Most New Runners Add Speedwork Too Quickly. Here’s How to Increase Intensity—Without Risking Injury.

As a physical therapist, there’s one injury-inducing mistake that Anh Bui, DPT, CSCS, sees beginner runners make all the time: “They’re adding intensity in way too soon without having an adequate aerobic base,” says Bui, who is also a level 1 USATF-certified coach with Run Resiliently Physical Therapy. “It’s like if you were going to lift weights for the first time, you wouldn't go straight into a one-rep max or even a five-rep max lifting routine. You would start with low intensity and high rep.”There are a lot of important adaptations that happen during the base phase of running—which consists of almost entirely easy runs and low-intensity efforts—one of which is getting your muscles, tendons, and bones used to impact, Bui says.Slow, easy running can also improve blood and oxygen flow and even build mitochondria, she says, which are your powerhouses in terms of generating energy for endurance exercise. “You can do a lot with just easy running,” Bui emphasizes.Now, once a runner has built that aerobic base, adding speed or hillwork (a.k.a. intensity) can definitely have benefits, including helping you run faster over a longer distance, says Greg Laraia, a running coach at Motiv in New York City. By adding intensity, you’re also “educating your body,” Laraia says, teaching it how to be uncomfortable and how to find specific paces. Intensity could also help improve your form and leg turnover, he adds.So, the key as a newer runner, or a runner coming back after a hiatus, is figuring out when you have an adequate base and can start layering in intensity without ending up with an injury. “People are impatient,” Laraia says. But it pays to do this right. Here’s how.When You Can Start Adding IntensityThe true answer is “it depends,” Bui says, because running history and genetics also play a role. But here are a few things she and Laraia consider before suggesting clients add intensity.You Built VolumeLaraia says volume should be a consideration for when to start adding intensity, but exactly how many miles you need to be able to run to start adding intensity varies. For a rough benchmark, Bui puts it at 15 to 20 miles a week. “I think in general, people can do a lot with 15 to 20 miles a week,” she says.You Know What Easy MeansMore important than an exact mileage to both experts is that the miles you’re running are at a truly easy pace. “If you’re running 15 miles, but you’re in zone 4 the entire time, the intensity is probably already too high,” Laraia says, adding that this is one of the biggest mistakes he sees newer runners making.You should be able to run your base mileage at a truly conversational pace before considering adding intensity, he notes. You can either gauge this through the talk test (can you actually have a conversation while running?) or with heart-rate data, aiming to be in zone 2 for your easy miles.“If I’m working with you as an athlete and I’m seeing consistency over four to six weeks and your heart rate’s lowering as we go then I know you’re running easy and I know you’re adapting to the base mileage we’re putting in so maybe we can test out some intervals and some intensity here and there,” Laraia says.You Run Consistently Speaking of consistency, no matter how many miles you run in a week, Laraia says a key is being consistent with that, not just being able to do it once. “I would definitely put consistency in a checklist,” he says, adding that ideally you’re running a minimum of three times a week for about six weeks. “If you’re consistent over time, you will get better, but if you’re inconsistent over time, you’re probably not going to make those adaptations,” he says.You’re Recovering WellLaraia and Bui agree that you should feel well-recovered from your current load before considering adding intensity. “Your energy levels need to be relatively good throughout the day,” says Bui. You should also feel like any soreness isn’t lingering beyond 48 hours postrun.Laraia adds that getting enough sleep and managing your life stress both factor in as well because intensity is, in fact, another stressor. “This ends up being one of the more important readiness pieces when we talk about when to add intensity,” Laraia says.You’re Not Injured All the TimeIn addition to not being currently injured, Bui considers whether a runner has a history of injuries like stress fractures or RED-S. “For those individuals, it might take them a long time of just easy running,” she says. “They’re just going to need to prove to themselves that they can handle easy mileage before stacking on intensity.”If you can check off all the above boxes, you have the green light to ease into intensity. One note of caution: Only change one variable at a time, Bui says, meaning don’t add more miles on top of intensity. Add one or the other at a time.Start With StridesBoth experts recommend strides, which could be four to eight reps of 15- to 30-second pickups in the middle or at the end of an otherwise easy run, because they don’t require you to hit a specific pace. For each stride, ramp up speed to about 80 percent effort, then start to slow back down.You could also do strides uphill at the same effort (again, aiming for 80 percent), which has the added benefit of helping you work on mechanics, Laraia says. “Hills teach you how to pump your arms, how to drive your knees, how to push off your toes, and give you a little bit of forward lean, and also help build strength,” he says.Laraia likes to put strides in the last two miles of an easy run.Try FartleksBui loves fartleks for beginners because it’s a way of DIYing intensity that gives them an opportunity to explore different paces without needing to know their “threshold” or half-marathon pace, for example. “It’s usually a combination of some fast intervals followed up by some jogging in between, but you’re just playing around with different speeds,” she says.That’s the whole point of fartleks: You set the intervals. Run hard when you can, then slow down until you recover.Measure Your IntensityNo matter what type of intensity you add, Bui likes gauging it with the talk test. When adding intensity, you should still be able to get a couple of words out before you need to catch your breath, she says, adding that this would roughly correspond to a threshold effort.If you prefer using rate of perceived exertion (RPE), Laraia says to aim for a 7 to 9 out of 10 based on the length of each effort (with shorter efforts at the higher end and vice versa). As you get used to intensity through the above workouts, you can start to home in on more specific paces and consider using heart-rate data to really dial in your intensity.Follow the 80/20 RuleThis “rule” states that 80 percent of your running should be easy and 20 percent should be more intense. But beginners tend to overdo it, getting closer to 50 percent of their miles at a pace that’s higher than zone 2. “Applying or starting to think about the ratio of how much high-intensity running to easy running is important,” Bui says.Listen to Your BodyAs you add in intensity, pay attention to how your body is adapting and pull back if it’s giving you signs you’re overdoing it. Bui says shin splints are the most classic sign, as well as aches and pains that get worse as you’re running and linger throughout the day.“Be very mindful of how you feel the day after incorporating intensity,” Bui adds. “If you’re feeling really sore, you probably overdid it, and if you’re feeling sore for more than two days, you definitely overdid it.”