Comfortably hard. Two words, and most runners only hear the second one.
The tempo run is a continuous effort at or near lactate threshold, the fastest pace you could sustain 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 requires significantly more recovery). The discipline of holding the right effort, not faster, is the actual skill the tempo run trains.
What the Effort Should Feel Like
Threshold effort is specific. Learning to find it and stay there is part of the training.
Breathing: Deep, rhythmic, and focused. You can manage 3 to 5 word responses to a question, but holding a conversation is out of reach. If you can chat normally, you're at steady-state, not tempo. If you can't speak at all, you've overshot into interval territory.
Muscles: Working but not burning. There's a sense of sustained effort in the legs, but it's manageable. If your legs feel like they're filling with concrete, you're above threshold.
Mental state: Attentive. You need to concentrate to hold the effort. It's not automatic like an easy run, and it's not desperate like a race. It sits in between: a deliberate, sustained focus.
RPE: 7 to 8 out of 10. Heart rate approximately 80 to 88% of maximum.
Pace reference: Roughly your 10K to half-marathon race pace, depending on fitness. But pace varies with conditions. On a hot day, on a hilly route, or after a hard training week, the same threshold effort will produce a slower pace. Trust the effort.
Why Continuous Matters
The tempo run's defining characteristic is that it's unbroken. Unlike threshold intervals (which split the work into segments with recovery), a tempo run holds threshold effort continuously for 20 to 40 minutes.
This continuity creates a specific training effect: your body learns to manage lactate production and clearance in a sustained, steady state rather than in bursts. It builds the metabolic discipline of holding a pace when the effort is accumulating and the temptation is to either speed up (and blow up) or back off (and lose the stimulus).
For marathon runners, this translates directly. The marathon is a continuous effort at a sustained intensity. The tempo run is the best simulation of that demand at a higher, more concentrated intensity.
Formats
Classic tempo. The standard version. After a 15 to 20 minute easy warmup, run 20 to 40 minutes at threshold effort, then cool down with 10 to 15 minutes of easy running. Simple, direct, and effective.
Tempo within a long run. A 20 to 30 minute block at threshold effort embedded in a long run, typically in the middle or final third. This is an advanced format that combines threshold development with endurance and fatigue resistance. It produces a demanding session and needs careful recovery planning.
Progressive tempo. Starts at steady-state effort and builds into full threshold over 30 to 40 minutes. Useful for runners who struggle to find the right effort from a standing start. The gradual buildup also reduces the risk of going out too fast.
When in the Training Cycle
Base phase: Minimal. Some coaches introduce a single light tempo session late in base (15 to 20 minutes at the lower edge of threshold effort) to prepare the body for the build phase workload. But the base phase is about aerobic development, and tempo work shouldn't compete with that priority.
Build phase: The primary tempo window. One to two threshold-focused sessions per week, with at least one being a continuous tempo run. This is where threshold fitness develops most rapidly. Expect the first 3 to 4 weeks to feel hard as your body calibrates; by weeks 5 to 6, the same effort starts to feel more manageable.
Peak phase: Tempo runs shift toward race-specific formats. Marathon-pace work takes priority, and tempo sessions may become shorter or less frequent. The threshold system is built; now the goal is applying it to race demands.
Taper: Short tempo touches (10 to 15 minutes) to keep the system primed without generating fatigue. The adaptation is already built. You're maintaining, not developing.
The Precision Problem
Tempo runs fail in two ways, and both come from pacing errors.
Too fast: The runner pushes into VO2max effort. The session becomes harder than intended, requires 2 days of recovery instead of 1, and doesn't develop the threshold system as effectively. The most common version of this is a runner who starts the tempo at the right pace, then unconsciously accelerates through the middle, finishing the last 10 minutes at a pace that's 15 to 20 seconds per kilometre faster than where they started. A good tempo run has even splits throughout.
Too slow: The runner stays in steady-state territory. The effort feels moderate but never reaches the threshold. The session produces a decent aerobic workout but misses the targeted lactate clearance and metabolic adaptations that make threshold work valuable. If your tempo run felt comfortable the entire time, it probably wasn't a tempo run.
When in doubt, aim for the slower end of threshold. The consequence of slightly too slow (a steady-state workout) is much less damaging than slightly too fast (an unplanned interval session with excessive fatigue).
Practical Guidelines
- Warmup: 15 to 20 minutes of easy running. Non-negotiable. Threshold effort on cold muscles is a recipe for injury and poor quality.
- Duration: 20 to 40 minutes of continuous threshold effort. Beginners start at 20 and build by 5 minutes per week.
- Cooldown: 10 to 15 minutes easy. Helps initiate recovery and flushes lactate.
- Frequency: 1 to 2 times per week during build phase. No more. Threshold work is stimulating but fatiguing.
- Terrain: Flat or gently rolling. Hills disrupt the continuous effort and make pacing erratic.
- The day after: Easy run or recovery run. Respect the session's cost.