A 13-year-old walks onto court in September looking different from the player who left in June. Taller, longer, a little unfamiliar in his own body. Within a few weeks the forehand that was his most reliable shot starts landing in the bottom of the net. His footwork to the wide ball looks heavy. He mistimes balls he used to take early without thinking. He starts losing to players he beat comfortably in the spring.

The family notices. The coach notices. And almost everyone reaches the same conclusion: something is wrong with the training, so the training needs more of something. More lessons. More reps. More tournaments to get the confidence back.

In most cases the player is simply growing, and the response that feels most natural is often the one the body is least ready for.

What is actually happening

Every adolescent goes through a year of peak height velocity, the point at which they grow fastest. A 2025 scoping review places its onset around 11.6 to 12.1 years for girls and 13.8 to 14.1 for boys, with wide individual variation in timing, speed, and duration. In that single year, the classic growth data shows boys gaining about 10 cm on average, more than double their usual yearly rate.

The nervous system has to recalibrate to all of it. Longer levers, a new centre of mass, different limb proportions. The racket arrives at contact a few centimetres from where the brain expects it. Researchers have a name for the visible result: adolescent awkwardness, a temporary dip in coordination and balance around the growth spurt.

Honesty matters here. A 2025 narrative review found no agreed definition or measurement method for adolescent awkwardness. It also found agreement on the basic pattern: when it happens, it happens around the peak of the growth spurt, and it is highly individual. Some players barely show it. Some lose a season of rhythm.

Two more details matter for parents. The dip can begin roughly six months before peak growth, so it often arrives before anyone notices the child has grown. And strength tends to peak later, between six months and a year after peak height. For a while, the player has a longer body without the strength to control it.

The injury window

The performance dip is the part everyone sees. The injury risk is the part almost nobody plans for.

A longitudinal study of talented youth soccer players followed them for three years around their growth spurt. Days missed to injury roughly doubled in the year of peak growth, from about 7 to almost 16 per player. Traumatic injuries rose during the spurt, and overuse injuries followed after it. A 2025 Portuguese cohort of 273 youth players found 42% higher injury incidence at peak growth than before it, with overuse injuries making up half. At an elite athletics academy, rapid growth in height and leg length was linked to more bone and growth plate injuries.

Tennis adds its own load on top. In five years of Australian national junior program data, the lumbar spine was the most injured region in both boys and girls, with the shoulder second. The serve is the main suspect: research on elite adolescent players shows the kick serve produces the highest forces on the back, and it is often introduced around age 13. In one MRI study, 64% of elite adolescent players had lumbar spine abnormalities without any pain.

Put those together. The age at which many players learn the kick serve, add volume, and start chasing points is the same age at which the spine and growth plates are most vulnerable. Nobody planned that overlap, which is exactly why someone needs to plan around it.

Three people, three different stories

Here is where the growth spurt becomes a system problem rather than a biology problem.

The tennis coach sees a forehand breaking down and responds with technical work: more feeds, more corrections, maybe a grip or swing-path change. The strength coach, if there is one, sees a player who has lost coordination and wants to back off jumping and add landing and balance work. The parent sees results falling and a rating slipping, and wants more matches to rebuild confidence.

Each response makes sense from where that person stands, and together they can be the worst possible combination: more technical change while the body is recalibrating, more serves while the spine is vulnerable, more matches while recovery capacity is lower. The trouble is that the three of them rarely compare notes.

The research points to the alternative. A two-season study at a professional football academy brought technical coaches, sports scientists, and medical staff together around players in the growth spurt. High-risk players got modified training load plus balance, coordination, and landing work. The authors concluded that injury incidence and burden in this group could be reduced. The interventions themselves were simple; the difference was that the adults worked from one plan.

What should change in that window

Training continues through the growth spurt, with different priorities. In practice, that looks like this.

1. Measure, don’t guess. Record standing height every two to three months from about age 11. A jump of more than a few centimetres in a quarter is your signal. You cannot plan for a window you cannot see.
2. Hold the volume steady. This is not the season to add a fifth practice day or a second tournament weekend. Avoid sudden spikes in hours on court, and treat a rise in soreness complaints as information, not weakness.
3. Find the new toss height. A player who grows 8 to 10 cm reaches a contact point that is suddenly higher, but the toss is still calibrated to the old body. The ball arrives early, the player gets cramped, and the body compensates: the trunk opens too soon, or the back arches to wait for the ball. Make re-finding the toss the priority. Toss-and-catch at full extension, tosses to a target height on the fence, then serves at moderate pace with honest counts until the toss and the leg drive line up again. Research on elite adolescent servers suggests the timing of key serve events, toss included, may matter more for the lower back than how far the spine moves. Add spin and speed only once the rhythm is stable, and delay the kick serve if it is new.
4. Shift the S&C emphasis. Less maximal jumping and heavy plyometrics, more balance, landing mechanics, trunk control, and mobility through the hips and thoracic spine. The goal is helping the nervous system learn the new body.
5. Lower the technical ambition. This is a poor time for a major grip or swing rebuild. Use constraints and game-based drills that let the player find the stroke again: rally to targets with height and margin, live-ball patterns, situational play. Feel the ball before fixing the mechanics.
6. Pick the calendar on purpose. Fewer events, chosen for what they build. A tournament with three matches a day asks the most of a body that is least ready for it.
7. Change the conversation. Tell the player what is happening. A 13-year-old who thinks he has “lost his forehand” is carrying a story that hurts more than the dip itself. One who knows his body is growing can be patient with it.

All of it can be done with a tape measure, a shared calendar, and adults who talk to each other.

The season that looks like going backwards

The player who grows through this window with a steady plan usually comes out the other side with a bigger serve, a heavier ball, and more reach than before. The one who is pushed through it with more of everything often comes out with a stress reaction in the lower back, a rebuilt stroke he no longer trusts, and a year of results that taught him the wrong lessons about himself.

Give the body time to catch up with itself, and the forehand will come back with more behind it.