The rest period between intervals is not dead time — it is an important lever that decides what your workout actually trains. A runner's guide to using recovery on purpose.
Let us take a workout: 15 × 1km, with 90 seconds of rest. Notice which of those numbers we tend to fixate on. The 15 reps, The 1km. The pace. The total distance. Almost never the 90 seconds. As runners, we often obsess over the “on” portion of our intervals: the speed, the distance, and the pace. However, science reveals that the “off” portion, which is the the rest period, which equally dictates the physiological adaptations we get from a workout.
To plan the rest, it helps to understand what the body is trying to put back together.
An interval session affects two different systems, and moves them out of balance:
The most important thing to note that is that you do not always want to fully recover before the next rep. In fact, manipulating how incompletely you recover is the secret to targeted interval training. That is why the exact same reps can produce three different physiological outcomes depending on how long you wait.
Coach Luke Humphrey (of the Hansons Marathon Method) puts the whole design principle in one line:
That is the entire game — a rest interval long enough to hit the target pace, short enough that the pace still counts as hard. Every rule below is a special case of that trade-off.
Goal. Push up the pace at which lactate starts piling up faster than you can clear it. Roughly, your one-hour race pace.
Rest. Short and moving.
Ratio. 3:1 or 4:1 (work:rest). For a 1000m rep, that could be about 60-90 seconds of recovery. For shorter LT intervals like 600m-800m, that could be 45-60 seconds.
The logic here is that threshold work is intense but not maximal. You want each rep to start with the aerobic system is still not fully recovered, so the reps stack a big internal load without. Too long a rest defeats the purpose of not accumulating enough time at the desired intensity.
Do not sit down. The single most common mistake at the threshold session is stopping between reps. When you stand still (or worse, sit), the aerobic engine — the Krebs cycle in your muscles — quiets down. Lactate clears more slowly, and it takes longer to spool back up on the next rep. Jogging (or a “float” — slightly quicker than a jog) or even walking between reps keeps the engine warm and actually helps you clear the byproducts of the previous rep.
Goal. Raise your aerobic ceiling. Time spent close to your VO2 max is the training stimulus.
Rest. Moderate. Trust your body.
Ratio. 1:1 or 2:1. For a 4-minute VO2 max rep, 2–4 minutes of easy jog or walk or even just stand.
There is an excellent study on this — runners were given 4-minute reps and told to choose their own rest without looking at a clock. They almost all landed on the same number — about 118 seconds. [^4] Not by design. That is roughly the time it takes for the phosphocreatine system to top up and for the body to feel like it can go again. Going by feel gets you very close to the “right” number.
The takeaway
Same 10 × 400m at the same pace can be a threshold workout, a VO2 max workout or a speed workout, depending only on the rest. Decide the goal first, then set the clock.
Goal. Accumulate as much time as possible at or near VO2 max.
Rest. Very short. Deliberately incomplete.
The trick here is exactly that the 15-second recovery is too short, so that the anaerobic system does not get to refill, and oxygen uptake does not get to drop off. So on rep two, the aerobic system has to take over. On rep three, it takes over more. By rep ten, your aerobic engine is doing work it would never have been asked to do at threshold pace.
In a well-known study by Rønnestad and colleagues, cyclists doing 30s/15s intervals improved their 20-minute time-trial power by nearly 5%, more than a comparable group doing traditional 5-minute intervals — and their lactate tolerance jumped significantly. For runners, the equivalent is something like 30s hard / 15s jog for 8–10 minutes.
Goal. Neuromuscular. Recruit fast-twitch fibres, sharpen top-end mechanics.
Rest. Long, and standing still.
Ratio. Effectively 1:20 or more. For a 10-second all-out sprint, 3–5 minutes of full rest, minimum. For a true max effort with the neuromuscular system fully back, even 10–20 minutes is not unreasonable.
This is the one place where jogging between reps is actively counterproductive. If any part of the goal is “run as fast as I possibly can”, your legs need to be genuinely fresh at the start of each rep. If we cut the rest here and we are no longer training speed. We will be training a compromised version of speed endurance in a fatigued state.
Rough guide:
| Goal | Rep length | Work : Rest | Rest duration | Rest type |
|---|---|---|---|---|
| Lactate Threshold | 1000m-3000m (~4-10 min) | 3:1 or 4:1 | 45–120 sec | Jog or float — keep moving |
| VO2 max | 2–6 min | 1:1 or 2:1 | 2–4 min | Easy jog or walk |
| Short HIIT | 30 sec | 2:1 | 15 sec | Very short jog |
| Pure speed / sprints | Under 20 sec | 1:12 to 1:20 | 3–5 min (up to 20) | Passive — stand still |
The recovery has to be balanced between short enough to maximize time spent at desired level, but not so short that you can’t sustain the pace.
— Luke Humphrey, Workout Variables: Recovery Jogs
You have just finished a hard 800m . Your hands are already moving. Where do they go?
Hands on the knees. Not on the head.
A 2019 study by Michaelson and colleagues, done on Division 1 women’s soccer players, ran a straight A/B on this — hands on knees versus hands behind the head during interval recovery. Hands-on-knees produced a significantly faster drop in heart rate and in exhaled CO2. The reason is mechanical. Bending forward and putting hands on knees flexes the thoracic spine and rotates the rib cage inward slightly. That geometry lets the diaphragm do its full stroke without fighting an over-expanded ribcage. You breathe deeper with less effort. Blood and gas exchange catches up faster.
Hands on head does the opposite — it opens the rib cage wide and makes the diaphragm’s job harder at exactly the moment it needs the most range.
There is also some evidence that a mixed recovery — a bit of movement, then some standing — is better than either alone. The point is that you don’t have to pick one and stick to it.
Runners increasingly do strength work, and the rest rules in the gym are different — because the energy systems being trained are different.
Rough guide:
| Goal | Set duration | Work:Rest | Rest between sets |
|---|---|---|---|
| Maximal strength & power (heavy squats, deadlifts, box jumps) | 5–10 sec | 1:12 to 1:20 | 1.5–3 min (up to 5) |
| Hypertrophy & muscular endurance (moderate weight, higher reps) | 15–30 sec | 1:3 to 1:5 | 1.5–2.5 min |
| Endurance circuits (bodyweight, mixed muscle groups) | ~15 sec | ~1:1 | Short, or alternate muscle groups |
The one runners underdo the most is the top row. Heavy strength work runs almost entirely off the ATP-PC system, and that system needs 2–3 minutes to be ready to lift the same weight again. Cut the rest to 60 seconds and you are no longer training maximal strength, but you moved into a hypertrophy session, at a weight that is too heavy for it. The set becomes worse at both jobs.
Here is a trick for endurance circuits — alternate muscle groups during the circuit. Ten seconds of squats, ten seconds of push-ups, ten seconds of pull-ups gives your legs a 1:2 rest ratio without you ever standing still. Heart rate stays up, but each individual muscle group gets meaningful recovery.
The rest interval is not the dead space between the “real” parts of the workout. It is part of the workout, and is the important part that decides what physiological benefit that the training gives you.
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