Girls and weights: does strength training at 13-14 stunt growth?

No. In the most cited review on the question, 22 experimental weight-training programmes in children and pre-adolescents did not influence growth in height or weight, with estimated injury rates between 0.053 and 0.176 per 100 participant-hours. Yet only 38.5% of children and adolescents meet muscle-strengthening recommendations — and being a boy is one of the factors that predicts meeting them. What the data actually say about strength in young female athletes.

Youth sport is still full of statements about the weights room that nobody has ever checked. "Weights stunt your growth." "Wait until you've finished growing." "Girls need flexibility more than strength." These claims share one feature: no consensus statement and no available meta-analysis supports them. And they carry a measurable cost, because the people left out are disproportionately girls.

Key points

  • 22 experimental programmes of weight training in children and pre-adolescents did not influence growth in height and weight; estimated injury rates between 0.053 and 0.176 per 100 participant-hours (Malina, 2006).
  • Only 38.51% of children and adolescents meet WHO muscle-strengthening recommendations of ≥3 days a week — and being a boy is among the predictors of meeting them (García-Hermoso et al., 2025; 1,273,544 participants, mean age 13.40 years).
  • The effect on strength is consistent: effect size 1.12 (95% CI 0.9-1.3) in children and adolescents, with maturity as a moderator (Behringer et al., 2010).
  • As prevention, strength training alone is associated with an injury risk of 0.338 (95% CI 0.238-0.480) — but in participants aged 12-40, not adolescents only (Lauersen et al., 2018).
  • The two conditions present in every document: qualified supervision and technique before load.

Do weights stunt growth? What the most cited review says

No. That is the short answer, and for once it rests on a piece of work designed to answer exactly this question.

In 2006 Robert Malina published an evidence-based review of 22 experimental resistance-training programmes in children and pre-adolescents, examining them on three fronts: training response, effect on growth and maturation, and injury. The conclusions: the programmes produced significant improvements in muscular strength during childhood and early adolescence, did not influence growth in height and weight, and changes in body-composition estimates were variable and quite small. On safety: only 10 studies systematically monitored injuries, and in total three injuries were reported, with estimated rates of 0.176, 0.053 and 0.055 per 100 participant-hours (Malina, 2006).

The author's conclusion is precise about its conditions, and worth quoting in that form: protocols with weights and resistance machines with supervision and low instructor-to-participant ratios are relatively safe and do not negatively impact growth and maturation. Not "weights are safe": these protocols, under these conditions.

One honest caveat, because it matters: that review covers children and pre-adolescents, and the programmes typically ran 8-12 weeks. It is not proof that anything done in a weights room at 14 is harmless — it is proof that the specific fear ("stunting growth") is not supported when training is designed and supervised. Malina also notes something less comfortable: strength gains were lost during detraining. Strength is not a deposit that stays: it is an adaptation that persists only while it keeps being stimulated.

Why the fear is about the growth plate

The fear has a precise anatomical target: the growth plate, the zone from which long bones lengthen during growth and which is mechanically weaker than mature bone. That this zone is vulnerable is true, and it is why adolescence has load-related conditions of its own — from apophysitis to Osgood-Schlatter disease.

What does not hold is the next logical step: that load should therefore be avoided. Consensus statements go the other way. The position statement on youth resistance training — adapted from the official statement of the UK Strength and Conditioning Association, then reviewed and endorsed by leading organisations in sports medicine, exercise science and paediatrics, with an author team drawn from paediatric exercise science, paediatric medicine, physical education, strength and conditioning and sports medicine — holds that youth resistance training is safe and effective when appropriately designed and supervised (Lloyd et al., 2014). The clinical report of the American Academy of Pediatrics, a revision of the 2008 policy statement (Stricker et al., 2020), points the same way, and flags the other side of the coin: a secular decline in measures of muscular fitness in modern-day youth, affecting athletes and non-athletes alike.

The documented risk is not load itself: it is load without supervision, without technique and with improvised progressions. Which, in practice, moves the question from "at what age?" to "with whom?".

How much strength does a 13-14-year-old girl actually gain?

Enough to be visible, and in a way that changes with maturation.

A meta-analysis of healthy children and adolescents under 18 calculated an overall effect size of 1.12 (95% CI 0.9-1.3) for muscle strength. The interesting detail lies in the moderators: maturity was a significant categorical moderator, and positive correlations were found for programme duration (r = 0.28) and frequency (r = 0.26). The authors conclude that the ability to gain strength increases with age and maturational status, but without a noticeable boost at puberty (Behringer et al., 2010).

That is worth translating. Before the growth spurt, gains come mostly from neural adaptations — the body learns to recruit better what it already has. Afterwards the structural component is added. There is no switch that flips at menarche: there is a curve that rises.

For young athletes specifically, the reference meta-analysis included 43 studies with an active control group, in athletes aged 6-18. Moderate effects on muscle strength and vertical jump (SMD 0.8-1.09) and small effects on linear sprint, agility and sport-specific performance (SMD 0.58-0.75). Effects were moderated by sex and by training type — worth noting, because sex as a moderator is a variable most sport-science research does not even test (Lesinski et al., 2016).

On parameters, the same analysis identifies what maximises strength gains: blocks longer than 23 weeks, 5 sets per exercise, 6-8 repetitions, intensity at 80-89% of one-repetition maximum and 3-4 minutes of rest. With a clear warning: those numbers describe what maximises performance in supervised studies of youth athletes, not a starting point. For a girl beginning at 13, the first block is her own body weight, movement quality and consistency — and consistency, as it happens, is exactly the parameter that correlates with results in the meta-analysis.

Does strength training prevent injuries?

This is the best-documented effect of all, and also the one where transferring across ages needs most care.

A systematic review and meta-analysis examined only randomised controlled trials in which strength training was the primary-prevention intervention: 6 studies, 5 different interventions, 7,738 participants aged 12-40, 177 acute or overuse injuries. The cluster-adjusted intention-to-treat analysis estimates a relative risk of 0.338 (95% CI 0.238-0.480): roughly one third. The result held across robustness tests, strength of evidence was rated high, no publication bias was found, and meta-regression shows a dose-response relationship: a 10% increase in strength-training volume was associated with a reduction in injury risk of more than four percentage points (Lauersen et al., 2018).

The limitation is the age range: 12-40 years, with results not broken down by band. It is not an estimate specific to 13-year-olds, and presenting it as one would be wrong. What can honestly be said is that the direction is unambiguous, that the lower end of the sample includes adolescents, and that for young female athletes there is a parallel and more targeted line of work: preventive neuromuscular training, whose effect on ACL injury risk is among the best established in women's sports medicine. Strength training and neuromuscular training are not the same thing, but they share much of their content.

And there is a third front, often forgotten: strength is not only prevention, it is also treatment. In adolescent patellofemoral pain — the most common knee problem in this age group — the approach with the best results is not rest but load management with strengthening exercise.

Why is it mostly girls who are left out?

Here the data are recent, enormous and rarely discussed.

A 2025 meta-analysis pooled 29 studies covering 1,273,544 children and adolescents in 36 countries (49.40% girls, mean age 13.40 years) to estimate how many meet the WHO recommendation of muscle-strengthening activity on at least 3 days a week. The overall estimate is 38.51% (95% CI 34.35-42.75). In subgroup analyses, the predictors favouring compliance include being a boy (García-Hermoso et al., 2025).

Six in ten do not get there, and the gap is not random. This is not a statement about girls' motivation: it is a statement about what is offered to whom. Whoever decides the content of a training session also decides who gets access to an adaptation that protects bone, reduces injury risk and improves performance. When that decision follows an unverified idea — "girls need something else" — the effect is not neutral.

The parallel with the rest of this blog is obvious. As with the menstrual cycle, with sports bras and with the words coaching staff use, the barrier is not biological: it is informational. Which is precisely why it can be removed.

Five principles that survive a reading of the data

These are not a training programme — that is written by whoever knows the athlete. They are the points on which the documents cited above converge.

BAB's role

BAB does not write training programmes and does not replace the people who do. It works one step upstream: it gives the athlete a way to observe how she is doing — perceived load, recovery, pain, energy — and gives the club aggregated, anonymous signals only, never an individual's health data. Because the difference between load that builds and load that breaks is rarely visible in the training plan: it is visible in how the athlete is doing the following week.

And because the sentence "weights stunt your growth" should not cost a fourteen-year-old the years in which she could build a body that holds up.

Sources

This article is for information only and is not medical advice or a training prescription. If pain persists during or after training, consult a healthcare professional.

Do weights stunt growth in girls?

No — and this is one of the few questions where the evidence is reasonably clear. An evidence-based review of 22 experimental resistance-training programmes in children and pre-adolescents concluded that protocols using weights and machines with supervision and low instructor-to-participant ratios are relatively safe and do not negatively affect growth and maturation: the programmes did not influence growth in height and weight, and across the 10 studies that systematically monitored injuries only three injuries were reported, with estimated rates between 0.053 and 0.176 per 100 participant-hours (Malina, 2006). The two conditions that recur everywhere in this literature are qualified supervision and technique before load.

At what age can a girl start strength training?

Consensus statements do not set a minimum chronological age: the criterion they use is the ability to receive and follow instructions and to perform a movement safely (Lloyd et al., 2014; Stricker et al., AAP 2020). In practice that is much earlier than most people assume — and well before the growth spurt. The practical question is not "from what age" but "with whom": the variable present in every document is qualified supervision, not the date on an ID card.

Does strength training actually make girls stronger before puberty?

Yes, but the response grows with maturation. A meta-analysis of healthy children and adolescents under 18 found an overall effect size of 1.12 (95% CI 0.9-1.3) for muscle strength, with maturity as a significant moderator: the ability to gain strength increases with age and maturational status, without a sudden boost at puberty (Behringer et al., 2010). In practice, before the growth spurt gains come mostly from coordination and the ability to recruit muscle; afterwards the structural component is added.

Does strength training reduce injuries?

It is the best-documented effect, but the number has to be read with the right age in mind. A systematic review and meta-analysis of randomised trials using strength training alone as primary prevention estimated a relative risk of injury of 0.338 (95% CI 0.238-0.480) — roughly one third — with strength of evidence rated high and a dose-response relationship: a 10% increase in strength-training volume was associated with more than a four percentage-point reduction in risk (Lauersen et al., 2018). The caveat: the 7,738 participants were aged 12-40, so this is not an adolescent-specific estimate. For young female athletes the most targeted evidence concerns preventive neuromuscular training, a close relative of strength work.

How many girls actually do muscle-strengthening activity?

Fewer than you would think, and fewer than boys. A meta-analysis of 29 studies covering 1,273,544 children and adolescents in 36 countries (49.40% girls, mean age 13.40 years) estimated that only 38.51% (95% CI 34.35-42.75) meet the WHO recommendation of muscle-strengthening activity on at least 3 days a week; among the factors predicting compliance is being a boy (García-Hermoso et al., 2025). This is not a statement about girls' motivation: it is a statement about what is offered to whom.

Do you need to lift maximal loads to train strength at 14?

No, and no consensus document recommends maximal lifts before puberty or during the growth spurt: they converge on qualified supervision, gradual progression and technique before load (Lloyd et al., 2014; Stricker et al., 2020). One honest clarification about the numbers that circulate: the dose-response meta-analysis of 43 studies in youth athletes aged 6-18 indicates that maximising strength gains requires long blocks (more than 23 weeks) and high intensities (80-89% of one-repetition maximum) (Lesinski et al., 2016) — but those parameters describe what maximises performance in supervised research settings, not a starting point. For a 13-14-year-old athlete, useful progression starts with body weight and movement quality.

Is strength training good for girls' bones too?

Mechanical loading is one of the stimuli that build bone, and adolescence is the window where it matters most: total bone mineral content plateaus on average 6 years after peak height velocity, roughly age 18 in girls (Baxter-Jones et al., 2011). On specific protocols, though, the strongest experimental evidence in adolescents concerns impact loading rather than weights: 10 minutes of jumping twice a week for 8 months increased femoral neck bone mineral content by 13.9% versus 4.9% in controls (Weeks et al., 2008). Strength and impact are not alternatives: they add up.