The X-Force line-up includes eight single-joint and six multiple-joint machines.
Above is a prototype of the X-Force Pec Arm Cross. The framework on the
left contains an electric motor at the bottom that powers a tilting weight
stack, which is the key to providing more work in less time.
by Ellington Darden, Ph.D.
Copyright © 2009. All rights reserved worldwide.
(This is a revised version of a brochure that I researched
and wrote for the IHRSA Convention and Trade Show
in San Francisco on March 16-19, 2009.)
Beginning in the early 1900s, there were a number of bodybuilding campaigns throughout the United States that claimed to make the weak strong.
These promotions were started by Bernarr Macfadden, a health enthusiast and magazine publisher — and were continued by Charles Atlas, winner in 1922 of the Macfadden-sponsored contest, "America's Most Perfectly Developed Man."
The overriding message of the advertisements, as well as their follow-up mail-order courses, was... Weakness is a crime. The underlying theme was... A lack of muscular size and strength is a disservice to self, country, and humanity.
Macfadden's and Atlas's courses motivated millions of males — before, during, and after World War I and World War II — to get bigger and stronger.
A 1902 edition of Macfadden's popular bodybuilding magazine,
Physical Culture. A young, muscular Macfadden was featured
on this cover. The periodical's circulation was highest
during the mid 1920s.
For the first half of the 20th Century, the basic method of gaining strength involved lifting barbells and dumbbells — mixed with body-weight exercises such as push-ups, sit-ups, and chin-ups. These routines focused on the raising or positive phase, with little regard to the lowering or negative.
In 1972, Arthur Jones — because of his disdain of physical weakness — initiated a more-advanced plan of strength building with his negative-accentuated techniques and Nautilus machines. Jones proved the effectiveness of negative training, but was unable — after many attempts — to manufacture machines that emphasized it safely and productively.
Ten, twenty, and thirty years passed and there was little progression — other than cosmetic — in the function of strength-training equipment. More recently, almost all leg, torso, and arm machines from popular manufacturers contained the same characteristics. Nothing was unique.
But that's going to change in 2009.
For the last two years, in an isolated biomechanical laboratory in Sweden, exercise-machine evolution has been moving forward at a fast pace. An innovative, refined, negative-accentuated system — which, in my view, will prove to be more effective than Jones's method — is ready to emerge.
Mats Thulin of Stockholm, Sweden, is prepared to launch X-Force.
Thulin has owned and operated, over the last three decades, 127 fitness centers throughout Scandinavia. With his knowledge of club management, devotion to exercise physiology, and grasp of engineering — in conjunction with the design help of a Swedish automotive team — Thulin brings X-Force to the market.
The ingenuity of X-Force is a patented, tilting weight stack that unloads the positive phase, and then, overloads the negative. X-Force supplies negative-accentuated exercise — 40-percent extra negative resistance compared to the positive — without the use of assistants, in a series of 14 strength-training machines.
Roll over Macfadden and tell Atlas and Jones the News!
X-Force signals an end to weakness... and the beginning of a new era in strength-training equipment.
The performance of a strength-training machine, or a barbell, requires the raising and lowering of resistance.
When you raise the selected resistance on the weight stack, you're moving vertically against gravity and performing positive work, or in the language of physiologists, concentric muscle action is occurring.
Lowering the weight under control brings gravity into play in another fashion. The lowering portion of an exercise is called negative work or eccentric muscle action.
During positive work, your muscle fibers are shortening. During negative work the same fibers are lengthening.
In the simplest terms, observing the weight stack move during an exercise reveals: up is positive, down is negative.
(Note: In physics, positive and negative are terms that refer to the resistance or external load. While these terms are not always technically correct in their applications in this article, their interchangeable use — positive = concentric and negative = eccentric — is accepted by athletes, coaches, and fitness-minded people.)
When I started training with weights seriously in 1959, no one paid any attention to the negative phase of an exercise. Using mostly barbells and dumbbells, we performed the positive part of each repetition with concentration. The negative phase, however, was done mindlessly. Sometimes the weight was simply dropped.
Generally, most individuals who strength trained didn't give the negative any attention. They just focused on the lifting.
My training continued in the above style until 1972. In the summer of that year, I read an article by Arthur Jones in IronMan magazine. A year earlier, Jones had established Nautilus Sports/Medical Industries in Lake Helen, Florida, and begun manufacturing a line of strength-training machines called Nautilus. In his article, Jones was irritated by the promotions of some of his competitors — competitors who manufactured friction-based machines that merely provided positive resistance. They were implying that negative resistance in a machine was a disadvantage. That prompted Jones to start experimenting with the negative phase of each repetition.
Jones was enthused by his initial gains in muscular size and strength. Toward the end of the article, he challenged bodybuilders not to think in terms of how much you can lift, but in terms of how much you can lower. That made a lasting impression on me.
Arthur Jones is shown doing negative-only pullovers on a Nautilus machine.
Notice that Jones had a spotter on the side and a spotter in the back.
Their job was to do the lifting or positive part of each repetition.
Several months later, I was in Munich, West Germany, at a scientific congress preceding the 1972 Olympics. In one of the sessions, Dr. Paavo Komi, a Finnish physiologist, described how he had trained a small group of Scandinavian weightlifters by having them lower — not lift — heavier-than-normal barbells from overhead to the floor.
His study then compared the effects of positive and negative work on the electrical activity of human muscle. He believed that his negative training of the Scandinavian lifters just might provide them with an edge in their approaching competition. Several days later, one of Dr. Komi's athletes won a gold medal and two won bronze.
I told Dr. Komi I was interested in his ongoing research and wanted to keep in touch. I also mentioned that I would soon be working with Arthur Jones at the Nautilus headquarters. Dr. Komi indicated that he'd experimented using hydraulic machines to help lift extremely heavy barbells for his athletes, but the machines had been difficult to manage.
In September of 1972, when I returned from Europe to Florida State University to complete my post-doctorate study in nutrition, I phoned Jones and told him about Dr. Komi and his research with negative work. "Bring those reports to me immediately," Jones replied. "We don't have any time to waste."
The next day I drove to Lake Helen and gave Jones Dr. Komi's printed materials. Jones read them, shook his head several times, smiled, and led me outside, around a corner, and into a secluded factory shop where prototypes were designed. "Feast on this, Ell Darden," he said, as my eyes bulged at a sea of large, heavily constructed machines — which he named Omni.
This was the Nautilus Omni Shoulder machine in 1973. The heavier-than-normal
resistance has been leg pressed to the top position, where it was then lowered
with the arms slowly to the bottom. On the right side of the photo was a
prototype for the Omni Supine Bench Press machine,
which was never manufactured.
By the end of the day, Jones had convinced me that the lowering of heavy weights correctly was almost always ignored, yet was a central factor in achieving maximum results.
In Jones's negative training, the selected resistance on each machine was approximately 40-percent heavier than you normally handled for 10 repetitions. As a consequence, one or two people were required to do the lifting or positive phase for you. Then, it was your job to lower smoothly the resistance back to the bottom position. Your assistants lifted the weight again, and you lowered it under control.
The object of Jones's negative exercise was to lower the weight slowly, very slowly, but without interrupting the downward movement. At the start of a negative set, you should be able to stop the downward movement if you try, but do not try. After 6 or 7 repetitions, you should be unable to stop the downward movement no matter how hard you try. However, you should still be able to guide it through a smooth descent.
Finally, after 2 or 3 more repetitions you should find it impossible to stop the weight's downward acceleration. At that moment, you should terminate the set.
Properly performed negative exercise, Jones concluded, assures more complete exercise of the muscles because the resistance always moves at a smooth, steady pace and, as a result, provides more thorough stimulation of the muscle fibers. This is in contrast to a tendency to jerk and drop resistance, the manner in which a great deal of lifting was performed then and even now.
There were logistics issues, however, with Jones's negative training.
First, is the paradoxical problem of your own strength gains. As you become stronger quickly from negative work, you must recruit two or more spotters to help with the lifting. Such serious lifting soon becomes boring for even the most motivated assistants. Furthermore, this lifting, especially on heavy leg presses and pullovers, has to be very coordinated or it can become dangerous.
Second, is the problem of continuity, maintaining the intensity of your negative work. You can easily lapse into resting too long between repetitions. A pause, or lag time, of only 3 seconds allows sufficient muscle recovery to give the illusion of improved performance, while undermining the anticipated training effect.
Furthermore, rest intervals of 3 seconds or longer between repetitions equate to performing a series of single-attempt efforts. Not only is this inefficient, it also increases the risk of injury.
Jones was in a quandary over designing machines with significantly more resistance on the negative stroke than on the positive stroke. He made many attempts — first, the Omni machines, which supplied a foot pedal to lift a heavier-than-normal resistance with the legs and then lower it with the arms; and last, with his servo-electrical machines that could be computer programmed to supply more resistance on the negative. Jones's endeavors provided benefits, but the machines were cumbersome and complex.
Jones sold Nautilus in 1986, and later retired from his follow-up company, MedX, in 1996. He died in 2007, without solving how-to construct an exercise machine successfully, with less positive and more negative resistance.
On November 13, 2008, I traveled to Stockholm, Sweden, to meet with Mats Thulin, whom I had met in 1980 at a Nautilus Seminar in Florida. Mats later became a distributor of Nautilus equipment in Scandinavia. Thulin had phoned a month earlier, enthusiastic about what he called, "a new way to accentuate the negative, without the use of the legs or the help of an assistant."
In Stockholm, when I critically examined what Thulin had done — and applied it under workout conditions — a lightning bolt went off in my head... "This is the MISSING KEY. Why didn't Arthur, one of his engineers, or even me — think of this approach decades ago?"
The approach that Thulin applies so effectively involves a tilting weight stack powered by an electric motor. As the user begins the positive stroke, the weight stack leans to a 45-degree angle — instantly reducing the selected resistance by approximately 29 percent. At the apex of the positive stroke, the tilted weight stack returns to vertical. The user then lowers 100 percent of the selected resistance.
Instead of continuing to search for ways to add resistance on the negative, which was the strategy Jones and others had chosen, Thulin figured out a way to subtract weight from the positive.
This was a brilliant step forward in the evolution of eccentrics, as well as the advancement of strength-training machines.
Here's photo of an X-Force weight stack that's tilted to
45 degrees for the positive stroke of the exercise.
For example, on the X-Force Pec Seated Press machine, let's say you select 140 pounds. As you enter the machine, seat yourself properly, pull a lever, and grasp the handles, the weight stack tilts to 45 degrees. As you perform the positive phase, you are moving 100 pounds of resistance. (Note: 100 is 29-percent less than 140 pounds and 140 is 40-percent more than 100 pounds.)
Quickly, in 0.5 of a second, the weight stack goes back to the vertical position as you do a controlled negative with 140 pounds. Ideally, you would continue performing 100-pound positives and 140-pound negatives for approximately 7 or 8 full repetitions.
In addition, a properly shaped cam is incorporated on each machine to vary the resistance curve appropriately.
Not only has Thulin solved the 36-year-old machine quandary, but he also has successfully overcome the two major problems with heavy negatives.
First, spotters or assistants are no longer needed, since the trainee should be able to lift the tilted — and thus reduced — resistance.
Second, what originally required a lag time — as the trainee rested while the assistants worked — is now filled by the trainee lifting the tilted resistance.
There's little chance to rest even partially when repetitions are performed correctly: positive, negative accentuated; positive, negative accentuated; and so on... as opposed to negative accentuated, rest; negative accentuated, rest; and the like.
Furthermore, X-Force's negative-accentuated training, compared to Jones's original lowering style, is safer for the muscles and connective tissues.
It will take only one, properly performed set on the X-Force Pec Seated Press machine — for instance — to feel the difference, compared to a normal set where the positive and negative resistances remain the same.
The reasons why one set on X-Force makes a meaningful difference are explained in the following sections.
Inroad is the depletion of momentary strength, repetition by repetition, from a set of an exercise.
For example, let's say on a seated biceps-curl machine, you can do 10 repetitions with 80 pounds of resistance. (Note: This is a conventional biceps machine and you have 80 pounds on the positive and 80 pounds on the negative.) In spite of your best effort, you cannot do an 11th repetition. Why did you fail? Did your biceps strength go from something above 80 pounds down to zero?
Your strength did not go to zero. If you're a typical trainee, your repetition-by-repetition strength drops an average of 2-percent per repetition.
On repetition 1, you are 100-pounds strong — and 100 pounds of strength easily curls 80 pounds of resistance. On repetition 2, you are 98-pounds strong and 98 pounds lifts 80 pounds, and so on. On repetition 10, you are approximately 80.5 pounds strong — and 80.5 pounds of strength is barely able, with a supreme effort on your part, to curl 80 pounds on the machine. On repetition 11, you are 79 pounds strong — and 79 pounds of strength will NOT curl 80 pounds of resistance.
Continuing that example, from one set of 10 repetitions, you've made a 21-percent inroad into your starting level of strength for your biceps. According to Arthur Jones, and much Nautilus research, the most consistent level of muscular growth occurs when a trainee makes an inroad of from 15 to 25 percent on the majority of his exercise sets.
From my own strength-training history, I knew that my strength was fairly typical. In fact, my average inroad on most exercises paralleled the 2-percent, repetition-by-repetition, inroad described above. On most of my exercises, I could expect to perform approximately 10 repetitions with 80 percent of the resistance I could do one time maximally. Using a repetition style of 2 seconds on the positive and 4 seconds on the negative, then 10 repetitions required approximately 60 seconds for me to perform.
When I arrived in Stockholm, two machines, the X-Force Horizontal Leg Curl and the X-Force Biceps Curl, caught my attention. These machines, minus the tilting weight stacks, are almost identical to ones I have in my private gym in Florida. Perhaps I could make some valid inroad comparisons between X-Force and my normal weight-stack machines?
The following day, on the X-Force Horizontal Leg Curl and the X-Force Biceps Curl, I calculated and selected the same amount of resistance for the positive phases as I had used the week before in Florida. Each repetition, however, would supply 40-percent more resistance on the negative phase. My goal was to perform as many repetitions as possible, using a 2-second-positive and 4-second-negative count.
Interestingly, on both X-Force exercises, I barely completed 7 repetitions and reached momentary muscular failure at approximately 42 seconds. The week before, using my conventional leg curl and biceps curl machines, I had reached failure on each at 10 repetitions and 60 seconds.
This demonstrated to me that, with X-Force, I achieved the same inroad, 21 percent, in 42 seconds, as opposed to 60 seconds. Thus, the X-Force Horizontal Leg Curl and Biceps Curl machines, for me, were 50-percent more demanding per repetition (3-percent inroad versus 2-percent) and required 30-percent less time to failure (42 seconds versus 60 seconds).
I quickly accessed that the X-Force Horizontal Leg Curl, compared
to a conventional leg curl, made a greater inroad, repetition by
repetition, into my starting level of strength.
Those two factors, degree of inroad per repetition and time required to failure, showed me that X-Force, compared to conventional equipment, provides more-efficient inroads. From my 30 years of training thousands of individuals, it's been my experience that growth stimulation is closely linked to inroad and a more efficient inroad is increased assurance of growth stimulation.
X-Force's accentuate-the-negative concept has my vote for efficiency in action.
Ten Reasons To
Accentuate the Negative
After reviewing the published literature on concentrics versus eccentrics,
Dr. Bjorn Alber, a Swedish sports medicine physician,
concluded in 2008 that... Eccentric training:
- Involves a heavier-than-normal overload — which means more force output and more muscle fibers recruited.
- Recruits more fast-twitch fibers — which contribute predominantly to muscular size.
- Insures a higher level of stress per motor unit — which supplies greater stimulation of the involved muscle fibers.
- Requires greater neural adaptation — which reinforces cross-education of strength gains from one limb or side to the other.
- Causes more microscopic fiber tears — which ignite the muscle-building process.
- Works the entire joint structure — which results in more strength, stability, range of motion, and healing properties.
- Applies well to post-surgical therapy — which is advantageous in rehabilitation.
- Maintains strength gains longer — which counter the detraining process.
- Transfers strength gains to concentric work — which is valuable in lifting performance.
- Allows greater work in less time — which means more efficient training sessions and faster results.
Note: Dr. Alber's overview was assembled from discussions I had with
him in Stockholm, Sweden, on November 17, 2008, and follow-up
e-mails from him on December 18, 2008.
In comparison to conventional strength-training machines, X-Force offers these advantages by considering the following factors:
- Inroad: As previously noted, because of the depth of inroad and the shorter time it takes to reach muscular failure, X-Force is more efficient.
- Stimulation: A more efficient inroad equates to enhanced muscular size and strength increases.
- Flexibility: To accentuate the negative allows more effective backpressure in the flexed position and more effective stretching in the extended position. Together, this contributes to full-range movement and improvements in joint flexibility.
- Control: With X-Force, the trainee has solo control during both the positive lifting and the negative lowering. There's no need for spotters or assistants to help with the performance of any repetition.
- Safety: The nature of accentuating the negative requires that each lowering phase be performed smoothly and slowly. And since the positive is always 29-percent less than the negative phase, the turnaround between the negative and positive transitions the user without straining into the next lowering phase. X-Force promotes better form and safety.
- Rehabilitation: Because of more control, better form, and safer conditions, X-Force is a valuable means of treating and working around injuries, as well as injured body parts.
- Results: Whatever the goals of resistance training, X-Force can more efficiently provide beneficial results.
The initial X-Force machines are as follows:
Horizontal Leg Curl
Lat Back Circular
Lat Back Pull
Lat Back Row
Pec Arm Cross
Pec Seated Press
Pec Angle Press
There are many ways to organize routines with X-Force machines. One way is to alternate two routines, A and B, as listed below:
- Leg Quadriceps
- Leg Press
- Deltoid Lift
- Deltoid Press
- Lat Back Circular
- Biceps Curl
- Triceps Press
- Abdominal Crunch
- Horizontal Leg Curl
- Leg Quadriceps
- Pec Angle Press
- Lat Back Pull
- Pec Arm Cross
- Pec Seated Press
- Lat Back Row
- Abdominal Crunch
My recommendation is to train on X-Force twice a week. For example, perform A Routine on Monday and B Routine on Thursday.
Concerning sets and repetitions, I'm a believer in one set to failure. Done properly, that's all you require for maximum stimulation. With X-Force, because of the added 40 percent on the negative, the repetition range for most trainees should be 6 to 8. Each repetition should be done with a count of 2 seconds on the positive and 4 seconds on the negative, or perhaps even slower, 3/5 or 4/6. When you can perform 8 repetitions in good form, that's the signal to add from 2- to 5-percent more resistance to that machine at the time of the next workout.
On my visit to Stockholm in November of 2008, Mats Thuline and I performed similar 8-exercise, X-Force routines — one set of 6-8 repetitions to momentary muscular failure — and each of us finished our workouts in 15 minutes.
Two 15-minute workouts a week on X-Force should be the basic frequency and duration for most fitness-minded individuals.
Bernarr Macfadden and Charles Atlas — during the first half of the 20th Century — publicized the idea that "Weakness is a crime." This in-your-face headline worked successfully because each promoter was able to show, through his articles and mail-order courses, the confidence-building powers of... bigger, stronger muscles.
One of the many versions of the Charles Atlas ad that was so effective during the 1930s and 1940s. These promotions were always peppered with phrases such as:
"Quit being a skinny weakling."
"Take charge of your life."
"Build a real HE-MAN body."
Atlas, with his physical promises, provided much-needed optimism that there would be better times ahead.
Many boys and men of that era were under muscled and thin. Often, they faced long grueling days of farm work. Food was scarce. Rest was skimpy. And a world war was looming on the horizon.
Macfadden and Atlas — with their muscle-development plans — offered hope... for pennies a day.
Millions of boys and men responded. Many applied the necessary discipline and patience — and their bodies responded by becoming bigger and stronger.
Arthur Jones, with his Nautilus machines and their popularity in the 1970s, provided more hope as thousands of fitness centers opened, purchased Nautilus equipment, and sold millions of exercise memberships throughout the United States.
Today, the landscape is different. The majority of boys and men no longer spend grueling days doing anything close to strenuous work. Computers have taken the place of plows, pitchforks, and outdoor activity. Food is not only plentiful, but also loaded with taste-tested calories.
Most boys and men, at first glace, are not skinny — they're fat.
But below those fat-thickened outer shells are inner bodies that are still under muscled and weak.
Mats Thulin and his X-Force machines deliver renewed hope. Hope based on the science of eccentrics. Hope in the form of revolutionary tilting weight-stack exercises that accentuate the negative.
It only takes 30 minutes of X-Force training per week to signal:
When researchers in 1953 first used the word eccentric to describe muscle
lengthening, it was spelled "ex"centric. X-Force, therefore, is a fitting
name for exercise equipment that overloads the eccentric
or negative movement. As a reminder, there are two
heavy X-supports that stabilize the axle of the
tilting weight stack on each machine.
Chuck Berry's 1956 recording, "Roll Over Beethoven," became an anthem globally accepted as symbolizing change — change that ushered in a new era called rock and roll.
X-Force, likewise, symbolizes change and a new era in strength-training equipment.
With Berry's guitar riffs in the background, here's my updated ending for his classic song...
Roll over Macfadden and tell
Atlas and Jones the News:
With X-Force's line-up, you've got
nothing but weakness to lose.
Roll over Macfadden and dig
these negative rhythm and rules.
X-Force. Negative training made simple, safe, and productive.
The Lat Back Circular, for negative-accentuated pullovers, is the
centerpiece of the X-Force upper-body machines. In my opinion,
Arthur Jones would have welcomed the technology and the
engineering behind this quality-designed equipment.
Notice: All contents, including text and images, are copyrighted © 2009 by Ellington Darden, Ph.D. They are not to be reproduced or transmitted in any way or in any format, without written permission. All rights reserved worldwide.