daily steps and the walking speed of a portion of those total daily steps are necessary to gain health benefit.

Gene-physical activity interactions: overview of human studies

Physical activity level is an important component of the total daily energy expenditure and as such contributes to body weight regulation. A body of data indicates that the level of physical activity plays a role in the risk of excessive weight gain, in weight loss programs, and particularly in the prevention of weight regain. Most studies dealing with potential gene-physical activity interaction effects use an exercise and fitness or performance paradigm as opposed to an obesity-driven model. From these studies, it is clear that there are considerable individual differences in the response to an exercise regimen and that there is a substantial familial aggregation component to the observed heterogeneity. Few studies have focused on the role of specific genes in accounting for the highly prevalent gene-exercise interaction effects. Results for specific genes have been inconsistent with few exceptions. Progress is likely to come when studies will be designed to truly address gene-exercise or physical activity interaction issues and with sample sizes that will provide adequate statistical power.

KIF5B gene sequence variation and response of cardiac stroke volume to regular exercise

A genome-wide linkage scan for endurance training-induced changes in stroke volume detected a quantitative trait locus on chromosome 10p11 in white families of the HERITAGE Family Study. Dense microsatellite mapping narrowed down the linkage region to a 7 Mb area containing 16 known and 14 predicted genes. Association analyses with 90 single nucleotide polymorphisms (SNPs) provided suggestive evidence (P values from 0.03 to 0.06) for association in the kinesin heavy chain (KIF5B) gene locus in the whole cohort. The associations at the KIF5B locus were stronger (P values from 0.001 to 0.008) when the analyses were performed on linkage-informative families only (family-specific logarithm of the odds ratio scores >0.025 at peak linkage location). Resequencing the coding and regulatory regions of KIF5B revealed no new exonic SNPs. However, the putative promoter region was particularly polymorphic, containing eight SNPs with at least 5% minor allele frequency within 1850 bp upstream of the start codon. Functional analyses using promoter haplotype reporter constructs led to the identification of sequence variants that had significant effects on KIF5B promoter activity. Analogous inhibition and overexpression experiments showed that changes in KIF5B expression alter mitochondrial localization and biogenesis in a manner that could affect the ability of the heart to adjust to regular exercise. Our data suggest that KIF5B is a strong candidate gene for the response of stroke volume to regular exercise. Furthermore, training-induced changes in submaximal exercise stroke volume may be due to mitochondrial function and variation in KIF5B expression as determined by functional SNPs in its promoter.

Effect of Endothelin 1 Genotype on Blood Pressure Is Dependent on Physical Activity or Fitness Levels

Contributions of the DNA sequence variation at the endothelin 1 locus to the risk of hypertension and to endurance training–induced changes in blood pressure were investigated in the Aerobics Center Longitudinal Study and the Health, Risk Factors, Exercise Training and Genetics Family Study cohorts. We identified 586 normotensive control subjects and 607 incident hypertensive case subjects from the Aerobics Center Longitudinal Study cohort (all whites) who were normotensive and healthy at their first clinic visit. The case subjects were diagnosed with hypertension during an average follow-up of 9.5 years, whereas the control subjects remained normotensive. The allele and genotype frequencies of 5 endothelin 1 haplotype tagging single nucleotide polymorphisms did not differ significantly between the case and control subjects. However, we observed a significant ( P =0.0025) interaction between the endothelin 1 rs5370 (G/T; Lys198Asn) genotype and cardiorespiratory fitness level on the risk of hypertension: among low-fit subjects, the rs5370 minor allele (T; 198Asn) was associated with higher risk of hypertension (odds ratio: 1.95; 95% CI: 1.36 to 2.81; P =0.0003), whereas the risk did not differ among genotypes in high-fit subjects. In the white Health, Risk Factors, Exercise Training and Genetics subjects (N=480), the rs5370 T allele was associated with blunted systolic blood pressure ( P =0.0046) and pulse pressure ( P =0.0016) responses to a 20-week endurance training program. The Lys198Asn variant of the endothelin 1 locus is associated with blood pressure phenotypes in whites. However, the expression of the genotype effect is modulated by physical activity or cardiorespiratory fitness level. Our study provides an illustrative example of how physical activity and fitness level modifies the associations between a candidate gene and outcome phenotype.

Variations in the four and a half LIM domains 1 gene (FHL1) are associated with fasting insulin and insulin sensitivity responses to regular exercise

AIMS/HYPOTHESIS

The expression of the four and a half LIM domains 1 gene (FHL1) is increased in the muscle of individuals who show an improvement in insulin sensitivity index (S(I)) after 20 weeks of exercise training. The aim of the present study was to investigate associations between three FHL1 single nucleotide polymorphisms (SNPs) and variables derived from an IVGTT, both in the sedentary state and in response to exercise training, in participants in the HERITAGE Family Study.

MATERIALS AND METHODS

SNPs were typed using fluorescence polarisation methodology. Analyses were performed separately by sex and in black and white individuals.

RESULTS

In black participants, no associations were found with any of the SNPs. In white women (n = 207), SNP rs9018 was associated with the disposition index (D(I)), which is calculated as S(I) generated from the MINMOD program (x10(-4) min(-1)[microU/ml](-1)) multiplied by acute insulin response to glucose (AIR(g); pmol/l x 10 min), and the glucose disappearance index (K(g)) training responses (p = 0.016 and p = 0.008, respectively). In white men (n = 222), all SNPs were associated with fasting glucose levels (p < or = 0.05) and SNP rs2180062 with the insulin sensitivity index (S(I)) (p = 0.04) in the sedentary state. Two SNPs were associated with fasting insulin training response. Fasting insulin decreased to a greater extent in carriers of the rs2180062 C allele (p = 0.01) and rs9018 T allele (p = 0.04). With exercise training, S(I) (x10(-4) min(-1)[microU/ml](-1): 0.68 +/- 0.20 vs -0.77 +/- 0.44, p = 0.046), D(I) (319 +/- 123 vs -528 +/- 260, p = 0.006) and K(g) (per 100 min: 0.09 +/- 0.04 vs -0.14 +/- 0.8, p = 0.03) improved more in the C allele carriers at rs2180062 than in the T allele carriers.

CONCLUSIONS/INTERPRETATION

Fasting insulin and S(I) responses to exercise training were associated with DNA sequence variation in FHL1 in white men. Whether these associations exist only in white men remains to be investigated.