What body fat is doing
In a growing teenager, body fat is not spare weight. It supports hormone production, the arrival and continuation of periods, immune function and bone development, alongside being an energy store.
Some increase in body fat through puberty is normal and expected in girls. It is part of maturing, not a training failure.
Why the lean-equals-fast idea is misleading
In some sports, leaner athletes do perform better, and that fact gets applied badly to children. Adult elite physiques are the result of years of development, and copying them at 14 tends to cut short the very development that produces them.
The pattern is common enough to be predictable: a young athlete gets lighter, improves for a season, then stops improving, picks up bone injuries and loses a year.
Builds a career
- Getting stronger
- Better technique
- Eating enough to train hard
- Sleeping properly
- Load that rises gradually
Borrows from next year
- Getting lighter
- Cutting food groups
- Training more on less fuel
- Weekly weigh-ins
- Comparing physiques
Two ways to get faster at 14
Signs that leanness is costing something
- Periods late to start, irregular, or stopped.
- Not gaining weight or height as expected through a growth phase.
- Bone stress injuries, especially more than one.
- Fatigue that does not lift with an easier week.
- Feeling cold much of the time.
- Performance flat or declining despite training well.
- Rules, anxiety or secrecy around food.
What to measure instead
Track things that reflect development: growth along her own trajectory, regular periods, energy at the end of a session and at school, recovery within a day or two, and simple performance tests such as a broad jump or a set of calf raises every couple of months.
Skinfolds, weigh-ins and body fat percentages give a coach nothing they can use in a young athlete, and give the athlete something she may carry for years.
If someone has commented on her physique
Comments from a coach or teammate about weight or leanness are a common trigger for restriction in teenage girls. Take them seriously: talk with her about it, and take it up with the club. Youth coaching should say nothing about a child's body composition.
If food has already become tense, involve a GP early and ask about a referral to someone experienced with young athletes.