Most families investing in junior tennis think in terms of court time. Hours per week, sessions per day, the quality of the coaching, the level of the competition. These things matter. But there is something happening every night that determines whether any of it actually sticks, and most families are unknowingly shortchanging it.

When a child falls asleep, the work does not stop. Growth hormone, which drives physical development and muscle repair, is released almost entirely during deep sleep. The motor patterns drilled during the afternoon session are consolidated into long-term memory overnight, the movement being encoded while the body is still. The neural connections that make technique automatic are strengthened. The immune system repairs the micro-damage that training produces. Sleep is not recovery from the work. It is the completion of it. Without enough of it, the hours on court are only half-finished.

The guidelines from the National Sleep Foundation are specific: children aged 6 to 12 need 9 to 11 hours per night, teenagers 8 to 10. These are not rough targets. They are the minimums at which the biology of development can function properly. Research consistently shows that young athletes in high-training environments fall short of these numbers, often without anyone noticing, because children adapt to feeling tired and stop registering it as a problem.

The injury data is the part that tends to change how parents think about this. A study published in the Journal of Pediatric Orthopaedics found that adolescent athletes sleeping fewer than 8 hours per night were 1.7 times more likely to sustain a sports injury than those who met recommended sleep durations. Fatigue compromises reaction time, coordination, and movement patterns — exactly the conditions under which ankle sprains, shoulder overuse injuries, and stress fractures occur. Sleep is not just about energy levels. It is a direct factor in injury prevention.

There is also something worth understanding about teenagers specifically. The difficulty getting a 14-year-old out of bed for a 6am session is not a character flaw. During puberty, a biological shift in the circadian system pushes the natural sleep and wake cycle later. Teenagers genuinely do not get sleepy at the same time younger children do. Their bodies are designed to wake later. A 6am training session for a 15-year-old is happening at a time when their biology is still, in a meaningful sense, in the middle of the night. Reaction times are slower. Learning is blunted. The hormonal environment for training adaptation is not yet optimal.

Stanford research on collegiate swimmers makes this concrete. When athletes were simply allowed to sleep more, with no other change to their training programme, they swam faster, reacted quicker off the blocks, and improved across every performance metric tracked. The training had not changed. The sleep had. That is worth sitting with.

For parents, this translates into a few things that are within reach. Guard sleep time with the same seriousness as court time. Chronic mild sleep restriction accumulates across weeks and months in ways that are easy to miss. Prioritise sleep before competition, but know that the night before a match matters far less than the accumulated sleep across the week beforehand. And where there is flexibility in scheduling, particularly for teenagers, later start times align better with how their bodies actually work.

The best coaching in the world is only partially finished at the end of the session. The rest happens overnight.