Training Through Puberty: How Growth Changes Everything for Young Athletes

She was the best midfielder on the team at eleven. Fast, coordinated, fearless on the ball. By thirteen, she was tripping over her own feet, missing passes she used to make in her sleep, and asking her parents if she could quit. Her coach called it a "motivation problem." It wasn't. It was puberty — the most dramatic physical transformation a human body undergoes outside the womb — and nobody had told her it was coming, or that it was completely normal.

Puberty rewires everything. It changes how athletes move, how they think, how they feel about themselves, and how they respond to training. Yet most youth sport programs treat a 13-year-old the same as a 10-year-old, expect the same performance trajectory, and make selection decisions during the most biologically volatile period of human development. The result is predictable: confused kids, frustrated coaches, and a massive talent drain as late-developing athletes walk away from sports they might have excelled in.

Peak Height Velocity and the "Clumsy Phase"

The centerpiece of adolescent growth is Peak Height Velocity (PHV) — the period during which a young person is growing at their fastest rate. For girls, PHV typically occurs around age 11-12; for boys, around age 13-14. During this window, the body can grow 8-9 centimeters per year, and in some cases, adolescents gain 10-12 centimeters in a single year. The Mirwald et al. maturity offset method — one of the most widely used tools for estimating PHV timing — has demonstrated just how much individual variation exists. Two teammates born in the same month can be separated by two or more years in biological maturity.

Here is what that rapid growth does to athletic performance: it temporarily destroys coordination. Bones grow faster than muscles and tendons can adapt. Limbs get longer before the neuromuscular system recalibrates its movement maps. The result is the "adolescent awkwardness" phase — a well-documented period where previously coordinated athletes suddenly look clumsy, lose agility, mistime movements, and struggle with skills they had mastered. A soccer player who could dribble through defenders at eleven now can't control a simple pass at thirteen. A gymnast who landed clean vaults starts under-rotating. A basketball player whose shooting form was textbook now can't find the hoop.

This is not a regression in talent. It is a biological recalibration, and it is temporary. But if coaches and parents don't understand what is happening, they read it as a loss of ability — and so does the athlete. That misinterpretation is where the damage begins.

Hormonal Shifts: Testosterone, Estrogen, and What They Mean for Training

Puberty is fundamentally a hormonal event, and the training implications differ significantly between boys and girls. In boys, testosterone levels can increase by as much as 20- to 30-fold during puberty. This surge drives increases in muscle mass, bone density, and red blood cell production. Boys in late puberty and post-puberty can build muscle and recover from strength training in ways that pre-pubertal boys cannot. This is why Lloyd and Oliver's Youth Physical Development (YPD) model emphasizes that structured resistance training becomes particularly effective during and after PHV in males — not before.

In girls, estrogen drives different adaptations: widening of the hips, increased body fat percentage (particularly in the hips and thighs), and changes in ligament laxity. The estrogen-driven increase in joint laxity, combined with wider hip angles, is one of the reasons female athletes experience ACL injuries at 2-8 times the rate of males in the same sports. This is not a reason to restrict girls from sport — it is a reason to prioritize neuromuscular training, landing mechanics, and hip/core strengthening programs starting well before puberty hits.

Both sexes experience significant changes in their center of gravity during puberty. Boys become relatively top-heavy as their shoulders broaden; girls carry more mass through the hips. Both shifts require the neuromuscular system to recalibrate balance and proprioception — another contributor to the "clumsy phase."

Early Maturers vs. Late Maturers: The Selection Trap

This is one of the most consequential and least understood dynamics in youth sport. An early-maturing 12-year-old boy might be 5'7", 140 pounds, with visible muscle definition and the beginnings of adult-level power. A late-maturing 12-year-old on the same team might be 4'11", 90 pounds, and still look like a child. They are the same chronological age. They may be separated by three or more years of biological age.

The early maturer dominates. He is faster, stronger...