Excerpted from The Ultimate Isometrics Manual by Paul Wade

Modern athletes (and coaches) are often so wrapped up in conventional methods of training—for example, the focus on picking weights up and putting them down again—that they rarely stop to actually understand the ABCs of strength development.

However as soon as you become cognizant with these fundamentals, you will realize why it is not so bizarre at all that isometrics works as well as it does. In fact, it becomes obvious. So, let’s briefly revisit the science.

We must begin by asking, what makes human beings stronger?

Neurological recruitment and Hebb’s Rule

Several factors contribute to strength development, but the most significant of these is neurological recruitment. Let’s say, for the sake of example, that a muscle has 100 muscle cells. Each of these is connected to the nervous system by a neuromuscular junction, a mini neurological "switch" which turns that cell on or off. This is our strength "hardware".

Individual muscle cells have no "dial" on them—just a binary on-and-off switch. They either fire completely, or not at all. (Biologists call this the all-or-none law.) As a result, how much force a muscle can develop depends on how many of the muscle cells get switched on. How effectively our nervous system can turn on those muscle cells represents our strength "software".

The force a muscle can generate depends largely on neurological recruitment.

Most untrained individuals have terribly inefficient software. They have the same number of muscle cells as strength athletes, but their nervous systems are not as good at recruiting those cells.

So, whereas a strongman or a kung fu master might be able to recruit 80% of his cells, the untrained Joe will only be able to manage, perhaps 30%. (This answers the age-old question as to why some individuals can be small, but far more powerful than much larger men. The small man can have next-gen software, while the larger guy is still working with Windows 2.0.)

Fortunately, anyone can improve the efficiency of their neurological recruitment. You can upgrade your strength software. This can be achieved by forcing as many of your muscle cells to fire as possible—maximal recruitment—and doing this repeatedly.

Doing so causes the neural pathways which make the muscle cells switch on to become more efficient communicators, according to a neurological principle known as Hebb’s rule (later paraphrased by the neuroscientist Siegrid Löwel as: cells which fire together, wire together).

In layman’s terms: repeated maximal muscle contractions are what make us stronger—and the more force your muscles repeatedly generate, the stronger you’ll get. No surprises so far.

But the next question is: how do we make our muscles generate maximum force?

Science has an answer to that one, too.

Muscle force and speed: Hill’s Equation

As far back as 1938 a brilliant English physiologist (and Nobel Prize winner) named Archibald Hill developed an equation which perfectly matched all the empirical data which had ever been gathered on muscle force and contraction:

(F + a)(V + b) = c

 

Where F is muscular force, V is muscular contraction speed (velocity), and a, b, and c are constants.

This equation—actually closely related to thermodynamics—later became summarized as the force-velocity relationship.

Thankfully for non-mathematicians, this relationship is typically expressed in terms much easier to understand than Hill’s Law. As it relates to concentric contractions (where the muscles shorten, as in lifting something up) this relationship can be put very simply:

Where muscle force is high, contraction velocity must be low.

 

In other words, the more force a muscle expresses, the slower it has to move. This is a tried and tested scientific law, but with a little thought, anyone can see that it’s true. Imagine moving an object very fast—like throwing a dart. To achieve high velocity, the force would have to be very low (the small, light dart). Now imagine trying to shift an iron anvil. You would only be able to lift the anvil off the ground very slowly, due to its weight. The more force your muscles produce, the slower they move.

The force-velocity relationship

Hill’s equation and the force-velocity relationship take this to its natural conclusion. If you look at the above graph, you’ll see that when moving an object, the more force a muscle produces, the slower it moves. This cannot continue indefinitely; and when maximal force is reached, the movement stops altogether.

To put this in another way: static muscles are capable of producing more force than moving muscles. Concentric motions—where you lift barbells, dumbbells, and other objects up, moving them through space—can never produce as much force as isometric holds. There is just no way around this.

The more force your muscles produce, the slower they can move any object. It’s physics.

The take-home message of this is revolutionary for the average strength athlete. The conventional methods of resistance training—lifting up barbells and dumbbells—are not the most efficient means to produce muscular force.

Because of the force-velocity relationship, the more force a muscle exerts, the slower it can lift an object: and it can produce more force isometrically—by contracting hard but not moving—than it possibly can by lifting weights up.

It might be said that Hill’s Law and the force-velocity relationship are just "theory": and that during actual lifting, isometrics cannot produce levels of tension or contraction superior to those achieved by moving live weights. In fact, a large body of research supports the fact that maximal isometric holds are superior to dynamic training (or any other known method) in terms of muscle fiber recruitment.

Incredibly, isometric training is capable of recruiting nearly 100% of a muscle’s motor units. In 2001, the Sports Science and Technology Unit (STAPS) of the University of Burgundy organized a series of research trials to discover which mode of contraction—concentric, eccentric, or isometric—recruited the most motor units.

The testing was conducted using cutting-edge electromyography, and the results were conclusive: maximal eccentric muscle contractions reached 88.3%; concentric contractions topped out at 89.7%; the isometric contractions were far more powerful, reaching an astonishing 95.2%.

We know that the final muscle fibers to be activated—the hardest fibers to reach during training—are the larger, Type II fibers: the ones which adapt to produce gains in strength and size. It follows then, that the resistance training method with the greatest power to recruit the largest proportion of muscle fibers will be the superior one. Isometrics is that method. In terms of recruiting motor units, it is peerless.

Unfortunately, very little of this data bled through to the general fitness-oriented public; at least, in the West. In the Soviet Union, it was a different matter—isometrics were taken seriously and used widely by Olympic athletes—with not insignificant benefits.

Isometric training is a superior form of resistance training. Biology substantiates it, physics explains it, and multiple studies prove it. Yes—previously, there have been methodological problems with isometric training: in particular the difficulty in recording the forces involved.

With the advent of the IsoMax however, these problems are a thing of the past. There is no reason not to fully embrace isometrics as a superior scientific strength training tool for the 21^st Century.