I put together a 4-week on-court endurance progression that slots around heavy hitting: two days a week of 3×6-minute shuttle circuits (baseline–service line–net–service line–baseline) with 1:1 work:rest, capped at 85–88% HRmax. It’s kept movement sharp through games 5–7 in matches; I can share the session sheet and RPE tracker — how would you adjust the work:rest for U16s versus ITF/Challenger players?
For our U16s I shift it to 4×4’ with 1:1.5–2 rest and a hard cut if mechanics slip — ‘stop one rep before form breaks’ — keeps HR mid‑80s without frying legs around heavy hitting. In tourney weeks I go 1:1 at 3’ and cue split‑step quality over pace; would love the sheet and I’ll share our simple RPE+HR drop‑off rule?
I’ve kept 3×6’ @85–88% but for U16s use 1:1.25 and “shadow-serve” rests. Offset cones 0.5–1 m to reduce decel load.
I’ve had better buy-in using HR-recovery gates for U16s: “restart <75% HRmax” instead of fixed rest, which early on lands about 1:1.5 and by week 4 creeps to about 1:1.25 while keeping 3x6’. Building on @liam_chen77, offset cones plus rounded turns (think bus not sports car) cuts the decel spikes; small caveat: watch calf tightness on back-to-back heavy-hitting days.