The 4-Hour Body: Ultraendurance Running

Kelly Starrett, founder of San Francisco CrossFit, casually mentioned to Tim that he just ran a 28.4-mile ultramarathon with 18,500 feet of elevation change. And that he was back to heavy lifting the next week.

Then the punchline: “I never ran more than five kilometers in preparation for it.”

Wait, what?

Chapter 30: The CrossFit Endurance Approach

Kelly pointed Tim toward Brian MacKenzie - a 6'2", 193-pound guy with “UNSCARED” tattooed across his fingers who looked like a cross between Henry Rollins and a Navy SEAL.

Brian came from triathlons. Like everyone in endurance sports, he trained 24-30 hours per week. 8 miles of swimming, 200+ miles of cycling, 50+ miles of running. His body was falling apart and his wife was unhappy.

So he started cutting training down.

In 2006, he ran the Western States 100-mile race on 10.5 hours of training per week. Down from 30. By 2007, he completed the Angeles Crest 100 (fourth-toughest 100-miler in the world) on just 6.5 hours per week. Strength training, CrossFit, intervals, pace work. He was faster at every distance - 100 meters to 100 miles.

His secret? 400-meter repeats. Lots of them.

The Proof

Brian had taken one trainee, nicknamed “Rookie,” from never-having-run-more-than-four-miles to completing a mountainous 50K ultramarathon in 11 weeks.

Another trainee - a 43-year-old marathoner with an 8:30 mile pace - couldn’t even do three 400-meter sprints. Brian gave her 16 minutes of sprint training per week plus four conditioning workouts. Less than three hours total per week. She called him crying before the NYC marathon: “This will never work.”

She finished in 3:32. An 8-minute pace - 30 seconds per mile faster than her previous best. Sixteen minutes of sprints per week gave her gears she never had.

Tim Gets Tested

Tim got a muscle biopsy at the Sports Science Institute of South Africa. They measured his endurance enzymes - the stuff that determines how well your body handles long efforts.

The doctor told him plainly: “You’d have trouble finishing a 5K.” Tim’s enzyme levels were worse than untrained couch potatoes.

But he saw the bright side. If he could pull this off with below-average genetics, anyone could.

Fixing the Undercarriage

Before real training could start, Tim needed four weeks of preparation. Your lungs and muscles are not what fails first in distance running. It is your ligaments, tendons, and the small muscles that hold everything together.

Tim’s first 400-meter repeats destroyed him. Tight hip flexors made him bend forward at the hips. His hamstrings tried doing the job of his glutes. Lower back pain for three hours. Knee pain on both sides.

The fix: hip flexor stretches, glute activation exercises, pigeon pose variations, pelvis repositioning drills, and barefoot jogging on grass three times per week (30 minutes each). That last one comes from Gerard Hartmann, trusted by Haile Gebrselassie (27 world records).

The Pose Method

Brian swears by the Pose Method, created by Russian Dr. Nicolas Romanov in Siberia. The core idea: use gravity and forward lean for movement, land on the balls of your feet, never fully straighten your legs, pull each foot toward your butt instead of pushing off, and maintain at least 180 steps per minute (90 per foot).

That last point matters most. Scott Jurek, seven-time Western States champion, confirmed it: “If you focus on higher stride rate, much of the rest corrects itself.”

Using video analysis, Tim improved his running economy 100% within 36 hours. The big takeaways: keep 90+ steps per minute per leg, lean forward like a falling tree (not from the hips), and keep arm movements small.

Fair warning: a follow-up study had to be cancelled because almost every runner in the unsupervised group developed Achilles tendon and calf problems. Take it slow.

Chapter 31: From 5K to 50K

To run a 50K, you need to understand fuel. Your liver and muscles store only 1,800-2,200 calories of glycogen. When you go anaerobic, you burn through those limited stores. Run out and you “bonk” - game over.

But one pound of fat holds roughly 4,000 calories. Even a lean 150-pound person at 5% bodyfat has 7.5 pounds of fat - enough for several hundred miles. The trick is staying aerobic at higher speeds, so your body keeps burning fat instead of glycogen.

That is the whole point of Brian’s training. He produces 100-mile runners on less than 30 miles of total running per week. His recipe: focus on all energetic pathways, never run more than 13.1 miles in training, and rarely go beyond 10K.

The Training Structure

A typical week has two components: morning strength/CrossFit and afternoon running intervals.

• Intervals: totaling about 1,600 meters per session (for example, 8 x 200m with 90 seconds rest, or 4 x 400m, or 2 x 800m)
• CrossFit: 2-10 minutes of metabolic conditioning
• Time Trials: testing progress at 1 mile, 5K, or 10K

Key rule: if your heart rate does not drop below 120 within two minutes after an interval, the workout is over. You have not recovered. Adding more would just slow progress.

Expect your times to get worse in the first three weeks. That is normal. Then you bounce back past previous bests.

Brian also pushes strength training hard. His reasoning: the soreness runners feel after long distances is mainly from a weak sodium-potassium pump, and strength training fixes that. “If I can get a runner’s back squat up, I see their marathon time drop.”

Nutrition

Brian calls nutrition the biggest problem in endurance sports. He recommends a Paleo diet - lean protein, vegetables, some fruit, lots of fat, no grains or starches. The high-carb pasta-and-Gatorade approach? He calls it crap.

Post-workout exception: Vitargo S2 for rapid glycogen replenishment - up to 1,100 calories per hour, versus 200-600 from whole food. During races: aim for 1 gram of carbs per hour per kilogram of body weight, in small portions every 20-30 minutes. Gulp water, do not sip - gulping triggers gastric emptying.

The Dean Karnazes Story

At 4 AM in Daly City, California, Dean Karnazes realized three things. He had just turned 30. He was running in his underwear after too much tequila. And he felt more alive than in the past 15 years.

He kept going. Called his wife from a 7-Eleven in Santa Cruz, 30 miles south. Quit his corporate job. Became an ultramarathon legend - 135 miles nonstop in 120-degree Death Valley, a marathon at minus 40 around the South Pole in tennis shoes, 50 marathons in 50 consecutive days across all 50 states.

Did It Work?

Tim’s chapter ends on a cliffhanger. He had designed a 12-week program with Brian to go from 5K to 50K. The book went to print before the race happened.

The lesson from these chapters: “run more miles to run longer” might be wrong. Intervals, strength training, and proper mechanics could replace most of those endless long runs.

Martin Gibala’s research backs this up. Six minutes of hard sprints three times per week doubled endurance capacity and increased endurance enzymes by 38%. The control group doing hours of moderate cardio? Zero change.

Work long or work hard. The results appear to be the same.

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This is part of my 4-Hour Body retelling series. New posts every Saturday.