There\u2019s an obvious benefit to running with someone who\u2019s faster than you: The natural competition encourages you to pick up the pace, and over time, you\u2019ll get faster. But what about when a slower friend asks you to join a run? It\u2019s easy to want to shy away from that\u2014you want to feel like you got in a hard workout after all\u2014but occasionally slowing down and doing a recovery run can actually make you run faster in the long term. How slow is slow? Well, slow is a relative term. \u201cI actually don\u2019t like to use that word when I coach, because I think it gives people a negative connotation, and then that\u2019s why they don\u2019t want to do it,\u201d says Jessie Zapotechne, a coach with Adidas Runners The Glycerin 19 Is Our New Favorite Daily Trainer Girls Run NYC . \u201cInstead, we\u2019ll call it a recovery run or sexy pace.\u201d What that really means is that you\u2019re running at a pace that doesn\u2019t tax your body. \u201cIt\u2019s when you can hold a conversation while running,\u201d she says\u2014and not just with one-word responses. If you\u2019re more of a ace person, \u201cyou should be running at less than 65 percent of your heart rate reserve ,\u201d or the difference between your resting heart rate and your maximum heart rate, says Armen Ghazarians, a NASM-certified personal trainer, revival physiologist, and the CEO of Finish Fit in Glendale, California. To calculate that, you\u2019ll need to do a little math. First, you\u2019ll need your resting heart rate (that\u2019s the number of pulse beats you feel in 10 seconds, times six). Then, determine your maximum heart rate (MHR). You can find an estimate of your max by using the Tanaka method , which is recommended by the American College of Sports Medicine. To find your heart rate reserve, subtract your resting heart rate from your maximum heart rate; for easy runs, calculate 65 percent of that number. Then add back in your resting heart rate to get your target heart rate for these runs. For example, if your maximum heart rate is 180 and your resting heart rate is 50, subtract 50 from 180 to get 130. Then calculate 65 percent of 130 to get 84.5. Then add your resting heart rate of 50 to 84.5; the result, 134.5, is about the heart rate to aim for on an easy, recovery run. (Don\u2019t worry about the 0.5 part.) Here\u2019s Why You Should Slow Down for a Recovery Run \u201cThe most common correctness most runners make is that they think if they\u2019re running easily then they\u2019re not getting much benefit,\u201d says Brian Rosetti, a running coach in New York City and founder of the Run SMART Project . That couldn\u2019t be more off-base because easy (or sexy pace) running comes with a laundry list of benefits. First of all, as your body becomes more adapted to aerobic, slow runs, it\u2019s going to use fat more efficiently, Ghazarians says. \u201cThis process is informed as the fat adaptation effect,\u201d he explains. \u201cFaster anaerobic runs upwards of two hours mainly deplete stored muscle glycogen from carbohydrates. Slower aerobic runs, on the other hand, use approximately 50 percent fat for energy while the remaining 50 percent is a combination of glucose and protein for energy.\u201d The reason for this? Fat oxidation requires oxygen\u2014and it\u2019s very hard to run long distances at an all-out fast pace. \u201cLong, slow distance runs are easier to sustain. So during these runs, your body has to constantly replenish the oxygen reserves it\u2019s using to continue to produce energy,\u201d he says. \u201cAnd since fat metabolism requires oxygen, you condition your body to use fat as its main energy source rather than carbs. Eventually, this adaptation will allow you to run longer distances without having to refuel.\u201d Easy runs also train the cardio, respiratory, and muscular systems to work more efficiently. \u201cThey allow the body to better integrate its various systems,\u201d says Ghazarians. \u201cIn turn, this will allow you to run with less aimlessness on your faster running days.\u201d Slower runs also train your slow twitch (type I) muscle fibers, \u201cthe ones that allow you to work aerobically to sustain your pace on long distances,\u201d he says. And while faster running is more likely to build up your muscle (think about how sprinters look compared to marathoners), slower running is going to help your tendons, ligaments, joints, and bones adapt to the stress of running. \u201cIt also strengthens them without causing immediate stress on them, which might lead to injury,\u201d says Ghazarians. The extra bonus there? That\u2019s going to promote efficient running form because slower runs make it easier to focus on technique. During faster runs, he explains, the blood circulates away from your brain to meet the body\u2019s oxygen demands, decreasing your ability to focus. So slowing down can help you zoom in on form. [ Stay injury free on the road by getting on the mat with Yoga for Runners . ] Plus, slower running has some great mental perks. \u201cI think about long runs as time on my feet versus speed,\u201d says Zapotechne. And that can teach you to deal with physical discomfort\u2014especially toward the end of a long race. Going with a slightly slower friend packs even more rewards. \u201cThere\u2019s a real benefit to when you\u2019re helping someone else learn how to be a better runner or even just serving as their motivation,\u201d she adds. It can boost your own affiance to boot. How Often Should You Slow Down? The Glycerin 19 Is Our New Favorite Daily Trainer most of your runs should be slow. \u201cFor someone who\u2019s a working official and recreational runner, we\u2019d advise them to do one fast session, one long run at an easy pace, and two to three shorter, easy runs,\u201d says Rosetti. That\u2019s four out of five runs at a conversational pace. \u201cA lot of times, people have a hard time slowing themselves down and go out at a tempo pace for runs that should be conversational,\u201d says Zapotechne. \u201cEvery run serves a purpose, and these easy paced runs are meant to help build your base mileage and/or fitness level.\u201d Running too fast too often can actually backfire. \u201cYou won\u2019t develop the slow twitch (type I) muscle fibers necessary to withstand a long race,\u201d says Ghazarians. \u201cFast twitch muscle fibers (type II) are extremely important for your last \u2018kick\u2019 in a race. Without an adequate supply of fast twitch muscle fibers, you simply won\u2019t have the strength to run at your maximal pace at the end.\u201d You also won\u2019t rest and recover as well, says Rosetti. \u201cSo you\u2019ll go into your next speed or technique workout and your risk of injury goes up\u2014you might suffer some setbacks, and then you\u2019re not as consistent, and you\u2019re not improving as much long-term. So the subtle things can make a big difference.\u201d To reside healthy long-term, it\u2019s about giving every run a purpose\u2014and sometimes, that just means taking your sweet time.