Zone 2 vs Intervals for Triathletes in 2025: What the Data Says
October 13, 2025•11 min skaityti•Mokymo patarimai
Zone 2 work builds the engine; intervals sharpen it. Most successful triathletes use both. Here’s how current evidence and best practice suggest you should balance them in 2025.
What Is Zone 2?
Low‑intensity aerobic training you can sustain while breathing mostly through the nose and holding a conversation. Typically Z2 by HR/pace/power. It develops aerobic base, fat‑oxidation, capillaries, and durability with low recovery cost.
What Are Intervals?
- Threshold (Z3/Z4): 6–20' repeats near LT/FTP to raise sustainable speed.
- VO₂max (Z4/Z5): 1–5' repeats at hard efforts to boost aerobic ceiling.
- Tempo (upper Z2/Z3): steady efforts to improve efficiency and race‑specific pace control.
- Hills/Sprints: short high‑force efforts to build strength and economy.
What the Data Says
- Most endurance improvements come from a high share of low‑intensity volume, with a minority of work at moderate/high intensity.
- Polarized or pyramidal distributions (often 70–90% low intensity, 10–30% moderate/high) are commonly associated with strong performance in trained athletes.
- Intervals efficiently raise VO₂max, threshold, and economy—especially useful for time‑crunched athletes when applied sparingly but consistently.
- Excess ‘grey‑zone’ volume can add fatigue without clear gains; purposefully place tempo and threshold to support race goals.
- Consistency and progressive load matter more than any single session—balance stress and recovery across the week.
When to Use Each
- Base (early): Emphasize Zone 2 to build durability; add small amounts of strides/technique and light tempo.
- Build: Keep Zone 2 as the backbone; add 1–3 quality interval sessions weekly (bike/run) aligned to event demands.
- Peak/Taper: Reduce total volume; maintain intensity with shorter, race‑specific intervals to stay sharp.
- Time‑Crunched: Keep some intervals, but still protect easy volume; avoid stacking too many hard days.
Weekly Templates
- Beginner (5–7 h): 4–5 Z2 sessions + 1 threshold/tempo + optional short strides; 1 rest day.
- Intermediate (7–10 h): 5–6 Z2 sessions + 2 quality (e.g., bike VO₂, run threshold); 1 lighter recovery day.
- Advanced (10–14 h): Majority Z2 + 2–3 key quality workouts; periodize between block emphases.
Common Mistakes
- Too much moderate intensity (the ‘always kind of hard’ trap).
- Skipping easy days; quality then suffers and injuries rise.
- Copying pro volumes or sessions without context.
- Ignoring nutrition, sleep, and stress—limiting actual adaptations.
How PaceTri Balances Zone 2 and Intervals
- Personalizes zone targets from your assessment (HR, pace, power).
- Schedules 1–3 quality days around your availability; protects recovery.
- Adapts progression week to week with clear intent for each session.