For the rider who wants more engine for the group ride and the coffee stop, and has about four hours a week to get it. At that volume the question is not how to spread intensity across zones — it is which two sessions to do, and the research is unusually clear about one of them: in a randomised trial of recreational cyclists, 4×8 minutes twice a week beat shorter intervals, longer intervals and easy-only riding by roughly double over seven weeks. This plan is built around that dose, rotated with 30/15 short-short intervals, anchored by one long easy ride, and bracketed by the same FTP test at the start and the end. Every session says what evidence stands behind it — and where the evidence runs out, it says that too.
The assistant adapts these sessions to your event date, days and fitness — then drops the whole block on your calendar. One conversation, no blank calendar.
Under about five hours a week, '80/20' is a rounding error you cannot act on. What you can act on: two quality sessions, one long easy ride, and nothing else hard. Never add a third hard day to make up for missing hours — recovery, not ambition, is the limit.
A 2025 meta-regression of 353 studies found endurance, interval and sprint training raise mitochondrial content by about the same amount — but per hour spent, interval training was about 1.7× and sprint training about 3.9× as efficient. When time is the constraint, the hard minutes are where the return is.
In trained recreational cyclists: +11.4% combined in VO2peak, power at VO2peak and threshold power after 7 weeks — against +5.5% for 4×4, +5.6% for 4×16 and +4.2% for easy riding only. Hardest you can hold evenly for all four, two minutes easy between.
Test the same way at the start and the end. FTP from 20 minutes is not an hour of power, and one before/after test cannot label you a responder — the same rider can respond differently to two identical blocks. Judge by the test and by how your interval watts moved.
- —The 12 weeks: Week 0 — FTP Test. Weeks 1–2 — 30/15 Starter + Ten-Second Sprints, Long Easy on the weekend. Weeks 3–8 — 4×8 twice a week (the tested dose; the trial ran seven weeks). Weeks 9–11 — rotate: 30/15 × 3 on Tuesday, 4×8 or Threshold 2×15 on Thursday. Week 12 — two easy days, then the FTP Test, and a coffee ride to celebrate.
- —Keep at least one easy or rest day between the two quality sessions. Any two days work — Tuesday and Thursday are just the most common gap in a working week.
- —Progress the watts, not the count. 4×8: when all four reps were even and the last one felt controlled, add 2–3% next time. 30/15: add reps before adding a set. Sprints: add one every second session, up to six.
- —The week with no time: do Ten-Second Sprints (40 min) instead of the missed session. Do not squeeze both quality sessions into two consecutive days to catch up.
- —Take an easy week when the signals say so, not because it is week four: the same watts feeling harder, a session you could not finish two times in a row, sleep or mood sliding for several days. Easy week = keep one quality session, shorten the long ride.
- —Optional, if you have extra time beyond the four hours: two short heavy strength sessions a week (3–4 lower-body lifts, 4–6 reps, stopped short of failure) buy efficiency and late-ride power — not a bigger engine. If it has to come out of the four hours, skip it.
- —What the evidence covers and what it does not: 4×8, 30/15 and short sprints have training studies behind them (the first in recreational cyclists, the second in trained-to-elite riders, the third mostly in non-athletes). The long easy ride, threshold 2×15, the 12-week order and the two-sessions cap are practice built on that evidence, not tested as a package. The %FTP numbers are starting points; the studies set intensity by effort and heart rate.
Built from the Blocks knowledge base: Seiler et al. 2013 (4×8 vs 4×4 vs 4×16 vs easy, recreational cyclists, RCT); Rønnestad et al. 2020 (30/15 short intervals, elite cyclists); a 2024 randomised crossover on 30/15 in well-trained women and men; Gist et al. 2014 (sprint interval training meta-analysis, 16 RCTs); Hazell et al. 2010 (10-s vs 30-s sprints); Mølmen et al. 2025 (meta-regression of training type on mitochondria, 353 studies); a 2022 study of time to exhaustion at FTP20 across 87 cyclists; and the base's frameworks on intensity by weekly hours, threshold work, testing, deloads and individual response. A general plan, not a personalised prescription.