19Is it possible to gain 63 pounds of muscle in less than a month? What about 15 pounds of muscle in twenty-two days? By any metric such results would be phenomenal but few people believe such a feat is manageable.

Yet in the early 1970s, Arthur Jones, creator of the Nautilus machines, claimed it was possible through his own brand of High Intensity Training (HIT). What’s more, he claimed he had scientific backing for his claims.

So what exactly happened during the Colorado Experiment conducted by Jones and was he telling the truth? Have strength enthusiasts been selling themselves sort by setting low targets for muscle gain? After all if such training can yield 15 to 63 pounds of muscle in one month it must be worth doing.

Background to the Experiment

Jone’s goal in conducting the experiment was to gain publicity and credibility for his particular type of High Intensity Training. As detailed by Randy Roach in ‘Muscle, Smoke and Mirrors’, Jone’s advocated a style of training that many in the bodybuilding industry were uncomfortable with. Jones maintained that a high intensity was required for optimal muscle building and promised that short bursts of high intensity interval training could produce remarkable results. An anecdote from the 1970s often told to demonstrate the intensity of Jone’s training was that renowned bodybuilding Champion Arnold Schwarzenegger couldn’t finish a workout with Arthur Jones because it was too hard.

arthur-jones-nautilusJones in Training

For the Colorado Experiment, Jones teamed up with Dr. Elliot Plese at Colorado State University’s Department of Physical Education Laboratory to conduct a one-month long study. The goals laid out at the beginning of the study were as follows

  1. To prove that very brief workouts are capable of producing rapid and large scale increases in muscular mass and strength.
  2. That nothing apart from a reasonably balanced diet is required.
  3. That the so-called “growth drugs” (aka steroids) are not required.

Jones himself was a very outspoken and often disliked voice in the fitness industry. He had a poor opinion of the general consensus on fitness and was not shy about it. In numerous interviews, seminars and publications, Jones would regularly take pot-shots at others in the industry for using false claims and unsound training principles. Take steroids for example. Jones held the view that drug use hindered rather than enhanced muscular growth and strength. In many ways he was a voice for those uncomfortable with the shift towards steroids in training that swept across the US (and most of the Western world) from the middle of the 20th century. For Jones what really counted was genetics and training. It couldn’t be any old training mind you, it had to be intense. Once such rules were applied, results would come. Or so it was promised.

The Experiment

In May 1973, Arthur Jones and Casey Viator began their training under the watchful eye of Dr. Plese. Everything they did would was monitored from their training to their eating patterns. It would be a month of training, eating, recovering and very little else. True to his word, Jones made sure they were put through their paces.

An illustrative example of a regular workout for Casey was as follows

  1. Leg Press 750lbs for 20 reps
  2. Leg Extension 225lbs for 20 reps
  3. Squat 502lbs for 13 reps
  4. Leg Curl 175lbs for 12 reps
  5. One-legged Calf Raise with 40lbs in one hand for 15 reps (Two-minute rest)
  6. Pullover 290lbs for 11 reps
  7. Behind-the-neck Lat Isolation 200lbs for 10 reps
  8. Row Machine 200lbs for 10 reps
  9. Behind-the-neck Lat Pull-downs 210lbs for 10 reps (Two-minute rest)
  10. Straight-armed Lateral Raise with Dumbbells 40lbs for 9 reps
  11. Behind-the-neck Shoulder Press 185lbs for 10 reps
  12. Bicep Curl Plate Loaded 110lbs for 8 reps
  13.  Chin-ups bodyweight for 12 reps
  14.  Tricep Extension 125lbs for 9 reps
  15.  Parallel Dip Bodyweight for 22 reps

The exercises were performed one after the other on Jone’s Nautilus Machines or MedX machines. Each set was done to failure and unless specified above, there was no rest between exercises. Jones once wrote of his training philosophy

“High-intensity training is not easy . . . the training sessions are brief, indeed must be brief, but there is an apparently natural inclination on the part of most subjects to hold back.”

In his 1999 autobiography, Viator described how Jones would often sit in on Casey’s training sessions and use a variety of tricks, including outright insults, to ensure Casey didn’t hold anything back. So the training was not only intense, it was supervised by a trainer who had no compulsion about a tough love approach.

Screen shot 2014-12-29 at 12.01.41

Jones and Casey

What were in the results?

In September of that year, Jones publicised the results in Ironman magazine. An abbreviated version is posted here.

The Colorado Experiment by Arthur Jones

The following is a brief, preliminary report of an experiment conducted at Colorado State University in May of 1973.

Location . . . Department of Physical Education, Colorado State University, Fort Collins, Colorado.

Supervision . . . Dr. Elliott Plese, Director of Exercise Physiology Lab., Colorado State University.

Dates … May 1, 1973 through May 29, 1973 for one subject (Casey Viator), an elapsed period of 28 days . . . and May 23, 1973 for the second subject (Arthur Jones), an elapsed period of 22 days…


First subject (Casey Viator), 28 days

Increase in bodyweight……..45.28 pounds

Loss of bodyfat…………..17.93 pounds

Muscular gain……………..63.21 pounds


Second subject (Arthur Jones), 22 days

Increase in bodyweight …….13.62 pounds

Loss of bodyfat……………1.82 pounds

Muscular gain……………..15.44 pounds


The results being claimed were nothing short of spectacular but Jones was quick to qualify such success:

It should be clearly understood that neither of the subjects was an “average” subject, and there is no implication that subjects of average or below average potential will all produce equal results from a similar program of exercises.

Casey Viator has trained on a fairly regular basis for a period of several years; with barbells and other conventional training equipment until June of 1970, at which point he placed third in the Mr. America contest and with both barbells and Nautilus equipment until June of 1971, when he won the Mr. America contest. From September of 1971 until September of 1972, he trained primarily with Nautilus equipment with limited use of a barbell, primarily the performance of barbell squats. From September of 1972 until December 23, 1972, he trained exclusively with Nautilus equipment limiting his exercises to “negative only” movements. At the end of that period of training he weighed 200.5 pounds.

In early January of 1973, he was involved in a serious accident at work and lost most of one finger as a result and almost died from an allergic reaction to an anti-tetanus injection. For approximately four months, most of January through April of 1973, he did not train at all; and since his level of activity was low, his diet was reduced accordingly. During that period of four months, he lost approximately 33.63 pounds but 18.75 pounds were lost as a direct result of the accident and the near-fatal injection. So his loss from nearly four months out of training was only 14.88 pounds, less than a pound a week.

The second subject (the author, Arthur Jones) has trained on a very irregular basis for a period of thirty-four years … and reached a muscular bodyweight of 205 pounds at one time, nineteen years ago.

The author did no training of any kind for a period of approximately four years until late November of 1972 and then trained on a fairly regular basis in the “negative only” fashion for a period of approximately six weeks. Training was ceased entirely in early January of 1973 … and no training was done again until the start of the Colorado Experiment.

The author’s bodyweight has varied from approximately 145 to 160 over the last ten years briefly reaching a level of 190 at the end of approximately six months of steady training that was concluded four years prior to the start of the Colorado Experiment.

So both of the subjects have demonstrated the potential for greater than average muscular mass and both subjects were rebuilding previously existing levels of muscular size.

Despite the predisposition of both men for muscle building, Jones seemingly left no doubts his form of training was effective. In fact he claimed both men had achieved such massive gains with workouts averaging 25minutes.

Was the Experiment Legitimate?


Unsurprisingly given the results claimed, scrutiny of the Colorado Experiment came quick and fast. After three decades, criticism has fallen under three broad spheres:

1) Replicability: The Colorado Experiment has never been repeated apart from individual cases by interested trainers. The whole point of the experiment was to gain scientific backing for High Intensity Training and the fact that no one has been able to repeat such results, or even a fraction of them, in a large scale study has hurt Jones’s findings. Jones did conduct another experiment, the ‘West Point’ experiment, using his form of training but finding the exact results from the study have proven difficult.

2) Selection Bias: Both Casey and Arthur had previously trained with weights before. Viator is famed for his amazing genetics and predisposition to muscle building. Likewise Jones had built a solid 190 pound physique years prior to the experiment. Many have speculated that the gains both men experienced came as a result of muscle memory (a physiological phenomena which makes it easier to put back muscle or strength that you lost).

3) Dirty Tricks: This is perhaps the most prevalent claim made against the experiment. Prior to the experiment Casey had lost over 40 pounds due to an allergic reaction to a tetanus shot. Coupled with such a hugh loss in bodyweight, roughly a month before the experiment Casey ate a restricted diet of 800 calories. This has led people to suggest that Casey’s staggering weight gain was due to a severe bounce back to his true size.

Other criticisms of the experiment have suggested that Casey took steroids during the experiment, something he denied until his death in 2013 or that Jones manipulated the results prior to publishing.

So was the Colorado Experiment a sham?

It’s difficult to say. Jones was very upfront about Casey’s genetic potential and the unique position both men were in. There is however another part to the tale that is often forgotten about

Returning to Jones’s Ironman article, the guru of high intensity training also noted that

Several members of the Denver Broncos Professional Football Team visited the lab for the purpose of observing the workouts, and then started training in an identical fashion during the last two weeks of the experiment . . . after the experiment, the Broncos placed an order for several Nautilus machines and drastically reduced their previous training schedule.

And while we were training in Colorado, members of several other professional football teams were training at our facility in Florida. . . in an identical fashion, three brief weekly workouts involving only one set of approximately a dozen exercises, with as much emphasis on the “negative” part of the work as possible.


One member of a Canadian professional team became so strong in the pullover exercise that he was using 675 pounds for several repetitions in good form . . . having started two months earlier with 275 pounds.

Lou Ross of the Buffalo Bills added 20 Pounds to his 6 foot, 7 inch frame … cut a full two-tenths from his already fast time in the 40 yard dash … added five and one-half inches to his high jump … and doubled his strength in many areas of movement. These figures having been provided by the Buffalo Bills coaching staff, who tested Lou before and after a two month Nautilus training program in Florida.

Mercury Morris of the World Champion Dolphins weighed-in 7 pounds above his previous highest weight and still ran the fastest 40 yards of his life when he was tested . . . following two months of Nautilus high-intensity training.

If one wants to learn about the real success of the Colorado experiment, the athletes mentioned in passing are perhaps the best case studies. Casey and Jones knew they would experience great results from the training, the athletes did not. So there’s a chance it wasn’t all ‘smoke and mirrors’, however small.

The Colorado Experiment is still shrouded in controversy. Some in the fitness industry cite it as proof that Jones’s methods were worth their weight in gold, others as proof that Jones was a trickster. Like so much else in the fitness industry, it’s up to the individual to believe in it or not.


  1. Interesting read. I may have missed it but did they train everyday for a month in the experiment? One other thing I picked up was the fact that circuit training has been around a lot longer than I thought. Good stuff as always bud!

    Liked by 1 person

    • Hey JB617, thanks for the kind words. I’m glad you enjoyed it. As far as I’m aware they trained on non-consecutive days although I’m open to contradiction on that. Jones’ philosophy was based on getting the most efficient results i.e. the fewest training days – albeit each session was intense.

      On circuit training I recently picked up a second hand copy from the 1960s which helped popularise the concept for the mass public. So watch this space!

      Liked by 1 person

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