April 21, 2026 //
Rob Anderson //
Gym News //
6 min read
Here is the thing. It might not be growing pains at all.
It could be something called "Sinding-Larsen-Johansson Syndrome" and if you have never heard of it, you are not alone. Most parents have not. But if your child plays football, rugby, or any sport that involves running, jumping, or changing direction, this is something you need to know about.
Your child comes home from training limping. They say their knee hurts just below the kneecap. You assume it is growing pains and tell them to rest for a few days.
Sound familiar?
Here is the thing. It might not be growing pains at all.
It could be something called “Sinding-Larsen-Johansson Syndrome” and if you have never heard of it, you are not alone. Most parents have not. But if your child plays football, rugby, or any sport that involves running, jumping, or changing direction, this is something you need to know about.
What Is Sinding-Larsen-Johansson Syndrome?
Sinding-Larsen-Johansson Syndrome (often shortened to SLJ Syndrome) is a condition that causes pain and tenderness just below the kneecap. It affects the growth plate at the bottom of the patella (kneecap), where the patellar tendon attaches.
During a growth spurt, bones grow faster than muscles and tendons can keep up. This means the quadriceps muscles at the front of the thigh pull harder and harder on the growth plate. Add a heavy training load on top of that and the growth plate becomes irritated and inflamed.
It is not a serious injury. It is not a sign that something has gone badly wrong. But it does need to be managed properly, because if it is ignored, it can get significantly worse and keep your child out of sport for months.
Who Is Most at Risk?
Sinding-Larsen-Johansson Syndrome most commonly affects children aged 9 to 15, during periods of rapid growth. It tends to be more common in boys, but girls are absolutely at risk too, particularly as female participation in football and rugby continues to grow.
The sports that carry the highest risk are those involving a lot of jumping, hopping, sprinting, and sudden changes of direction. Football and Rugby sit right at the top of that list.
Research published in the British Journal of Sports Medicine has found that young athletes who train more than 16 hours per week are significantly more likely to develop growth-related knee conditions like Sinding-Larsen-Johansson Syndrome .
The message is clear, just like other growth related injuries – too much, too soon is the most common cause.
The 4 Warning Signs to Watch For
You do not need to be a physio to spot Sinding-Larsen-Johansson Syndrome early. Here are the four signs that should prompt you to take action:
Gradual pain that gets worse with activity and eases with rest. This is not the kind of pain that comes on suddenly from a tackle or a fall. It builds slowly over days and weeks.
Pain, swelling or tenderness just below the kneecap. If you press gently on the bony bump just below your childs kneecap and they wince, that is a key indicator.
Pain when running, jumping or hopping. Particularly when landing from a jump or accelerating into a sprint.
Stiffness or increased pain the morning after training. If your child wakes up the day after a match or session and their knee feels worse than the night before, that is a significant warning sign.
Does Your Child Have to Stop Playing?
No. In most cases, they do not.
This is the part that surprises most parents. Complete rest is rarely the right answer. In fact, research shows that prolonged rest can actually weaken the surrounding tissues and make recovery slower.
The goal is to keep your child active but at the right level. That means modifying training, reducing the activities that cause the most stress on the growth plate, and gradually building their capacity back up.
The key tool for making that decision is called the 2/10 Pain Rule.
The 2/10 Pain Rule
The 2/10 Pain Rule is a simple, practical guide used by sports physios and youth conditioning coaches to help young athletes stay active safely during recovery.
Here is how it works:
During activity: Pain must be 2 out of 10 or less. If it goes above that, the activity needs to be reduced or stopped.
After activity: Pain must settle within one hour of stopping. If it is still there an hour later, the load was too high.
The next morning: Pain must not be worse than it was the day before. If your child wakes up stiffer or more sore, the previous session was too much.
Use this rule at every training session and every match. It takes the guesswork out of the decision and gives your child a clear framework to manage their own symptoms.
How to Build Capacity
Managing Sinding-Larsen-Johansson Syndrome is not just about reducing load. It is also about building the strength and resilience to handle load better. Here are three key areas to focus on:
Strength: Stronger quadriceps reduce the stress placed on the growth plate. Pain-free static holds and wall squats are a great starting point, they build quad strength without the high impact of running and jumping.
Recovery: Sleep and nutrition are non-negotiable. The growth plate repairs itself during sleep, and without adequate protein and calories, that repair process is compromised. If your child is training hard and not sleeping or eating well, they are fighting a losing battle.
Modification: Reduce the volume of high-impact activities like plyometrics, sprinting, and jumping until symptoms settle. Your child can still train, they just need a smarter version of training for a period of time.
The Return to Sport Ladder
When symptoms are under control, the return to full training and competition should be gradual. Rushing back is the most common reason young athletes relapse.
The return ladder works from the bottom up:
Walking and cycling are the starting point. From there, progress to light jogging, then running, then sprinting, then change of direction work, then jumping and hopping, then a full training session, and finally match or competition.
The rule is simple: only move up a step when pain is 2/10 or less during the activity AND the following morning. If symptoms flare, drop back one step and build again.
When Should You See a Professional?
If your child has had knee pain for more than two weeks that is not improving, or if pain is above 5/10 during normal daily activities like walking up stairs, it is time to get a proper assessment from a specialist physiotherapist with experience treating youth specific injuries. Unfortunately, often those who mainly treat adults can misdiagnose these conditions as adult injuries.
At The Athlete Academy, we work with young athletes to assess training load, build physical capacity, and manage conditions like SLJ Syndrome so that your child can stay in the game and perform at their best.
If you are concerned about your child’s training load or knee pain, click the link below to access our FREE Peak Performance Profile, a quick 2 minute assessment that looks at the key factors affecting your child’s performance and injury risk, including sleep, recovery, and workload.
