The Colorado Study: An In-Depth Review

Every now and then, the Colorado experiment pops up to justify some new variation on High Intensity Training - typically, the recommendation is that single sets of exercises, taken to failure, are superior to multiple sets while taking much less time. Similarly, other forms of HIT as HIIT - high intensity interval training, such as tabata or sprint intervals - have recently become popular for their supposedly superior results in comparison to steady state cardio. What is the Colorado experiment? Why is it so entrancing?

The Colorado Experiment was an experiment undertaken by Arthur Jones and Casey Viator in May of 1973. Arthur Jones is the inventor of the Nautilus machine and founder of the Nautilus company which bears its name. Nautilus machines were developed to make use of “variable resistance”, which differs from the typical flat resistance seen in a free weight - the spiral shaped cam around which the machine was built and named supposedly smoothed out the force curve of the lift, making it easier for the lifter.

Jones is also known for being quite a bit of an eccentric - he had a supposedly awful diet, drank coffee and ate fast food all day, smoked heavily, and was really into big game hunting. He was also known for constantly marrying young, attractive wives. He’s publicly stated that steroids are both dangerous and ineffective, but at the same time there’s testimonies that he got other bodybuilders into them to begin with. He’s truly a blast from the past, the most old school motherfucker you’ll ever see.

Viator was, and is, the youngest Mr. America of all time. He had won it at the age of 19, in 1971, just two years previous. Oddly, this was about the peak of his career - he went on to place third in the Mr. Olympia in 1982, but that’s about it. He was also an employee of the Nautilus company after 1970.

As the story goes, Jones wanted to demonstrate the value of a HIT style of workouts, all performed on the Nautilus machines. So, he developed a protocol and enlisted Viator to help him demonstrate its efficacy. In order to ensure that there would be no accusation of wrongdoing, he had the process overseen by Dr. Elliot Plese of Colorado State University. Here’s the rough outline of what happened:

• Casey begins the experiment at 166.87 pounds and 13.8% bodyfat.

• Casey trains exactly 14 times over 28 days, each exercise being done in a HIT with a single set to failure and all exercises being done in rapid succession - typically, the workouts were supposed to last about 30 minutes. This equates to about 7 hours of total training time.

• All exercises were performed on Nautilus machines, including many exercises which were performed solely with eccentric (negative only without the concentric/positive contraction) repetitions - the machines were designed to make this possible, since doing a lot of negative reps is hard otherwise without the help of a dedicated training partner.

• "Casey doesn’t eat too much" - "just 4-5k calories per day" - this is an odd statement given how much most people eat. He also supposedly has A Guy to follow him around and make sure he’s not violating the experiment or taking steroids. They totally swear.

• Casey ends the experiment at 212.15 pounds with 2.47% bodyfat. This equates to a gain of 45 pounds of bodyweight, but since his body composition also went down, it means that he lost quite a bit of fat in the process - meaning that his total muscle gain comes out to 63 pounds.

It should be evident that the results above are shocking. This seems like an astronomically high number - 63 pounds of muscle in only 28 days, with only 7 total hours of training. Then there’s the fact that it was all done on machines (since we know that free weights tend to be superior) and that it was done without steroids. This comes out to a bit over 2 pounds of muscle a day, which seems odd given that we know that it’s pretty hard for seasoned athletes to build muscle and may only be able to build a few pounds in a year of dedicated training. Additionally, Ellington Darden states that he gained 27.25 of those in the first week - roughly 4 pounds of muscle per day - before slowing down a bit in the remaining three weeks. Again, that comes out to 4 pounds of muscle per day - only working out every other day for a half hour. In comparison, my own recent weight gain experiment involved gaining 35 pounds in two months - and even then I gained quite a bit of fat in the process and was training 2-3 hours a day.

Naturally, this is a huge deal for Jones, who had run the whole thing in order to demonstrate the effectiveness of his equipment and his program. Knowing that he has a winner, he immediately starts sending out newsletters and selling books based on this experiment, and suddenly everyone in the world is super jacked doing HIT training on Nautilus machines. Wait, that last part isn’t true at all.

Since 1973, there hasn’t been any massive justification of Jones’ methods. In fact, no one has even been able to replicate this experiment with any degree of similarity. In a particularly devastating personal account, amateur lifter Stephen Wedan recounts how he trained based on Jones’ recommendations for a period of several years without seeing much of any results. Having met Jones in person, he later went to visit the Nautilus headquarters in 1976, where he met Viator personally and had a chance to go through a workout with him in the HIT style. There he gets a chance to ask Viator why it’s not working for him, and he gets an answer that (to the trained observer) is highly revealing:

“Viator's answer to my question seemed to be pure reflex: He said I wasn't taking each set to utter failure when I trained in Stetson's weight room. I assured him that I was. For the only time in my life, I was using a training partner, a six-foot eight-inch guy named Gary. We were well-matched in strength as well as temperament, and the two of us held each other accountable in every workout. This included taking each set to utter failure.

Viator countered by pointing out that while I lasted longer than many in my initial workout with him, I didn't actually complete it. This suggested that I wasn't as faithful to high intensity principles as I claimed, although he was too polite to put it that bluntly.”

This is particularly blunt (and shameless) application of the No True Scotsman fallacy - suggesting that, if you’re not getting shocking results from a HIT program, it’s not because the program doesn’t work, it’s because you’re not properly performing the workout. Already, you can see that everything smells sort of suspicious - shocking results, haven’t been reproduced, a guy who counters with his own personal experience is put down pretty hard, and numerous accusations of steroid use and study rigging are thrown around regularly. The Colorado experiment looks, acts, and smells like the 1970’s equivalent of “THIS ONE WEIRD TRICK TO BUILD A LOT OF MUSCLE” or “THIS 5 MINUTE ROUTINE TO GIVE YOU RIPPED ABS”. If it quacks like a duck, it’s probably a duck. So here are my major explorations of the various issues surrounding the Colorado experiment.

• The Colorado experiment isn’t a study, and has virtually no scientific credibility.

The Colorado experiment was, quite evidently, a marketing stunt. It was designed to sell machines and workout programs. This doesn’t necessarily invalidate it, but it casts suspicion on its motives and explains why the experiment lacks a lot of the hallmarks of scientific rigor.

In a typical study, we’d expect to see a lot of different subjects undertaking the protocol. There’s a lot of inter-individual variation, so we’d expect that some people would react well and some would react poorly, and then we’d average those results together to get an accurate picture of how well the program worked overall. Instead, we’ve got a sample size of 1 - this corresponds to that advice you got from your weird uncle saying that something “totally worked for him” even when it’s bad advice that won’t work for 99% of the population. Typically, bigger sample sizes are better because they overcome a lot of issues of selection bias, allowing scientists to avoid cherry picking good results to make an argument that doesn’t fit with the overall data. With a sample size of 1, it’s highly possible that we simply found the single mutant on the planet who will react well to a program that wouldn’t work well for literally anyone else. Which leads us to point number 2:

• Casey Viator may have been the single mutant on the planet who would react well to this program that literally wouldn’t work well for anyone else.

One common defense of the experiment is that Viator simply had amazingly superhuman genetics, which explains why he was able to get such a massive effect out of the program when others since have had much more mediocre results. At the same time, there’s only so far you can stretch that argument, particularly given his later (relatively) disappointing track record with bodybuilding competitions. Sure, he looked hella amazing and competed up on stage with the world’s best, but if he was really such a monster that he could do that feat without drugs, how did he not go on to dwarf his competition repeatedly over the next ten years of his prime? Did he simply choose not to compete? Or more likely - did he compete but not have much of a significant edge over his competition, who were probably just as gifted as him?

Another problem with attributing his transformation almost solely to genetics is that it implies that the program itself doesn’t matter. If Viator simply had unusually brilliant genetics for building muscle and strength, then it wasn’t the program itself that’s responsible for his transformation, and we can safely ignore it. You could also argue that he had genetics that were somehow uniquely suited for that specific program. But, if he also reacted well enough to his previous training to reach the level of Mr. America before ever touching a Nautilus machine, then we have a descriptor for that: it’s that he did have all-around good genetics. It’s not like he was some puny weakling who had never had any success before Jones’s style of training.

• Casey Viator totally wasn’t taking steroids. We swear.

Unfortunately, this one is about as unverifiable as literally any other steroid non-usage claim out there. Unless you see someone physically shooting up, or they personally admit to usage, or fail a drug test, there’s not really any way to tell for certain whether or not any particular lifter is using. We can assume that a probable majority of high level athletes in any sport are using, but there’s likely still some genetic outliers who can compete at an elite level without the use of any drugs, so it’s hard to make any blanket statements.

Given the lack of rigor seen elsewhere in the experiment (point 1), it’s not unreasonable to assume that Viator could have been using, even though he vehemently denied it until his death. Some testimonies have claimed that he’s admitted privately that he was not only using steroids but also sneaking in extra workouts outside of the experiment. This would make sense - in Viator’s position, he can make such an admission privately but would be unable to make a public admission without ruining the financial compensation he gets out of the experiment - including his job with Nautilus. Thus, in the absence of any drug testing back in the day, and the absence of anyone catching him in the act, we can’t be sure. Usually, it’s a waste of time to speculate, so I’ll only say that we can’t be certain whether he did or didn’t take steroids.

• Casey Viator was rebuilding muscle previously lost - and we know that this is much easier than building muscle a first time.

It’s openly admitted that Viator lost a good deal of muscle prior to the experiment. In 1971, he had won his Mr. America title at 218 pounds. By 1972, he had lost a bit of weight due to taking time off from training - leaving him around 200. After that, he suffered a serious injury that nearly cost him the pinkie finger on his right hand. He suffered an allergic reaction to an anti-tetanus injection, and as a result was hospitalized and severely ill. As a result of this hospitalization, he lost another 33 pounds directly before participating in the Colorado experiment, which was used as a way to get him back into shape.

There’s a well known phenomenon of “muscle memory”, in which it’s easier to rebound and rebuild a quality after you’ve already built it the first time. For muscle, this happens through myonuclei adaptations - myonuclei help determine your responsiveness to training, and can be lost more slowly than the attributes they oversee, so it’s possible to train hard, develop myonuclei, take some time off, and then start training again and build up quickly because those myonuclei are still around and haven’t been lost. This is a vast oversimplification of the process, and you should see Greg Nuckols’ article (linked above) for a much more nuanced take on the subject. This is also why many lifters take deloads, and why block periodization relies on alternating training focused on different qualities - in one block, you can focus on one quality while another one rests, and in this way take advantage of a controlled deload for one quality while training another one hard.

This helps explain why Viator saw such rapid results on the program - because he had taken some time off and lost some weight, and was now rebuilding muscle that he had previously lost. This may also explain why some other HIT advocates have managed to show off similarly impressive transformations - because many of them trained differently before HIT, built up muscle, detrained due to life demands, and then tried HIT and immediately rebounded back to their previous level.

It also explains why Tim Ferriss, who used a similar approach for his 4 Hour Body, was able to gain 34 lbs in 4 weeks with a similarly low volume, high intensity program - in his case, exercising only a total of 4 hours over those 4 weeks, two half hour workouts per week. Tim admits in the post to previously having been heavier, although in his case not much heavier - and also had certainly not trained to the extent that we would expect Viator would have in preparation to win the Mr. America. Unfortunately, this brings us to another point:

• “Muscle memory” is frequently abused in order to sell workout programs.

Can the success of either Viator or Ferriss, or anyone who has succeeded on such a program, be attributed entirely to muscle memory? No. Certainly the program was responsible for those results. But what should be understood is that if muscle memory is the primary mechanism by which the lifter saw rapid and massive results, this is again a huge blow to the program itself - because it means that any sufficiently intense program is likely to show similar results in that lifter. What this means is that it’s not the HIT program that did the trick - but the HIT program is selected because it means minimal time spent in the gym. This allows the results of the rebound to look particularly surprising, even though they could have likely been beaten by programs with higher volume performed by the same lifter.

This trick isn’t new. It’s been used in the fitness industry to sell programs (whether conscious of the deception or not) for decades. The method is simple: lose weight or detrain, stage a very public use of the lifter’s new and exciting program method which takes full advantage of that rebound to show huge results, and then sell the program and related products to unsuspecting fitness newbies looking to get the most bang for their buck. By the time they’ve realized that the program itself doesn’t really work, (or to be specific, isn’t the miracle program they expected) it’s too late: that deceptive transformation has already raided their wallets. In the end, without muscle memory, many “shocking transformation” programs are really either just brutally hard or are average programs with average results.

Is the HIT system effective? Yes, in a certain context. But it’s not, nor has it ever been a miracle program, because:

• HIT style programs are highly effective relative to their time investment, but are a poor long term strategy for serious results.

HIT style programs like the one that Jones and Viator tossed together are good at one thing: provoking a high response relative to the amount of time invested in them. This makes them extremely useful for those looking to minimize their time in the gym and get on with their lives. I would argue that this is one of the big reasons for the success of Ferriss’ 4 Hour Body book - because that’s exactly what his audience is, a cohort of busy professionals looking to maximize their results with only a small amount of time to spend in the gym. When it comes to long term success, however, HIT will likely only build a baseline level of fitness and is inadequate to serve as elite level training in any sport.

Over time, the single best predictor of improvement is volume. Low volume programs like a HIT program retain a relatively stagnant degree of volume, and that means that over time you may build some strength/speed/muscle, but sooner or later you’d probably plateau and be unable to continue developing without further volume. You can only get to a certain intensity before you lose the ability to go further.

In the Colorado experiment as strictly performed, all of the exercises were completed on machines. This violates studies which have since demonstrated that free weights remain the most effective way to build strength, muscle, and joint stability. Free weights typically activate a greater deal of musculature and are more specific to real world tasks when it comes to improving strength. (Though this is a far from closed topic.) Thus, it seems likely that doing the experiment with free weights should have shown optimal results.

Eccentric contractions enable lifters to use more weight, and were a huge factor in the Colorado experiment as initially performed. However, as these machines are now mostly extinct, it would be hard to replicate this element of the experiment since the machines were specifically designed to allow easy performance of eccentric only training without a significant concentric component. Additionally, research on eccentric training confirms it may be superior but not amazingly so for building muscle. It certainly isn’t ideal for building traditional concentric strength (due to the principle of spec), though it may be useful in some cases for preventing injury.

Research confirms that more volume is better overall, and there’s very little debate. At the same time, research also confirms that each set of an exercise performed after the first has a diminishing effect on overall results. In one study, 4-6 sets produced almost as much as twice the effect of one set - but obviously took 4-6 times as long, making it a much less efficient process. HIT style programs take advantage of this effect, using just one set in order to get a shocking return on time investment relative to a traditional slog in the gym. But at the same time, they’re not superior to the traditional slog in terms of overall results. Thus, if Viator truly did gain as much muscle as he did during that experiment, chances are he would have gained even more muscle if he had simply worked out more.

HIT programs also work well for maintaining strength and muscle. Even just a couple workouts per week may be sufficient, as Bret Contreras experienced. This makes them a highly effective tool if you need to take time off from training or need to focus on some other fitness quality for a bit.

• People seem to question many of the things in the study, but there’s one odd blind spot in their criticisms.

One criticism Darden addresses in his defense of the experiment is that the before and after pictures don’t look like he gained 45 pounds in the process. Darden’s defense is that Jones didn’t use contrast lighting because he wanted Viator’s pictures to have a more professional, medical feel. But at the same time, it’s clear that he has gained a significant amount of weight, particularly in the legs, chest, and arms. 45 pounds worth? Probably.

Much more glaring for me, however, is his supposed body composition changes. If Viator had gained those 45 pounds but retained roughly the same body fat percentage, we would expect that about 85% of that gain would be from lean mass with the remaining 15% from fat mass. This corresponds with 38.25 pounds of muscle - still a massive number, but not quite as shocking or astronomical, and more in line with the results that others have seen on crash programs like the Colorado experiment.

But the magic part that drives the experiment into the realm of just a little bit too good to be true is the part where his body composition vastly improved during the training program - from around 13.5% to around 2.5%. This means that not only was he gaining the 38.25 pounds of muscle that he would have seen if his body fat percentage had remained steady, he was also losing 25lbs of fat and replacing it with muscle in the process. Typically, while gaining weight body composition worsens as fat is gained during the process. This isn't always the case, but it's certainly less common to see that number move in the opposite direction, and downright strange to see it move so far in the opposite direction.

Getting down around 2.5% body fat is extremely difficult, and is usually the product of a bodybuilder purposefully and carefully dieting down to reach that point. In fact, many probably don’t ever reach that point: bodybuilders typically get into the single digits for competition, but the exact percentage varies. Checking around on forums, you get the impression that most bodybuilders show up on stage to compete in the 5-8% range, with some gifted individuals being able to get leaner and some managing to look good even as high as 10%. In short, even for stage ready bodybuilders, 2.5% would be an amazing number. Typically, we expect body fat percentage to WORSEN over the course of a bulk, and NOT improve - so losing 11% body fat seems like a pretty absurd claim

Which is also extremely strange, given that in the after pictures he looks nowhere near as lean as a stage ready bodybuilder. This, for me, is one of the biggest holes in the story. In the after pictures, Viator looks about as lean as he was in the before pictures, just much bigger. He absolutely doesn’t look like he’s stage ready, instead looking more like someone in the 10-15% range - in other words, much closer to his initial body composition. Admittedly, he’s not posing and possibly not flexing purposely at all, but even then we would expect to see an amazing degree of vascularity in someone that lean, and he displays very little.

In order to accept that Viator’s transformation really did reach an absurd 63lbs of muscle, it’s also necessary to accept that his body composition had to improve markedly. Otherwise, the math simply doesn’t add up. But while he looks much bigger in his after pictures, he doesn’t look much leaner - this is one piece of solid evidence that’s still around and can’t really lie.  

• Most importantly, no one has ever replicated Viator’s results on such a program.

People have come close, probably. People have gained 20 or 30 pounds, probably either because they’re beginners trying out a serious program for the first time or because they’re former serious exercisers jumping back into it after some time off. Also, many people fail to realize that by force-feeding yourself a ton and working out a decent amount, you can gain muscle relatively quickly - typically, exercisers remain around their current weight and slowly recomp to get leaner/more muscular, so they aren’t really aware of how significant muscle gain can be in the right conditions. Sumo wrestlers, for example, carry more muscle mass than even bodybuilders - not because they’re lean, but because they build so much overall mass that they gain a ton of lean tissue even when a large percentage of it is fat tissue.

Much of the Colorado experiment can’t be replicated, in large part because the initial equipment that it was performed on is no longer around. It could be done with free weights, or any other equipment available to us today, but it wouldn’t justify the original protocol performed 40 years ago.

• The Colorado experiment is slowly fading into obscurity.

The events of the Colorado experiment all occurred roughly 40 years ago. In the intervening time, much of the original documentation and material on the subject has been effectively lost. Some of the stuff Jones has written about it is still archived in some places, but it’s far from a complete picture. A search of the Colorado experiment on Google turns up a bunch of speculation and review, but very few original sources. It’s likely that this trend will simply continue, and within another 40 years the Colorado experiment will largely be forgotten, if not resurrected every 10 years or so to try and sell some new variant of HIT to a new generation of unsuspecting newbies.

Jones is dead, and Viator is dead. Many of the people who were probably tangential to the experiment are also probably dead by now too. In short, the book is mostly closed. Since Viator and Jones never publicly admitted to any rigging of the experiment, chances are that we’ll never know for sure and it’s probably a waste of time to speculate.

• The Colorado experiment keeps being used to justify HIT programs, and it’s a lot of the same voices over and over.

The proponents of HIT programs are few, but they’re typically not serious athletes, Mike Mentzer and Dorian Yates aside. As already noted, there’s Tim Ferriss, but his audience isn’t actual athletes so much as busy professionals, so it makes sense and fits well with his crowd. Ellington Darden is one who pops his head up occasionally - he’s a doctor and former Nautilus employee who’s been regularly writing books on the subject since the original experiment.

Meanwhile, these programs and books are often of the stereotypical “get jacked in 15 minutes a day” type. It’s not hard to tell a person to just do one set to failure on a variety of major important movements per day in my opinion, but apparently this justifies a great deal of words written on the subject, repeatedly every few years. There’s very little in the way of innovation on the subject, just a lot of rehashing of the same dated material.

So what do I think? I think it’s highly possible that Viator did gain as much muscle as he did - provided the caveat that I also think he was probably violating the strict terms of the experiment. He could have been working out more than was prescribed and he could have been taking steroids. That he had great genetics is accepted, though I don’t think that legendary genetics is a good answer for those kind of results. I also believe that it’s highly possible that the results of the experiment were falsified to some extent or another - in particular, the claim that he sits at 2.5% bodyfat at the final weigh in (when the pictures don’t seem to suggest anything near that level of leanness) seems highly suspect. But then again, we'll never know for sure, and sadly that means that that book will never fully be closed.

This only further obscures the much more important point, which is that the Colorado experiment absolutely shouldn't be taken as any kind of recommendation on how to train. Such an experiment is far removed from most people's situations, and the achievements of one highly dedicated bodybuilder shouldn't be taken as the holy word of God when it comes to providing rules and guidelines for how to train. If anything, it simply demonstrates what's humanly possible on one far end of the spectrum. Even then, this achievement is highly suspect.