The "Speed Gene": Are You Genetically Built to Sprint, Go the Distance, or Both?

Are you training against your genetics without even knowing it? Join your host, Genetics Expert and International Fitgenes Educator & Trainer Dr. Sam Shay, DC, FMCP, alongside co-host Mikayla Wachsmann, MS, CNS, and Lily - his "Frenchie". Discover how a single gene (ACTN3) - nicknamed the "speed gene" - reveals whether your body is naturally wired for explosive power, endurance, or a mix of both. Dr. Sam breaks down the 3 genetic profiles behind muscle fiber type, the evolutionary reasons this variation exists in human populations today, and how knowing your profile helps you train smarter, recover faster, and avoid unnecessary injury. Key topics covered in this episode: • ACTN3 Genotypes: How RR (fast-twitch/power), XX (endurance/efficient), and RX (blended) shape natural athletic strengths and limitations. • Sprint vs. Endurance Genetics: Why some thrive at explosive, ballistic movements like sprinting and heavy lifting, while others excel in long-duration activity. • The Evolutionary Story: How migration, foraging, energy conservation, and cold survival shaped the endurance-biased X variant across diverse populations. • Injury Prevention: Why XX individuals are more prone to injury during rapid movements and benefit from slower, high-rep training - while RR individuals need prioritized recovery. • Training Smarter: How athletes and everyday clients (from jiu-jitsu competitors to gym goers) adapt pacing, intensity, and recovery based on genetics. • Beyond Genetics: Why diet, recovery, hormones, and mindset still shape performance alongside genetic data for long-term health and wellness. Loved learning the code behind your muscle fibers? Don't leave your training to guesswork - subscribe and drop us a review to help others decode their DNA! Connect with Dr. Sam Shay: • IG:   / fitgenesusa   • Website: https://www.fitgenesusa.com Health practitioners: Ready to offer personalized, root-cause care? Elevate your practice at https://FitgenesUSA.com to become a certified practitioner today. TIME STAMPS 00:00 - Intro 00:57 - Welcome: Muscle Fiber Type & Exercise 01:24 - ACTN3 "Speed Gene" & Performance 02:41 - How ACTN3 Codes Alpha-Actinin-3 04:04 - ACTN3 Variants (RR, RX, XX) 05:41 - Protein Synthesis & Stop Codons 08:15 - Fast Twitch (RR) Traits & Explosiveness 08:49 - Slow Twitch (XX) Traits & Endurance 09:32 - Population Fiber Type Distribution 10:37 - Evolutionary Theories & Migration 13:12 - Aerobic vs Anaerobic Glycolysis 16:10 - FitgenesUSA for Practitioners 18:18 - Personal Stories & Adaptability 20:50 - Overtraining Risks in Endurance Sports 22:26 - Exercise Goals: Health, Sport, Sculpt 23:18 - Overtraining & Cortisol Breakdown 27:33 - Injury Risks & Safe Training for XX 31:22 - Jiu-Jitsu Strategy by Fiber Type 33:06 - Marital Frisbee & Genetic Differences 36:02 - Overcoming Genetic Mismatch 37:07 - General Guidelines & Recovery 40:35 - Outro & FitgenesUSA Resources DISCLAIMER The information provided in this podcast is for educational and informational purposes only and is not intended as medical advice, diagnosis, cures or treatment. Neither Dr. Sam nor the publisher takes responsibility for possible health consequences. Always consult with a qualified healthcare provider before making any health changes. Dr. Sam Shay, DC, FMCP is the founder of and has a direct financial interest in FitgenesUSA testing. References: • Baltazar-Martins G, et al. Effect of ACTN3 Genotype on Sports Performance. Sports. 2020;8(7):99. https://www.mdpi.com/2075-4663/8/7/99 • Eynon N, et al. Genes for elite power performance: ACTN3. Sports Med. 2013;43(9):803-17. https://pubmed.ncbi.nlm.nih.gov/23681... • Yang N, et al. ACTN3 genotype and elite athletic performance. Am J Hum Genet. 2003;73(3):627-31. https://pubmed.ncbi.nlm.nih.gov/12879... Alpha-actinin-3: https://en.wikipedia.org/wiki/Alpha-a... • Alpha-actinin is an actin-binding https://en.wikipedia.org/wiki/Actin protein limited to skeletal muscle. It is localized to the Z-disc (https://en.wikipedia.org/wiki/Sarcome...) and dense bodies to anchor myofibrillar actin filaments (https://en.wikipedia.org/wiki/Alpha-a.... • Fast vs slow twitch muscle fibers: • Skeletal muscles (https://en.wikipedia.org/wiki/Skeleta...) is composed of slow twitch (type I) and fast twitch (type II) fibers involved in muscle contraction (https://en.wikipedia.org/wiki/Muscle_.... Slow twitch use oxygen efficiently, while fast twitch fire rapidly for more power. Alpha-actinin-3 is found in type II fibers. • Variations evolved to accommodate energy needs worldwide (https://en.wikipedia.org/wiki/Alpha-a.... Over 75% have ACTN3 577R. Homozygous individuals (ACTN3 577XX) have no alpha-actinin-3 (16%-20% of population) (https://en.wikipedia.org/wiki/Alpha-a..., but have high alpha-actinin-2 (https://en.wikipedia.org/wiki/Alpha-a....