You’ve probably heard about zone 2 training, which typically shows up as easy runs and most of the long runs on your schedule. It helps you to build your aerobic capacity to run 5Ks, marathons and any distance above or in between.

But runners also know that a robust, successful training plan includes a variety of other workouts alongside those zone 2 runs, such as intervals, tempo efforts and strength sessions. Too much intensity and not enough time spent in zone 2 means that you won’t be able to run as long or develop a solid aerobic base. On the flip side, if you spend 100% of your time training your aerobic base, you’ll likely miss out on getting faster and reaching your full performance potential.

To strike the right balance between pushing the pace and building endurance, here’s a look at how much of your training should happen in zone 2 – and how to put that into practice.

The general rule on how much time to spend in zone 2

A go-to rule of thumb is to stick to the 80/20 method, where 80% of your overall training volume is spent in zone 2 on a five-zone model, says Mireille Siné, a USATF- and 80/20 Endurance-certified running coach based in Los Angeles. This means that easy runs, long, slow distance runs and cross-training ideally make up 80% of your training, while workouts outside of zone 2, like speed workouts and tempo runs, make up the other 20%. ‘The key thing to remember with zone 2 is that it’s there to make it easier for you to go harder on your hard days by taking it easy on those zone 2 days,’ she says.

In practical terms, if you run five to six days a week, you’ll stay in zone 2 for three to four of those training days, explains Siné explains. Or, if you train 20 days of the month, 16 of those should include zone 2 efforts. In terms of mileage, Siné suggests that runners who average about 25 to 30 miles per week run about 18 to 24 miles per week in zone 2.

When to break that rule

The 80/20 split might look different for different race distances. For example, if you’re training for a 5K or 10K, you’re likely working more on speed than if you’re training for a half marathon or marathon, which require more aerobic fitness than speed and power, says Siné.

Half and full marathoners may therefore stick with the 80/20 split, while 5K or 10K runners might lean closer towards a 70/30 split, because they would need to spend more time working at or near threshold effort to prepare for race day, says Siné. ‘Two hard workouts, such as intervals and a tempo workout, would be the sweet spot,’ she explains, while a more advanced runner might add a third high-intensity day.

The zone 2 balance across race distances may look different when it comes to the duration of each training run, too. ‘If you’re training for a 5K, a 25- to 35-minute zone 2 session will be one of your most common workouts,’ Marnie Kunz, a USATF- and RRCA-certified running coach previously told Runner’s World. ‘For longer races, such as half marathons and marathons, your zone 2 training runs may be 40 minutes and more.’

Another variable is your zone 2 balance. This might look different when you follow the three-day method of race training, because you’ll focus on running three key workouts per week – long runs, tempo runs and speed workouts, for example. As such, your running might lean more on intensity. But outside of those three key runs, you’ll likely cross-train for two to three days. This might look like swimming, cycling or using the elliptical for as long as you would an easy run – and you’ll stick to zone 2 for those sessions.

Most individuals will start running by keeping the bulk of their training in zone 2, then layering in harder, faster workouts as they progress to build speed and race-specific fitness. But the more time you spend in zone 2, the more you’ll build your aerobic base – and the more you can push your mileage.