In the fall of 1994, triathlete extraordinaire Mark Allen famously tried to run a fast, all-out marathon with the hopes of breaking 2:20 and qualifying for the 1996 U.S. Olympic Trials Marathon.

Already a five-time Ironman world champion, Allen, then 36, skipped Kona that year and instead spent the summer training for the late-September Berlin Marathon. He was already the fastest runner in the sport of triathlon, having run a sub-30-minute open 10K and a 2:40 marathon split in the 1989 Ironman World Championship, and wanted to see if he could run a standalone marathon at an elite level.

In Berlin, he was on his goal pace through the halfway point, averaging about 5:25 per mile for the first 13.1 miles. Following a strategy that he hoped would allow him to run a negative second-half split, he started to pick up the pace only to have his legs start to get tight and eventually lock up. He struggled through mile 18 and then pulled the plug on the race because he says he could barely run.

Allen’s triathlete physique and multisport training gave him the aerobic fitness and strength to run 6:06 mile pace for 26.2 miles at the end of an Ironman, but it only allowed him to run 5:20 pace for about 14 miles. In hindsight, Allen thinks he would have had to drop 10 to 15 pounds off his 6-foot, 160-pound triathlon-tuned frame to be able to run a marathon at a truly elite level.

“People ask me, ‘Why didn’t you try to run marathons?’” Allen said. “And I tell them that it’s just such a different event than running a marathon at the end of an Ironman, and it requires a different kind of training. And it takes a huge toll on your body to go that far and that fast.”

Real talk: Running a marathon is hard

There’s plenty of good that can come from an age-group triathlete switching gears later in the season to train for an open marathon. You’ll no doubt feel fast because of all of the up-tempo run-sharpening workouts you’ll do in your marathon buildup. You might also feel leaner and lighter in an open marathon if you’ve taken a slight break from the cycling and swimming volume you did for most of the year.

But as Allen’s experience suggests, running an all-out open marathon is nothing like running a marathon at the end of an Ironman.

The running section of an Ironman is all about running with strength and, let’s be honest, that often means survival shuffling on the run as a result of your fitness, fueling efficacy, and fatigue. To run a fast, standalone marathon, you need to be specifically trained for running 26.2 miles as fast as your training allows and be able to ride the razor’s edge of fueling and hydrating just enough to avoid bonking.

The fatigue hits you immediately when you start running in an Ironman, because you’re already six or seven hours into your race. Fatigue doesn’t present itself until the latter miles of a standalone marathon, but maintaining the intensity and fast pace deep into a marathon can be much more daunting than what you experience running in an Ironman, said Mike Ricci, a USA Triathlon Level 3 coach and age-group athlete based in Boulder, Colorado.

“The first thing I always tell people is that I honestly think running a fast marathon is harder than an Ironman."

“And I know that may sound ridiculous, but in an open marathon, when you’ve fallen off pace by 10 seconds a mile or 15 seconds a mile, it really plays with your head because it’s so hard to get back to your intended pace to run 2:50 or whatever your goal time is,” Ricci said. “But running an Ironman marathon is really about strength and not as much about speed, and it’s all about being able to pick that aerobic pace you can run as long as you can until you can’t.”

The advantages of running an open marathon are that you’re presumably fully tapered and rested, most importantly, you’re completely fresh when you’re at the start line. And that means, in theory, you’ll want to run just under the red line of performance for the entire 26.2 miles (or as long as possible) — something that’s not remotely possible in an Ironman because your body is so burdened by the massive fatigue and hydration/fueling depletion you’re carrying off the bike into T2.

Even though the marathon at the end of an Ironman is mostly a Zone 2 effort, it rarely feels great from start to finish, but how you run depends on how well you maintain your fueling. However, the intensity becomes acute because an open marathon is run at a Zone 3 effort for most runners.

“The idea of maintaining a goal pace at Zone 3 or Tempo pace for 3 hours in an open marathon is very hard to do,” Ricci said. “In an Ironman, you kind of get what you get on the run because it’s so hard to dial an exact pace for the Ironman marathon because of all the variables that can impact your experience.”

RELATED: Which is Harder: Marathon or Ironman Training?

How cycling fitness affects your Ironman marathon split

Another key aspect of the Ironman marathon is making sure you have a recent bike-fit that allows you to ride in an efficient aero position as much as possible during the 112-mile bike section of an Ironman, said Sara Fix, a 28-time Ironman finisher and USAT Level I triathlon coach based in suburban Chicago.

“If you cannot get cycling trained and don’t get fit on the bike, it doesn’t matter how good of a runner you are, it’s not going to come together for you during an Ironman,” Fix said. “I still believe it’s a runner’s sport, but it’s not going to work out if you can’t run off the bike. If you don’t have the bike fitness or if you have been able to maintain consistent fueling on the bike, you’re not going to be able to run.”

That said, Fix helps athletes roughly predict the pace they can run by adding a minute per mile to their mile repeat pace on the track or 2 minutes per mile to their faster long run training pace. For example, if an athlete can run 6:30-6:40 repeats on the track and hold 7:30-7:40 pace for their long training runs, they should be able to run 8:30-8:40 pace and shoot for a 3:40-3:50 marathon during an Ironman. Likewise, a triathlete who runs 7:50 pace on the track and 9-minute pace during long runs could target a 10-minute/mile pace and a 4:15-4:25 run split to finish a race.

“That’s just a way to estimate it, but it’s based on executing on the bike and fueling well,” Fix said.

“But even with a perfectly executed bike ride, you still have to be ready to be persistent and keep fueling well to have a successful run. So many people wind up walking during the run section because they’re not fully prepared for what it takes to run a marathon in an Ironman.”

Fix recommends getting proficient with running off the bike during training and practicing it during short-course races. She encourages athletes to make brick workouts a regular part of their training regimen by combining run-bike sessions two or three times per week, if possible. Those types of brick workouts will not only help you practice getting off your bike and going through the motions of a transition into your running gear, but it will also help you get used to running with fatigue and the discomfort and awkwardness that comes from transitioning from being on the bike to trying to get into a consistent running rhythm.

In his prime, three-time Ironman world champion Craig Alexander used to do long, moderately hard rides and then get off his bike and run 16 x 1-mile at tempo pace. While it’s unrealistic for an age-grouper to do that, running similar brick efforts can be extremely helpful. For example, that might mean riding for 2 hours followed by 8 x 1-mile at tempo pace.

RELATED: 4 Secrets to Brick Workout Success

How much faster will I get in a marathon vs. Ironman marathon?

How fast you can expect to run an open marathon compared to what you’ve run in an Ironman depends on a lot of factors. That includes how long your marathon training block is, what kind of mileage and workout intensity you’re able to log, how well you recover during your pre-race taper period and, of course, the race-day weather and your mid-race hydrating and fueling efforts.

There are a lot of running workouts running coaches use to predict marathon times, including Yasso’s 800s, a half marathon time trial or a fast-finish long run. For example, with Yasso’s 800s, if you can run 2:55 for every rep of a 10 x 800-meter workout with a 2:55 jogging rest interval, then you’re likely fit enough to run a 2:55 marathon. (Same goes for 2:40, 3:15 and 3:30, etc.)

Ricci estimates that most age-group triathletes can run a minute per mile faster in an open marathon than the pace they run in an Ironman marathon. That means if you run 9-minute miles for a 3:55 split in a triathlon, you can probably shoot for 8-minute pace at a 3:30 effort in an open marathon. Now will you actually run that? That’s up to a lot of factors.

The key to running a good open marathon is being able to run consistently without going out too fast, running too hard midway through the race or failing to replace some of your glycogen stores, Ricci said. Hydrating at every aid station and taking in 100 to 250 calories every hour will usually help you stave off a big bonk, even if you still wind up slowing down in the final miles.

On the contrary, dialing in your running pace for an Ironman has a lot less to do with how good of a runner you are or fast you’ve already run a marathon. Instead, it’s mostly about how well you are able to fuel, hydrate, and perform on the bike. Knowing precisely how many calories and how much liquid you need to replace every hour on the bike — and then doing it well — is crucial.

RELATED: Want to Avoid Bonking? Learn the Science Behind It

The run-walk method

While Fix and Ricci try to train athletes so they can run the entire marathon course, both suggest adopting some kind of a run-walk method before things get so dire that walking is the only recourse to make it to the finish line. Forcing yourself to struggle through the first 14 miles only to have to walk the final 12 isn’t as efficient of effective as alternating between jogging and walking the entire way.

The run-walk method has been popular in running since 1980, when Olympian Jeff Galloway ran a 2:16:35 marathon while taking walk breaks each mile. The strategy, which involves running for a predetermined length of time, taking a planned walk break, and repeating on a set schedule, is designed to give the body and mind a brief reprieve from the stress of racing. Most people associate the run-walk method with beginners, but more experienced runners and triathletes can (and do) use it – both in open marathon races and in Ironman.

“It takes some time to figure out how to run all the way through, but the goal is to train yourself to run and not to walk,” Fix said. “But all athletes are different and there are different body types and sometimes it doesn’t work out so perfectly. You have to figure out what you consume and the intensity you can handle throughout a race to get it right. Learning the sport, improving your fueling strategy and understanding how your body absorbs training and adapts under fatigue are key steps you can take to improve your run in an Ironman.”

RELATED: Video: The Run-Walk Philosophy

Training for an open marathon vs. Ironman marathon

As for training for an open marathon, Ricci and Fix both recommend focusing on a marathon-specific build-up and backing off (but not eliminating) swimming and cycling. Swimming and easy spinning can provide active recovery sessions and short and fast bike intervals or hill repeats can be substituted for running intervals.

In an open marathon, you have to be patient and trust the process of getting through the opening miles running at a pace that will seem almost pathetically slow, relative to your fitness. The key is containing yourself and settling into an easy rhythm, even if it means erring on the side of starting slower than you anticipated for the first few miles.

“I definitely promote and encourage my athletes to have fun and be more laid back after their triathlon season, but also staying active,” Fix said. “You have to recover, but you also have to get some fire back and a marathon could be a good way to do that. But if you’re going to do a marathon to end your season, I don’t recommend doing it just with the tri fitness they’ve built, but instead doing right with some real marathon training. And that’s going to take some work, too.”

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