Over the past year there have been several arguments in high intensity training circles over whether there is a difference between positive (concentric) and negative (eccentric) strength. Some of these have been semantic arguments about the definition of strength, some attempted to provide alternative explanations for the observed difference during test results, some are still talking about the debunked theory of intramuscular friction. Some of these arguments were part of criticisms of the practice of hyperloading the negative portion of an exercise and equipment designed for this purpose, which will be addressed in a second article.
Negative strength is greater than positive strength.
Strength is the ability of your muscles to produce force. A muscle must produce force to lift a weight. A muscle must produce force to hold a weight motionless. A muscle must produce force to lower a weight more slowly than the acceleration due to gravity (if it didn’t the weight would simply drop). Strength can be positive (concentric contraction, lifting), static (isometric contraction, holding), or negative (eccentric contraction, lowering).
When a muscle contracts concentrically heads on the myosin filaments attach to the actin filaments forming cross-bridges which bend and pull, then release and repeat, causing muscle fibers to shorten. When a muscle contracts isometrically or eccentrically it forms more of these attachments. If the force against the muscle exceeds the force of contraction it begins to lengthen, and as the cross-bridges are stretched forcing detatchment they immediately reattach (approximately two hundred times faster than during concentric contractions). This difference in cross-bridging mechanics makes the motor units significantly stronger when contracting isometrically or eccentrically, so to stop lifting or begin lowering a weight your body recruits fewer motor units in the working muscles to reduce the force produced. Because of this it is less metabolically demanding to hold or lower a certain amount of weight than to lift it.
Another protein in muscle fibers called titin also contributes to the increase in eccentric strength. It is “wound” by the action of the myosin and actin during concentric contractions, then stiffens to resist lengthening during eccentric contractions.
This difference in positive and negative strength is easy to demonstrate. Perform a few strict test repetitions on a good biceps machine or barbell curls until you find a weight that is just slightly too heavy for you to lift. Rest for several minutes (to satisfy those who suspect congestion due to pump and the resulting friction is a contributing factor). Increase this weight by approximately twenty five percent and have someone help you lift it, then hold the movement arm or barbell motionless while they gradually transfer it to you. Although it is too heavy for you to lift you will find you are able to hold it, and lower it slowly under strict control.
While the implications for training will be discussed in more detail in another article there is one important consequence of this I want to mention now. Occasionally a novice trainee will stop exercises short of momentary muscular failure (MMF) because they are afraid they will drop the weight or movement arm and possibly injure themselves. While this concern may be reasonable when performing exercises where grip strength can be a limiting factor it is usually unfounded because of the difference in positive and negative strength (if this difference did not exist you would drop the weight whenever you reached MMF during an exercise).
Even after you have achieved MMF (the inability to continue positive movement in the prescribed form) you will be strong enough to hold the weight motionless for a period of time afterwards and lower it slowly. It is important to teach this to novice trainees to improve their confidence in their safety and willingness to continue to contract intensely as they approach failure when learning high intensity training.
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It’s almost like the body has a built-in way of being able to lower more weight than it can lift? Or a built in safety mechanism if you will? This is a very interesting topic. There was of course much talk about this with the RenEx guys and the X-Force machines. I will have to try what you say to try here, Drew.
Just to be clear. My comment here regarding RenEx and X-Force is simply an acknowledgement of their different views of loading negative contractions.
Donnie,
Their criticisms of hyperloading the negative and the X-Force machines in particular are still valid and this is something I will be discussing in the next article.
Looking forward to that article, Drew.
I’ve done negative only exercises on other HIT programs and effective as they might be, I always felt impending danger was lurking when I would come crashing down from weighted negative pull ups and dips.
I had to learn, once that point is reached and form is being compromised, it’s time to stop the exercise.
Thank you for the article.
Ben,
That is one of several problems with negative only training I’ll be discussing in the article.
Great information. I’ve never heard of titin . . . going to have to research it.
I cue myself to focus on this especially with my back work. It’s sometimes difficult to limit the use of momentum as failure approaches. Like on a pull-down, If I can’t drive the elbows back and down to full contraction and hold for a brief pause at that position, the weight was obviously too heavy to achieve the repetition in good form w/o the use of momentum – as the hold at full contraction should be stronger than the properly performed concentric I should have used to get it there.
Also, I’ve found that beginning HITers (not people that are new to lifting altogether – just new to HIT) often demonstrate these differences in rep portion strength to the highest degree, failing at like 6-10 concentrically but seemingly being able to do negatives for days… Whereas advanced HITers fail to be able to even loosely control negatives just a few reps beyond concentric failure. Thus far, I’ve just attributed this to a lack of understanding of what true MMF is on behalf of the trainee, and an underestimation of their actual strength. But there definitely appears to be some adaptation that takes place over time, or some skill accumulation that narrows this gap.
Could you please elaborate on why you think this is?
Thanks!
Dustin,
It takes time and practice for most people to learn to inroad deeply and achieve real momentary muscular failure. Obviously, it is harder to hold a weight statically after achieving real failure than if you just stop when the exercise starts getting hard. However, you can still hold a weight long after failure, and you can still lower a heavier weight under control than you can lift, all else being equal.
Hi Drew,
A great explanation on the cross-bridging mechanics actin/myosin/titin, I now clearly understand why the differences in strength levels. And why we only have three different strength levels.
Read some articles, you have reactive strength, maximum strength, convert power to strength endurance, …just to name a few. Or strength train this way for explosive power or strength train this way for whatever!
It is all in the cross bridge mechanics and the best way to engage as many of the actin/myosin/titin filaments. HIT!
drew why the 180 about randy’s NO machines. didn’t you try to sell them at one point? there is way more evidence to support X- force type loading from biomachanics to darden’s studies. Ken just has nothing to show for 30 years of SS. Where are his case studies. Show us the beef.
Chris,
I never agreed with the claims RenEx made about positive versus negative strength, however I do agree with their other criticisms of X-Force. While Randy’s ARX machines can be used in negative only fashion they are not negative only machines; they provide “accommodating resistance”. The user determines how they train on them, including whether to “hyperload” the negative.
Over the past thirty years Ken has taught thousands of people how to train more safely and efficiently and developed what are arguably the best tools made for that purpose. There are hundreds of personal training studios and thousands of personal trainers using SuperSlow and in the United States alone who have helped improve the lives of hundreds of thousands of people over the years and even saved quite a few. Ken’s RenEx machines are being used in real exercise research at John Hopkins University Medical School. The X-Force machines are in only two locations in the United States after a few years on the market, and in at least one of those locations nearly a third of the machines broke down in the first few weeks. Ell is using X-Force for a fat loss program, not a clinical study, and he could produce the same or better results more safely training people on conventional selectorized machines.
I’ll be talking about the implications of the differences in positive and negative strength for exercise in the next article and will discuss the X-Force machines there.
I am definitely looking forward to what else you have to say about all this Drew. Much of what the RenEx guys have written about all this makes a great deal of sense to me. I have never really tried hyperloading the negative. I do know that when the load passes a certain point for me that the exercise turns go from feeling in control to just trying to survive. So increasing the the negative load past a certain point would do the same thing? Granted you haven’t said anything about more load during the negative in this article.
Donnie,
I agree with RenEx on this and will be writing more about application in the next article.
This may be getting a bit off topic. Regarding hyperloading the negative on an ARX machine. If I’m understanding the way an ARX works, the machine moves at the set speed regardless of the effort of the user, right? Or in the other words any movement the machine makes is due the machines motor right?
Donnie,
Yes, which allows the user to determine the resistance at any time. This is very different from the X-Force which uses a motor to tilt the stack to alter the resistance (in a manner which makes proper turnaround performance impossible, and some times when you don’t want it to change).
Drew,
If it’s appropriate in the context of your article on negatives could you address the following:
Hyperloading the negative manually. I’ve been experimenting with having my son manually add a little more resistance on the negative. I have worked out a clear cut set of instructions and so far I like this method.
Negative emphasized methods like the one you used for awhile. Perhaps Darden’s 30-30-30 method would fit under this heading. From my experiments with 30-30-30 it seems like a way to use fatigue to put yourself in a position where the last negative is really intense.
Thanks,
David
David,
Manual resistance and Darden’s 30/30/30 reps will be mentioned.
I have known Ken for 13 years and he always treated me kindly. I have nothing bad to say about him as a person. When it comes to his life work, I feel he has gone backwards as regarding the excessive set times. And after 30 years I have yet to see a case study done by him (BIG dosen’t count). To me, it is ironic that he has turned SS into that which he hates the most- Aerobics with weights.
Chris,
This is something I also disagree with Ken about. I prefer to keep people closer to a 60 to 90 second set duration and I think even that is erring on the long side for safety.
Drew,
How does Ken Hutchins train? Not only his TUL, but also the exercises and frequency.
Brian,
Ken performs brief, full-body workouts using SuperSlow/RenEx protocol as outlined in the most recent SuperSlow technical manual and The Renaissance of Exercise Vol 1. I do not know his workout frequency.
Drew,
The reason why I asked about Hutchins’ training is I find that with longer TUL’s(more than 90sec)it takes me longer time to recover. I don’t know if that’s due to greater inroad because I fail with less weight or is it due to system fatigue.
Brian,
A longer set duration does produce a much deeper inroad and probably places even more demands on recovery. I’ve had better results with shorter TUL, but there are cases when I would still use longer ones.
The disparity between muscular strength during concentric, isometric and eccentric contraction is a well-documented phenomenon.
From a purely empirical standpoint, there exists the Force-Velocity curve for skeletal muscle fibers. Maximum volitional tension occurs with no movement (isometric contraction), and force output decreases hyperbolically as concentric velocity increases. If we were to go from 0% maximum velocity (100% maximum force output) to 1% of maximum velocity, relative force would not decrease by a mere 1% but instead 5% (95% max force corresponds to 1% max velocity).
Muscle force output increases precipitously upon a reversal of contractile velocity (eccentric contraction) but quickly flatlines after -1% of contractile velocity.
“Skeletal Muscle Structure, Function and Plasticity” Second Edition
Richard L. Lieber, p.62
The biochemical explanation for maximum force output during isometric contraction is that IC is where cross-bridge attachment is at its maximum. Force generation depends upon the total number of cross-bridges attached. In order for skeletal muscle to propel movement, it must power filament sliding (known as the “walk-along” mechanism). As this occurs, cross-bridges must detach from their corresponding actin filaments and then reattach to others in order to shorten sarcomere length. As muscle velocity increases, fewer and fewer cross-bridge attachments exist at any given point in time.
For eccentric contraction, absolute tensions are high relative to the muscle’s maximum tetanic tension generating capacity. A higher force is required to overwhelm the muscle’s ability to maintain an isometric contraction.
“Skeletal Muscle Structure, Function and Plasticity” Second Edition
Richard L. Lieber, p.63
Eccentric exercise occurs when the structural integrity of the sarcomeres of the muscle fibers are compromised (known as muscle lengthening). Myofibrillar discombobulation and disorganization has been observed in a micrograph by Dr. Jan Frieden in humans 3 days after eccentric exercise. Redistribution of proteins associated with myofibrillar cytoskeleton were observed, which indicates the muscularly injurious effects eccentric exercise has, particularly upon fast-twitch muscle fibers.
Note: by use of the term injurious, I do not mean injury in the pathological sense, but instead as an event that damages muscle tissue and requires structural repair.
“Skeletal Muscle Structure, Function and Plasticity” Second Edition.
Richard L. Lieber, p.312
To demonstrate the differences between the lifting, holding and lowering phases of repetitions from a purely physical standpoint (a major flaw in Arthur Jones’s thinking) one must perform a test that most thoroughly eliminates friction, strength/resistance curve discrepancies, stroke length, etc.
I suspect that a free weight trap shrug serves this for purposes of demonstration very well. If repetitions are performed a low enough velocity, the differences in difficulty should not be so profound as a 40% difference between CC and EC nor 20% between CC and IC. As Jones himself pointed out, it requires 1 unit of force greater than the selected resistance to move it, exactly the force of the resistance to hold it, and 1 unit less to slow it down. However, greater speeds of lifting require greater amounts of force and greater speeds of lowering require less force. Those with access to dynamic exercise machines with visual feedback of force output (RenEx, ARx, etc.) ought to note that the force they must produce less force during the lowering and more force during the lifting of any given repetition during any exercise, but the disparity is nowhere near 40%.
Minor Correction: “When a muscle contracts concentrically heads on the myosin filaments attach to the actin filaments forming cross-bridges which bend and pull, then release and repeat, causing muscle fibers to shorten.”
Cross-bridges are composed of myosin arms and heads. Each individual arm is a part of the body of a myosin filament and each head is composed of a myosin heavy chain ending and two myosin light chain filaments. Cross-bridges are only components of the myosin filaments. They attach to the actin filaments to form what is instead called the AM (Actin-Myosin) complex.
“Guyton and Hall Textbook of Medical Physiology” 12th Edition, p.74,75.
This may seem like a petty correction, but it is significant because it is necessary to note that cross-bridges are attached to active sites on actin filaments during isometric contraction. It is more relevant to point out that cross-bridges actually detach from the actin filaments during concentric contraction, and this is what leads to the disparity in concentric strength from other types. At any one time, fewer cross-bridge attachments exist during concentric contraction and this is the key component in differences in muscular strength during different phases of exercise. There is, however, no increase or decrease in the amount of cross-bridges.
Daniel,
The slower you contract concentrically the smaller the difference between positive and negative strength due to the smaller difference in cross-bridges, but while detachment is a factor there are also differences in cross-bridge mechanics and in the action of titin which contribute to this difference. The second edition of Lieber’s book is from 2002 and while it is a great resource it is out of date on some things. See the papers Dr. Reedy recommended in the friction article. There is probably l
I don’t know the exact percentage, and while it might not be the forty percent Arthur claimed the difference in positive and negative strength is definitely not small even at slow speeds. This can be easily demonstrated with motorized machines with force measuring capability, and subjectively by applying additional manual resistance during the negatives to subjects during exercise using equipment with good resistance curves and extremely low friction (although I recommend extreme caution if anyone tries this).
Arthur was wrong about needing 1 more unit of force to move a weight positively and one less to move it negatively. You need more force to accelerate it against gravity, and less to allow gravity to accelerate it downwards, but the same amount to hold or lift or lower at a constant velocity after initial acceleration. Also, the issue here isn’t the amount of force required when lifting and lowering a weight, but the amount of force a muscle is capable of producing during concentric and eccentric contractions.
I asked my teacher why is it that we can lower more weight then we can concentrically lift, and he said because gravity is helping us lower it, and not when we lift it, do you know how i could simplify what you said in this article and explain it to him?
Paul,
Our muscles are capable of producing more force when contracting eccentrically than concentrically because of differences in cross-bridge mechanics.
You can refer him to the explanation given to me by Dr. Michael Reedy from the Duke University Cell Biology Department quoted in Positive Versus Negative Strength – The Friction Theory is Wrong
Hi Drew,
I`m not convinced that a claimed higher number of cross-bridges and their higher kinetic during isometric/eccentric muscle action is the primary reason for higher isometric/eccentric strength.
To make a single cross-bridge ready for its next stroke one molecule of ATP has to be cleaved.
A higher number of cross-bridges and/or their higher kinetic doesn`t change that. So even if the same level of strength can be produced with fewer motor units during isometric/eccentric action I don´t see a satisfactory explanation for the decreased energy turnover because I can not see a lower need for a decreased number of necessary cross-bridge cycles whether the are performed by the same or a lower number of motor units.
Additionally I can`t see a satisfactory explanation in the cross-bridge hypothesis for the fact that eccentric strength rises with fatigue.
Hey Mike,
The number of cross bridges has more to do with the length and the rate of change in length, the difference in positive and negative strength is due to differences in how cross bridging occurs, and the difference in how cross bridging occurs is what is responsible for the difference in metabolic cost. This was explained in Positive Versus Negative Strength – The Friction Theory is Wrong
Eccentric strength does not increase with fatigue, it just appears to reduce more slowly than concentric strength. This is because muscular fatigue is not due simply to a reduction in ATP but a variety of factors which along with differences in concentric and eccentric cross bridge mechanics impact concentric and eccentric strength to different degrees (damage to myosin heads, reduced Ca ion possibly due to t-tubule damage, reduction in pH, increase in concentration of inorganic phosphate, etc.).
Hi Drew
I would like to reply with a translated (German to English) quote (page 367/368) out of the textbook “Sportbiologie” (10th edition from 2009, ISBN 978-3-938509-25-8) by the German scientist Prof. emerit. Dr. phli. Dr Hc. Juergen Weineck MD:
“As apparent from illustration 206 (Weineck/Schnell 1986) positive dynamic maximum strength – something similar applies to static maximum strength- decreases quite fast with rising fatigue (number of repetitions) while negative dynamic maximum strength increases. The fact that negative dynamic strength (braking force) increases with rising fatigue stands in context with the fact that with an increasing number of repetitions the muscular ATP stores noticeably decline and thereby the plasticizer function of ATP decreases more and more. The cross bridges between the myosin heads and the actin filaments can untie noticeably harder and thereby increase the resistance against muscular stretching. The negative dynamic strength can not be increased by fatigue unlimited since at the limits – which varies substantially interindividualy- mediated by the receptors of the tendons (Golgi-Receptors) a termination of work occurs by reflex action so that the muscle is protected from tearing apart.”
I would like to add that the extreme of ATP deficit is the state of rigor mortis. Thus I still disagree that a passive component like cross bridges in rigor mortis position does not make a significant contribution at least to higher negative strength. Even in a fresh muscle there are some cross bridges in rigor mortis position leastways because cross bridges act (must act) asynchronous.
Hey Mike,
Negative strength does appear to reduce more slowly than positive strength (something Arthur Jones noticed during MedX research at the University of Florida in the 1990’s) however it definitely does not increase with fatigue. Otherwise you could perform negative-only repetitions for hours on end without failing which obviously is not the case. This is also easily disproved using motorized machines like the ARX which measure and display force input during the positive and negative. This was either mis-translated or very poorly worded, or simply wrong.