Tweens and Sport, Part 1: What nobody tells you about the years that change so much

7 days ago

14 min read

This is part 1 of a two-part series. Part 1 explains how puberty affects young athletes, and what happens when the adults around them get it wrong. Part 2 covers what helps: fuelling, training, coaching language, the role of parents, and kit.

I have a simple goal. I want as many children as possible to move their bodies in ways they enjoy and are safe, and to continue doing so their entire lives. The physiological and psychological benefits of regular, enjoyable movement and sport participation are so far-reaching that I'd need a whole textbook to explain them. If you are reading this, I am sure I am preaching to the converted.

I want this for everyone. For the child who doesn’t think they are “sporty” enough to keep playing, the one who wants to quit at thirteen because they're not winning anymore, and the one who smashes it on the field and dreams of being a professional athlete one day.

This post is about one of the biggest barriers standing between children and lifelong movement and sport involvement. It happens during a window most of us don't understand well enough, and right when the adults around young athletes respond in ways that make everything worse. I see it and hear it every day.

Short on time? Here’s the main idea. The detail follows.

Puberty changes how a young athlete’s body grows, moves and uses fuel, often faster than they or the adults around them can keep up with. Girls usually experience a temporary performance dip as their bodies put energy into growth and reproductive development, and the accompanying weight gain is healthy and necessary. Boys go through puberty later, so the window when bones outgrow tendons and ligaments coincides with the pressure to specialise mounting and injury risk climbing.

When adults respond with more training, less food or comments about bodies, young athletes are more likely to get injured, struggle with food, or leave sport altogether. These three risks peak in the same window, and that's no coincidence. In part 2, I cover what helps.

A note on language: For the purpose of this article, "male/boy" and "female/girl" refer to biological sex and the physiological pathways associated with testosterone and estrogen. I recognise that biological sex and gender identity do not always align, and that transgender, non-binary, and intersex adolescents navigate these changes with unique needs.

What puberty actually does to a young body

Imagine mastering a complex sport skill when the equipment keeps changing. Every few weeks, the bat or racket size changes. The distance to the goal has shifted. The bar is narrower or at a different level.

Except the equipment that changes is your body.

This is what early adolescence feels like for a young athlete, typically between ages nine and thirteen for girls and eleven and fifteen for boys. Most adults around them have either forgotten what it felt like or never understood what was happening. I will be honest: we do know a fair amount about puberty and athletic development, but unfortunately it stays in textbooks and at academic conferences, and the people who need to know this stuff (aka the teens, their parents, and the average coach) don’t.

Puberty is not just about growing body hair and getting taller. It is a full biological reorganisation, physically disruptive in ways that are rarely explained to the athletes going through it, or the adults watching from the sideline.

Here are some of the things that are happening:

Height increases dramatically. At peak growth, girls typically gain 7 to 9 centimetres a year. Boys gain 8 to 10 centimetres. That is not gradual. It is a rapid, structural change happening to a body that still needs to perform.

Weight increases alongside height. Young athletes can gain around 10 kilograms in a single year during peak growth. Often, most of this weight gain can happen in bursts over a few weeks. This is normal. It is healthy. And it is necessary.

Of course, appetite increases significantly during this peak growth window. This is the body signalling exactly what it needs. But even that isn’t gradual and systematic. It is often up & down, and it can make everyone feel confused.

Legs and torso do not grow at the same rate. Infants, toddlers, and young children have proportionally more torso and head than limbs. During puberty, leg growth typically occurs first, around or just before peak height velocity. Trunk growth follows. A young athlete's proportions are shifting constantly, affecting balance, coordination, and how movement feels.

Bones grow faster than connective tissue can adapt. Muscles respond to growth relatively quickly. Tendons and ligaments do not. Connective tissue properties change significantly throughout adolescence, affecting joint stability, flexibility, and injury risk.
Bone mass is being built at a rate that will never happen again. Approximately 25 percent of peak adult bone mass is accumulated during the two years around peak height velocity. The nutritional and physical environment during this window has lifelong consequences for bone health.

Most young athletes also arrive at this window with significant gaps in their fundamental movement skills. Fundamental motor skills are the building blocks of all physical activity: running, jumping, throwing, catching, balancing, kicking, and hopping. Research consistently shows that many children and adolescents have not fully developed them, even those who are highly trained in a specific sport. A competitive swimmer may have beautiful technique in the water but struggle to throw a ball accurately, land a jump safely, or change direction on land. These gaps matter enormously during puberty, when the body is already reorganising structurally and needs broad movement competency to adapt well.

Girls tend to lag behind boys in object control and locomotor skills, while boys more often lag in body control and balance. Better movement dexterity, body control, timing, rhythm, and coordination support both better performance and lower injury risk. This is trainable. But it requires time, the right environment, and adults who understand what they are looking at.

Metabolism and fuelling change as your child moves through puberty. Children's bodies don't fuel exercise the same way adults' do. Before puberty, they rely more on fat and recover quickly between bursts of activity. During puberty, hormones like testosterone, estrogen and growth hormone start to shift this. Muscles grow, and the body gets better at using stored carbohydrates (glycogen) for fast, high-intensity effort, but also needs more fuel. Girls and boys also start to use fuel a little differently.

This is a time when your child's nutrition requirements are high. Regular meals and snacks that include carbohydrates and other nutrients support both growth and sport.

For a deeper look at the specific nutritional needs of young athletes, including energy, iron, calcium, and hydration, I have written about this in detail here

The difference between boys and girls. And why it’s harder for girls

Everything above applies to all young athletes. But for girls, an additional layer rarely acknowledged in sporting environments has significant consequences for both performance and long-term engagement in sport.

Boys get a neuromuscular boost during their growth spurt that naturally elevates speed, power, and coordination. Girls not only miss out on that boost; they actually experience a performance dip. Their bodies do enormous biological work during puberty, but that work goes toward reproductive development, not performance gains.

As female limbs lengthen and hips widen, most muscle groups do not automatically keep up. Girls effectively become relatively weaker because muscles now operate at a mechanical disadvantage with longer levers. Girls struggle to control longer limbs, a higher centre of mass, and more mobile joints. This makes it harder to stabilise. Deficits in strength at key links in the chain, notably the hip, drive these changes.

This does not mean anything is wrong with her body. It is a developmental difference, one that time and well-placed, targeted physical training can address. But it requires understanding what is happening, not panicking and blaming the wrong things.

"When you get to puberty, and you slow down, I don't think anyone gets anybody prepared for that kind of plateau. We need to educate girls on why it's happening, to let them know we're on their side. We understand what they're going through."

— Jenny Stout, former Olympic sprinter, Out of the Race: Why girls quit sport

The increase in body fat is essential.

Female puberty is marked by an increase in body fat, beginning even before the growth spurt. This is a biological prerequisite for the reproductive system to function, biology's way of ensuring there is enough fuel to support both growth and reproduction. Weight gain, specifically the increase in body fat around the hips, stomach, and arms, is one step in a cascade of hormonal shifts that began a few years earlier and ultimately lead to her first period.

Elite sprinter Isabelle Kyson describes exactly this moment in the documentary Out of the Race: Why girls quit sport

“When I was younger, I was really successful, and I was winning medals in almost every event. However, when I was about 12 years old, before I started my period, I experienced this weight gain, and I gained six kilograms in the space of six weeks. And despite me training harder than I ever had before, my performances were only going backwards, and this was just really disheartening to see."

Starting a period means your young athlete is healthy. Delayed menarche, defined as no period by age 15, or delayed puberty, no signs of breast development by age 13, signals a problem that needs medical attention, not a wait-and-see approach.

Remember, girls go through puberty earlier than boys, so an early-developing girl can find herself significantly bigger than almost everyone around her, boys and girls alike, for a couple of years. That is a long time to feel out of place in your own body. And it is precisely at this moment that she is most sensitive to commentary about how she looks.

The four years after a first period are one of the most nutritionally vulnerable windows of a girl's life. Bone mass is still being actively built. Hormonal systems are still stabilising. Energy needs are high. And this is precisely when food restriction causes the most damage.

Boys have their own challenges too

It would be a mistake to frame puberty as only a female problem. Adolescent boys face their own significant risks during this window, particularly around injury.

Boys go through puberty about two to three years later than girls, so their vulnerability window extends further into the mid-teen years, often when training demands and competitive pressures are intensifying.

While boys do get a neuromuscular boost during their growth spurt, there is a lag before those natural gains in strength and function fully kick in. It takes time to adapt to a changing body, recalibrate motor control and coordination, and adjust to growing limbs and increasing mass.

The danger zone for young male athletes is just before, during, and immediately following their growth spurt. During this window, bones are growing faster than the surrounding soft tissue can adapt. Flexibility decreases. Joints are under stress. And overuse injuries become significantly more common.

One of the most common conditions affecting young male athletes during this window is a cam deformity of the hip, a structural change to the hip joint that can progress to more serious injury if not identified and managed. Knee injuries are also common, along with tendinopathy affecting the shoulder, hip, and lower leg.

Early specialisation, committing to a single sport year-round, significantly increases injury risk during this window. A lack of variety in movement, combined with increasing weekly training loads, is a recipe for overuse injury, particularly between the ages of eleven and fourteen. After age fourteen, risk decreases, though late-maturing boys remain vulnerable until they reach skeletal maturity.

One important reminder: Two fifteen-year-old boys can differ biologically by as much as three years. Chronological age tells you very little about where a boy is in his development.

Puberty brings rapid gains in strength, power, speed and endurance for boys in a relatively short window. But more power doesn’t mean more control. Rapid growth disrupts coordination. Boys need help adjusting, coping with added stresses and strains, and learning to handle their new bodies. And grace to understand that two boys of the same age can be at very different developmental stages.

A note before we go further

The next section touches on eating disorders and disordered eating. Please be mindful of how you share or discuss this information with young athletes. For some vulnerable individuals, learning that eating less delays puberty, or hearing detailed descriptions of restriction, can reinforce rather than discourage harmful behaviours. This is not a reason to avoid the conversation. It is a reason to have it carefully, with the right support.

If you are concerned about a young athlete's relationship with food or their body, please reach out to an accredited dietitian or mental health professional with experience in eating disorders. Early, well-supported intervention makes a significant difference.

If you are a young person reading this and something here has stirred something for you, please talk to a trusted adult or seek support.

Three things that can happen when we get this wrong

When sporting environments don't account for what puberty does to young athletes, and adults respond with pressure, more repetitive training, restriction, and body commentary instead of support, three things can happen.

They get injured.

The mechanical changes of puberty create real vulnerability for all young athletes.

For girls, compensatory movement patterns develop as the body tries to manage longer legs and weaker hips. The quadriceps tend to keep up with growth, so girls rely on them more. This changes how they jump and land, accelerate and decelerate, and change direction. These compensatory strategies significantly increase stress on the knee and ankle joints. Talk to almost any adult female who played sport as a young girl, and most will tell you they had knee problems as a teenager.

For boys, rapidly growing bones, decreasing flexibility, and high training loads create the conditions for overuse injury, particularly at the hip, knee, and lower leg. The danger zone is just before, during, and immediately after the growth spurt, which for boys falls two to three years later than for girls, extending the window of vulnerability well into the mid-teen years.

Underfuelling makes all of this significantly worse. A tired, underfuelled athlete loses concentration and form, makes more mistakes, and becomes vulnerable to injuries. We'll cover more in the next session.

Suffering a first major injury is consistently cited by young female athletes as one of the primary reasons they stop participating in sport altogether. Which brings us to the second consequence.

Eating becomes a problem.

When energy demands are high from growing and playing sport, young athletes need more food throughout the day: more meals, more snacks, more carbohydrates (including sugar), protein, and fat (and vitamins and minerals, too). In Singapore, that means careful planning ahead, support from responsible caregivers, and inevitably relying on packaged food.

When energy intake consistently fails to meet demand, the body enters a state of disruption we now understand as Relative Energy Deficiency in Sport, or REDs. The consequences are similar to a device’s “low power mode”, where every system in the body runs in deficit: impaired bone development, suppressed hormonal function, increased injury risk, gastrointestinal problems, low mood, and diminished cognitive and sporting performance.

For some athletes, it goes further. Young athletes are at increased risk of developing a disordered relationship with food. High energy demands, a rapidly changing body, and a sporting environment that often prioritises and rewards leanness create the conditions for food and body image problems to take hold. When the adults in their lives start commenting, the risk increases further.

And if the messages around them, either from parents, coaches or social media, are all about clean eating, diets, “good” and “bad” food, portion control (“are you sure you want to eat that” and “how can you still be hungry”), things can quietly shift their relationship with food.

Around one in five athletes experience an eating disorder or disordered eating, and adolescent athletes are at greater risk than adults, making them one of the most vulnerable populations. Dieting is one of the clearest warning signs. Girls who diet severely are 18 times more likely to develop an eating disorder than girls who don’t.

Boys are not exempt. For boys, the picture might look different but is no less concerning. The pressure pushes them to get bigger, leaner, or stronger faster than biology allows. Boys who are developing later than their peers are particularly vulnerable. Watching teammates gain strength and muscle while their own bodies haven't caught up yet creates enormous pressure to do something about it. That something is often "protein maxxing", supplement use, or illegal performance-enhancing substances, driven not by genuine need but by the anxiety of falling behind during an uneven developmental window.

Comments about weight and body shape from parents or coaches consistently increase the risk of disordered eating, even when well-intentioned or well-meaning. In a study of adolescent elite athletes, 12 percent had received critical body weight comments from their coach. Adolescent female athletes experience higher coach-related pressure than adult athletes, making this window particularly high-risk. The research is clear: those comments have lasting effects.

Dietary restriction, appearance-based comments and attaching moral value to food by dividing it into good and bad are well-established precursors to eating disorders. It is also consistently the first response adults reach for when a young athlete's weight changes and performance dips. No sport is exempt. No athlete is immune.

They quit

As cited in Gooderick and Maloney, by age fourteen, girls drop out of sport at twice the rate of boys. The reasons are overlapping and complex, but many centre on the experience of puberty in a sporting environment that was not designed with a changing female body in mind.which

Girls become more body-conscious during puberty, which is developmentally normal. What is not inevitable, but is extremely common, is that the sporting environment amplifies that self-consciousness rather than containing it. Revealing kit. Appearance-focused commentary. Sarcasm, teasing or dismissive "banter". Comparison with teammates or siblings.

These struggles arrive when girls are most self-conscious and most sensitive to social judgement. The common assumption is that competitive sport is simply less appealing to girls than boys, but the evidence suggests it is more about confidence and feeling ill-equipped to compete than a lack of desire.

When nobody explains what is happening, the message she receives is: your body is the problem. You are not good enough. You do not belong here.

For many girls, the logical response is to remove themselves from the environment that delivers it.

The dropout window, the injury window, and the underfuelling window are the same window. That is not a coincidence.

In summary

Puberty is healthy, appropriate and somewhat confusing. Weight gain, growth, the performance dip, and the clumsy months are all signs of a healthy body maturing into adulthood.

What goes wrong is that adults around young athletes often misread what they see and respond with more of the wrong kind of training, stricter food rules, or comments about bodies.

The good news is that we can change this.

In part 2, I look at what we can do instead: better fuelling, better training, better communication, and better systems. Read part 2: what actually helps young athletes through puberty

If you would like support navigating this for your child or your team, I would love to hear from you.

References

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