Stasis Versus Dynamism Part II:
Early Roadblocks to Progression

by Doug McGuff, MD, © 1999

Spinal Cord Reflex Inhibition

The first roadblock to weight progression occurs as the subject progresses from beginner to intermediate stages and happens between the 6th to 12th week of training. What typically happens is the subject will be making rapid progress with big weight increases every workout, but on the next workout will be unable to even budge the selected weight. If you then decrease the weight to that of the previous workout, the client is still unable to move the resistance. This phenomenon occurs most commonly in pressing movements, particularly chest press and leg press. It occurs more commonly in females than males. In females, it tends to occur at around 300lbs of resistance on the Med-X leg press and around 100-140lbs on the chest press. Once this happens the client seems to have trouble with any weight, even their beginning resistance seems unmanageable. I have had many instructors consult me for similar problems. Why does this happen?

The answer, I believe, is a simple spinal cord reflex. We possess pressure receptors in the dermis of our skin. While present all over, they are very pronounced in the palms of our hands and soles of our feet. They provide feedback to our brain and spinal cord about the amount of weight pressing on us. This information is critical to our survival, let me illustrate how. Suppose you are working underneath a heavy object (a car for instance) when the support jack gives way...immediately you bring your hands up to catch the load. As the load contacts your hand, the pressure receptors are activated and the information is relayed to the central nervous system. The instantaneous decision that must be made is "do I push this off of me, or do a try to slip from under the load and escape". If the pressure receptors indicate a manageable load, motor unit recruitment is augmented and you push it off of you. If the pressure indicators indicate an unmanageable load, motor unit recruitment is inhibited and you quickly try to escape the falling load. As a subject progresses, he becomes muscularly capable of handling a load that his pressure receptors still indicate is unmanageable. At this point the pressure receptors feed back to the motor pathways in the spinal cord and inhibit motor unit recruitment. This effect is most pronounced in chest press and leg press because the information from these pressure receptors is also tied in with proprioceptive feedback. The pressure receptor feedback is augmented in leg press and chest press because the proprioceptors tell us the load is oriented in such a way that in can fall on top of our body. Realize the proprioceptors do not realize that the machine is made such that we won't be crushed. The more rapidly a subject is progressing, the more pronounced this phenomenon is when it occurs.

So how do we deal with this when it happens? At the immediate time of occurrence the effect may be so pronounced that you may have to skip the movement. Using some thick bathroom sponges between the hands and movement arm may blunt the pressure receptors enough to disinhibit motor unit recruitment. Another trick, at the immediate point, is to lift the weight for the client and let them begin with a negative. About 70% of the time we find this trick will allow the subject to go at or beyond their usual TUL with a weight they couldn't budge initially. To break this tendency for future workouts, we recommend a few sessions of heavy statics or negative only repetitions. This seems to "reset the thermostat" of the pressure receptors so that the threshhold for inhibition of motor unit recruitment is now higher. We also ask our clients to focus on the sensations at their proximal joints rather than the sensations where the hands or feet contact the movement arm. Our experience with this is extensive enough that I consider this theory substantiated, and I recommend it without reservation.

Sticking Points on Compound Movements

At Ultimate Exercise we love compound exercises for reasons discussed in previous articles. The major disadvantage of these movements is the sticking point that occurs at "minimum moment arm". Minimum moment arm occurs when all joints involved in the movement are at 90 degrees and leverage is at a minimum. The sticking point is like a small hump in the road. When the resistance is modest the effect of the hump is like a molehill. When the resistance becomes more pronounced the effect is mountain-like. It is the difference between pushing a Ford Festiva over a hump in the road, versus pushing a Ford F-350 over the same hump. We noticed this at Ultimate Exercise when our clients would have a sudden 20 second drop in their TUL. Initially, we took this as an indicator of overtraining and adjusted volume and frequency. However, we found this phenomenon to be a false marker of overtraining...adjusting volume and frequency did not fix the problem. Once again standardization proved critical to problem-solving, as we found that the TUL drop was consistently 20 seconds (the amount of time to do a 10/10 SuperSlow repetition). This fact along with the non-random position failure at the position at minimum moment arm alerted us to the problem. The problem was not recovery related, it was equipment related. Med-X, despite being the best equipment available, still has this sticking point problem. Because of the dramatic leverage effect of minimum moment arm this is technically very hard to overcome. However, in the future I hope that it will be overcome so that we can continue to progress weight without changing protocol. Certainly, if my car can incorporate technology that transfers power "from the wheels that slip to the wheels that grip", then we can find the technology to overcome this problem.

So how have we altered protocol to overcome this problem? The answer is combining dynamic and static repetitions. As a subject inroads and becomes weaker, the effect of the sticking point becomes harder to overcome, so that eventually the sticking point cuts them a rep short. The answer is to do the number of dynamic (standard) reps possible followed by a static contraction. Typically, for most subjects this amounts to 3 reps plus a static. Interestingly, once we incorporated this technique the subject's TUL would return to the normal range. Since we use a 10/10 protocol, the effect of internal muscular friction is evenly distributed between the positive and negative portion of the rep. There is 10 seconds of weight plus internal friction, and 10 seconds of weight minus internal friction; thus, the effect of friction cancels out. In a static there is no movement so the contribution of friction is nil. Thus turning the last rep into a static also cancels friction and thus the TUL returns to baseline. As the weight continues to progress, the effect of the sticking point becomes more pronounced and we eventually have to incorporate a 2 reps plus static routine, but again TUL remains fairly stable and we are able to continue to progress resistance. We have used this in advanced subjects with good success, and usually don't find it necessary until weights become quite heavy. Good record keeping using TUL and a standardized protocol should alert you when to try this experimental technique.

Motor Control Deficiency

Recently I have read some debates and discussions of ideal repetition speed. These discussions have been critical of the SuperSlow protocol and it's claim that 10 seconds incorporates the ideal speed range for most movements. Some theorists believe that rep speed should be varied based on the range of motion; that is, short range movements should take 4-6 seconds and long range movements might require 13 or more seconds. The idea being that the motion speed in degrees per second should be the standard, and that protocols that do not account for a constant speed in degrees per second are arbitrary (note that this term is used by Objectivists as a smear: it means "a claim put forth in the absence of evidence of any sort, perceptual or conceptual; its basis is neither direct observation nor any kind of theoretical argument"). The recommendation for 10 second reps is in fact based on perception, conception and direct observation. I will offer a theoretical argument as well. The main determinant of an ideal speed of motion is the size of the motor units (number of fibers per unit) and total number of motor units. The extraocular eye muscles have only 1-3 fibers per motor unit, but there are literally millions of individual motor units that can be recruited in graduated fashion. According to the logic of SS detractors, the eyes have a very short range of motion and thus smooth movement through a full range should only take 1 second. In reality, the extraocular eye muscles can literally go through a perfectly smooth range of motion over 45-60 seconds. In general, muscles surrounding smaller joints have smaller sized motor units but greater total numbers of motor units. With a greater number of motor units, recruitment can be graduated smoothly producing slower, smoother movement. Joints with a greater range of motion tend to have individual motor units that are larger (made up of tens of thousands of fibers), but fewer individual motor units. In this situation movement cannot be graduated as smoothly. Instead power output is massive but less controlled. There is also a rostral-caudal (head to toe) progression, with the upper body having more of the smaller motor unit but greater total units relationship. Thus we can see that while the wrist curl is a very short- stroke movement, the muscles involved have motor units that are made up of fewer fibers but there are hundreds of thousands of motor units that can be recruited in a smooth, graduated fashion. As such, almost any subject can do a 10 second wrist curl while under meaningful load. The leg press has a fairly long stroke, faulty logic would suggest a longer repetition time to hold the angular velocity constant. However, the muscles of the hips and thighs are made up of very large motor units but fewer total number of motor units. As such, controlled, graduated effort is difficult. With fewer total motor units, the muscle is recruited in much bigger chunks so to speak, and slow smooth movement is more difficult. Exceptional subjects can move 10/10 under meaningful load, but most can't move slower than 7/7 after the 3rd or 4th rep. This relationship of motor unit size to total number of motor units is why you can sign your name with your hand, and why you can't sign your name by pinching a pen between your butt cheeks. Thus, we see that 10 seconds is ideal for almost all movements. While certain movements have shorter strokes, this tends to be offset by greater total motor units capable of graduated recruitment. The longer stroke movements tend to have fewer total motor units and thus cannot move as slowly on an angular velocity basis. Thus SuperSlow is not arbitrary, it is conforming to the dictates of reality.

The above discussion has relevance to our discussion of roadblocks to weight progression. As you progress in a set, you recruit motor units in larger and larger numbers, and your ability to move slowly is compromised. This is why it is easier to do a proper SS rep early in the set with reasonable weights. When you are near the end of the set or using much heavier weights, you are recruiting more motor units simultaneously and your ability to control speed wanes. The sticking point problem also augments simultaneous recruitment and can also invoke undesirable speed increases. Once again, a certain number of reps followed by a static seems to be a solution to this problem. Many subjects have a tendency toward motor units made up of large number of fibers but fewer total individual motor units. These subjects recruit in a less graduated fashion. These people are called "motor morons" by Ken Hutchins (someone with cerebral palsey represents someone that is almost totally incapable of graduated motor unit recruitment). Such subjects can do 1 or 2 reps in good form. But as the muscle fatigues, more motor units have to be recruited simultaneously and slow/smooth movement breaks down. I believe these people are physiologically incapable of doing 4-8 rep SS exercise. If you try to enforce standard protocol in these subjects, weight progression can come to a screeching halt. We find these subjects do much better if you have the do 1-3 reps (whatever they are capable of) in perfect form and then simply perform a static from that point on. You can identify these subjects easily: they are the ones whose form comes unglued after the 2nd or 3rd rep. Once you identify this kind of motor control problem, I believe you should recognize the underlying problem and modify the protocol as discussed. This will save your client from months of frustration and feelings of inadequacy. In the article that follows we will discuss how we are experimenting with protocol in accordance with our theories about the changing contribution of various stimuli as a subject progresses.