# VO2max interval optimization

**Load this doc when:** designing high-intensity interval sessions, choosing rep length or
work:rest, or trying to rebuild sustained aerobic power.

**Data/knowledge split:** MCP gives you the power/HR streams and interval stats to *check* whether a
session did what you intended (was power sustained across reps?). This doc gives the *design logic*.

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## The target: maximize time spent ≥90% VO2max

The organizing principle of VO2max interval design is **accumulating time at or above 90% of
VO2max** — that's the stimulus, not simply "going hard." Design sessions to spend the most quality
minutes in that band that the athlete can repeat and recover from.

## What a large meta-analysis found (dose-response)

A systematic review with pairwise and network meta-analysis (**51 studies, 1,261 athletes**) found
inverted-U dose-response relationships and identified an optimum around **~140 s work duration** and
a **work-to-recovery ratio of ~0.85**, with ~3×/week over 3–6 weeks as an effective pattern (Yang,
Wang & Guan 2025, *BMC Sports Sci Med Rehabil* 17(1):156; PMID 40605061;
DOI 10.1186/s13102-025-01191-6).

> **Caveat — modality.** This meta-analysis is weighted toward **running-based** HIIT. The ~140 s /
> 0.85 optimum is a strong starting anchor, but see the cycling-specific conflict below before
> treating "longer is better" as settled *for cyclists*.

## ⚠️ Genuine conflict: rep length in cycling vs running

The claim that **longer reps (3–5 min) accumulate more time ≥90% VO2max than 30/30s** is
**supported in running but contradicted in cycling.** Do not present it as settled.

| Modality | Finding | Source |
|---|---|---|
| **Running** | 3-min intervals accumulated **more** time >90% VO2max (~328 s) than intensified 30-s intervals (~201 s), even with 30-s intensity raised | Fleckenstein, Braunstein & Walter 2025, *Front Sports Act Living* 6:1507957; PMID 39835194; DOI 10.3389/fspor.2024.1507957 |
| **Cycling (acute)** | **30-s** work intervals induced **more** total time ≥90% VO2peak than longer intervals in well-trained cyclists — the opposite result | Rønnestad & Hansen 2016, *J Strength Cond Res* 30(4):999–1006; PMID 23942167; DOI 10.1519/JSC.0b013e3182a73e8a |
| **Cycling (adaptation)** | Over 3 weeks, effort-matched **short** intervals (30/15 s) beat long (5-min) intervals — e.g. +4.7% 20-min power — in elite cyclists | Rønnestad, Hansen, Nygaard & Lundby 2020, *Scand J Med Sci Sports* 30(5):849–857; PMID 31977120; DOI 10.1111/sms.13627 |

Reinforcing the cycling short-interval side: effort-matched acute responses (Almquist et al. 2020,
PMID 32267032) and a microcycle shock-block (Rønnestad et al. 2021, PMID 33735833).

**Why they might differ:** protocol construction differs (cycling short-interval work is typically
30/15 s series to exhaustion; the running comparison used fixed-volume intensified 30-s reps),
so part of the divergence may be design, not pure modality. Either way, **for cyclists the
best-controlled evidence favors short 30/15-style intervals for accumulating time ≥90% VO2max**,
which cuts against a blanket "bias toward longer reps."

> ⚠️ **Under-researched — track individual response.** Optimal rep length for a *given cyclist* is
> not resolved. Use the MCP interval/stream data to verify what actually keeps power ≥90%-effort
> band across reps for this athlete, and let that — not a rule — drive the choice.

## Practical prescription

- **Default menu for cyclists** (bias to what the cycling evidence supports, then verify per rider):
  - **Short intervals:** 30/15 s (≈13 reps × 2–3 series) — strong for time ≥90% VO2max and
    adaptation in cyclists (Rønnestad 2020/2021).
  - **Longer intervals:** ~3–5 min reps at ~0.85 work:rest — the meta-analytic optimum region
    (Yang 2025); useful for **sustained** aerobic power and for riders who tolerate short intervals
    poorly. If rebuilding sustained power specifically, longer reps have a rationale — but this is
    a reasoned choice, not a proven superiority in cycling.
- **Prescribe from power.** For MTB especially, HR lags and misleads (`mtb-xco-demands.md`,
  `data-confounds.md`).
- **Verify the session worked:** pull the interval stats/streams from MCP and check power held near
  target across reps. Fading power = too much intensity or too little recovery; adjust work:rest.

## Frequency vs distribution

For *how often* to do hard sessions and how they fit the week/season, see `periodization.md` — the
argument there (after Seiler 2024) is that the **long-term integration** of frequency, intensity,
and duration matters more than chasing the acute maximum of any single session.