Comfortably hard. Two words, and most runners only hear the second one.
The threshold run is a sustained effort at or near lactate threshold — the fastest pace you could hold for roughly an hour in a race. It should feel challenging but controlled: you're working, you know you're working, but you could keep going. The moment it stops being comfortable, the moment you're gritting your teeth and clinging to pace, you've crossed a line and turned it into a different workout.
This distinction isn't philosophical. Running too fast changes the physiological stimulus. It shifts the session from threshold development, which builds sustainable speed, to VO2max stress, which builds top-end power but costs far more recovery. The discipline of holding the right effort — not faster — is the actual skill the threshold run trains.
Why One Threshold Run
There are many ways to deliver threshold work: a continuous tempo, threshold repeats with short recovery, a marathon-pace block, a steady progression. They differ in format, but they all target the same adaptation — teaching your body to clear lactate faster so you can hold a strong pace longer.
We prescribe one threshold run rather than a menagerie of named variants because the adaptation is what matters, not the packaging. A runner doesn't need to memorise the difference between a tempo and a cruise interval to get faster. They need to spend regular, well-judged time at the edge of sustainable effort. The coaching handles the format; the runner shows up and holds the line.
Variety, when it helps, comes from the run itself — the duration of the sustained block, where in the run it sits, and the modifiers we can layer on (a progression finish, marathon-pace segments in a long run). The effort type stays constant so the runner always knows what "threshold" asks of them.
What the Effort Should Feel Like
Breathing: Deep and rhythmic, but controlled. You can speak a short sentence, not hold a conversation.
Effort: RPE 7 out of 10. Comfortably hard — the emphasis on both words. You're working honestly, but you are not racing.
Heart rate: Roughly 80 to 88% of maximum. A useful check, but effort leads; heart rate lags and drifts with heat and fatigue.
The test: Could you hold this for an hour if you had to? If the honest answer is no, you're running the workout too fast.
How to Execute
Warm up thoroughly — 15 to 20 minutes of easy running so the threshold block starts on prepared legs. Settle into the sustained effort and hold it: smooth, even, controlled. Resist the urge to drift faster as you warm to the work — the discipline is the point. Finish with an easy cooldown.
Some days the sustained block is one continuous effort. On others the coaching may break it into a couple of longer segments with brief easy running between — same total time near threshold, slightly more forgiving on a tired day. Either way, the target effort is identical.
Where It Fits
Threshold work belongs to the build and peak phases, once an aerobic base is in place. It's the bridge between easy volume and race-specific fitness: the workout that turns a big aerobic engine into sustainable race pace. In taper, a short threshold touch keeps the system sharp without adding fatigue.
One well-judged threshold run a week, held at the right effort, does more for marathon performance than three ragged ones run too hard.