5 Best Interval Sessions for Runners and Triathletes
Increase your speed, endurance and anaerobic capacity — with the right sessions at the right time. Below are five interval structures that cover the full spectrum, from raw VO2max development through to race-pace sharpness, along with what each one is actually for and where it fits in a training week.
4×4 Minutes — The Classic VO2max Session
4 reps × 4 minutes hard, 3 minutes easy recovery.
Best for: increasing your aerobic ceiling and maximal oxygen uptake. Run at Zone 4–5. This is the benchmark VO2max session used across endurance sports — hard enough to push your ceiling, short enough to hold form for all four reps.
10×400m — The Speed Endurance Session
10 reps × 400m, 90 seconds recovery.
Best for: race pace sharpness and speed tolerance. Run at Zone 4–5. A staple for runners preparing for 5km and 10km efforts, where holding pace under fatigue matters as much as raw speed.
3×10 Minutes — The Threshold Builder
3 reps × 10 minutes, 2 minutes recovery.
Best for: raising lactate threshold and sustainable race pace. Run at Zone 4. This is the session that moves the needle on how long you can hold a hard-but-controlled effort — directly translatable to half marathon and marathon pacing.
30/30 Fartlek — Speed Without Rigidity
30 seconds hard, 30 seconds easy, embedded in an easy run.
Best for: transitioning from base work into intensity. Run at Zone 4–5. A useful bridge session when moving out of a base-building block, letting you reintroduce sharpness without the structure of a full track session.
Pyramid Fartlek — The Complete Mixed-Effort Session
1–2–3–4–3–2–1 minutes hard, with equal easy jog recovery.
Best for: developing aerobic power, pacing control and speed endurance in one session. Run at Zone 4–5. The pyramid structure forces genuine pacing discipline — get the early reps wrong and the long middle effort will punish you.
Fuelling Your Interval Sessions
Sessions at Zone 4–5 place real demand on your carbohydrate stores, even at 45–60 minutes total duration. A light pre-session fuel — rather than training fasted — helps you hold quality through the final reps, when form typically breaks down first. For longer combined sessions (interval work plus an easy warm-up and cool-down over 90 minutes), a fast-acting carbohydrate source between reps or at halfway can make the difference between finishing strong and fading on the last rep.
Whatever your next block looks like, our Fuel App builds a personalised fuelling plan around your training and race schedule — worth a look before your next hard session.