How it works

The protocol

Reduced-exertion high-intensity interval training is a small family of protocols built around very short all-out efforts. The version here is two twenty-second sprints inside a ride of about nine minutes, twice a week.

The sprints are the point. The stimulus comes from effort that is genuinely maximal, not from volume, so everything around them — the warm-up, the three minutes of recovery between them — exists to make each one a true maximal effort rather than a tired approximation of one.

What the evidence supports

Published trials of protocols of this shape report improvements in cardiorespiratory fitness in the groups studied, from a very small weekly time commitment. That is a finding about a population in a trial. It is not a prediction about you, and we are not going to dress it up as one.

What the literature does not establish is that this is better than doing more. If you have the hours, the evidence favours using them. This is for people who do not.

The design documents in this project cite the trials directly, including the ones that complicate the picture.

What the app does while you ride

1. Pairs with your trainer and reads the resistance range it says it supports.
2. Confirms it can actually be told what resistance to apply, and refuses politely if not.
3. Sets minimal resistance for the easy parts and your chosen load at each sprint, checking every command was accepted.
4. Records power and cadence throughout, at whatever rate your trainer reports them.
5. Drops the resistance and stops, on every path out — including the ones that go wrong.

You choose the load

Today you pick the resistance yourself and adjust it during the ride. That is deliberate: choosing it for you means prescribing a physical load to a person, and the numbers that would justify doing that have to be measured on real hardware first. Until they are, you are a better judge of it than we are.