Most runners plan their reps and guess the recovery. That is backwards. The same five kilometres split into 5 x 1 km can be a controlled threshold session or a flat-out race, and the only thing that decides which is the recovery between them.
The right recovery depends on one question: were the reps faster or slower than your critical speed?
Reps faster than critical speed
Above critical speed, you are spending a limited reserve of hard-effort capacity with every second (Jones and Vanhatalo, 2017). Heart rate, breathing and blood lactate keep climbing until you stop. The recovery’s job is to refill enough of that reserve that you can run the next rep at the same quality.
Recovery works fast at first and then slows down. The first 30 seconds do a lot. The next two minutes do less each. So for short, very fast reps you need more recovery than feels necessary.
- Example: 6 x 300 m at 1,500 m race pace, with about 3 to 4 minutes of walking between reps.
- Rule of thumb: the faster and shorter the rep, the longer the recovery relative to it.
If your last reps are much slower than your first, the recoveries were too short, not your fitness too low.
Reps at or just below threshold
These are tempo reps and cruise intervals, at a pace you could hold for around an hour. Here you are not running out of anything. The recovery just keeps the session from drifting too hard.
- Example: 4 x 1.6 km at threshold pace, 90 seconds easy jog.
- Example: 10 x 3 minutes at threshold pace, 1 minute jog. Stronger runners can cut that to 45 or even 30 seconds.
- Longer reps: 3 x 10 minutes at threshold needs only 2 to 3 minutes between.
The common mistake here is the opposite one: taking long, standing rests that turn a threshold session into a series of short races.
The fast-float session for marathoners
Experienced half and full marathoners can use recoveries that aren’t really recoveries. You alternate a slightly-faster-than-marathon pace with a steady pace only 10 to 15% slower, and never stop.
- Starter version: 8 km easy, then 3 x (2.4 km at marathon pace to 3% faster, 800 m easy to moderate).
- Full version: 8 x (1 km at 105% of marathon pace, 1 km at 90% of marathon pace).
You spend a long time at a hard but manageable effort, which is exactly what the second half of a marathon asks for. Progress it by adding reps, lengthening the fast kilometre to 2 km, or speeding up the float to 95% of marathon pace. Build up to it over several weeks. It is harder than it looks on paper.
Walk, jog or stand?
- Standing: avoid it for more than about 30 seconds. Moving keeps blood flowing back from your legs.
- Walking: for recovery between very fast reps, when you want the next rep as fresh as possible.
- Easy jogging: the default for threshold work.
- Steady running: only in fast-float sessions.
Set recoveries by time rather than distance. A 200 m jog takes a tired runner far longer than a fresh one, so time keeps the session honest.
Adjusting for Malaysian heat
Heat raises your heart rate for the same pace and slows recovery between reps. On a hot evening, either lengthen the recoveries or slow the reps, but don’t try to hit your cool-morning splits with the same rests. Better still, run hard sessions early. For why that burn in the last reps isn’t lactic acid poisoning you, read Is Lactic Acid Why Your Legs Burn?
References
- Jones AM, Vanhatalo A (2017). The ‘critical power’ concept: applications to sports performance with a focus on intermittent high-intensity exercise. Sports Medicine, 47(Suppl 1), 65-78.
- Davis J. Running Writings, articles on interval recovery and critical speed. runningwritings.com
