TimerPlanWork-to-rest ratios
A work-to-rest ratio is the length of the effort against the length of the recovery, and it decides what the session trains: roughly 1:1 for conditioning, 1:2 or longer for speed, and 2:1 or shorter for muscular endurance. The effort is the part people plan; the rest is the part that makes it a different session.
Cutting the rest does not make a session harder in a useful way — it makes each effort slower, so a speed session quietly becomes a conditioning session with worse form.
The other thing the rest decides is length. Eight rounds of forty seconds on and twenty off is eight minutes, not five and a half, and sessions described as “twenty minutes of intervals” almost always mean twenty minutes including the standing about.
The ratios, and what each one is for
| Ratio | Example | Trains | Feels like |
|---|---|---|---|
| 1:3 | 15 on, 45 off | Speed and power | Short, sharp, plenty of standing |
| 1:2 | 20 on, 40 off | Speed endurance | Hard efforts, real recovery |
| 1:1 | 30 on, 30 off | Aerobic and anaerobic together | The classic conditioning session |
| 2:1 | 40 on, 20 off | Conditioning, muscular endurance | Relentless |
| 3:1 | 45 on, 15 off | Muscular endurance | A class circuit |
| 2:1 maximal | 20 on, 10 off | Both, if truly maximal | Four minutes that feel much longer |
The last row is the odd one: the same 2:1 ratio as 40/20 but with efforts short enough to be genuinely maximal, which is what makes Tabata different from a fast circuit.
The arithmetic people skip
Eight rounds of 40/20 is 480 seconds — eight minutes, of which 160 seconds is rest. A session described as “twenty minutes of HIIT” is usually twelve minutes of work and eight of recovery, and the honest way to plan it is to write down both.
The interval and HIIT plan does that arithmetic across blocks, including a warm-up block of a different shape, and shows the working time separately from the total.
Running the session
Set each block on the online timer as you come to it, or use the classroom timer full screen if a group has to see it — the colour thresholds work across a room with the sound off, which in a gym it usually is. Use the stopwatch afterwards if the splits matter: knowing that round eight was four seconds slower than round two is the part a countdown cannot tell you.
Frequently asked questions
What does 20/10 for eight rounds actually do?
That is Tabata, and it is four minutes of genuinely maximal effort — the original study used a stationary bike at an intensity most people never reach in a class. Done at that intensity it improves both aerobic and anaerobic capacity, which is unusual for four minutes of anything. Done at moderate intensity it is a brisk four minutes and nothing more, which is the honest version of most Tabata classes.
Why is 45/15 so common in classes?
Arithmetic. Forty-five and fifteen make a minute, so eight exercises take exactly eight minutes and a class timetable fits together without anybody doing sums. It sits near a 3:1 work-to-rest ratio, which is muscular endurance rather than speed — fine for a general class, wrong for anyone training to be fast.
Should the rest be complete or active?
It depends which end of the range you are at. For speed work the rest exists so the next effort can be maximal, so it should be genuinely restful and long — walking, not jogging. For conditioning the point is to keep the heart rate up, so active rest is correct, and that is why 1:1 sessions feel harder than their ratio suggests.
How long should the whole session be?
Work backwards from the total including rest, which is what the interval plan works out. Twenty to thirty minutes of intervals is a full session for most people; beyond that the last rounds are usually slower than the first, and slow rounds at the end of an interval session train something nobody intended.
How this works
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