Building physicality in young footballers: play, growth spurts and the long game

Ask a few parents what strength and conditioning means for a young footballer and you'll probably hear about gyms and weights. When Harry Knock joined us on Project Footballer, he painted a very different picture. Harry was introduced on the show as one of Chelsea's strength and conditioning coaches - at the time of recording he was lead strength and conditioning coach for the under-13s - and in his view, physical development starts long before a child ever picks up a weight.

He was joined by our hosts Marcelo and Yuri. Between them they covered when physical work should begin, what growth spurts do to a young player and how families can think about it all without losing sight of the ball.

It starts with play, not weights

Harry's definition is the place to start. As he put it, "strength and conditioning is a journey of an athlete from a young age" - and that journey looks completely different in the early years, during maturation and afterwards. Resistance training is one part of it, introduced according to where a child is in their development.

For the youngest children, it looks a lot like playtime. Harry described sessions built around unstructured play: invasion games, dodgeball, hand-eye coordination games, monkey bars, tug-of-war, obstacle courses and a bit of parkour. The idea is to throw lots of different challenges at children and let them work out the answers, like how to get up and over a tall box. At Chelsea, he said, players are exposed to multi-sport activities from the under-8s, including badminton, volleyball and gymnastics, and that variety carries on through the academy.

"If we can create really skilled learners, that's a fantastic foundation to have."

His own background backs this up. Harry played lots of different sports growing up - exactly what he now advises young athletes to do - and was at AFC Wimbledon from around 11 or 12 until 17 or 18, in the same youth team as Ethan Pinnock, who has also been on the show. He also cited a book, The Athletic Skills Model, on former Chelsea player Zenden, who came to football relatively late after a lot of judo and was comfortable in body contact as a result - other sports add to what a player can bring to their game.

Training age and why foundations matter

One of the most useful ideas Harry shared was training age - how long a child has been doing structured physical development, as opposed to how old they are. He gave the example of a 13-year-old who might already have three years of experience, compared with a 16-year-old who has none at all.

His argument is that those foundations are hard to make up later. Once children have learned basic movement patterns - squatting, lunging, hinging, pushing, pulling - through play and well-coached practice, the work can build slowly over years. He described teaching movement technique to nine and ten-year-olds, with any progression drip-fed gradually and only when the individual is ready. The panel agreed you can't simply cram it all in at 16 to catch up.

He was just as clear that there are no quick fixes. Families sometimes come to him wanting their child to be quicker within a few weeks. Harry's response is to zoom out and think in terms of a six to ten-year plan, with the building blocks put in place early.

Growth spurts: a new body to learn

Growth and maturation came up again and again. Harry explained that during a period of rapid growth, bones can grow faster than the surrounding connective tissue, limbs get longer, weight goes up and a child's centre of gravity shifts. Coordination can go off for a while. A player might seem to have lost a yard of pace, or the ball suddenly slips under their foot.

In Harry's view, that's normal and predictable - and the answer is to help them relearn the basics.

"You have to re-teach youngsters how to sprint and change direction after they've gone through this because it's a new body."

At Chelsea, he said, staff monitor players' height and weight regularly and carry out physical testing three or four times a year. When a player is growing quickly, they look more closely at training load, sleep and tiredness, and may ease off for a while. He was wary of simple growth rules of thumb, though, because so many factors are at play.

He also noted that growth-related aches, often around the knee or heel, are common at this stage. Yuri asked whether a player who eases off every time they grow ends up missing too much football. Harry's answer was balance and the long view - keeping players involved where appropriate so they aren't starting from scratch, managed individually. Any pain that persists or stops a child playing is a conversation for a GP or physio, working alongside qualified coaches.

Honest conversations - no one on their own

The panel talked about young players who are hurting but don't want to say so, worried about losing their place or about what a parent might think. Harry's answer was a joined-up approach, with the player at the centre and coaches, parents and support staff all pushing in the same direction. Set that honesty out from the start, he said, and players are far more likely to speak up early. The message to them is simple: "we're all working with you together. You're not on your own with this".

It's a useful reminder for parents too. A child who feels they must play through pain to keep someone happy is less likely to flag a problem early.

Fitting it into a busy week

Plenty of families already juggle training, matches, homework and siblings. Harry said he wants children to play as much football as they can - but to cope with it without breaking down. Sometimes that means a trade-off, and he warned that piling extra training from unreliable sources onto a full week risks fatigue, burnout and injury.

He was clear there are no hard and fast rules, and that consistency matters more than volume. If you're looking for help, his advice was to find someone "well-read and puts the athlete at the centre" - someone open, who can explain things in a way that's easy to understand. And physical work doesn't have to be a chore: "there's no reason why it can't be fun."

Our take

Harry's central message - build broad movement foundations early, through play and variety, then progress slowly and patiently - is a sensible one for any family. Growth spurts, clumsy phases and dips in form are part of the journey, not verdicts on a child.

There was a healthy debate on the show about balance. One of the hosts worried that parents might swap ball work for gym time, particularly with younger children, and Harry agreed that the younger ages should be about unstructured play. Our view: for most young players, physical development should sit alongside plenty of football and other sports rather than replace them, and any structured work should be led by qualified coaches.

What parents can do

Prioritise play and variety. Climbing, chasing games and other sports - gymnastics, martial arts, racket sports - all build the movement skills Harry described.

Think in years, not weeks. There's no shortcut. Small, consistent habits beat short bursts of intense extra work.

Choose qualified help. If you look for structured strength and conditioning outside a club, find a properly qualified and appropriately vetted coach who explains things clearly, works in an open, supervised setting where parents are welcome, and puts your child first.

Expect a clumsy phase. If your child suddenly looks awkward or loses a bit of pace during a growth spurt, be patient. They're learning to use a new body.

Take pain seriously. Don't encourage a child to play through pain. If pain persists or stops them playing, speak to a GP or physio.

Protect rest and sleep. Harry listed rest, recovery, sleep, good food and hydration among the basics. Busier isn't always better.

Keep the conversation open. Make sure your child knows they can tell you and their coaches when something doesn't feel right, without fear of letting anyone down.