The Man Who Gained 63 Pounds of Muscle in a Month: Looking Back on Arthur Jones’ Controversial ‘Colorado Experiment’

In 1973, fitness entrepreneur Arthur Jones created an experimental workout regimen that still baffles the industry.

What if you learned that an exercise system existed that could help you gain 63 pounds of muscle in a single month? It seems too good to be true — but maybe it isn’t.

In 1973, Arthur Jones, the man behind the Nautilus exercise machines, advertised that his high-intensity training method had done just that. Known as the “Colorado Experiment,” Jones’s claims continue to divide the fitness community.

The Background

Arthur Jones was one of the most fascinating characters in the history of fitness. A former filmmaker from Oklahoma who later became an entrepreneur and inventor, Jones founded the Nautilus exercise equipment company in 1970 to reimagine how the public worked out.


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Jones took issue with the strength curve typically used in exercises. Specifically, he noted that the force exerted on the muscle tended to vary — sometimes radically — throughout a movement. The back squat is an example of this: The maximum effort is exerted as a person drives the weight up, while there’s relatively little effort needed near the top of the movement.

Jones’s machines, on the other hand, were designed to keep constant force on the muscle throughout the entire movement, which he believed to be the key to greater muscle growth and strength.

To go along with the equipment, Jones also advertised a new way of working out known as high-intensity training. In this system, lifters would push their muscles to the absolute point of failure, if not further, to achieve optimal growth. Rather than training multiple sets per muscle group, Jones preferred to use one set for maximum effort.

This method was in stark contrast to high-volume workouts used by bodybuilders at the time. In Arnold Schwarzenegger‘s book, The New Encyclopedia of Modern Bodybuilding, the seven-time Mr. Olympia winner details one advanced chest workout that requires more than a dozen sets. (1) Jones’s plan included anywhere from eight to 14 total sets per day for the entire body.

How hard was Jones’s system? There’s an apocryphal story about Schwarzenegger’s inability to keep up with the workouts after only three sessions. Later, Schwarzenegger — or, allegedly, an editor ghostwriting under Arnold’s byline — penned a story for bodybuilding publisher Joe Weider’s Muscle Builder/Power magazine that included the line, “[If] I had to do this every day, I’d opt for a hernia, go back to Austria, and become a ski instructor.” (2)

Here’s just a glimpse of what the program entailed.

Jones’s views on fitness were controversial — so, too, was his assertion that traditional exercise routines and equipment couldn’t compete with his Nautilus machines. He decided to put his theories to the test by crafting what would be known as the Colorado Experiment. (3)

The Experiment

In 1973, Jones and professional bodybuilder Casey Viator trained exclusively using Jones’s equipment and system for 14 sessions over 28 days. The goal was to see how much muscle they could pack on and then show their results to the world.


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To avoid criticism of his methods, Jones joined forces with Colorado State University to create a scientific environment that helped legitimize the whole thing. (4) The two men were meticulously measured before, during, and after the experiment to ensure that the readings were accurate. And Dr. Elliot Plese, of the Department of Exercise Physiology at the school, supervised the proceedings.

The workouts themselves were then monitored and logged. Here’s an example of what one of Viator’s sessions looked like, according to Jones’s former employee and fitness writer, Ellington Darden: (4)

Thursday — May 3, 1973

Note: Only one set per exercise. Workouts typically lasted around a half hour.

  1. Bent-Armed Pullover with EZ-Curl Bar
  2. Bent-Over Row with Barbell
  3. Overhead Press with Barbell
  4. Chin-Up*
  5. Dip*
  6. Shoulder Shrug with Barbell
  7. Bench Press with Barbell*
  8. Biceps Curl with Barbell*
  9. Overhead Triceps Extension with Dumbbell
  10. Behind Neck Chin-Up*
  11. Lateral Raise with Dumbbells
  12. Leg Extension Machine*
  13. Squat with Barbell
  14. Leg Curl Machine*

*Negatives only

The Results

When the experiment was over, Jones declared that he lost 1.82 pounds of body fat and gained 15.44 pounds of muscle. This was an overall weight increase of 13.62 pounds in 22 days. Viator lost 17.93 pounds of body fat, and increased his total body weight by 45.28 pounds for a purported increase in muscle of 63 pounds in 28 days. Notably, he added two inches to each arm and five to his chest. (3)

Jones pointed out in his writings that Viator — an active bodybuilder who had won two AAU (Amateur Athletic Union) Mr. USA titles and an AAU Mr. America title — was returning from a series of injuries that caused significant muscle loss in the months before the experiment.

Therefore, Viator’s results could have been aided by muscle memory. Though there’s no definitive proof, studies have shown evidence that people who gain muscle and subsequently lose it can rebuild it faster than those who never trained in the first place. (5)(6)

Jones also stressed that no steroids were used during the experiment and said the drugs were not “desirable” for muscle growth if one trained correctly.


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In Iron Man magazine, Jones wrote that several individuals later joined in on the experiment, including NFL players like Hall of Famer Dick Butkus. They also supposedly boasted increases in strength in the hundreds of pounds, rapid weight gain, and quicker 40-yard dash times. (2)

People in the industry rightly took notice of such outlandish claims. Weider, one of Jones’s fiercest rivals in the fitness space, soon printed interviews with Schwarzenegger in Muscle Builder/Power, in which Arnold claimed, “I came back looking terrible…I never looked so fat” after training with Jones. (7)

Though, arguably, Weider had the incentive to criticize his competition, his words were nevertheless impactful in the fitness industry.

Was the Colorado Experiment Legitimate? 

How legitimate, then, was the Colorado Experiment? Darden says that he has personally trained other clients using similar workout regimens and saw muscle increases of anywhere from 17 to 29 pounds in a matter of weeks. (4)

In 1975, Jones also conducted a similar experiment at the United States military academy West Point, albeit with slightly different training protocols and lower training intensities. An article in the Athletic Journal once more showed increases in strength and muscle mass, but not to the extent that Jones or Viator enjoyed. (8)

But ever since the Colorado Experiment’s results went public, the facts around it have only gotten murkier.

In 1980, Weider’s Muscle & Fitness magazine published a tell-all article supposedly written by Viator in which he “came clean” about sneaking out to do extra workouts during the experiment. Viator later claimed he had written about 30% of the article and that it was mostly Weider propaganda. (9)

Then in an interview with FLEX magazine in 2013, Viator said that he intentionally kept his diet to less than 800 calories per day in the lead-up to the experiment to ensure that he lost as much mass as possible to make his progress all the more impressive. (During his time in Colorado, Viator said he consumed around 5,000 calories per day.) (10

In the same interview, Viator also admitted to receiving “a healthy cash incentive per pound of muscle that I gained” while training in Colorado, though no amount was revealed.

Next is the issue of whether or not Viator used anabolic steroids. Jones, Viator, and Darden (who began working for Nautilus shortly after the experiment) denied any drug use, but others have disputed that. Notable strength coach and proponent of the 5×5 workout program Bill Starr later wrote:

“What the public didn’t know was that Casey was taking steroids the whole time without telling Arthur and he was also sneaking out to a local YMCA to train with some real weights. I know this because Casey told me so…” (11)

While it is impossible to verify Starr’s claims, allegations like this continue to hound the experiment’s validity to this day.

The Legacy of the Colorado Experiment

In the end, Arthur Jones believed he found a way to drastically increase muscle growth and strength that was far superior to what the fitness world was accustomed to. And while both he and Viator came out of Colorado with a documented increase in muscle mass, the details surrounding the experiment have kept the rumor mill churning ever since. 


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Jones later wrote that his goal was to “conduct an experiment under conditions that could not be disputed.” (12)

It’s ironic, then, that the legacy of the Colorado Experiment some 50 years later is one of more questions than answers. 


  1. Steve Shaw, ‘Arnold Schwarzenegger Volume Workout Routines,’ Muscle and Strength, January 12, 2020.
  2. Ellington Darden, The New High-Intensity Training, (Rodale, Inc., 2004), 42.
  3. Arthur Jones, ‘The Colorado Experiment.’ Iron Man, 1974. Available to download from
  4. Ellington Darden, ‘The Colorado Experiment: Fact or Fiction,’ T-Nation, June 13, 2016, 
  5. Seaborne RA, Strauss J, Cocks M, Shepherd S, O’Brien TD, van Someren KA, Bell PG, Murgatroyd C, Morton JP, Stewart CE, Sharples AP. Human Skeletal Muscle Possesses an Epigenetic Memory of Hypertrophy. Sci Rep. 2018 Jan 30;8(1):1898.
  6. Yuan Wen, Cory M Dungan, C Brooks Mobley, Taylor Valentino, Ferdinand von Walden, Kevin A Murach, Nucleus Type-Specific DNA Methylomics Reveals Epigenetic “Memory” of Prior Adaptation in Skeletal Muscle, Function, Volume 2, Issue 5, 2021,
  7. Randy Roach, Muscle, Smoke and Mirrors (Bloomington, 2011), 377, 397, 420.
  8. Dr. James A. Peterson, ‘Total Conditioning: A Case Study,’ The Athletic Journal, September 1975.
  9. Brian D. Johnston, ‘In Conversation with Casey Viator,’ (McGraw Hill, 1992), 42.
  10. Chris Lund, ‘Looking Back,’ FLEX magazine,
  11. Bill Starr, ‘Keeping Strength in the Strength Program,’ Starting Strength, 2009.
  12. Arthur Jones “The Colorado Experiment Part One: The Purpose of the Experiment”

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