Youth and adolescent runners
Evidence: moderate
Children are not small adults. They have a smaller trainable VO2max response, lean on aerobic metabolism, and are vulnerable at the growth plates during the growth spurt. Broad athletic development beats early specialisation, well-supervised resistance training is safe, and energy availability matters most in adolescence.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Training a child or adolescent is not training a scaled-down adult. Physiology, growth and injury risk all differ, and the long-term goal of producing a capable adult athlete often conflicts with chasing fast results before maturity.
Trainability and maturation
Children respond to endurance training differently from adults. The trainable improvement in VO2max is smaller in pre-pubertal children than in adults given a comparable stimulus, partly because much of the change tracks growth and maturation rather than the training itself (Lloyd & Oliver 2012). Children also rely more heavily on aerobic, oxidative metabolism and have a limited anaerobic, glycolytic capacity that only matures through adolescence (Lloyd & Oliver 2012). This is why short, repeated high-intensity efforts feel different for children, and why training built on adult interval logic transfers poorly.
The Youth Physical Development model maps the trainability of different qualities onto biological maturation rather than chronological age, centred on peak height velocity, the point of fastest growth during the spurt (Lloyd & Oliver 2012). Two children of the same age can sit years apart in maturity, so age alone is a poor guide to what a young runner is ready for, an extreme case of the individual variation seen in all runners.
Growth, the growth spurt and injury
Around peak height velocity, bones lengthen faster than muscles and tendons adapt, which can produce temporary clumsiness and a dip in coordination (Bergeron et al. 2015). Injury vulnerability rises in this window, and the pattern differs from adults. Where adults accumulate soft-tissue overuse injuries, growing athletes are prone to apophyseal injuries at the growth plates, such as Sever’s disease at the heel and Osgood-Schlatter disease at the knee, where tendon attaches to immature bone (Bergeron et al. 2015). Loads that an adult skeleton tolerates can concentrate at these sites in a growing one.
Broad development over early specialisation
The strongest recommendation for young runners is to develop broadly rather than specialise early. Varied activity, exposure to many movement skills and general athletic development build a wider foundation than high running mileage does, and they leave more options open (Bergeron et al. 2015). Early single-sport specialisation carries real costs: higher rates of overuse injury, greater risk of burnout and dropout, and exposure to chronic low energy availability and RED-S (Bergeron et al. 2015). Early results are a weak predictor of senior success, and the runners who specialise soonest are not the ones who last.
Resistance training is safe and useful
The old belief that lifting weights stunts growth or damages growth plates is wrong. Well-supervised, age-appropriate resistance training is safe for children and adolescents and improves strength, motor skill, bone health and injury resilience (Lloyd et al. 2014). Supervision and technique matter more than load, but the activity itself is beneficial, not something to defer until adulthood. The case overlaps with the wider one for strength training for runners.
Energy availability and bone
Adolescence is when most bone mass is laid down, which makes adequate fuelling especially important. Chronic low energy availability in this window impairs bone development and drives RED-S, with consequences that include bone stress injuries (Bergeron et al. 2015). A young runner who under-fuels does not just train worse now; they may build a weaker skeleton for life.
Volume and patience
Age-appropriate volumes, gradual progression and long-term patience serve young runners better than maximising training now. The aim is a healthy, capable adult athlete, and on that horizon long-term development reliably beats early results (Bergeron et al. 2015). The same principle of building from a sound base applies to every runner, as set out in the basics. Decisions about an individual young runner’s training, growth and health belong with their coaches and clinicians.