Puberty is a biological transition marked by rapid physical and hormonal changes that transform a child’s body into an adult’s. The question of whether this process makes you run slower has a nuanced answer: it often causes a temporary reduction in performance for all young athletes. However, the long-term changes are highly variable and depend significantly on the athlete’s sex and their individual timing of maturation. This temporary slowing is primarily due to mechanical adjustments, while the lasting performance trajectory is driven by diverging hormonal shifts.
The Immediate Impact of Rapid Growth
The most immediate cause of a perceived slowing during puberty is the adolescent growth spurt, a period of rapid skeletal lengthening that can temporarily disrupt the body’s mechanics. The sudden increase in height and weight, particularly the lengthening of the limbs, alters the body’s center of gravity. This change in mass distribution forces the nervous system to quickly learn new balance and motor control parameters, which can lead to temporary “clumsiness” or a coordination deficit in running and other complex movements.
Skeletal growth often outpaces the growth of muscles, tendons, and fascia, creating a period where the muscles are relatively tighter and less efficient at generating force. This disproportionate growth changes the leverage of the limbs, requiring the athlete to control a larger, heavier frame with muscles that have not yet fully strengthened to match the new bone length. The result is a temporary loss of biomechanical efficiency, making the familiar act of running feel awkward and less powerful.
The bones are also temporarily more vulnerable during the period of peak height velocity because the growth plates are weakest when growth is most accelerated. This increased vulnerability, combined with the new biomechanical demands, can lead to a higher risk of overuse injuries like apophysitis. This phase is characterized by a temporary decrease in the body’s ability to control stiffness, which is necessary for efficient running and utilizing elastic energy.
Hormonal Changes and Diverging Performance Paths
Beyond the mechanical issues of rapid growth, the profound hormonal changes of puberty establish distinct long-term performance paths for male and female athletes. Before puberty, the performance difference between sexes in running is minimal, but a major divergence begins with the onset of sex hormone production.
In male athletes, the dramatic increase in testosterone levels—which can rise by 20 to 30 times by adulthood—is the primary driver of long-term speed and power gains. This surge leads to significant muscle hypertrophy, resulting in greater skeletal muscle mass and strength, especially in fast-twitch muscle fibers. Testosterone also stimulates the production of hemoglobin, increasing the blood’s oxygen-carrying capacity, which enhances endurance and aerobic performance.
For female athletes, the rise in estrogen directs development toward increased body fat percentage, a necessary biological component for maturation and reproductive function. While female athletes also gain muscle mass and strength during puberty, the relative increase is much less pronounced than in males. This shift in body composition, along with the development of a wider pelvis, often alters running biomechanics and can contribute to a plateau in speed development.
The hormonal changes result in adult males typically being 10% to 30% faster, stronger, and more powerful than females in events that rely on muscular power and endurance. This performance gap widens significantly after the onset of male puberty. The long-term physiological advantages gained by males ultimately translate into greater speed and power capabilities post-maturation.
Training Adjustments During Athletic Maturation
Navigating the pubertal growth period requires a shift in training philosophy, prioritizing adaptation and injury prevention over performance metrics. Because the central nervous system is adjusting to a new body size, coaches and athletes should focus on maintaining and improving coordination and skill development. This means incorporating coordination-focused exercises and movement-based strength work, rather than simply increasing the intensity or volume of runs.
The risk of injury, particularly to growth plates, increases during peak height velocity due to the differential growth rates of bone and soft tissue. To mitigate this, strength training should be implemented, beginning with bodyweight resistance to build a foundational base before introducing heavier loads. Emphasis should be placed on functional movements like squatting, lunging, and jumping, ensuring the athlete can control their new body mass through a full range of motion.
It is helpful to monitor the athlete’s psychological well-being and be patient with temporary performance declines. Coaches and parents should focus on the process of development and flexible goal setting, rather than strict adherence to pre-pubertal personal best times. Providing support and encouragement during this period of physical and emotional volatility ensures the athlete remains engaged in the sport.