Threshold alternations
Alternating threshold and marathon pace with no standing rest, training the body to clear lactate while still running fast.
Also called: alternating tempo, float intervals.
Alternations are a staple of elite marathon groups, and the reason is specific: the marathon-pace segments are not recovery, they are still work, so you never stop clearing lactate under load. That is a closer match to what actually happens in a marathon than any session with a jog recovery. Expect the first alternation to feel almost too easy and the last to feel like a race.
The session
Shown at a 4:00 marathon reference — 1 h 17 total, about 13.1 km, including 55 min of quality work.
Warm-up
- 12 min easy (6:43–7:24/km)
Main set
- 5 × (1000 m @ 5:14/km (T) — 5:14, 126 s/400 m lap + 1000 m float @ 5:41/km (M) — 5:41, 136 s/400 m lap)
Cool-down
- 10 min easy (6:43–7:24/km)
Why this session works
Alternating threshold and marathon pace with no rest trains lactate shuttling — clearing while still running fast. A staple of elite marathon groups for exactly that reason.
Source: Casado et al. 2022. Training phase: build.
Run it at your own paces
Open the workout generator and enter a recent race time — every rep length, recovery and target pace is recalculated for your fitness, and the session exports to .fit for a Garmin watch.
Frequently asked questions
What is a threshold alternations?
Alternating threshold and marathon pace with no standing rest, training the body to clear lactate while still running fast. Alternations are a staple of elite marathon groups, and the reason is specific: the marathon-pace segments are not recovery, they are still work, so you never stop clearing lactate under load.
How long is this session?
At a 4:00 marathon reference it comes to 1 h 17 and about 13.1 km, of which 55 min is prescribed quality work. The generator scales both to your own paces, so a faster runner covers more ground in the same time.
Who is this workout for?
It is written for the build phase of a marathon build. The distances shown suit a 4:00 marathoner; enter your own recent race time in the generator and every rep length and target pace is recalculated for you.
More threshold and tempo sessions
- Tempo run — One unbroken block at threshold pace — the effort you could hold for about an hour in a race.
- Cruise intervals — Threshold pace broken into repeats with short jogs, so you accumulate far more time at the ceiling than one continuous block allows.
- Tempo sandwich — A threshold block, a marathon-pace middle, then a second threshold block on tired legs.
- Progression run — A run split into thirds, each faster than the last, finishing at or near threshold.