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Youth Physiology – Michael’s Message

Youth Physiology – Michael’s Message
September 15, 2017 Nick Seitz

Youth Physiology

This past weekend, I had the honor of presenting at one of the first USA Triathlon Youth & Junior Elite certifications. I presented on several topics including youth physiology, draft legal racing, and run/swim/strength training for the junior elite athlete.

The foundation of each of these topics is a firm understanding of youth physiology which I wanted to take an opportunity to share with you all today.

Today, we see youth athletes pushed earlier and earlier to train at higher volume levels, specialize in single sports, and compromise long-term potential for short-term gains. Unfortunately, this epidemic is leading to higher levels of burn-out, injury, and poor mental health. Instead, we must recognize that youth athletes are not built like adults and therefore their training should look very different. Furthermore, a 9-year old athlete needs very different workouts than a 15-year old athlete.

An understanding of youth physiology will clarify this. I will present this in 2 stages of development: pre-puberty and post-puberty.


The young athlete’s body is a sponge in many ways: Able to soak up training with long-lasting effects. In other ways, training certain areas will only leave the athlete mentally fried with little impact on long-term fitness. The key to coaching young athletes is knowing what will have an impact and what will not.

Young bodies lack the ability to respond to certain physiological demands placed upon them. For example, a young athlete’s body has a limited ability to store glycogen (carbohydrates) at the tune of about 50-60% the storage capacity of adults. Therefore, their ability to do quality anaerobic work, which depends largely on carbohydrates for fuel is limited. Additionally, youth consume much less oxygen into their lungs on every breath and pump less blood (carrying this oxygen to working muscles) per heart beat than adults.

Because of this, the ability to train VO2 Max effectively is stifled by the limitations of the heart and lungs. Lastly, due to poor sweat mechanisms and utilization of fat as fuel, youth athletes have a very poor ability to develop aerobic endurance, something that can be developed for much of a person’s life. Therefore, adopting a high-volume training program will prevent the young athlete from developing what can truly impact change in their bodies and stifle long-term development.

So, what should young athletes focus their workouts on? Though their bodies are limited in many areas, there are certain things that are critical for development. Much like speech, young athletes either develop these things or limit their potential for the future. The first of these is technique. We learn muscle movements better at a young age with neural pathways to muscles being created with relative ease. Therefore, we must insist on proper technique with young athletes, creating a foundation for a lifetime.

Additionally, the young body is ripe to develop max speed. Rich with ATP, the primary energy source for short, explosive efforts, young athletes can near fully develop their speed. Once developed, athletes will rely on this speed for a lifetime carrying it across longer and longer distances.


Several changes happen in the body at puberty that trigger the need for a change in training. The athlete who has hit puberty can begin to train more like an adult but not fully. Specifically, endurance training and threshold development should be held back as the body does not reach full potential here until adulthood and will continue to develop for much of a person’s life. Hence, we see long course athletes thriving into their 40s whereas a teenager will struggle at the marathon or Ironman distance.

Throughout the teenage years though, we must train certain physiological systems as they will struggle to be developed fully in adulthood. This largely includes anaerobic endurance and VO2 Max development. With puberty, the ability to store glycogen and process oxygen greatly improves.

More so, the post-puberty years contain a critical period for development of both as anaerobic endurance potential and VO2 Max decline steadily with the onset of adulthood through the rest of one’s life. Therefore, a post-puberty athlete should seek to get these numbers as high as possible in their teenage years.


Though there is still a good dose of aerobic develop in any endurance athlete’s program, youth and junior athletes should place a heavier emphasis on speed, anaerobic development, and VO2 Max compared to adults. In the early years pre-puberty, it is essential that we develop coordination through proper technique and fast twitch muscle fibers through explosive speed.

The body (and mind) is ripe to absorb both, which will have a lasting impact on the athlete. With the onset of puberty, several changes happen in the body, allowing a young person to absorb more training above the anaerobic threshold.   As an athlete approaches puberty, we should begin introducing athletes to small doses of anaerobic endurance and VO2 Max workouts, and then post-puberty, there should be a heavier focus on both.

Technique remains a focus throughout an athletic career, regardless of age. Aerobic development focus is minimal at a young age and progressively grows in importance throughout the years with heightened emphasis as athletes move into adulthood.

To learn more about our specialized approach to youth coaching, click here! Mental and physical endurance are vital to the long term success of young athletes- both in sport and life. Myself or any of our coaches would be thrilled to talk further if you have any questions.

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