Athlete summary
Hard days are not only VO2 intervals. Tempo and sweet spot sit at or above the first lactate threshold (LT1) and cost roughly as much autonomic recovery as a high-intensity session. Koyaro therefore places quality roles with at least one rest or endurance calendar day between them (~48 h), unless an explicit block-HIT or race-week protocol opts in to stacking.
max_hard_days_per_week still caps how many quality days you get; spacing caps adjacency.
Why this is the default
Seiler, Haugen & Kuffel (Med Sci Sports Exerc 2007) showed that exercise at or above LT1 drives a much larger autonomic recovery cost than easy work below LT1 — tempo is not a cheap “grey zone” freebie next to threshold. Seiler (IJSPP 2010) summarizes best practice as roughly two high-intensity sessions per week for most endurance athletes; more is not free.
That does not invent a new RCT law of “exactly 48 hours.” It is the default coaching rule the day picker must honor when another legal layout exists.
Explicit exception: block HIT
Rønnestad and colleagues’ block HIT protocols stack hard days on purpose as a short overload. Consecutive quality days must stay an opt-in protocol (allow_adjacent_quality=True on the microcycle scheduler — tracked with), never an accident of even day spreading.
Race-week pins (openers / race) are already explicit event anchors outside the free quality mix.
Citations
| Key | Paper | Takeaway |
|---|---|---|
seiler-2007-autonomic-recovery | Seiler S, Haugen O, Kuffel E. Autonomic recovery after exercise in trained athletes: intensity and duration effects. Med Sci Sports Exerc. 2007;39(8):1366–1373. doi 10.1249/mss.0b013e318060f17d | Recovery cost jumps at/above LT1; tempo ≈ HIT for autonomic tax. |
seiler-2010-best-practice | Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5(3):276–291. | ~2 HIT sessions/week is enough for most; more is not free. |
ronnestad-block-hit | Rønnestad et al. — block high-intensity training protocols | Consecutive hard days are a prescribed overload, not a scheduler leftover. |