Kids and Strength Training: What the Science Actually Says
Kids and strength training:
what the science
actually says.
"Lifting weights stunts your kid's growth" is one of the most persistent fitness myths in parenting. The research is clear, the major paediatric bodies agree, and the truth is the opposite of what most parents have been told.
If you've ever asked a parent whether their kid lifts weights, you've probably heard a variation of the same response: "No, I read somewhere that it stunts their growth."
This is so widespread it's become parenting folk wisdom. It's also wrong. Not "the science is mixed" wrong — flatly wrong, contradicted by every major paediatric body, and not actually based on any credible study at any point in the last 50 years.
This piece is for the parent who's wondering whether kids strength training is safe, who's heard the myth, and wants the actual evidence-based answer. Here it is.
Where the myth came from
The "lifting stunts growth" idea comes from a real concern about growth plate injuries. Growth plates are the cartilaginous regions at the ends of growing bones — they're the bits that lengthen as a child grows. Damage to a growth plate can, in rare cases, affect bone development.
In the 1970s and 80s, when adult-style powerlifting was first being tried on adolescents, there were a small number of injury reports. The reaction in the medical community at the time was conservative: "better safe than sorry — keep kids away from weights."
That guidance got absorbed into popular culture and stuck for 50 years. Meanwhile, the actual science moved on entirely. Subsequent research found that those early injuries weren't from strength training per se — they were from inappropriate loading, no supervision, and bad technique. Properly coached strength training in kids turns out to be one of the safest forms of exercise there is.
What the major paediatric bodies actually say (now)
This is the part most parents haven't seen. Here's the official position of the bodies that set guidance for paediatric exercise:
The American Academy of Pediatrics (AAP)
In their 2020 policy statement on resistance training for children and adolescents, the AAP states clearly that strength training is safe and beneficial for children when properly supervised, and that the historical concerns about growth plate damage and stunted growth have not been borne out by research.
The UK Chief Medical Officers
The UK's guidance for children aged 5–18 explicitly recommends "muscle-strengthening activities" at least three days per week. The guidance lists strength training, climbing, and bodyweight exercises among the recommended forms.
The NHS
The NHS exercise guidance for children mirrors the CMO advice and specifically endorses "activities that strengthen muscles and bones" for kids 5+, including resistance training under supervision.
The National Strength and Conditioning Association (NSCA)
Position statement: properly designed and supervised resistance training programs are safe and effective for children, and the benefits outweigh any potential risks.
That's a clean sweep. Every credible body looking at this has reached the same conclusion: properly coached strength training is safe for kids and actively recommended.
What the research actually shows kids gain
The benefits documented in the research literature go well beyond "they get stronger." Here's what's been shown:
1. Reduced sports injuries
Kids who strength train are significantly less likely to be injured in their other sports. The most cited research shows ACL injury rates in young female athletes drop by up to 60% in groups that follow proper resistance training programmes alongside their main sport. The reason is straightforward: stronger joints, better coordination, more resilient connective tissue.
2. Better bone density
The bone-building stimulus in childhood and adolescence sets the baseline for adult bone density. Kids who strength train build more bone density during their growth years, which protects against osteoporosis 50 years later. This is one of the most clear-cut long-term benefits — and it can't be matched by any other form of exercise.
3. Improved coordination and motor skills
Kids who learn movement patterns under load develop better proprioception, coordination, and movement quality than kids who don't. This translates to improved performance in every other sport they try.
4. Mental health benefits
Recent research is converging on something parents already know intuitively: physical mastery is one of the most potent confidence-builders for kids and teens. The feeling of "I couldn't do this last week and now I can" is genuinely transformative for self-image, especially in adolescence.
5. Healthier body composition
Childhood obesity is one of the most pressing public health issues in the UK. Resistance training, more than cardio alone, has been shown to improve body composition in young people — adding lean muscle and reducing body fat percentage.
Kids fitness classes for ages 5–15.
Three age-banded classes built around fundamental movement, age-appropriate strength, and a love of being active. DBS-checked coaches. Free trial class.
See kids classesWhat "properly coached" actually means
The repeated phrase across all of this is "properly coached." That's not a throwaway qualifier. It's the entire safety story. Here's what to look for in any kids strength training programme:
Age-appropriate loading
The youngest groups (5–8) should use almost exclusively bodyweight. The middle groups (9–12) introduce light loads — empty bars, light medicine balls, low resistance. The older groups (13+) progress to real weight, but always scaled to the individual.
If a 6-year-old is being asked to deadlift a loaded barbell, that's a red flag. Don't return.
Technique-first programming
Good kids coaches obsess over movement quality before they care about load or speed. If a child can't squat well, no coach should be loading their squat. The first weeks and months should be almost entirely about pattern-learning.
Small group sizes
Kids strength training in groups of 20+ is hard to do safely — too many bodies, too few eyes. Look for classes capped at 10–12 max, with a coach actively supervising every rep.
Qualified coaches
The minimum bar should be a Level 2+ PT qualification, paired with kids-specific certification (e.g. CrossFit Kids, NSCA Youth, or equivalent). Plus an enhanced DBS check — non-negotiable for anyone working with children.
A "no comparing" culture
The single best predictor of a healthy kids fitness environment is whether kids are pushed against each other (bad) or encouraged to focus on their own progress (good). Watch how the coach speaks to the kids in a class before you sign up.
What strength training is NOT for kids
To be clear about what we're not endorsing:
- 1-rep max powerlifting attempts in pre-adolescents. Inappropriate for the age group.
- Bodybuilding-style hypertrophy training. Not the focus at any age before mid-teens.
- Heavy loading on poor technique. Bad for any age, but especially kids.
- Adult-style training calorie or load expectations. Kids don't need to be pushed the way adults do.
Done properly, kids strength training looks more like play with structure than mini-bodybuilding. Games, races, partner challenges — wrapped around real movement learning. The kids don't even know they're "training." They just know they're having fun.
The honest conclusion for parents
If you've been holding your kid back from strength training because of the growth-plate myth, the science genuinely doesn't support that anymore. The risk profile of properly coached strength training for kids is lower than the risk profile of football, rugby, gymnastics, or pretty much any other organised sport.
The benefits are bigger than for adults. Bone density built in childhood lasts a lifetime. Movement skill learned young transfers into every other sport. The confidence kids build through physical mastery shapes how they see themselves for years.
If your kid wants to try it, the evidence is on their side. Find them a properly coached class — like our age-banded kids classes — and let them go.
