Running With Muscle – Diamond Hill CrossFit
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Running With Muscle


Running With Muscle


After finishing a marathon first in her age group, Karly Wilson looked at the women next to her on the podium and noticed she was bigger—more muscular—than her fellow competitors.

The 28-year-old weighs 125 lb. That’s 35 lb. more than when she started running six years ago. Rather than slowing her down, the muscle has made her faster and less prone to injury, she said.

“People have to know that there is a healthier way to run,” she thought while standing on that podium.

Wilson knew that muscle, unusual for an endurance athlete, had allowed her to run a marathon a month, and she’s racked up more than 55 since 2011.

Chris Hinshaw, the former All-American swimmer and professional triathlete who now leads the CrossFit Specialty Course: Aerobic Capacity, said he knows exactly why Wilson’s muscles didn’t slow her down. However, he warns that just as marathon runners need strength and high-intensity training, CrossFit athletes need endurance training.

The Transition

ALT TEXTWilson, still slight, is 35 lb. heavier than she was six years ago. (Courtesy of Karly Wilson)

Karly ran her first marathon in April 2011. She finished in 3:36, and just like that she was hooked. She signed up for a marathon in May, and then in June, and soon she was running a marathon a month, clocking in times between 3:40 and 3:55.

In 2012, she signed up for a Ragnar Relay race. She was on a team with Zach Wilson, the man who would become her husband. Karly told Zach some of her nagging injuries were getting worse: Her poor ankle mobility and a tight IT band were causing her to hobble when she ran.

Zach suggested CrossFit.

“He took CrossFit Endurance before I met him, and he utilized it, and he was really fast. And so I was confused how some individual could be so fast without the traditional long-distance running,” Karly said.

Curious, she decided to give CrossFit a try. She dedicated herself to learning the Pose Method of running and added CrossFit training. She decreased her mileage and gained muscle—over the course of a few years the 5-foot-1 athlete went from 90 lb. to 125 lb.

Five years after incorporating CrossFit and weight training, Wilson is still running at least a marathon a month, and she just put up her best time ever: a speedy 3:05.

“I have never felt so good during a race,” Wilson said about her record time.

“My training up to that (race) was (mostly) CrossFit and weightlifting—I didn’t run more than 15 miles prior to that race,” she said.

Growing up, Wilson was always told runners were skinny. She struggled with an eating disorder as a young woman and believed small meant fast.

When she first started doing CrossFit and incorporating weights into her training, the numbers on the scale began to climb. She said it was disconcerting to look down at the scale and see 95 lb., then 100, then 105.

ALT TEXTWilson at about 90 lb. before CrossFit. (Courtesy of Karly Wilson)

At first, these changes made running a little more difficult. She was changing her running technique, her nutrition and her training methods.

Her first marathon after making these changes “wasn’t my worst marathon, but it wasn’t my best,” Wilson said.

“It was just average. So it was like, ‘Something is working. I am not super slow, but I’m not fast. I’m sitting average, but I felt really good during the run,’” she said.

About six months in she noticed something interesting.

“I was still running marathons during that time, but I noticed my recovery rate was insane. The next day (after a marathon) I could go do a workout. It wasn’t something that was keeping me off my feet for three or four days,” she said.

Karly and Zach opened CrossFit Undeniable in Westminster, Colorado, in October 2012, and Karly kept working on her running form and CrossFit training.

In early 2014 her running times began to drop.

“I was no longer doing any traditional training,” Wilson said.

She does a CrossFit workout Monday through Saturday in the morning, and then she either squats or runs in the evening. She decreased her mileage by approximately 50 percent, with the longest runs topping out at about 18 miles.

She qualified for the 2018 Boston Marathon with a time of 3:26, under the 3:35 cutoff for her age group.

“I am hitting under 3:30, which is really good for runners in general, and I’ve been able to maintain that doing them back to back,” she said.

Wilson said she still feels like an anomaly in the running world.

“I’ll show up to a lot of these races, and I am the biggest girl among a lot of my competitors that are running seven-minute miles. It’s kind of hard, but it’s awesome, too, because I get to show people out there that you can run with muscle and you don’t have to completely watch the way that you eat and make sure you aren’t gaining a pound here or there,” she said.

Wilson’s nutrition is different from that of her fellow competitors as well. Instead of carb loading the night before, she eats her normal Paleo Diet. Many marathon runners consume high-carbohydrate energy shots or gels during a race, but Wilson just drinks water, with a caffeinated pre-workout drink at Mile 15.

“I feel like I run off muscle,” Wilson said. “I think that muscle helps—I think it helps with fatigue.”

ALT TEXTTop CrossFit athletes are not endurance specialists, but many perform very well in endurance events. (Naveen Hattis/CrossFit Journal)

How Muscle Helps Marathon Runners

Hinshaw said Wilson is on the right track.

To understand why, he said it’s important to know most of the population has about a 50-50 balance of slow-twitch and fast-twitch muscle fibers. When an athlete is doing traditional marathon training, he or she is developing slow-twitch muscle fibers—typically only half the overall number.

“That means a massive percentage of their available muscle-fibers arsenal is passive. It’s not developed. To develop fast-twitch muscle fibers you need to do high-intensity training,” Hinshaw said.

If there’s very little sprinting in a marathon, how do these fast-twitch muscle fibers help?

Hinshaw said when the slow-twitch fibers fail, the brain then recruits the fast-twitch fibers.

“If you never train your fast-twitch muscles through high intensity, they will never be able to be recruited,” he said.

As a marathon runner reaches the end of a race, Hinshaw said the body’s ability to recruit and utilize the fast-twitch muscle fibers becomes critical in performance.

ALT TEXTChris Hinshaw (second from left) said trained muscle groups can help clear lactate produced by working muscles. (Alicia Anthony Baldwin/CrossFit Journal)

Another factor at play, Hinshaw said, is the role muscles play in clearing fatigue from the body.

When our muscles shift from aerobic to anaerobic metabolism during intense exercise, they produce pyruvate, which is then converted to lactic acid if oxygen is not available. Lactic acid is very quickly broken down into lactate, which causes the release of hydrogen ions. The body metabolizes lactate for energy, but when lactate accumulates too fast for the body to clear it, it builds up in the muscles and bloodstream. Contrary to popular belief, lactic acid does not cause fatigue. It’s actually the buildup of hydrogen ions from the breakdown of lactate that causes the feeling of fatigue.

What’s significant to Hinshaw is the role of muscles—both working and non-working muscles—in clearing lactate to avoid that buildup.

“Research has shown that aerobically trained runners can oxidize approximately 90 percent of the available lactate. However, as a fast running pace is sustained, (the athlete) will eventually exceed the metabolic capabilities of (his or her) muscle fibers … which disrupts the contraction of the working muscle,” Hinshaw said.

During aerobic work, mitochondria provide most of the energy. These organelles convert oxygen and other chemicals into adenosine triphosphate (ATP), the chemical that powers the metabolic activity of the cell. Training increases the amount of mitochondria and improves their efficiency. Hinshaw says an appropriate endurance training program will increase the size and volume of mitochondria in slow-twitch and fast-twitch muscle fibers, which will increase the capacity for aerobic energy resulting from glycolysis.

ALT TEXT“Not one athlete I have ever coached has gotten weaker by incorporating running.” —Chris Hinshaw (Courtesy of Chris Hinshaw)

“Because of its aerobic development, (your body) can clear that fatigue at the rate that it’s coming in,” Hinshaw said. He said when an athlete generates a high level of speed, “that lactate starts accumulating in your body, and when it does accumulate, it goes into the bloodstream. That lactate is solely just trying to find vacant muscle groups to clear it. It goes into your upper body—your arms, your shoulders, your back, your pecs.”

Hinshaw said the upper body might not seem relevant to marathon runners, but those muscles help the body get rid of the lactate, reducing fatigue.

Endurance athletes, of course, have limits to the amount of muscle they should put on their bodies. Runners have to lift their weight off the ground with each step, and large muscles are too heavy to move for long distances. A bodybuilder’s muscles would not be helpful in a marathon, for example, but modest amounts of well-trained muscle might be worth a little extra weight. The ideal weight differs from runner to runner, but generally endurance runners want to be at the lowest weight they can sustain while optimizing recovery and performance.

“If a marathoner wants to improve their overall work capacity, they must look at their entire body as a unit,” Hinshaw said.

ALT TEXTHinshaw explained that well-rounded training ensures fast-twitch muscles can assist movement when slow-twitch muscles fail. (Shaun Cleary/CrossFit Journal)

Building strength in the entire body also helps create stability, Hinshaw said.

“A marathon runner deep into their race, (in) the 18th or 19th, the 20th mile … efficiency starts to fail,” Hinshaw said.

Strengthening ligaments, tendons and muscles throughout the body can help a long-distance runner support the body’s structure and stay efficient even under fatigue, he explained.

Stronger muscles, ligaments and tendons are less vulnerable to tears and strains, and a stronger muscle doesn’t need to work as hard as a weaker muscle, so it requires less oxygen and circulating blood. This, in turn, reduces the demand on the heart.

Another advantage of muscle is force absorption. The body absorbs three to four times the runner’s body weight with every step. Building strength helps the body absorb that force, reducing fatigue and preventing injury. Further, trained muscles produce force quickly and efficiently, which reduces ground contact time and improves overall speed as runners are propelled through the air.

ALT TEXTCrossFit athletes are often great at producing speed and power, and many have improved overall athleticism by increasing their endurance and stamina. (Thomas Campitelli/CrossFit Journal)

Go Long

If long-distance runners need to develop their fast-twitch muscle fibers, Hinshaw says the opposite is true for CrossFit athletes.

“CrossFitters are missing out on what marathoners know, and marathoners are missing out on what CrossFitters know,” he said, because many CrossFit athletes make the mistake of not developing their slow-twitch muscle fibers.

“If (CrossFit athletes) have been neglecting their slow-twitch fibers by not doing longer time domains, slowing down, they have neglected their body’s total capacity to develop work product,” Hinshaw said.

Hinshaw said CrossFit athletes express fear that they’ll get weaker by doing longer, slower workouts.

“There is not one single elite-level athlete—and I coach Mat Fraser, I coach Katrin Davidsdottir, I coach the Mayhem team, all three champions last year—and not one athlete I have ever coached has gotten weaker by incorporating running,” Hinshaw said.

He’s certain athletes who don’t train the aerobic system are making a mistake.

“By neglecting their slow-twitch fibers, they are neglecting the contribution in overall strength,” he said.

The first Games athlete Hinshaw worked with was Jason Khalipa, when the 2009 champion was training for the 2013 Reebok CrossFit Games. In 2012, Khalipa found himself near the bottom of the leaderboard in every endurance event. The next year, after working with Hinshaw, he won Row 1 and Row 2, the big endurance events of the year, and placed second overall at the Games.

“He was a 230-lb. guy,” Hinshaw said, “and people looked at (his finish) as a miracle. Well, he just did something back then that no one else was doing. He developed his slow-twitch muscle fibers, and his overall capacity as an athlete went up.”

ALT TEXTThe benefits of strength are obvious for sprinters, but endurance athletes can also benefit from the increased stability and force production of appropriate amounts of trained muscle. (Shaun Cleary/CrossFit Journal)

Strength for Speed

Wilson hears her fellow runners talking about the performance benefits of compression socks or shoes, but she thinks they’d be better served working on their strength and running form.

“You can’t put a ton of weight in an overhead squat if you don’t have good positioning. Same thing with running,” she said.

She knows the fear of getting bulky is hard for endurance athletes to overcome, but Wilson said she wishes marathon runners knew how good she feels after building strength.

“My posture has changed the way that I breathe, how I hold my core. Everything has changed in gaining that muscle, and it hasn’t hindered me at all,” Wilson said.

After hitting her goal of running 50 marathons, Wilson has a new goal: she wants to double that and run 100 marathons using CrossFit.

“I wish I would have known about CrossFit when I first started,” Wilson said, “I want people to know that this is a great way to train for a marathon.”

About the Author: Hilary Achauer is a freelance writer and editor specializing in health and wellness content. In addition to writing articles, online content, blogs and newsletters, Hilary writes for the CrossFit Journal. To contact her, visit

Cover image: Thomas Campitelli/CrossFit Journal

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