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Is Physical Fitness Genetic?

IS PHYSICAL FITNESS GENETIC? 

By Annelie Smith. RD IFNCP.  
Head of Clinical and Mentorship 3X4 Genetics. 

Physical fitness may mean different things for each one of us. It may involve adequate energy and capacity to perform daily tasks or the ability to take part in specific sports activities that require various amounts of strength, speed, power, or flexibility.  

Given the vast number of exercise programs, gyms, and blanket recommendations about fitness and exercise, you may think that your response and physical adaptation to exercise is predictable. Yet, from experience, we have seen that individuals following the same training method or program will respond differently.  

GENETICS AND TRAINING 

Genetics account for as much as 66% to our overall athletic status, as found by heritability studies. This includes the ability to adapt to training load, building muscle and connective tissue, and improving endurance, speed, and strength. The rest of the variance in athletic performance and fitness is due to factors such as nutrition, environment, training practice, and opportunities to take part. 

In a study conducted on 175 subjects who were given both endurance and power training exercises, it was found that some participants responded more favorably to endurance exercise while others responded to power exercise to improve their fitness levels. VO2max is a measure of fitness, which is the maximum amount of oxygen your body can use during exercise. In this study, it was found that genetics accounted for approximately 50% of improvements in VO2 max following training. This showed that there are no “responders” or “non-responders” to exercise but merely responders and non-responders to the type of exercise. 

GENETICS AND ENDURANCE ATHLETE STATUS  

Studies show that genetic factors account for up to 70% of the variability in endurance-related exercise ability. These factors include how muscles are formed, the way energy is generated, access to the body's fuel stores, and how oxygen is carried in the blood. 

MUSCLE FIBERS AND GENETICS 

Genes impact the type of muscle fibers in our body. We refer to slow twitch muscle fibers which are more suitable for endurance exercise, and fast twitch fibers which favor the ability to do power-type exercises like sprinting. Our genes affect the formation of these fibers.  

GENETICS AND ENERGY 

When we train, we increase the number of mitochondria in our cells. Mitochondria are the “powerhouses” of our cells responsible for generating energy. Some individuals have a genetic advantage to the number of mitochondria they have at a baseline and how exercise can increase the number of them. This gives them an advantage in the rate at which their fitness and endurance levels increase.  

LINK BETWEEN GENETICS AND MUSCLE GROWTH, POWER AND STRENGTH 

The rate of muscle growth stimulated by resistance and strength exercise is affected by genetics. Muscle type and growth are important for power-related types of performances including weightlifting, sprinting, kicking, and jumping ability. The heritability of power-based abilities has been reported in the literature to range from approximately 49-86%. This includes the impact of genetics on the formation of muscle fiber types and muscle mass, body height, and the production of anabolic hormones such as testosterone. Similarly, genetics impact strength development in athletes by affecting muscle fiber type and size, neurological adaptation, energy production capacity, and the amount of circulating testosterone.  

DOES GENETICS AFFECT OUR RATE OF RECOVERY? 

Recovery from exercise plays a key role in the ability to improve fitness. The rate at which one can recover directly impacts the fitness improvements made in response to training. Genetics plays a large role in this, particularly in the areas of oxidative stress and inflammation. Oxidative stress is the imbalance of potentially damaging substances generated by the cells to produce energy and their removal. These substances are sometimes called free radicals and are associated with muscle inflammation, soreness, and damage. 

In conclusion, genetics play a significant role in fitness and adaptation to sporting types, athletic performance, and exercise capacity. Knowing more about your genetic makeup can guide you to train to your strengths and support your weaknesses, allowing you to personalize your training program and to reach your best fitness level.