The Varying Ratio of Positive to Negative Strength

A few years ago I wrote an article titled The Ratio Of Positive To Negative Strength And Implications For Training in which I explained that rather than a fixed ratio the difference between positive and negative strength varies with different concentric contraction velocities due to the force-velocity curve. Although your negative strength does not vary at different contraction velocities, your positive strength varies inversely to contraction velocity, so the ratio changes if you lift a weight more quickly or slowly. The ratio also changes as a muscle fatigues, with negative strength decreasing more slowly than positive strength, probably due to eccentric contractions being more metabolically efficient.

This has been known since the 1950’s and it’s implications for the ratio of positive to negative strength should be obvious, but for a long time many people have believed there is a specific ratio of positive to negative strength. The most popular being the claim by Nautilus inventor Arthur Jones that negative strength is approximately forty percent higher than positive strength. Recently, exercise physiologist and HIT instructor Ryan Hall made an interesting discovery about how Arthur Jones came up with these numbers. He wrote,

Drew,

I have been working on updating my “Exercise and Genetic Variability” presentation, and correlating genes with some of the testing Jones performed on the pre-MedX Nautilus servo-powered isokinetic devices. Some of the information I ran across while perusing the earlier research reminded me of this conversation [referring to the discussion quoted in The Ratio Of Positive To Negative Strength And Implications For Training – DB].

Much of the testing that Jones observed concerning the ratio between concentric, isometric, and eccentric strength was performed on the pre-MedX isokinetic machines. I had to look closely and study each graph, which revealed something to me. Almost all of the testing was performed using a leg extension machine, which was set to 110 degrees ROM, with the speed of movement set to 25 degrees per second, for both the concentric and eccentric phases of the movement. Each repetition would be completed in a little over 4 seconds for each phase (8 seconds for the entire rep). This time interval doesn’t include the turnarounds, which were totally unloaded due to the nature of a servo-powered motor. However, having the concentric phase standardized to a predetermined speed would account for Jones’ observation of a consistent ratio between the different phases in a fresh muscle.

Jones’ testing also demonstrated that this ratio doesn’t remain the same for a fatigued muscle, which is consistent with the research literature. I just thought you would find this interesting.

Ryan

The ratio of positive to negative strength varies

Jones also believed the difference in positive and negative strength were due to intramuscular friction, which we now know is wrong. In The Future of Exercise he wrote,

Everything in the known universe that has both mass and motion also has friction, and muscles are no exception. Whether it is an automobile, an airplane, a snake or a human muscle, friction acts the same way: inhibits positive function while enhancing negative function, thus reduces your positive strength while increasing your negative strength.

He reasoned that if negative strength is approximately forty percent greater than positive strength, muscular friction must reduce positive strength by twenty percent while increasing negative strength by the same amount, and isometric strength is exactly halfway between the two (During a phone conversation in the late 1990’s when I asked Jones why he thought the ratio of positive to negative strength changed with fatigue he said it might be because friction increased as the muscles became more ‘pumped’). In The Metabolic Cost of Negative Work he wrote,

While it is certainly true that an exerciser can lower more weight than he can lift, it does not necessarily follow that his muscles are actually stronger during negative work than they are during positive work.

The muscles may be stronger; but even if so, they are not as much stronger as they appear to be. The apparent gross difference in strength is, I think, primarily a result of friction… internal muscular friction.

While lifting a weight, the muscles must contract with sufficient force to move the imposed resistance… but they also have to overcome their own internal friction. Thus, doing positive work, friction is working against the muscles.

Whereas, during negative work, friction is working for the muscles instead of against them.

Jones was wrong about isometric strength levels also. Isometric strength is relatively constant like eccentric strength so while the ratio of isometric to negative strength would be relatively constant the ratio of positive to isometric strength would vary with lifting speed. Isometric strength would only be halfway between positive and negative strength at a specific, slow lifting speed.

It is important to understand these claims about the ratio of positive to negative strength because they have influenced resistance selection recommendations for various exercise protocols like negative-only, negative-accentuated, and isometric training, as well as exercise equipment designs. For example, the typical recommendations for negative-only training and static holds are to use loads forty and twenty percent heavier than you use for normal repetitions.  This would be too much if you normally lift very slowly or too little if you normally lift more quickly than the speed of movement used in Jones’ tests. A safer approach when starting to perform exercise protocols limited to negative and/or static contractions is to err conservatively and only increase the load by around five to ten percent. If it isn’t heavy enough you can always increase the load on subsequent workouts.

 

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  • Jon Apr 3, 2017 @ 15:51

    That was a very interesting article. Do we actually get anymore benfit from a negative than a positive? I would guess it would depend on how you use the variables. Thanks for publishing that.

    • Drew Baye Apr 4, 2017 @ 9:38

      Hey Jon,

      All else being equal concentric contractions are more metabolically demanding and eccentric contractions cause more microtrauma. Both are beneficial, but there are situations where you may want to emphasize one over the other. For example, with someone who is very deconditioned or has compromised cardiovascular function you may want to spend more time performing the less metabolically-demanding negative initially.

  • Jacopo Apr 4, 2017 @ 3:40

    Very interesting. It sounds like it’s just a matter of gravity and acceleration: the greater the acceleration the more is the difference between positive and negative strength, and viceversa.

  • Paul Wylie Apr 4, 2017 @ 3:49

    Hi Drew, Interesting article! Thanks for posting. I’ve been using the Negative Emphasied reps 3-4/10 with very good results with clients on Medx equipment. Have you still been using that with your clients? I started the neg emphasied reps after reading Dardens Body Fat Breakthrough. Have you used X Force machines lately?

    Thanks
    Paul

    • Drew Baye Apr 4, 2017 @ 9:31

      Hey Paul,

      I still use these with some clients, but I’m not seeing any long-term difference in strength or size gains between 4/1/4 and 4/1/10.

      I have used X-Force machines, and would strongly discourage people from doing so. They are very poorly designed and the mechanism used to alter the resistance between the positive and negative phases interferes with proper turnaround technique.

  • Michael MacMillan Apr 4, 2017 @ 10:26

    Drew,
    Thank you for addressing a highly misunderstood area. Here are some facts about eccentric muscle activity:
    1) Maximum power for eccentric movement occurs at Zero Velocity (Eccentric movements have a negative velocity).
    2) Eccentrics do not involve cross bridge mechanics but rather the passive elasticity of the molecule Titin.
    3) What makes eccentrics critical to the process of hypertrophy is that eccentric action allows “micro injuries” to occur to the contractile mechanism without major failures. Repairs of these micro-injuries are the primary event to adding new myofibrils, i.e. hypertrophy.
    4) The ‘window of effectiveness’ for eccentrics is between the one rep max at the low end and the point of eccentric failure at the high end. Only an eccentric load within this zone is both safe and effective.

    These just a few observations from working in this area for over thirty years. Don’t be too critical of the X-Force machines, although they are fairly rudimentary they are still the best commercially available negative machines available.
    ………………………………………….Michael MacMillan

    • Drew Baye Apr 4, 2017 @ 10:53

      Hey Michael,

      Thanks for the additional info. The way it was explained to me by Dr. Michael Reedy of Duke University a few years back is,

      “In a nutshell – more crossbridges attach and hang on tightly – due to to either or both causes of recruitment:

      1) backbending distortion of one-headed crossbridges allows the second head of each myosin to attach, and they backwalk a few steps, smoothing the plateau of force that develops in phase 2 of ramp-stretch. (I love this idea, inspired from the Linari paper, but good evidence for it is not available yet.)

      2) all weak-binding M*ADP*Pi heads of myosins that collide with backsliding actin hang on tightly to resist lengthening– and the more generous interface geometry for braking attachments by M*ADP*Pi allows more myosins to attach and evolve into brakes than are able to attach and evolve into purely isometric or shortening motors.”

      No doubt the elasticity of titin also plays a major role in this.

      As for X-Force I’ve tried most of their machines (the ones that weren’t out of order after being in Gainesville for only a few weeks) and there are major design flaws in addition to the problems with the way the resistance is changed during the turnarounds. I wouldn’t use or train people on the X-Force machines if someone gave them to me. I’m not joking when I say I’d junk them or sell them for scrap. A much better option if people want a more challenging negative are purely motorized machines which allow the performance of smooth, controlled turnarounds with no jarring change in resistance.

      Your MaxOut towers were a much better option than the X-Force machines because they allowed the user to select the additional load for the negative and could be attached to much better machines like Nautilus or MedX. It is a shame they are now associated with Barwis.

      • Michael MacMillan Apr 6, 2017 @ 9:31

        Thanks for the kind comments on the Maxout (since morphed into ExMed).
        The “Winding Theory of Muscle Function” was published in 2012. It explains how Titin wraps around the actin molecule and prevents an overload from pulling the sliding filaments apart (Nishikawa KC, et al. Proc R Soc B 2012; 279(1730):981-990). There are some great diagrams.

        • Drew Baye Apr 17, 2017 @ 14:42

          Thanks Michael, I found the full text here and will read it tonight.

  • Glenn Magee Apr 5, 2017 @ 9:25

    Hey Drew,

    We know that Arthur Jones was an arrogant individual who described himself (on Letterman) as being “right of Attila the Hun”. I’m wondering how a collective of intelligent men surrounding him couldn’t convince him that there was no significant friction (practically zero) in an average human joint. I wonder if guys like Mentzer and Darden were too afraid to challenge his assertions on physiology (mostly correct), or if Jones just dismissed dissenters as being intellectually inferior.
    As for Nautilus equipment made in the 70’s and 80’s, what made him choose bicycle chain rather than cable that has much much less friction? And brass bushes rather than nylon (which had been around for 30 years by then)? My memory of using this equipment for 5 years was of the annoying click click of every link and the significant discrepancy between the positive and negative in every machine. It’s no wonder these guys promoted forced reps to level out this discrepancy. I know you have discussed this issue at length several times. It amazes me that there are still equipment manufactures today that are not addressing this issue adequately. I used a new triceps push-down machine the other day and found it riddled with excessive friction and bounce. Apart from about 30′ of cabling, it had 9 pulley wheels.. Not even worth the scrap metal value.
    Appreciate your articles.

    Cheers,

    Glenn

    • Drew Baye Apr 5, 2017 @ 9:46

      Hey Glenn,

      Most of the HIT people, including Darden, Mentzer, and myself, were unaware of the error for longer than we should have been, and many still believe the difference in positive and negative strength is due to friction.

      Ken Hutchins did try to talk with Arthur about the friction problems in many of the machines, but had a difficult time getting him to listen. A lot of this is documented in Ken’s SuperSlow Technical Manual and his articles in the old SuperSlow Exercise Guild’s quarterly newsletter The Exercise Standard.

  • David Sears May 14, 2017 @ 10:20

    Drew,

    What is your opinion on emphasizing the negative by carefully applying manual resistance to the stack on the negative? I’ve tried this a few times when training with my son and really like it. I understand that there is no way to quantify how much resistance he’s adding but it seems to work well.

    • Drew Baye May 30, 2017 @ 23:27

      Hey David,

      It has some usefulness in certain situations but I don’t recommend it in most cases for safety reasons. If it is not done correctly it can be dangerous on many exercises.