Guide
A high-intensity running trainer with the evidence attached, 4 x 4 and 10-20-30
Two interval sessions from published studies, with the sources named. What each session is, what "hard" means, why they build the engine that sprinting and the 400 m need, and how to run them with a sprint timer and cadence metronome on your wrist.
Why a sprint app has an interval trainer
Sprinting makes you fast over 100 m. It does not build the engine that lets you hold speed to 400 m, or recover between reps, or run again on Thursday. That engine is aerobic, and the training with the clearest evidence for it is high-intensity intervals: minutes hard, minutes easy, repeated.
Both sessions below are taken from a published study, named the way the researchers named them and credited in SpeedRun's coaching library. Neither is a mode the app runs for you: you time the blocks yourself, on a plain running watch face or a kitchen timer, and lean on SPRINT and the cadence metronome to keep the hard efforts honest. Or skip both and just sprint. Free runs measure everything the same way.
Session one, 4 x 4 minutes
The study behind it compared four ways of spending the same oxygen cost over eight weeks, in moderately trained men, and the four-minute intervals improved maximal oxygen uptake more than the steady running did. Hard, in the paper, is 90 to 95 percent of maximum heart rate. The watch cannot know your true maximum, so it cues the same structure by breathlessness: too breathless to talk in sentences, nowhere near a sprint.
Session two, 10-20-30
This one is easier to start and has a specific appeal for anyone chasing speed: the ten-second fast block inside every minute is a strong pickup, not a sprint, repeated on legs that are already working, with a shuffle underneath. In both studies behind it the session replaced about half of the runners' existing training rather than being added on top, and performance still improved. Nothing in it lasts longer than ten seconds, so the first session is survivable.
Start with a dose you can finish
A published protocol is what the study's subjects did in week eight, not what they did on day one. If either session is new to you, run a shorter version first, one or two rounds of 4 x 4 instead of four, or two blocks of 10-20-30 instead of three, and add a round on the weeks you finish comfortably. The sessions that get abandoned are usually the ones that were too much on the first attempt.
What SpeedRun does during the session
- SPRINT gives you a 3-2-1 countdown for the hard reps you choose to time, so a 10-20-30 block's ten-second bursts land as sprints on the records screen.
- Live speed, heart rate and cadence stay on your wrist the whole way, hard block or easy.
- The cadence metronome and voice callouts run in your earphones if you want them, on any part of the run.
- The whole session, warm-up, hard blocks, easy jogs and cool-down, saves to Apple Health as one outdoor workout.
There is no program to start, switch or end, so you can change your mind mid-run: shorten the session, add a round, or drop into easy jogging whenever you like. The run keeps measuring your sprints throughout, so a 10-20-30 session still records your fastest 100 m.
How the two fit into a week
Speed and intervals are both hard days, and hard days need easy days between them. A week that works for most people who are not full-time athletes is one sprint session, one interval session, and two or three easy runs, with a rest day after each hard one. Two or three genuine speed sessions a week is the ceiling the hamstring research points to; the guide on starting sprint training safely has the numbers.
What it will not do
It will not tell you your VO2 max improved by a number, because the watch cannot measure that, and we would rather not invent it. What it will show you is the honest downstream signal: your best average speed over 400 m, week by week, on the records screen, next to your 100 and 200 m. If the engine is growing, that is where it shows.
