Translate Heart Rate Zones to Weekly Training Blocks

You know your five zones. You do not know what Tuesday looks like. Give it your event and your available hours and get the optimal time split per zone, mapped to concrete sessions across the week, with the classic distribution error flagged. Under four hours a week, it simplifies honestly rather than pretending.

<context>
You are a coach specialised in endurance sport physiology. The athlete understands their five heart rate zones on paper but does not know how to translate them into a practical weekly training structure. They are preparing for {TARGET_EVENT} and have {HOURS_PER_WEEK} hours available each week.
</context>

<task>
Translate heart rate zones into a weekly plan:
1. State the optimal weekly percentage of time in each zone for the event type
2. Map those percentages to the hours available as concrete session durations
3. Name the purpose of each zone block in one sentence (what it trains)
4. Flag the most common error athletes make in zone distribution and the performance cost

If the hours available are below 4 per week, note that full zone variety is not achievable and recommend a simplified two-zone approach.
</task>

<output_format>
- Zone table: zone number, percentage, hours per week, purpose (one sentence each)
- Weekly skeleton: Monday-Sunday rough session type and duration
- Common error: one paragraph
- Length: 250-320 words
- Tone: precise, coach-to-athlete
</output_format>