Zone 2 Cardio Plan

This skill builds an aerobic-base training block organized around heart-rate zones, with Zone 2 as the foundation. It picks a modality, lays out a weekly structure, and progresses load toward an endurance goal. The default is a 4-week block, repeatable. This is general fitness guidance, not medical advice - anyone with cardiac risk factors, on heart-rate-affecting medication, or returning from illness or injury should clear endurance training with a physician first.

Establish Zones First

Anchor every prescription to heart rate, not pace or feel alone. Estimate maximum heart rate as 220 minus age as a starting point, and flag it as a rough estimate - a lab or field test is more accurate. Define the zones as percentages of max HR: Zone 1 (50-60%) recovery; Zone 2 (60-70%) aerobic base; Zone 3 (70-80%) tempo; Zone 4 (80-90%) threshold; Zone 5 (90-100%) VO2 max. Give the user their actual beats-per-minute ranges, not just percentages. The Zone 2 test in practice: a pace where the user can hold a conversation in full sentences but would prefer not to. If they can't talk, they're too high; most people drift into Zone 3 and stall their base.

Choose the Modality

Match the modality to the goal and to joints. Running builds the most specific endurance and the highest impact; cycling and rowing are lower-impact and let beginners hold Zone 2 longer without form breakdown; rucking (loaded walking) suits those building work capacity with minimal equipment. Default to the user's stated goal sport. If they have no specific goal, default to whatever they will do consistently and can sustain for 45+ minutes without joint pain. It is fine to mix modalities across a week to manage impact, but keep the bulk of Zone 2 volume in one primary modality for adaptation.

Build the Weekly Structure

Most aerobic adaptation comes from time in Zone 2, so the week is mostly easy volume. For a typical 4-day week: three Zone 2 sessions plus one higher-intensity session. Polarize the distribution - roughly 80% of weekly time in Zone 1-2, 20% in Zone 3-5. Do not let the easy days creep into Zone 3; that "moderate-intensity rut" is the most common failure. Place the hard session with at least one easy or rest day on either side. A sample week: Zone 2 (45 min), rest, Zone 2 (45 min), Zone 4/5 intervals (e.g. 5×3 min hard / 3 min easy), rest, Zone 2 long (60-75 min), rest.

Set Session Duration and the VO2 Stimulus

Zone 2 sessions should be long enough to matter: start at 30-45 minutes and build toward 60-90 for the long session. Below ~30 minutes the aerobic stimulus is thin. For VO2 max and top-end fitness, prescribe one weekly interval session in Zone 4-5: classic formats are 4×4 min hard / 3 min easy, or 30/30s (30 sec hard, 30 sec easy ×10-20). Keep intervals to one session per week during a base block - more high intensity erodes the aerobic emphasis and recovery.

Progress Toward the Goal

Default progression is volume before intensity. Increase total weekly Zone 2 time by no more than ~10% per week to protect tendons and avoid overuse. Build for 3 weeks, then take a recovery week at ~60% volume before the next block. Tie progress to a measurable goal: a target resting heart rate, a longer continuous Zone 2 session, a faster pace at the same heart rate (aerobic decoupling shrinking), or a benchmark like a 5K time or a set distance. Re-test the benchmark at the end of each block and adjust zones if resting or max HR has shifted.

Deliverable

Produce a 4-week training block the user can follow directly, containing: (1) their personal zone table in actual bpm ranges (with the estimation method flagged); (2) the chosen primary modality and the reasoning; (3) a week-by-week calendar naming each session's zone, duration, and format (including the one weekly interval session and the week-4 recovery week at ~60% volume); (4) the progression rule capped at ~10% weekly volume; and (5) the benchmark to re-test at block end. Include the medical-clearance caveat up front.

Quality Bar

A plan is done well when: every session names a target HR zone in actual bpm, not just a vibe; the week is genuinely polarized (mostly easy, a little hard) rather than uniformly moderate; the modality fits the user's goal and joints and is one they'll repeat; progression is explicit and capped (~10%/week, with a recovery week); and success is tied to a concrete, re-testable aerobic-endurance metric. The medical-clearance caveat is present.

What NOT to Do

• Don't prescribe by pace or RPE alone - without HR zones the user defaults to too-hard, the central mistake this skill exists to prevent.
• Don't let "easy" days drift into Zone 3; protect the aerobic base.
• Don't stack multiple high-intensity sessions into a base block, or skip the recovery week.
• Don't ramp weekly volume aggressively; injury ends a block faster than any plateau.
• Don't treat the 220-minus-age estimate as ground truth - individual max HR varies by ±10-15 bpm; adjust zones from observed data (talk test, decoupling, a field test) rather than defending the formula.
• Don't chase pace on Zone 2 days; the target is the heart-rate ceiling, and pace at that ceiling improving over weeks is the progress signal, not something to force.
• Don't program strength or lifting work, high-intensity interval conditioning or HIIT, or mobility/flexibility drills here - hand those to Strength Training Plan, Conditioning & HIIT Program, and Mobility Routine respectively.
• Don't pose as a medical provider; flag the clearance need and stop short of diagnosing or treating.