Endurance | ACTN3 (rs1815739)

How ACTN3 Affects Endurance and What It Means for You

Endurance is the ability to sustain physical activity over extended periods and depends on efficient cardiovascular function, energy availability, and muscle fiber composition. The ACTN3 gene plays a role in determining the balance of muscle fiber types. Different variants of a single ACTN3 variant called rs1815739 are associated with a tendency toward slow-twitch fibers, which resist fatigue and support endurance, or fast-twitch fibers, which produce power and speed but tire more quickly.

Why This Matters

Your ACTN3 genotype is one piece of the puzzle that shapes athletic potential. It does not determine your destiny. Training, nutrition, sleep, injury history, mindset, and other genes all influence performance. Understanding your ACTN3 result can help you tailor training and recovery strategies to match your natural tendencies and goals.

Quick Takeaway

• If you have two effect alleles (TT), you tend to have more slow-twitch fibers and a genetic advantage for endurance activities.
• If you have one effect allele (CT), you likely have a mixed fiber type and flexibility to train for either endurance or power.
• If you have zero effect alleles (CC), you tend to have more fast-twitch fibers and a predisposition for sprinting and power sports.

Genetic Interpretations

Nutrition to Support Endurance and Muscle Performance

Regardless of genotype, nutrition fuels performance, recovery, and adaptation. Adjust proportions and timing to match your training type and goals.

• Carbohydrates: Complex carbs such as whole grains, oats, sweet potatoes, and legumes provide sustained energy for aerobic sessions. Aim to periodize carbohydrate intake around high volume or high intensity workouts.
• Protein: Sufficient protein supports muscle repair and adaptation. Target about 1.2 to 1.8 g per kg body weight daily depending on training load. Include high quality sources like lean meats, dairy, eggs, legumes, and plant proteins.
• Fats: Healthy fats from nuts, seeds, avocados, and fatty fish support hormone health and provide a secondary fuel source for longer efforts.
• Hydration and electrolytes: Maintain regular fluid intake and replace sodium, potassium, and magnesium during prolonged sessions to protect performance and prevent cramping.
• Meal timing: Pre-workout meals should be carbohydrate focused 1 to 3 hours before exercise. Post-workout, aim for carbohydrates plus protein within 30 to 90 minutes to support glycogen repletion and muscle repair.

Supplements That May Help

Supplements are optional additions to a strong nutrition plan. Talk with your healthcare provider before starting any new supplement.

• Omega-3 fatty acids: May reduce exercise-induced inflammation and support recovery.
• Antioxidants: Vitamin C and E and polyphenol-rich foods can support recovery when used sensibly, but high doses around training may blunt adaptation, so use appropriately.
• Creatine: Useful for high-intensity efforts and strength development and can be beneficial for CT and CC genotypes working on power. It also supports repeated sprint performance for endurance athletes.
• Iron: Important for oxygen transport. Consider testing levels before supplementing, especially for women, endurance athletes, or those with fatigue.
• Beta-Alanine: May improve high-intensity endurance by buffering muscle acid during intense efforts.

Lifestyle and Training Recommendations

• Train according to your goals: build an aerobic base for endurance, focus on speed and power for sprint events, or mix modalities if you are versatile.
• Prioritize sleep: 7 to 9 hours per night supports recovery, hormone balance, and performance adaptations.
• Include structured recovery: active recovery, mobility work, foam rolling, and scheduled rest days reduce injury risk and support long term gains.
• Strength training: All athletes benefit from regular strength work. For endurance focus on muscular endurance and single leg strength. For power focus on explosive lifts and plyometrics.
• Periodize training: Use blocks of focused training with progressive overload and planned deloads to maximize adaptation.

Recommended Blood Tests and Monitoring

• Complete blood count and ferritin to screen for iron deficiency, especially in endurance athletes.
• Vitamin D level to support bone health, immune function, and muscle performance.
• Basic metabolic panel to check electrolytes and kidney function if using supplements or training heavily.
• Thyroid panel if experiencing unexplained fatigue or changes in weight and performance.

Other Considerations

• Injury risk: Fast-twitch dominant athletes may be more prone to muscle strains when training explosively. Slow-twitch dominant athletes may face repetitive strain injuries with high mileage. Plan prevention strategies accordingly.
• Performance is multifactorial: environment, coaching, equipment, and psychology all shape outcomes.
• Genetic results are one tool: use them to inform training and lifestyle choices, not to limit your goals.

Disclaimer

PlexusDx provides educational information about genetic predispositions only. This content is not medical advice. Always consult your healthcare provider, coach, or a qualified professional before making changes to your training, diet, or supplements.