A growth spurt changes how a teenager's body handles training. This guide is for players and parents. The short version: keep the strength work, and cut back jumping, sprinting and hard braking for a few weeks.
What a growth spurt is
A growth spurt is a stretch when a teenager grows much faster than usual. The fastest point is called peak height velocity. In one long Canadian study it came at about 13.5 years in boys and 11.8 in girls, but the range is wide. At the peak, a boy can grow 7 to 12 cm in a year.
Age alone doesn't tell you where a player is. Two 14-year-olds can be at very different stages, and many boys are still growing at 16 and 17. Some feel clumsy for a while. The usual explanation is that bones grow first and muscles and tendons catch up later, but the research is mixed.
Signs of fast growth
Any of these can mean a fast phase. No height measurements? Use the cut-backs below until the signs settle.
- Shoe size has gone up in the last 6 months, or trousers and sleeves are suddenly short.
- Family, school or the coach say they've shot up this year.
- Footwork or the serve looks less smooth for a while.
- Jump or sprint scores have stalled or dropped, with nothing else changing.
- Pain just below the kneecap or at the back of the heel. This one needs a doctor or physio.
Why knees and heels hurt
Tendons attach to bone at growth areas. In a spurt the tendon pulls hard on that spot. Just below the kneecap, doctors call the common form Osgood-Schlatter. At the back of the heel, it's Sever's disease, the most common cause of heel pain in children.
Both hurt more with running and jumping and ease with rest. Both usually settle as growth finishes, but that's no reason to play through pain.
How to adjust training in a growth spurt
The rule: cut back jumps, sprints and hard braking. Keep strength and technique. Every rep stays fast and clean and rest times stay the same. These sizes are my practical numbers. No trial has tested them.
- Jumps: about half. Planned 3 sets of 10? Do 3 sets of 5.
- Sprints: about 60% of the reps. Planned 6? Do 4.
- Braking, changes of direction and reaction drills: about half.
- Running conditioning: cut it the same way, or do about half on a bike.
- Don't make anything harder. Skip depth jumps, drop jumps and max tests while the spurt lasts. That's my own cautious rule.
What to keep
Strength work helps muscles and tendons catch up with bone. It also hits the body much more softly than jumping and sprinting. Trials in people aged 12 to 40 found it cut sports injuries by about two thirds, though few were growing players.
- Weights: all of it, progressing as planned. For juniors, a qualified adult watches and the reps stay clean.
- Med ball throws, warm-up, mobility, and calf, groin, hamstring, shoulder, forearm and trunk work: all of it.
- Landing drills with no jump, like stepping down and sticking the landing: keep them.
- Jump and sprint scores often stall or drop in a spurt. That's growth. Write "growth phase" next to the result.
How long, and how to come back
Follow the cut-backs for at least 8 weeks. One quiet month is often a measuring error or a pause. A real spurt usually runs for many months. Growth has slowed when it's under about 0.5 cm a month for at least 2 months. If you don't measure, wait until the signs have been gone for 2 to 3 months.
Let me be honest about the evidence. The growth numbers come from football academies, nearly all boys. I found no study in girls, tennis or padel. The size of the cuts and the 8 weeks are my practical numbers. They're the best guide I have, and a few careful weeks cost very little.
- Weeks 1 and 2 after growth slows: jumps about three quarters, sprints about 80%, braking about three quarters. Still no depth or drop jumps.
- From week 3: back to the plan.
Optional: measuring height at home
Measure about once a month, in the morning, before training. Use the same wall, hardback book and metal tape each time, and the same adult if you can.
- Shoes and socks off, back to the wall, heels together, bum and shoulders on the wall, eyes ahead. Stand tall, no tiptoes.
- An adult lays the book flat on your head, back edge on the wall. Mark under it, then measure floor to line to the nearest millimetre.
- Do it twice. If the two numbers are within 0.5 cm, take the average. If not, measure a third time and take the middle one.
Fast growth means 0.6 cm or more in a month. A study of 101 elite young footballers linked that pace to higher injury odds, about 1.6 times. The same pace is 1.2 cm in 2 months, 1.8 cm in 3 months or about 7 cm in a year. All of this comes from boys playing football. The 2 and 3 month numbers are my own arithmetic.
When to see a doctor or physio
In a growing player, where it hurts matters more than how much. Chest pain, fainting or a blow to the head need a doctor straight away.
- Pain just below the kneecap or at the back of the heel, even 1 or 2 out of 10.
- Limping or swelling.
- Pain at night or at rest.
- Pain that gets worse with jumping or running.
Based on Kemper (2015), Johnson (2022), Hall and Erskine (2025), Towlson (2020), Gholve (2007), Lauersen (2018) and Lloyd (2014).