Familial risk ratios for high and low physical fitness levels in the Canadian population

PURPOSE

To estimate the familial risk of being physically fit or unfit in Canada.

METHODS

The sample consisted of 11,680 participants from 4144 nuclear families of the 1981 Canada Fitness Survey. Indicators of physical fitness included estimated physical working capacity at a heart rate of 150 beats x min(-1) derived from a step test (PWC150), hand grip strength, sit-ups, and trunk flexibility. Probands were defined as reference individuals who were physically fit (95th, 85th, and 75th percentiles) or physically unfit (25th, 15th, and 5th percentiles) for each fitness indicator, respectively.

RESULTS

Standardized risk ratios, adjusted for age and sex (SRR), for spouses and first-degree relatives of probands exceeding the 95th percentile are 1.63 and 1.81 for PWC150, 2.38 and 3.16 for grip strength, 2.63 and 3.98 for sit-ups, and 2.59 and 3.56 for trunk flexibility, respectively, whereas the SRR for spouses and first-degree relatives of probands below the 5th percentile are 1.54 and 1.34 for PWC150, 1.83 and 1.85 for grip strength, 1.13 and 1.53 for sit-ups, and 1.42 and 1.84 for trunk flexibility, respectively. The familial risks tend to be greatest at the extremes (95th and 5th percentiles) and the risks for first-degree relatives of physically fit probands are generally greater than those for spouses for grip strength, sit-ups and trunk flexibility, whereas those for PWC150 show no clear pattern.

CONCLUSION

There is significant familial risk for being physically fit or unfit in the Canadian population. The pattern of SRR suggests that the familial risk for indicators of strength and flexibility may be due, in part, to genetic factors, whereas the shared family environment is largely contributing to the familial risk for PWC150.

Angiotensin-converting enzyme ID polymorphism and fitness phenotype in the HERITAGE Family Study

It has been suggested that genetic variation in the angiotensin-converting enzyme (ACE) gene is associated with physical performance. We studied the association between the ACE insertion (I)/deletion (D) polymorphism and several fitness phenotypes measured before and after 20 wk of a standardized endurance training program in sedentary Caucasian (n = 476) and black (n = 248) subjects. Phenotypes measured were oxygen uptake (VO(2)), work rate, heart rate, minute ventilation, tidal volume, and blood lactate levels during maximal and submaximal [50 W and at 60 and 80% of maximal VO(2) (VO(2 max))] exercise and stroke volume and cardiac output during submaximal exercise (50 W and at 60% VO(2 max)). The ACE ID polymorphism was typed with the three-primer PCR method. Out of 216 association tests performed on 54 phenotypes in 4 groups of participants, only 11 showed significant (P values from 0.042 to 0. 0001) associations with the ACE ID polymorphism. In contrast to previous claims, in Caucasian offspring, the DD homozygotes showed a 14-38% greater increase with training in VO(2 max), VO(2) at 80% of VO(2 max), and all work rate phenotypes and a 36% greater decrease in heart rate at 50 W than did the II homozygotes. No associations were evident in Caucasian parents or black parents or offspring. Thus these data do not support the hypothesis that the ACE ID polymorphism plays a major role in cardiorespiratory endurance.

Skeletal muscle adaptation to exercise: a century of progress

Skeletal muscle physiology and biochemistry is an established field with Nobel Prize-winning scientists, dating back to the 1920s. Not until the mid to late 1960s did there appear a major focus on physiological and biochemical training adaptations in skeletal muscle. The study of adaptations to exercise training reveals a wide range of integrative approaches, from the systemic to the molecular level. Advances in our understanding of training adaptations have come in waves caused by the introduction of new experimental approaches. Research has revealed that exercise can be effective at preventing and/or treating some of the most common chronic diseases of the latter half of the 20th century. Endurance-trained muscle is more effective at clearing plasma triglyceride, glucose, and free fatty acids. However, at the present time, most of the mechanisms underlying the adaptation of human skeletal muscle to exercise still remain to be discovered. Little is known about the regulatory factors (e.g., trans-acting proteins or signaling pathways) directly modulating the expression of exercise-responsive genes. Because so many potential physiological and biochemical signals change during exercise, it will be an important challenge in the next century to move beyond "correlational studies" and to identify responsible mechanisms. Skeletal muscle metabolic adaptations may prove to be a critical component to preventing diseases such as coronary heart disease, type 2 diabetes, and obesity. Therefore, training studies have had an impact on setting the stage for a potential "preventive medicine reformation" in a society needing a return to a naturally active lifestyle of our ancestors.

The Na(+)-K(+)-ATPase alpha2 gene and trainability of cardiorespiratory endurance: the HERITAGE family study

The Na(+)-K(+)-ATPase plays an important role in the maintenance of electrolyte balance in the working muscle and thus may contribute to endurance performance. This study aimed to investigate the associations between genetic variants at the Na(+)-K(+)-ATPase alpha2 locus and the response (Delta) of maximal oxygen consumption (VO(2 max)) and maximal power output (W(max)) to 20 wk of endurance training in 472 sedentary Caucasian subjects from 99 families. VO(2 max) and W(max) were measured during two maximal cycle ergometer exercise tests before and again after the training program, and restriction fragment length polymorphisms at the Na(+)-K(+)-ATPase alpha2 (exons 1 and 21-22 with Bgl II) gene were typed. Sibling-pair linkage analysis revealed marginal evidence for linkage between the alpha2 haplotype and DeltaVO(2 max) (P = 0.054) and stronger linkages between the alpha2 exon 21-22 marker (P = 0.005) and alpha2 haplotype (P = 0.003) and DeltaW(max). In the whole cohort, DeltaVO(2 max) in the 3.3-kb homozygotes of the exon 1 marker (n = 5) was 41% lower than in the 8.0/3.3-kb heterozygotes (n = 87) and 48% lower than in the 8.0-kb homozygotes (n = 380; P = 0.018, adjusted for age, gender, baseline VO(2 max), and body weight). Among offspring, 10.5/10.5-kb homozygotes (n = 14) of the exon 21-22 marker showed a 571 +/- 56 (SE) ml O(2)/min increase in VO(2 max), whereas the increases in the 10.5/4.3-kb (n = 93) and 4.3/4.3-kb (n = 187) genotypes were 442 +/- 22 and 410 +/- 15 ml O(2)/min, respectively (P = 0.017). These data suggest that genetic variation at the Na(+)-K(+)-ATPase alpha2 locus influences the trainability of VO(2 max) in sedentary Caucasian subjects.

Reproducibility of maximal exercise test data in the HERITAGE family study

PURPOSE

The reproducibility of responses to maximal cycle ergometer testing was determined using data from the HERITAGE Family study at four Clinical Centers in the United States and Canada.

METHODS

Reproducibility was determined from maximal exercise test data obtained a) on 2 d in a sample of 390 subjects (198 men and 192 women), b) across 4 d in an Intracenter Quality Control (ICQC) substudy with 55 subjects who were not part of the main study, and c) across 2 wk in a Traveling Crew Quality Control (TCQC) substudy with the same eight subjects who were tested at each of the four centers. Reproducibility was evaluated using technical errors, coefficients of variation (CV) for repeated measures, and intraclass correlation coefficients (ICC) for selected variables obtained on the main cohort, as well as on the ICQC and TCQC substudies.

RESULTS

With the exception of systolic and diastolic blood pressures and respiratory exchange ratio, all the other variables (heart rate, ventilation, VO2, and VCO2) were highly reproducible, with CV below 10% and ICC over 0.86. These results were similar to those previously reported on the same subjects at a submaximal power output associated with 60% VO2max. Results were consistent for the main cohort, the ICQC sample, the TCQC sample, and across all four Clinical Centers.

CONCLUSIONS

Day-to-day variations are small and reproducibility is high for maximal values of heart rate, ventilation, VO2 and VCO2 at each of the four Clinical Centers of the HERITAGE Family Study.

Human angiotensin I-converting enzyme gene and endurance performance

Human physical performance is strongly influenced by genetic factors. A variation in the structure of the human angiotensin I-converting enzyme (ACE) gene has been reported in which the insertion (I) variant is associated with lower ACE levels than the deletion (D) gene. We have previously reported that the I variant was associated with improved endurance performance in high-altitude mountaineers and British Army recruits. We now examine this genotype distribution in 91 British Olympic-standard runners (79 Caucasians). DNA was extracted from the buccal cells contained in 10 ml of saline mouthwash donated by the subjects, and the I and D variants of the ACE gene were identified by PCR amplification of the polymorphic region. There was an increasing frequency of the I allele with distance run [0.35, 0.53, and 0.62 for </=200 m (n = 20), 400-3,000 m (n = 37), and >/=5,000 m (n = 34), respectively; P = 0.009 for linear trend]. Among 404 Olympic-standard athletes from 19 other mixed sporting disciplines (in which endurance performance was not necessarily a key factor), the I allele did not differ significantly from that found in control subjects: 0.50 vs. 0.49 (P = 0.526). These results support a positive association of the I allele with elite endurance performance.

Familial aggregation of VO(2max) response to exercise training: results from the HERITAGE Family Study

The aim of this study was to test the hypothesis that individual differences in the response of maximal O(2) uptake (VO(2max)) to a standardized training program are characterized by familial aggregation. A total of 481 sedentary adult Caucasians from 98 two-generation families was exercise trained for 20 wk and was tested for VO(2max) on a cycle ergometer twice before and twice after the training program. The mean increase in VO(2max) reached approximately 400 ml/min, but there was considerable heterogeneity in responsiveness, with some individuals experiencing little or no gain, whereas others gained >1.0 l/min. An ANOVA revealed that there was 2.5 times more variance between families than within families in the VO(2max) response variance. With the use of a model-fitting procedure, the most parsimonious models yielded a maximal heritability estimate of 47% for the VO(2max) response, which was adjusted for age and sex with a maternal transmission of 28% in one of the models. We conclude that the trainability of VO(2max) is highly familial and includes a significant genetic component.

Phenotypic differences in cardiovascular regulation in inbred rat models of aerobic capacity

The Dark Aouti (DA) inbred strain of rats has superior aerobic treadmill running capacity compared with the Copenhagen (COP) strain of inbred rats. This difference in aerobic capacity provides a model to explore the genetic basis of variation in this trait. The present study evaluated intermediate phenotypic differences between 10 male COP inbred rats and 10 male DA inbred rats that might contribute to the difference in aerobic capacity between the strains. Five autonomically regulated cardiovascular variables were evaluated during rest or exercise by measuring the response to autonomic antagonists. The DA rat had enhanced autonomic function for the regulation of peripheral blood flow and cardiac output. Specifically, at rest the DA rats had significantly more sympathetic (123 +/- 8 vs. 99 +/- 7 beats/min) and parasympathetic (35 +/- 5 vs. 12 +/- 3 beats/min) tonus for heart rate control and more sympathetic support of blood pressure (70 +/- 7 vs. 38 +/- 6 mmHg) compared with the COP rats. During three graded levels of treadmill exercise the DA rats had higher blood pressures (16% on average) and higher heart rates (4% on average) relative to the COP rats. In addition, the DA rats had a 27% greater heart weight-to-body weight ratio compared with the COP strain of rats (3.63 +/- 0.08 vs. 2.85 +/- 0.07 g/kg). All five of these intermediate phenotypes could participate as variables causative of the difference in treadmill running capacity between the DA and COP strains of rats.

Angiotensin-converting-enzyme gene insertion/deletion polymorphism and response to physical training

BACKGROUND

The function of local renin-angiotensin systems in skeletal muscle and adipose tissue remains largely unknown. A polymorphism of the human angiotensin converting enzyme (ACE) gene has been identified in which the insertion (I) rather than deletion (D) allele is associated with lower ACE activity in body tissues and increased response to some aspects of physical training. We studied the association between the ACE gene insertion or deletion polymorphism and changes in body composition related to an intensive exercise programme, to investigate the metabolic effects of local human renin-angiotensin systems.

METHODS

We used three independent methods (bioimpedance, multiple skinfold-thickness assessment of whole-body composition, magnetic resonance imaging of the mid-thigh) to study changes in body composition in young male army recruits over 10 weeks of intensive physical training.

FINDINGS

Participants with the II genotype had a greater anabolic response than those with one or more D alleles for fat mass (0.55 vs -0.20 kg, p=0.04 by bioimpedance) and non-fat mass (1.31 vs -0.15 kg, p=0.01 by bioimpedance). Changes in body morphology with training measured by the other methods were also dependent on genotype.

INTERPRETATION

II genotype, as a marker of low ACE activity in body tissues, may conserve a positive energy balance during rigorous training, which suggests enhanced metabolic efficiency. This finding may explain some of the survival and functional benefits of therapy with ACE inhibitors.

Spectrum of aerobic endurance running performance in eleven inbred strains of rats

The goal of this study was to identify inbred rat strains that could serve as useful models for exploration of the genetic basis of aerobic endurance performance. Six rats of each gender from 11 different inbred strains were tested for 1) maximal running capacity on a treadmill and 2) isolated cardiac performance. Running performance was estimated from 1) duration of the run, 2) distance run, and 3) vertical work performed. Cardiac output, during constant preload and afterload, was taken as a measure of cardiac performance from an isolated working heart preparation. The COP rats were the lowest performers and the DA rats were the best performers by all estimates of running performance. Across the 11 strains, the distance run correlated positively with isolated cardiac performance (r = 0.87). Estimates of performance were as follows (COP vs. DA strain, respectively): duration of run, 19.9 +/- 1.8 vs. 41.5 +/- 2. 2 min; distance run, 298 +/- 30 vs. 840 +/- 64 m; vertical work, 15 +/- 1.7 vs. 40 +/- 4.4 kg/m. These approximately 2.5-fold differences in running performance between the COP and DA suggest that these strains could serve as models for evaluation of the genetic basis of variance in aerobic performance.

Elite endurance athletes and the ACE I allele--the role of genes in athletic performance

Genetic markers that might contribute to the making of an elite athlete have not been identified. Potential candidate genes might be found in the renin-angiotensin pathway, which plays a key role in the regulation of both cardiac and vascular physiology. In this study, DNA polymorphisms derived from the angiotensin converting enzyme (ACE), the angiotensin type 1 receptor (AT1) and the angiotensin type 2 receptor (AT2) were studied in 64 Australian national rowers. Compared with a normal population, the rowers had an excess of the ACE I allele (P<0.02) and the ACE II genotype (P=0.03). The ACE I allele is a genetic marker that might be associated with athletic excellence. It is proposed that the underlying mechanism relates to a healthier cardiovascular system.

Strength training: importance of genetic factors

PURPOSE

This study focuses on the quantification of genetic and environmental factors in arm strength after high-resistance strength training.

METHODS

Male monozygotic (MZ, N = 25) and dizygotic (DZ, N = 16) twins (22.4 +/- 3.7 yr) participated in a 10-wk resistance training program for the elbow flexors. The evidence for genotype*training interaction, or association of interindividual differences in training effects with the genotype, was tested by a two-way ANOVA in the MZ twins and using a bivariate model-fitting approach on pre- and post-training phenotypes in MZ and DZ twins. One repetition maximum (1RM), isometric strength, and concentric and eccentric moments in 110 degree arm flexion at velocities of 30 degrees x s(-1), 60 degrees x s(-1), and 12 degrees x s(-1) were evaluated as well as arm muscle cross-sectional area (MCSA).

RESULTS

Results indicated significant positive training effects for all measures except for maximal eccentric moments. Evidence for genotype*training interaction was found for 1RM and isometric strength, with MZ intra-pair correlations of 0.46 and 0.30, respectively. Bivariate model-fitting indicated that about 20% of the variation in post-training 1RM, isometric strength, and concentric moment at 120 degrees x s(-1) was explained by training-specific genetic factors that were independent from genetic factors that explained variation in the pretraining phenotype (30-77%).

CONCLUSIONS

Genetic correlations between measures of pre- and post-training strength were indicative for high pleiotropic gene action and minor activation of training-specific genes during training.

Three mitochondrial DNA restriction polymorphisms in elite endurance athletes and sedentary controls

This study examined the associations between elite endurance athlete (EEA) status and three mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) in the subunit 5 of the NADH dehydrogenase (MTND5) locus and one in the D-loop region. A group of 125 Caucasian male EEA well endowed with the phenotypic expression of VO2max (78.9 +/- 3.8 mL x kg(-1) x min(-1), mean +/- SD) and 65 sedentary controls (SCON: VO2max = 39.8 +/- 8.2 mL x kg(-1) x min(-1)) participated in the study. VO2max was determined during an incremental exercise test on a cycle ergometer or a motor-driven treadmill. mtDNA was extracted from white blood cells or lymphoblastoid cell lines and specific regions were amplified by the polymerase chain reaction. The Pearson Chi-square statistic test and Fisher exact test revealed no significant association (P > 0.05) between any of the three mtDNA RFLPs and EEA status. The MTND5-BamHI RFLP at bp 13,470 (morph 3) was found in 12.8% of the EEA and 12.3% of the SCON (chi2 = 0.009, P = 0.92). The prevalence of the MTND5-Ncil RFLP at bp 13,364 (morph 2) was 12.9% and 14% for the EEA and SCON, respectively (chi2 = 0.043, P = 0.83). The D-loop-KpnI RFLP at bp 16,133 (morph 1) was found in 5.8% of the EEA and in 1.6% of the SCON (Fisher exact test = 1.80, P = 0.18). The MTND5-HincII RFLP at bp 12,406 (morph 1) was not present in this study sample. These results indicate no evidence for a difference in the frequency of two polymorphic restriction sites in the subunit 5 of the NADH dehydrogenase gene of mtDNA and one in the D-loop region between elite endurance athletes and sedentary controls.

Muscle-specific creatine kinase gene polymorphisms in elite endurance athletes and sedentary controls

The purpose of this study was to investigate the association between elite endurance athlete (EEA) status and two restriction fragment length polymorphisms (RFLPs) at the muscle-specific creatine kinase (CKMM) gene locus. Genomic DNA was extracted from white blood cells or lymphoblastoid cell lines of 124 unrelated Caucasian male EEA (VO2max > 73 mL.kg-1.min-1) and 115 unrelated Caucasian sedentary male controls (SCON). The genetic polymorphism at the CKMM locus was detected by the polymerase chain reaction and DNA digestion with the NcoI and TaqI restriction endonucleases. The allelic frequencies for the NcoI and TaqI RFLPs were not different (P > 0.05) between EEA and SCON subjects. The three expected genotypes for CKMM-NcoI (1170/1170 bp, 1170/985 + 185 bp, and 985 + 185/985 + 185 bp) and CKMM-TaqI (1170/1170 bp, 1170/1020 + 150 bp, and 1020 + 50/1020 + 150 bp) were observed in the EEA and SCON groups. These genotype frequencies were in Hardy-Weinberg equilibrium, but they were not significantly (P > 0.05) different between the EEA and SCON. A strong (P < 0.001) linkage disequilibrium was detected among the NcoI and TaqI RFLPs in both EEA and SCON. These findings indicate that the skeletal muscle CK-NcoI and CK-TaqI gene polymorphisms are not associated with the elite endurance athlete status.

Absence of linkage between VO2max and its response to training with markers spanning chromosome 22

An extensive search for linkage between DNA markers and the response of VO2max to training has recently been launched in the HERITAGE Family Study. This is the first report on a genome-wide search strategy to locate chromosomal regions and positional candidate genes for cardiorespiratory endurance phenotypes. Linkage between seven markers spanning chromosome 22 spaced approximately 10 cM apart (D22S264, D22S274, D22S301, D22S304, D22S421, IL2RB, and PDGFB) and VO2max at baseline, as well as its response to endurance exercise training, was examined using the sib-pair linkage method. Markers were genotyped in at least 210 sib-pairs derived from 128 adult brothers (25 +/- 6 yr; mean +/- SD) and 138 sisters (24 +/- 6 yr) from 86 Caucasian families. VO2max, maximal heart rate, and maximal oxygen pulse were measured during stationary cycle tests before and after a standardized 20-wk endurance training program. On average, the initial VO2max was 2654 +/- 767 mL.min-1 while training increased VO2max significantly by 430 +/- 239 mL.min-1 or 16% (P < 0.0001). The VO2max response was adjusted for age and initial VO2max. No evidence of linkage was found between any of these markers on chromosome 22 and VO2max or its trainability.

Could the A2A11 human leucocyte antigen locus correlate with maximal aerobic power?

1. The power of the aerobic metabolic pathway correlates well with successful physical performance in endurance sports events. The ability to alter the pathway through training presents well-known limitations, and consequently a good genetic endowment is essential to participate in elite sporting activities. 2. In 32 subjects (16 healthy pairs of male twin sportsmen, 8 monozygotic and 8 dizygotic) zygosity was determined by means of the genetic analysis of human leucocyte antigen (HLA) system specificities at class I and II loci and other genetic variants. The subjects performed a progressive exercise test on a treadmill to ascertain the maximal oxygen uptake (VO2max), measured by an automatic breath-by-breath analyser. We have considered the relationship between the A, B and C loci of the HLA system and VO2max. 3. We found a high correlation between the presence of both HLA A2 and A11 and VO2max. In the A2A11 group (n = 6) we found a VO2max (mean +/- SD) equal to 71 +/- 4 ml min-1 kg-1. The group without this pair of alleles (n = 26) showed a much lower aerobic power (58 +/- 5 ml min-1 kg-1). Differences between the two groups were found to be largely significant (P < 0.001). It is noteworthy that in two pairs of dizygotic twins, the higher VO2max value corresponded to the twin with the A2A11 allele. 4. The very marked concordance between the presence of the A2A11 locus of the HLA system and the VO2max could be of great interest for the identification of outstanding performers.

Mitochondrial DNA sequence polymorphism, VO2max, and response to endurance training

Mitochondrial DNA sequence variation was determined in 46 sedentary young adult males who took part in ergocycle endurance training programs in two laboratories to assess whether mitochondrial DNA variants were associated with individual differences in maximal oxygen uptake (VO2max) and its response to training. VO2max was obtained from a progressive ergocycle test to exhaustion. White blood cell mitochondrial DNA was characterized with the restriction fragment length polymorphism (RFLP) technique using 22 restriction enzymes and human mitochondrial DNA as a probe for hybridization. Multiple mitochondrial DNA variants were detected with 15 of the enzymes. Some subjects exhibited many RFLPs, while others showed no variation. These RFLPs (morphs) were generated by base substitutions located in gene regions coding for mitochondrial proteins as well as in the noncoding regions. Carriers of three mitochondrial DNA morphs, two in the subunit 5 of the NADH dehydrogenase gene and one in the tRNA for threonine, had a VO2max (ml.kg-1.min-1) in the untrained state significantly higher than noncarriers, while carriers of one mitochondrial DNA morph in subunit 2 of NADH dehydrogenase had a lower initial VO2max. Endurance training increased VO2max by a mean of 0.51 of O2, with individual differences ranging from gains of 0.06 to 1.03. After adjustment for training site and initial VO2max, a lower response was observed for three carriers of a variant in subunit 5 of the NADH dehydrogenase detected with HincII (mean gain of 0.28 I; P less than 0.05). These results suggest that sequence variation in mitochondrial DNA may contribute to individual difference in VO2max and its response to training.