Five HIIT Sessions and a Flat Scale

What the cluster suggests: accumulated fatigue with inadequate recovery - increased sympathetic drive (resting HR +8 bpm), a genuine performance decrement (8% lower interval power), sleep restriction at 5.5 h, and appetite dysregulation. That is consistent with nonfunctional overreaching.

What it is not: proof of overtraining syndrome. That diagnosis requires a performance decrement lasting weeks to months plus mood disturbance, and it is a diagnosis of exclusion. You are not diagnosing it; you are removing the obvious stressors and re-measuring.

Legitimate alternative explanations you must rule out:

• Resting HR is noisy - caffeine, alcohol, hydration, illness, stress, ambient temperature, and when she measured it. Ask how she measured it.
• An 8% drop across six weeks can also reflect under-fueling. 1,600 kcal with seven hard sessions a week and 10-hour workdays is plausibly below her needs, and "always hungry" points the same direction (low energy availability).
• Unchanged scale weight does not mean unchanged body. Early training stress causes water retention that can mask fat loss, and her body composition may have shifted.

Also question the label. Five 30-minute "HIIT" sessions is almost certainly not interval training. True HIIT means short work bouts with genuinely hard efforts and long recoveries; 30 minutes of continuous hard-ish work is moderate-to-high intensity steady state with a small anaerobic contribution and a much larger recovery cost than she thinks.

Week 1 is a deload, not a new program.

• Resistance training 3x/week, full-body, 2 sets of 8–12 at RPE 6–7, volume cut roughly 40% from her current load.
• One short interval session (8–10 minutes of total work, e.g., 6 x 30 s hard / 90 s easy), not five.
• Two zone-2 sessions, 30–45 min, conversational pace, HR roughly 60–70% max or RPE 3–4.
• Two full rest days. Total training days: five, not seven.
• Sleep target 7–7.5 h, discussed as part of the program, not as a lecture.

Weeks 2–6 progression:

• 3 resistance sessions (the main driver of body-composition change and the thing she is currently not doing enough of).
• 2 true interval sessions, capped at 10–12 minutes of work time each: 4 x 4 min hard / 3 min easy, or 8–10 x 30 s / 90 s.
• 2 easy aerobic sessions for volume - cheap, high-recovery-cost-free work.
• 1–2 full rest days.

Rationale to give her: intensity is the variable that requires recovery; low-intensity volume is comparatively free. You cannot make intervals hard if she never arrives recovered. Re-test resting HR and interval power at week 4 - those are your markers, not the scale.

Agree with the part that is true and correct the part that is not.

True: per minute, hard intervals burn more calories than easy work, and they improve cardiorespiratory fitness efficiently. EPOC - the "afterburn" - is real but small, on the order of a modest percentage of the session's cost, not a game-changer.

Not true: fat oxidized during a session is not the same as fat lost over a month. Fat loss is driven by cumulative energy balance across weeks, plus adherence and recovery. Five hard sessions she cannot recover from produce less total work and worse adherence than two hard sessions she can.

Framing that keeps her bought in: "You are keeping your hard days - we're making them actually hard, which they currently aren't. What we're cutting is the medium-hard gray zone that costs you recovery and gives you nothing extra."

Then hand off the nutrition question. At 1,600 kcal with her activity and hunger signals, calorie and macro framing is a dietitian's job, not yours. Refer, and coordinate the training plan around whatever plan the RD sets.