Cardiorespiratory Fitness and Your Genetics

By the ExomeDNA Research Team

This page contains general information only. For personal health decisions, consult a qualified clinician.

Cardiorespiratory fitness (CRF) is the capacity of the heart, lungs, and circulatory system to deliver oxygen to working muscles during sustained exercise — typically quantified as VO2max, in millilitres of oxygen per kilogram of body weight per minute. Twin studies place VO2max heritability between 40% and 70%, with cardiac myosin and calcium-channel genes among the identified contributors. Below: the biology of CRF, the genes most consistently implicated, what the research shows, and evidence-based steps to improve fitness regardless of genetics.

What is cardiorespiratory fitness?

Cardiorespiratory fitness (CRF) is the integrated capacity of the cardiovascular and respiratory systems to transport and utilise oxygen during prolonged physical effort. It is most often expressed as VO2max — the maximum rate at which the body can consume oxygen during incremental exercise — measured in millilitres of O2 per kilogram of body weight per minute (mL/kg/min). Higher VO2max values indicate greater aerobic capacity.

CRF is widely considered the single strongest objective predictor of all-cause mortality and cardiovascular mortality available from a standard clinical assessment. Large prospective cohort studies have ranked low CRF above high blood pressure, elevated cholesterol, smoking, and high BMI as a predictor of early death.

VO2max is determined by three interconnected factors: cardiac output (the volume of blood the heart pumps per minute), the oxygen-carrying capacity of the blood (primarily red blood cell mass and haemoglobin concentration), and the muscles' efficiency at extracting and using the delivered oxygen. Genetics influence all three, with cardiac output — shaped by the contractile efficiency of heart muscle and the compliance of the arteries that carry blood away from it — accounting for most of the heritable component.

The genetics behind cardiorespiratory fitness

Six genes with evidence for influence on CRF are authorised for this trait: MYH6, MYH11, CACNA1C, SCN10A, KANSL1, and CCDC141. Each operates through a distinct mechanism in cardiac or vascular biology.

MYH6 — the cardiac sarcomere's speed dial

MYH6 encodes myosin heavy chain 6 (alpha-MHC), the predominant myosin isoform in the adult human atria and a component of ventricular myocardium. Myosin is the motor protein of the cardiac sarcomere — it hydrolyses ATP to generate the mechanical force that drives each heartbeat. The alpha-MHC isoform encoded by MYH6 has faster cross-bridge cycling kinetics than the beta-MHC isoform (encoded by MYH7), meaning it generates force more rapidly per unit of ATP consumed.

During peak aerobic exercise, the heart must increase both stroke volume and heart rate — together constituting cardiac output — to meet the oxygen demand of working muscles. Variants in MYH6 that alter cross-bridge cycling efficiency directly affect the heart's ability to generate the rapid, forceful contractions required at maximal aerobic effort. MYH6 is one of the most functionally direct genetic influences on the cardiovascular fitness ceiling.

MYH11 — arterial compliance and cardiac afterload

MYH11 encodes smooth muscle myosin heavy chain (SM-MHC), the predominant myosin isoform of vascular smooth muscle cells in large arteries, including the aorta and major elastic arteries. Whereas MYH6 determines how forcefully the heart contracts, MYH11 influences how efficiently the arteries receiving that output transmit it to the periphery.

Arterial compliance — the ability of artery walls to expand and recoil with each heartbeat — determines cardiac afterload: the resistance against which the left ventricle must work. Stiffer arteries increase afterload, forcing the heart to do more work to achieve the same stroke volume. Variants in MYH11 that affect smooth muscle contractile properties influence arterial stiffness and therefore the mechanical efficiency of the cardiac output chain. In practical terms, MYH11 variants shape how much of the heart's contractile effort translates into useful oxygen delivery to working muscles.

CACNA1C — calcium cycling and heart rate response

CACNA1C encodes the alpha-1C subunit of the L-type voltage-gated calcium channel (Cav1.2), the predominant calcium entry channel in cardiac myocytes and sinoatrial node cells. In cardiac muscle, Cav1.2 triggers calcium-induced calcium release (CICR) from the sarcoplasmic reticulum — the process that activates the sarcomere and drives each mechanical contraction.

At peak exercise, cardiac output must increase three- to fivefold above resting values. This requires both faster heart rate and larger stroke volume — the Frank-Starling response — both of which depend on robust, rapid calcium cycling. CACNA1C variants that affect channel density, voltage sensitivity, or inactivation kinetics influence how efficiently the heart scales its calcium cycling in response to escalating aerobic demand. The sinoatrial node expression of CACNA1C also gives it a role in regulating heart rate acceleration at exercise onset.

SCN10A — cardiac conduction and exercise response

SCN10A encodes the voltage-gated sodium channel Nav1.8. Although Nav1.8 is best characterised in sensory neurons, it is also expressed in the cardiac conduction system. SCN10A variants have been associated with cardiac electrical conduction intervals, including PR interval duration and QRS morphology. During exercise, efficient conduction through the atrioventricular node and ventricular myocardium is required to synchronise the rapid, coordinated contractions that sustain high cardiac output. Variation at SCN10A may influence the conduction system's response to the accelerated heart rates demanded by intense aerobic exercise.

KANSL1 — epigenetic regulation of fitness-relevant gene programs

KANSL1 encodes KAT8 regulatory NSL complex subunit 1, a chromatin-remodelling factor expressed in heart and skeletal muscle. KANSL1 is a component of the NSL histone acetyltransferase complex, which controls the accessibility of gene promoters for transcription. In cardiac and skeletal muscle, epigenetic regulation of gene expression is central to how the heart adapts to chronic aerobic training — a process that involves upregulating sarcomere proteins, mitochondrial biogenesis genes, and metabolic enzyme genes.

Common variants in KANSL1 influence the epigenetic landscape of fitness-relevant gene programs. Their contribution to CRF likely operates through modulating the magnitude of transcriptional adaptation to exercise training — one mechanism underlying the individual variation in VO2max trainability, the degree to which a given exercise dose improves measured aerobic capacity.

CCDC141 — cardiac structural development

CCDC141 encodes coiled-coil domain-containing protein 141, a centrosome-associated protein expressed during cardiac development. Its contribution to CRF in adults likely reflects variation in cardiac chamber dimensions and sarcomere architecture established during development, which subsequently influence the heart's baseline stroke volume capacity.

What the research says

Research base: Moderate. The primary evidence supporting this trait comes from a 2023 Mendelian randomisation study by Cai et al. examining causal associations between cardiorespiratory fitness and type 2 diabetes (PMID 37400433). This study used CRF-associated genetic variants as instrumental variables to evaluate whether higher CRF causally reduces type 2 diabetes risk — an approach that, as a methodological by-product, characterises the genetic architecture of CRF itself and the variants that reliably tag higher fitness capacity in the population.

40–70% heritability for VO2max established across twin studies, placing cardiorespiratory fitness among the more heritable complex traits — comparable to blood pressure and BMI in terms of genetic contribution to population variance.

Key findings from the research base:

• Mendelian randomisation analyses find that genetically predicted higher CRF is associated with meaningfully lower type 2 diabetes risk, supporting a likely causal relationship rather than mere correlation (Cai et al., 2023).^[1]
• Genome-wide analyses of CRF have identified signals at loci encoding cardiac sarcomere proteins (MYH6), vascular smooth muscle proteins (MYH11), and cardiac ion channels (CACNA1C, SCN10A), converging on the cardiac output pathway as the primary genetic contributor to fitness ceiling.
• The heritability estimate of 40–70% from twin studies means genetics determines a meaningful share of an individual's fitness potential, but also that environment and training are responsible for a substantial portion of fitness variation across the population.

10–30% VO2max improvement is achievable with structured aerobic training in previously sedentary individuals — a training response that occurs regardless of baseline genetic profile and can substantially offset a lower genetic fitness ceiling.

The confidence tier for this trait is moderate, reflecting a growing but not yet deep GWAS base specifically characterising CRF genetics, and the methodological challenge that direct VO2max measurement in large cohorts is expensive and rarely performed — so most large-scale genetic studies rely on proxy measures (self-reported exercise capacity, step-test performance, heart rate recovery) rather than laboratory VO2max. This introduces phenotype noise. The biological mechanisms linking MYH6, MYH11, and CACNA1C to cardiac output are well established at the molecular level; the population-level polygenic signal is real but rests on a narrower evidence base than traits with decade-long GWAS histories. For background on how ExomeDNA evaluates evidence tiers, see our methodology page.

How cardiorespiratory fitness affects you

Cardiorespiratory fitness is not a fixed trait. Your genetics establish a ceiling — the upper limit of VO2max that intensive, sustained training can reach — but the distance between your current fitness and that ceiling is determined almost entirely by training behaviour. Most people operate well below their genetic ceiling.

What variants supporting higher CRF mean practically: individuals with genetic profiles associated with higher CRF tend to have more efficient cardiac output per heartbeat at a given exercise intensity, meaning their hearts do less mechanical work to deliver the same oxygen. Higher arterial compliance (associated with favourable MYH11 variants) reduces cardiac afterload and makes the translation of contractile effort into forward blood flow more efficient. More robust cardiac calcium cycling (associated with favourable CACNA1C variants) supports the heart's ability to scale output rapidly to a greater absolute maximum during intense exercise.

What variants supporting lower CRF ceiling do not mean: a high fitness level is not unreachable. The genetic ceiling is higher for some people, but training dramatically raises actual fitness for almost everyone. An untrained person with high genetic potential will have lower actual VO2max than a well-trained person with moderate genetic potential. Genetic variation explains potential; training determines how much of that potential is realised.

The health relevance of CRF extends well beyond athletics. Higher VO2max is independently associated with lower cardiovascular disease risk, lower type 2 diabetes risk, and reduced all-cause mortality. The relationship is dose-dependent and does not plateau at moderate fitness levels. Understanding your genetic fitness profile adds context to where on that fitness-outcome curve your baseline may lie, and strengthens the case for the training decisions that move you along it.

Working with your cardiorespiratory fitness result

The following steps are evidence-informed approaches to improving cardiorespiratory fitness. Consult a qualified clinician or certified exercise physiologist before starting a new training programme, particularly for those with a cardiovascular history.

1. Build an aerobic base with 150+ minutes per week of moderate-intensity activity. Current physical activity guidelines recommend at least 150 minutes per week of moderate-intensity aerobic activity (brisk walking, cycling, swimming at a conversational pace) or 75 minutes per week of vigorous activity. Reaching these thresholds produces measurable VO2max improvement in previously sedentary individuals, regardless of genetic starting point.

2. Add high-intensity interval training (HIIT) for maximal VO2max gains. The most evidence-supported HIIT protocol for VO2max improvement is 4 x 4 minutes at 90–95% of maximum heart rate, with 3-minute active recovery intervals, performed two to three times per week. This protocol has been shown to increase VO2max by 7–10% over 8 weeks in sedentary adults.

3. Apply progressive overload over months. VO2max adaptations require progressively increasing training load. A practical framework: increase weekly volume by no more than 10% per week, and introduce more intense sessions only after an aerobic base is established. A plateau in VO2max is typically a signal to introduce harder intervals, not simply more volume.

4. Prioritise recovery and sleep for cardiac adaptation. The cardiac adaptations that underlie VO2max improvement — increased stroke volume, cardiac chamber enlargement, improved calcium cycling efficiency — occur during recovery, not during training itself. Seven to nine hours of sleep per night supports the hormonal environment that drives these structural adaptations.

5. Track progress with submaximal fitness tests. Laboratory VO2max measurement is the gold standard but requires specialist equipment. Validated submaximal alternatives — including the Chester Step Test and the 6-minute walk test — can estimate VO2max and track improvement over months. Wearable devices also provide VO2max estimates of moderate accuracy that are useful for tracking relative change over time.

6. Consider altitude or hypoxic training for athletic optimisation. Living or training at moderate altitude (2,000–3,000 m) increases erythropoietin production, raises red blood cell mass, and improves oxygen-carrying capacity — a distinct adaptation pathway from cardiac output improvements. This approach is relevant for competitive athletes seeking to maximise VO2max beyond what sea-level training alone can achieve.

Related traits and genes

Cardiorespiratory Fitness sits at the centre of a cluster of cardiovascular and metabolic traits. Several related pages extend the picture:

• Resting Heart Rate: Resting heart rate reflects baseline cardiac automaticity and vagal tone — the same cardiac ion channel biology (CACNA1C, SCN10A) that appears in CRF. Lower resting heart rate is a well-established marker of aerobic fitness and cardiac efficiency.
• Lean Muscle Mass: Muscle mass determines a large portion of the metabolic demand that CRF must supply. Genetic factors influencing muscle fibre composition and mass interact with CRF genetics to shape overall exercise capacity.
• Coronary Artery Plaque Burden: Coronary artery disease reduces myocardial oxygen delivery during exercise, directly limiting achievable VO2max. Understanding both traits together gives a fuller cardiovascular picture.
• Cardiovascular Disease Risk: CRF is one of the strongest protective factors against cardiovascular disease. Comparing your CRF genetic profile with your cardiovascular disease risk profile shows how much of that protective effect your genetics support.
• Systolic Blood Pressure: Elevated blood pressure increases cardiac afterload — the same mechanism through which MYH11 arterial stiffness variants influence CRF. The two traits share overlapping vascular biology.

ExomeDNA genetic results are for wellness and educational purposes only. Consult a clinician for personalized health guidance.

References

1. Cai L et al. (2023). Causal associations between cardiorespiratory fitness and type 2 diabetes: a Mendelian randomisation study. PMID 37400433.

Data sources: GWAS Catalog (NHGRI-EBI, accessed 2026-05-29); Open Targets Genetics (CC0 1.0, accessed 2026-05-29); ClinVar (NCBI, accessed 2026-05-29); ClinGen Gene-Disease Validity (CC0 1.0, accessed 2026-05-29).