I Added 10 More Miles a Week to Marathon Training—and Seriously Felt the Difference at Mile 20

4:09:48. That was my finish time at this year’s New York City Marathon. It was also—to the second—my finish time in the same race last year.Putting aside the wildness of that (but what does it mean?) I learned a few lessons as I cruised through the five boroughs for the seventh time.Specifically, although I ran the exact same time, my splits looked quite different. I ran the latter miles faster and they felt easier this year. And that comes down to one key training adjustment I made: adding more overall mileage to my week.Here’s how and why I maximized my volume during this training cycle, and how it paid off in my strongest finish yet (even if not a PR).I ran the London Marathon in April, and both New York and Sydney last year, using an artificial intelligence training app. I programmed in that I wanted to run three days a week so I could continue to strength train two to three days a week as well. Plus, I walk quite a bit as someone who lives in New York City (around four to five miles a day on top of any running).But then I reported on a series of articles about durability for Runner’s World and I started thinking more about total weekly mileage and how much I had (or had not) been doing. Turns out, I peaked around 30 to 35 miles for all three of those marathons. It made me realize there was room for growth.When I got the opportunity to run New York again this year, I figured out how high I could go mileage-wise without upping my risk for injury.I started by talking to Andrew Kastor, head coach of the Asics Mammoth Track Club. Before our call, I sent him the training plan I planned to follow for this upcoming training cycle: the Runner’s World Break Four Hours plan. (I also intended to continue strength training twice a week.)The peak week mileage for that plan: 48 miles, with at least four days a week of running. This may not seem like a ton to people who swear by super high mileage, but it is a steep increase relative to my previous builds. “Between 32 and 50 is night and day,” Kastor says. “You’re going to notice a big difference in your staying power after mile 20.”Importantly, I built a pretty solid base before starting the training plan 16 weeks out from race day and felt ready to jump into week one when the time came. This plan also leverages mileage ranges, rather than firm numbers, allowing me to further customize it.Kastor likes the approach of mileage ranges and uses it with many of his athletes. “It kind of takes a little bit of the edge off or the pressure off,” he says, because you can choose the lower end of the range if you’re feeling fatigued.He also advised me to add in the optional up-to-three-mile run in my plan every other week (where you see 0 to 3 miles). “It’ll be worth it the last mile of the race or the last two miles of the race [when] you’re able to hold that 9:07 pace or that nine flat pace,” he says.The Strategies That Helped Me Avoid InjuryKastor encouraged me to pay attention to how I was feeling as the training stacked up, and to pull back if I noticed symptoms of overtraining, like an elevated resting heart rate, reduced heart rate variability, or subjective measures like excessive fatigue or feeling flat in workouts. “If [the] legs are not bouncing back week after week, then that’s a sign of overtraining and that you need to pull back and not just pull back with mileage, but take two days off to let your legs recover and heal up,” he says.I actually felt great throughout my training, which I also attribute to switching up my strength training a bit under the guidance of my physical therapist (I focused more on heavier weight and much less volume, while adding isometrics for tendon health.) Mentally, I also started looking more forward to my running days versus my off days, which is likely due to the fact that I was running more regularly.In addition to watching for signs of overtraining, Kastor also emphasized the importance of recovery and nutrition when increasing mileage. “In order to do more mileage, you have to sleep well and eat well,” he says.I focused specifically on eating more carbs than I ever have in training before. (I recently realized I was so focused on protein that I was coming up short on carbs.) As for sleep, I’m always pretty protective of that. So I just kept doing what I was doing: aiming for eight to nine hours a night.Per Kastor’s suggestion, I also committed to a sports massage every other week during my training, and used the Therabody JetBoots PRO Plus immediately after long runs and occasionally in the evenings on other days. (I feel like they relax my whole nervous system before bed.)Modern running shoes can also help you handle more time on your feet, Kastor explains. “Generally, because people can handle a little bit more volume with the cushion of the shoes, they’re not breaking down as much,” he says.I trained in a higher cushioned shoe—the Asics Gel-Nimbus 28—which is known for its premium cushioned, long-lasting ride, according to Runner’s World reviewers. It provided me with a high-energy return and support for the extra miles.Courtesy Caitlin CarlsonHow Mileage Boosts DurabilityWhen I spoke to experts in durability about how to increase it for late-race performance, they told me that weekly mileage plays a major role. Research, too, backs up the importance of volume, stating long runs of at least 90 minutes and higher training volumes overall improve durability. And other research suggests more volume (especially easy miles) can lead to faster marathon finish times.“We start where the athlete is with their fitness and then we progress upward because volume is king,” Kastor says. “More is better as long as you stay healthy.”He adds that there’s something about the repetition of running frequently that seems to help, citing his wife, marathon Olympic bronze medalist Deena Kastor, as an example. At one point, she was running upward of 140 miles, hitting 13 runs a week, he says. “She would wake up from a nap and be really sleepy, rubbing her eyes, lace up her shoes, and go for a run,” he says. “I think what’s overlooked generally is the role of the nervous system and [how it] plays into the efficiency of running mechanics. If you [run] over and over and over and over again, then you get really, really good at it.”How the Volume Increase Paid OffSo, you know I did not PR after adding more mileage to my training plan. But! Take a look at the times for the final four miles in 2025 versus 2026:2025: 23: 9:4124: 10:0025: 9:5026: 9:512026:23: 9:2324: 9:3825: 9:1826: 9:02I was clearly significantly stronger during the latter miles this year than I was last year, and it was amazing to see and feel that difference. In 2025, I’m honestly surprised I was able to hold the paces I did—I remember feeling pretty wiped, which is why I held back some this time. This year, I felt like I was cruising down 59th Street on the way to mile 25, and even later in the day, I felt good enough to walk almost a mile to dinner and back home.I felt so strong at the end of this year’s marathon that I know the “mistake” I made was to not trust my training earlier in the race. I was so afraid that I would run out of steam if I held the 8:47 pace I hit at miles 4 and 5 that I pulled back.So for me, the race was much more of a mental one than a physical one. Now I just have to trust that next time, I can hold faster paces earlier on and still finish strong.At the end of the day, I realize that I was so focused on my physical training plan and even nutrition that I didn’t think about the psychology of it all. Because I’d run all my long runs at a much easier pace (with the exception of a handful that called for some tempo miles in the middle), I kind of freaked out at the idea of running 26 miles at a 9:00 pace. Now, I truly believe I can. And more mileage is definitely a big part of why.