There comes a time in every runner’s life when it’s time to kick things up a notch. That means one thing and one thing only: interval training.
There’s a reason loads of runners don’t like intervals. They hurt. They’re exhausting and they force your legs, lungs, and central nervous system to work harder than ever. Your first Rolling 400s might seem like the hardest thing you’ve ever done, but follow a good plan (a coach or running app can help) and you won’t just find your fitness improving, you’ll notice your mental resilience hardening, your legs bearing the burden with greater efficiency, and faster run times. Do it enough and you might even learn to love them.
From your Fartlek to your Over/ Unders, below is an expert guide to the different types of interval training and what they're best for.
What are running intervals?
“Intervals are simply planned changes in pace," says Ben Lucas, head coach at the TCS Sydney Marathon. “You run hard for a set time or distance, ease off to recover, then go again.” Nothing else to it. “The principle is stress and adaptation: push the body past its comfort zone, give it just enough recovery to do it again, and over time your engine gets bigger.”
While running’s post-pandemic boon and the rise of tracking apps like Map My Run has caused more people get into the sport (and take serious note of their metrics), Lucas says running intervals isn’t anything new. In fact, it’s simple, and time-tested. “Intervals aren’t some fancy hack,” he says. “Coaches have used them for close to a century.” In fact, European distance squads in the ’30s–’50s were already doing structured track reps. “It’s how legends built their fitness long before GPS watches and lactate testing existed,” Lucas says. “Science has just helped us understand why they work so well.”
What are the different types of interval?
We asked Brett Durney, a lifelong runner and co-founder of Fitness Lab to break down the most common types of interval training.
“Fartlek is a Swedish term meaning ‘speed play,’” says Durney. “It involves unstructured or semi-structured changes in pace, often guided by feel rather than strict timing.” For example, running hard to a lamppost and then jogging to the next junction. “It blends aerobic and anaerobic systems and is useful for building speed endurance without the rigidity of track based sessions.”
These are repeated 400-meter or 800-meter efforts with controlled recovery, typically active recovery such as a light jog. “The term rolling implies that the session maintains rhythm rather than coming to a complete stop,” says Durney. “These sessions are particularly effective for improving VO2 max and race pace tolerance, especially for 5K and 10K runners.”
“Over/unders involve alternating slightly above and slightly below a key threshold pace within the same repetition,” says Durney. “For example, one minute faster than 10K pace, followed by one minute slightly slower than 10K pace. This helps train the body to tolerate and clear lactate efficiently while maintaining forward momentum.”
Pyramid intervals increase and then decrease the duration or distance of efforts within one session. For example, 200m, 400m, 800m, 400m, 200m, or one minute, two minutes, three minutes, two minutes, one minute gradually getting slower, and then faster as you come back down the other side of the ‘pyramid’. “These sessions allow you to work across multiple energy systems and develop pacing control,” says Durney.
“Tabata is a Japanese interval protocol consisting of 20 seconds at full intensity, followed by 10 seconds rest, repeated 8 times, totaling four minutes,” Durney says. “It’s designed to push both aerobic and anaerobic systems to near maximal output in a very short time frame. While often associated with cycling, it can be applied to running, particularly hill sprints or treadmill efforts.”
The EMOM concept can apply to everything from sprints to HIIT circuit sessions in the gym. “You set a fixed amount of work to complete at the start of each minute, and once you complete the work, the remaining time within that minute becomes your rest,” says Durney.
Your goals may vary, but a decent training block will likely include a mixture of all of the above, with the intensity gradually increasing as you go on. You might also do some heart rate-based intervals which ask you to work at a certain percentage of your maximum effort. This helps you understand your own effort rates and pacing ability based on how you feel in your body, without necessarily consulting a watch—a useful skill for learning to regulate your speed, and exertion.
Will intervals improve your overall fitness?
“The physiological benefits of interval training are really broad,” says Durney. “They affect everything from cellular energy production to how efficient the cardiovascular system is.”
Essentially, when we run intervals, our bodies experience constant surges in the demand for oxygen. Our heart rate spikes, breathing becomes labored, and our muscles burn through available energy stores at a much faster rate than usual. This changes how the body uses energy. In the muscles, interval training increases mitochondrial density. More mitochondria—the powerhouses of the cells—give more capacity to generate energy aerobically.
The benefits are well documented. A study published in the Journal of Applied Physiology found that just seven HIIT sessions split over two weeks increased mitochondrial enzyme activity by up to 32 percent in untrained athletes.
“Training intervals regularly also increases stroke volume, the amount of blood the heart pumps with each beat,” Durney says. “Hearts that are stronger and more efficient deliver more oxygen to working muscles without the heart-rate needing to elevate as high.” In fact, research published in the journal Medicine & Science in Sports & Exercise found that interval training is far better at this than continued steady jogs.
Durney adds that Interval training also improves our VO₂ max (the maximum rate of oxygen our bodies can consume and use during intense exercise). A meta-analysis of 32 studies found that short bursts of activity, as in HIIT training and intervals, produced greater improvements in VO₂ max than steady-state exercise.
“Sprint sessions also have an effect on our hormones too, with adrenaline and noradrenaline increasing blood flow to muscles, and helping to unlock energy stores,” says Durney (it’s the same mechanism that helped us run away from saber-toothed tigers way back when). “Intense sessions also spike testosterone levels to help with muscle repair, with our metabolisms staying high while we recover, in a calorie-torching process known as ‘post-exercise oxygen consumption.’”
All of which is great, but your first interval session won’t come with a science exam. At its core, Jackson Gray, owner of Flow Athletic. and trainer to world champion athletes, views running fitness as an easy to remember triangle. “Long runs widen the base, high-intensity intervals increase the height,” he says. “We want to make our triangle cover as much area as possible. The longer distance we’re training for, the more we focus on the base (i.e. distance). The shorter, more intense the event, the more we want to aim to increase the height (i.e speed).”
How often should you do interval training?
“A good rule of thumb for any event over an hour is to have half of your training focused on intervals,” says Gray. “This ensures you're getting enough intensity while still able to get longer, more steady paced workouts in to help you experience what it will be like on race day.
If that sounds like a lot, don’t worry. Intervals may feel daunting at first, but no good trainer will throw you in at the deep end; the aim is to gradually build up fitness in a structured and persistent way rather than burning you out in week one.
“For most runners, two quality sessions per week is the sweet spot,” says Lucas. “This provides stimulus, without frying your nervous system. Doing two out of four runs as interval variations in a half-marathon plan sounds about right: one sharper/VO₂ max session, one threshold/strength session; the other two should be genuinely easy.”
And remember: “People mess up by making every run ‘moderately hard’, and never truly recovering,” warns Lucas. “If everything feels hard all week, you’re overdoing it.”
A good interval training drill to help improve your 5K time
A good place to start with running intervals is improving your 5K time. This will, in turn, serve as a cornerstone for improving your 10K, and half marathon times, too.
Durney calls the below “a very effective and simple session.”
- Run six to eight x 800 meters at slightly faster than your current 5K pace
- Recover with a 90-second to 20-minute easy jog between efforts
For example, if you run a 4 minutes 24 second per kilometer (a 22-minute 5K), your 800 meter reps might sit around 3 minutes 20, to 3 minutes 25 per rep. (It works at slower paces too!).
“This works because 800 meters is long enough to meaningfully challenge VO₂ max, develop pace tolerance, and improve lactate handling, while still being repeatable with controlled recovery,” Durney says. “Completed once per week within a structured plan, this can drive significant improvements.”
A good interval training drill to help improve your half marathon time
If you’re looking to build up pace over longer distances, the focus should shift towards sustained threshold and race pace efforts (i.e. pushing yourself to run faster, for longer). For full or half marathon prep, Lucas recommends working through the below twice per week:
- Completed three × 10 minutes at a comfortably hard (threshold) pace
- Followed by 2–3 minutes easy jog between sets.
“In a half marathon effort, you shouldn't be gasping,” he says. “Rather, you should feel in control. This builds the lactate threshold and the ability to hold pace for a long time without fading.”
For something slightly more structured on one of your interval days, Lucas recommends you:
- Run five sets of 1 mile at slightly faster than half marathon pace, with two minutes recovery jog between sets.
“This one is really tough but it gets results,” he says. “Intervals aren’t magic, but they are great for creating targeted stress. Use them twice a week, keep your easy runs easy, and you’ll get faster without burning out.”
This story originally appeared in British GQ.