The Ratio Of Positive To Negative Strength And Implications For Training

While writing the article on the force-velocity curve and it’s implications for training  it occurred to me that it contradicted the claims of Nautilus inventor Arthur Jones of a specific ratio of positive to negative strength. I considered mentioning it in that post, then decided it I ought to save it for a separate article, then forgot about it since I did not add it to my “to write” list. Thankfully, Ryan Hall reminded me of this recently. In reference to the force-velocity curve graph below he wrote,

…as long as the eccentric component is relatively slow, ie. not dropping the weight, eccentric strength is more along the lines of 180% greater than static strength. What would have more of an impact would be the speed of the concentric component, as force drops off precipitously with even small increases in velocity. This looks like another Jones guess shown to be incorrect.

The Force-Velocity Curve

Take a look at the right side of the graph above showing the drop in muscle contraction force as contraction velocity increases. It is obvious the ratio of positive to negative strength is dependent on concentric contraction velocity. The slower the positive phase of a repetition is performed, the smaller the difference between positive and negative strength, the faster, the larger.

If you graph the ratio of eccentric to concentric strength at different muscle contraction velocities, you’ll see the difference between the two increases rapidly as speed increases. It is important to keep in mind that even relatively fast speeds during strength training are slow compared to how fast you can move when you are not working against significant external resistance. Most repetition speeds occur at contraction velocities towards the left of the graph. It is also important to keep in mind this ratio can vary between muscles based on fiber type, can vary with body temperature, and that the same contraction velocity can result in different joint angular velocity or exercise movement speed depending on muscle length, fiber arrangement, and musculoskeletal geometry. Realize the graph below is a rough estimate based on averages and was designed to show how much the ratio of eccentric to concentric strength varies with concentric contraction velocity, rather than an attempt to provide exact ratios.

Eccentric to Concentric Strength Ratio Curve

If the ratio of eccentric to concentric strength increases with concentric contraction velocity, the greater your speed of positive movement the less resistance you can use and the more your muscles will be underloaded during the negative. Conversely, the slower your positive speed the less your muscles will be underloaded during the negative. However, because the positive is more metabolically costly than the negative, the longer the duration of the positive movement the more fatigued you will be between negatives. The optimum positive movement speed is probably somewhere in between; slow enough to minimize the difference in positive and negative strength without being of such long duration that the fatigue occurring during the positives significantly reduces the resistance that can be used.

Since most studies comparing the effects of eccentric and concentric contractions on muscular strength and size show the negative to be more effective, and of the few studies comparing positive-emphasized to negative-emphasized repetitions most show better results with negative-emphasized, I suspect the optimum positive movement speed is somewhat less slow than the negative, however more and better research is needed. I would be interested to conduct a study done somewhat along the lines of what I suggested in my recent post on The 21 Convention, comparing time and work matched protocols using varying ratios of positive to negative duration. I have discussed the possibility of this with James Steele and hope we are able to put something together eventually. I suspect either negative-emphasized or SuperSlow reps (equally slow positive and negative) may end up being the best way to train, however Ryan Hall recently mentioned a study in which positive-emphasized reps were more effective than negative-emphasized.

Another consequence of this is that for machines like the X-Force which hyperload the negative how well they balance the difficulty between the positive and negative depends on the cadence used. I think if the goal is to match the difficulty of positive and negative work, however, the only way to do this is with the accommodating resistance provided by machines like those made by ARX.

Although it probably only applies to a very, very small number of readers, if anyone out there is still doing infimetric training (working contralateral muscles against each other instead of using external resistance) this would also suggest you should move as slowly as you can without segmentation.

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