Interval training is one of the simplest ideas in running: run hard for a set time or distance, recover, repeat. That is it. But despite the simplicity, it is the method that most consistently moves the needle for runners who want to get faster.
The reason it works comes down to stress and adaptation. When you run at a genuinely hard effort, not slightly uncomfortable but actually hard, your body responds by building more capacity. Your cardiovascular system gets stronger. Your muscles become more efficient. Over time, your easy pace starts to feel easier, because your ceiling is higher.
How Interval Training Fits Into Your Week
Most runners who add interval sessions to their week make one common mistake: they run too many of them. One or two quality sessions per week is plenty for most people. The rest of your running should stay easy.
This is where Zone 2 training comes in. Easy, conversational running builds your aerobic base and handles the bulk of your weekly volume. Intervals sit on top of that base, not in place of it. If you skip the easy running and try to do intervals every other day, you will get tired, beat up, and slower.
A simple structure that works for most runners: four to five total runs per week, with one long run at an easy pace, one or two interval or quality sessions, and one to two easy recovery runs to fill the gaps. That is a week that builds fitness without overloading your body.
Types of Interval Sessions
Not all speed work is the same. The type of session you choose depends on what you are training for and where you are in your training block.
Short Intervals (200m to 400m)
These are fast and hard, close to your 1K to mile race pace. They build speed and teach your body to move efficiently at high effort. A classic example is eight reps of 400m with 90 seconds of easy jogging between each. Short intervals are useful for 5K and 10K runners and for building leg speed during the early phase of a marathon block.
Middle Intervals (800m to 1200m)
These sit at or around your 5K race pace. Hard enough to be uncomfortable, long enough to build real aerobic capacity. Five reps of 1000m with two minutes recovery between each is a solid bread-and-butter session for runners improving their 5K or 10K times. This is the type of session most people mean when they talk about "track work."
Longer Intervals (1600m to 2000m)
Closer to your 10K or half marathon effort, longer intervals are demanding to run and demanding to recover from. Four reps of 1600m at 10K pace with two and a half minutes recovery is a solid session used in longer-race training blocks. These sessions produce real fitness gains, but they also take more out of you, so recovery between them matters.
If you are just getting started with intervals, shorter and simpler is better. A basic session like six reps of 400m, well executed and properly recovered from, beats an ambitious workout you can only half-commit to.
How to Actually Run an Interval Session
The effort matters more than the pace. Many runners get attached to a target pace and push harder than they should when the number slips. But running at the right effort level, genuinely hard but controlled, is what produces the adaptation you are after.
Warm up properly before any interval session. Ten to fifteen minutes of easy jogging at minimum, with a few short strides to prime your legs. Starting cold into hard efforts is how you get injured.
The recovery periods matter too. If you jog slowly between reps, you will keep your heart rate elevated and make each interval harder. If you walk, you allow more full recovery. Both approaches are valid, depending on the session goal. For most runners, a light jog between reps works well: slow enough to catch your breath, but not so long that you fully reset.
After the session, cool down properly. Ten minutes of easy running and some light stretching. Recovering properly after a hard run is where the adaptation actually happens, so treating it as part of the session, rather than an afterthought, makes a real difference.
Interval Training vs Fartlek vs Tempo Runs
These three methods often get lumped together as "speed work," but they are meaningfully different.
Fartlek training is unstructured. You run harder when you feel like it, recover, run hard again. It is flexible and low pressure, great for runners who find formal intervals intimidating or who run on trails where precise distances are hard to measure.
Tempo runs are sustained efforts at roughly your threshold pace, the effort level you could hold for about one hour in a race. A classic tempo run is 20 to 40 minutes at a comfortably hard pace. They build lactate threshold, which directly affects how fast you can race. Unlike intervals, there is no hard stop and start, just a sustained block of quality effort.
Interval training is more structured than fartlek and more intense than tempo work. The hard efforts are shorter and faster, with deliberate recovery built in. All three methods have a role in a well-designed training week, and they complement each other rather than compete.
When to Add Intervals Into a Training Block
If you are building toward a race, the timing of your interval sessions matters. With a half marathon training plan, for example, you might introduce interval sessions in weeks four through eight, then shift to more tempo and race-pace work in the final weeks before the event.
Hill training is a natural companion to intervals. Hills build strength and reinforce good running mechanics under fatigue. Many coaches alternate between hill sessions and flat interval sessions across the week, giving you speed work variety without repeating the same stress pattern.
Pay attention to how you feel going into interval days. If you are carrying fatigue from a hard long run, an extra easy day is often smarter than grinding through a speed session on tired legs. Quality matters more than ticking boxes.
Gear That Makes Speed Sessions More Practical
A few things make interval sessions more enjoyable and easier to execute consistently.
A GPS watch or running app to measure splits and rest intervals precisely. Knowing your actual pace removes the guesswork and helps you run the right effort across all reps, not just the first two.
Lightweight, breathable running shoes with some responsiveness. You do not necessarily need a full-carbon race shoe for training intervals, but a trainer that feels good at pace helps you run the session as intended.
Running sunglasses, particularly if you train in the mornings or evenings. Most interval sessions happen before or after work, which means running directly into low-angle light. Glare at those hours is real, and it affects how well you can see the path ahead. A photochromic lens like the Adaptor handles the full range of light across a session, from shaded streets to direct sun, without needing to swap eyewear mid-run. Re. frames are built not to bounce, which matters when you are running at pace.
Layering for cold mornings. On winter training days, starting warm and being able to shed a layer mid-session works well. A light jacket you can tie around your waist handles most conditions.
Building the Habit
The biggest reason runners do not improve their speed is inconsistency. One interval session every few weeks does not do much. But one session per week, done consistently across eight to twelve weeks, moves the needle in a real way.
Start simple. Pick one session (six reps of 400m works for almost everyone at the start). Do it once a week for a month. Recover properly. Track how the effort feels over time. When sessions start to feel more manageable, you can adjust volume or introduce a second quality session per week.
The underlying principle is the same as most things in running: do the work, recover well, and show up again. Strength training alongside your running helps too, keeping your legs resilient through a harder training block.
If you are putting together your training kit, the Re. lens guide can help you find the right lens for when and where you run.
Tim Golubev
Founder, Re. (Re Your Run)
Tim built Re. after years of running in sunglasses that bounced, fogged, and ended up on his forehead. After discovering the UV damage that builds up without eye protection (even on cloudy days) and hearing the same frustrations from hundreds of other runners, he decided it was a problem worth fixing properly. With a background in Product across multiple industries, he approached it like any product problem: figure out what's broken, then build something that actually fixes it. He runs daily, co-founded Rose Bay Run Club, and Re. is his attempt to make one less thing that gets in the way of a good run.
