Once you've built a base of easy running, sooner or later you'll add some faster sessions. Two names come up constantly: tempo runs and intervals. They're both "hard", but they train different things – and mixing them up is a common reason runners feel tired without getting faster.
A quick look at the two thresholds
As you run faster, your body passes two important points:
- The first threshold. Below it, running is easy and conversational. That's where your easy and long runs belong.
- The second threshold (often called the lactate threshold). Up to here, your body can clear the lactate it produces about as fast as it makes it. Beyond it, lactate builds up quickly and you have to slow down within minutes.
Sports scientists often describe these points by blood lactate values of roughly 2 and 4 mmol/L, though the exact numbers vary from person to person. The useful takeaway: tempo runs live just below the second threshold; intervals go above it.
Tempo runs: "comfortably hard"
A tempo (or threshold) run is a sustained effort you could hold for a long time in a race – roughly the pace you could keep for about an hour. For many recreational runners that's somewhere between their 10 km and half-marathon race pace.
How it feels: controlled but focused. You can say a few words, not full sentences. If you're gasping, it's too fast. If you could chat, it's too slow.
What it trains: your ability to hold a strong pace for longer – exactly what decides 10 km and half-marathon results.
Examples:
- 15–20 minutes continuous at tempo effort, after a 10–15 minute easy warm-up.
- "Cruise intervals": 3 × 8 minutes at tempo with 2 minutes easy jogging between. Breaking it up lets you do more at the right effort.
Intervals: short, hard, with recovery
Intervals are repeated hard efforts above threshold, with recovery in between. The classic version for distance runners is around 5 km race effort.
How it feels: hard. Talking is out. But each repetition should be similar in pace – if the last one is much slower than the first, you started too fast.
What it trains: your maximum aerobic capacity (VO2max), running economy at speed, and the feel of fast running.
Examples:
- 5 × 3 minutes hard, 2 minutes easy jog.
- 6 × 800 m at about 5 km race pace, 400 m jog between.
- Short hill repeats: 8 × 45 seconds uphill hard, walk or jog back down.
Do you need both?
If you're training for a 5 km, intervals carry more weight. For a half marathon, tempo work is closer to what the race asks of you. Most runners benefit from some of each across a training block – but not necessarily every week.
The bigger point is how much hard running you do in total. When researchers looked at how successful endurance athletes train, they found most of their sessions are easy and only a minority hard – roughly 80/20. In practice, for most recreational runners that means:
- Running 3 times a week: one quality session (tempo or intervals), the rest easy.
- Running 4–5 times a week: up to two quality sessions, never on back-to-back days.
- New to running? Build several weeks of consistent easy running first. Strides – 4–6 relaxed 20-second accelerations at the end of an easy run – are a gentle first step.
Common mistakes
- Every run becomes a tempo run. Medium effort every day leaves you too tired for real quality and too fast for real recovery.
- Racing the intervals. The goal is a set of even repetitions, not a heroic first one.
- No warm-up. 10–15 minutes easy plus a few strides before any hard session.
- Too much too soon. Start with less hard time than you think you can handle and add a little every week or two.
The bottom line
Tempo runs teach you to hold a strong pace; intervals raise your ceiling. Keep them separate, keep them controlled, and protect the easy days around them. That combination – not more hard days – is what makes runners faster.
Sources
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5:276–291. doi:10.1123/ijspp.5.3.276
- Stöggl TL, Sperlich B. The training intensity distribution among well-trained and elite endurance athletes. Front Physiol. 2015;6:295. doi:10.3389/fphys.2015.00295