What goes up must come down.

If you lift something, you have to lower it.

You cannot participate in resistance exercise without loading an active muscle as it lengthens. It is a full 50% of the lifting equation, and yet so many people spend years in pursuit of muscle strength and size without fully optimizing this phase of their training.

When an active muscle lengthens, this is known as an “eccentric” muscle contraction. These are more casually known as “negative” muscle contractions, and anyone who has spent time in a weight room with some training partners has probably “done negatives” at one point or another.

But why? What’s the point? For what purpose would a person accentuate or amplify this phase of muscle contraction, and how does it fit in with the rest of one’s training regimen?

Can You Feel The Tension?

As is pointed out very clearly in this meta-analysis from Dr. Brad Schoenfeld, the primary components of the resistance exercise stimulus are Mechanical Tension, Muscle Damage, and Metabolic Stress. Mechanical tension appears to be the most important of these three.

Read the detailed study on The Adaptive Triangle

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Mechanical tension is normally represented by “the weight on the bar” in the gym, and there is a good reason that almost every single resistance exercise protocol recommends an increase in weight over time.

More mechanical tension = greater strength stimulus.

More mechanical tension = greater magnitudes of microtrauma to the muscle fibers.

Here are some highlights from Dr. Schoenfeld’s meta-analysis that are pertinent here:

• “Mechanically-induced tension produced both by force generation and stretch is considered essential to muscle growth, and the combination of these stimuli appears to have a pronounced additive effect.”
• “During eccentric contractions, passive muscular tension develops because of lengthening of extramyofibrillar elements, especially collagen content in extracellular matrix and titin. This augments the active tension developed by the contractile elements, enhancing the hypertrophic response.”
• “Passive tension produces a hypertrophic response that is fiber-type specific, with an effect seen in fast-twitch…fibers.”

Preferentially recruiting fast-twitch fibers, enhanced muscle hypertrophy response, maximal strength development…mechanical tension seems to be a keystone of any resistance exercise effort.

So how do we maximize it?

Well, it turns out that every skeletal muscle is able to produce its maximum-possible amount of force—and thus accommodate mechanical tension to its maximum capacity—only in the eccentric phase of motion, as the active muscle lengthens.

Here’s some data to back this up:

This is data from a set of ARX Leg Press performed on January 3rd, 2021 by a thirty-two-year-old male.

The black line depicts the amount of force, in pounds, he is able to produce in the concentric, or “positive” phase of motion. The red line depicts the amount of force, in pounds, he is able to produce in the eccentric, or “negative” phase of motion.

It is clearly seen that as he moves into mechanical advantage and his hips and knees extend, he is able to produce over a thousand pounds at the end of the concentric phase of motion.

This is not to say he could have lifted a thousand pounds of weight—he wouldn’t have been able to move one thousand pounds through his weakest range of motion at the start of the lift—but only that he is able to produce a thousand pounds of force for a moment in time in his strongest position during a concentric contraction.

But look what happens during the eccentric! As he resists the irresistible force and his active muscles are made to lengthen, he is able to produce almost double the amount of force that he produced in the concentric, over two thousand pounds at some points.

This same difference between negative and positive strength exists for every skeletal muscle.

It’s obvious here that if mechanical tension represents the “keys to the kingdom” with regards to the strength and hypertrophy stimulus, there is no better way to maximize it than properly-loaded eccentric contractions.

From Dr. Schoenfeld:

“The hypertrophic superiority of eccentric exercise is largely attributed to a greater muscular tension under load. It is theorized that this is because of a reversal of the size principle of recruitment, which results in fast-twitch fibers being selectively recruited.

This was demonstrated by Nardone and Schieppati, who showed de-recruitment of the slow-twitch soleus muscle and a corresponding increase in activity of the gastroc during eccentric plantar flexion contractions. There is also evidence that eccentric contractions result in additional recruitment of previously inactive Motor Units.”

Safe, maximal eccentrics = maximal mechanical tension = maximal strength and hypertrophy stimulus.

Damaged: Good!

One of the stimuli associated with an increase in lean mass and strength is muscle damage, or “microtrauma to the muscle fibers.”

Because of the way that the actin and myosin filaments overlap during muscle contraction, any time a skeletal muscle lengthens under load there is microscopic damage that occurs to the muscle fiber components.

The greater the mechanical tension on the muscle as it lengthens, the greater the damage.

Why is this good? A few reasons.

First, as this study highlights, the local damage to the muscle fibers provokes a satellite cell response from the body. Satellite cells are undifferentiated cells that only fulfill a need when they’re called upon.

These cells can become new muscle cells and new muscle tissue, and it appears that damage to the existing structure is a powerful stimulus to this process.

Put in a more nerdy way by Dr. Schoenfeld:

“The response to myotrauma has been likened to the acute inflammatory response to infection. Once damage is perceived by the body, neutrophils migrate to the area of microtrauma and agents are then released by damaged fibers that attract macrophages and lymphocytes.

Macrophages remove cellular debris to help maintain the fiber’s ultrastructure and produce cytokines that activate myoblasts, macrophages, and lymphocytes. This is believed to lead to the release of various growth factors that regulate satellite cell proliferation and differentiation.

Furthermore, the area under the myoneural junction contains a high concentration of satellite cells, which have been shown to mediate muscle growth. This gives credence to the possibility that nerves impinging on damaged fibers might stimulate satellite cell activity, thereby promoting hypertrophy.”

Aside from satellite cell recruitment and the ensuing healing response, there is also a benefit from muscle damage in the form of muscle tissue remodeling.

So how do we safely maximize the microtrauma to the muscle fibers? It turns out that eccentric contractions are where the vast majority of muscle damage occurs, and as mentioned above, the greater the mechanical tension on the muscle as it lengthens, the greater the damage.

And it’s not just eccentrics with any level of mechanical loading. High levels of mechanical loading during eccentric contractions induce the strongest microtrauma effect, while low levels of mechanical loading exert little to no effect.

For example, marathon runners are not known for their massive, muscular legs even though they incur a large amount of muscle damage during a race. This is because the mechanical loading is not meaningful enough to provoke the adaptive response.

You need heavy eccentrics. And with ARX, you have instant access to any level of mechanical loading instantly and automatically.

Spring Time

Another aspect of eccentric contractions that has direct applications to explosive power and sport performance is the nature of the muscle-tendon systems responsible for mammalian locomotion, which function both as shock absorbers on one hand, and springs on the other.

When the force exerted on the muscle exceeds the force developed by the muscle, work is done by the stretching muscle and it absorbs mechanical energy in the process—the active muscle lengthening in an eccentric contraction. What happens to that absorbed energy depends on how the muscle is being used.

The energy can be dissipated as heat, in which case the muscle is functioning as a damper or shock absorber—like when you’re walking downhill—or it can be stored temporarily as elastic recoil potential energy and subsequently recovered and added to the force of the subsequent stride—like when you’re running or making powerful strides on ice skates.

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So if a muscle is chronically subjected to eccentric loading, does it respond with increased stiffness of this muscle spring? If so, a stiffer spring could have two impacts.

First, it could act to protect the stretching muscle from stretch overload damage.

Second, a stiffer spring could enhance the amount of elastic recoil energy available in the stretch-shortening cycle, increasing the power output and explosiveness of the ensuing stride.

Regarding the first impact, this is one of the reasons that eccentric training is so valuable for aging populations and the deconditioned elderly. Eccentric exercise programs are huge for retaining strength during the aging process, while also being far more accessible to feeble participants because of the reduced oxygen demand of eccentric work.

Perfect for those who are terminally out of shape, but who need mechanical loading and strength increase.

Regarding the second impact, spring study was a good test of this “thickening spring” hypothesis. After training one group with eccentric loading versus another group with concentric loading, they found that the “increased force production in the Eccentric group apparently stimulated significant increases in isometric strength and fiber size, neither of which occurred in the Concentric group.” They also included a hopping test to see if “thickening the springs” of the participants’ muscle-tendon systems would allow for greater performance in explosive movements. The answer is clear in this chart showing the two groups’ performances at the eight-week followup testing, expressed here as a percentage of their initial test performance:

Along the same lines, this study found that as a result of the increased stiffness—tighter muscular spring—in muscle following eccentric exercise, there may be improvements in sport performance activities, such as jumping. The study compared basketball players trained for six weeks with either high-force eccentric exercise or with a traditional strength/power resistance program, and noted increases in vertical jumping height in excess of 8% in the eccentrically-trained group, whereas those in a traditional resistance training group showed no change in jump height.

The Missing Piece is Found

You now have a new perspective on just how huge eccentric training is to a human’s physical health, strength, and performance.

Properly-loaded eccentrics maximize mechanical tension, the primary driver of the resistance exercise stimulus that provokes the adaptive responses of strength, lean mass retention and gain, and resilience of the bones and connective tissues.

Properly-loaded eccentrics also optimize the physical, structural changes we desire in the muscle tissue through microtrauma to the muscle fibers.

This trauma activates nearby satellite cells along with mediators of the inflammatory response that are necessary to recover, reorganize, and rebuild the muscle tissue over time.

And finally, properly-loaded eccentrics cause the muscles to respond with alterations in the spring properties of the muscle.

This makes them perfect for elderly and deconditioned populations because of the reduced metabolic demand, while also making them perfect for athletes because of the amplification of their explosive power as their “springs” become thicker and stronger.

So when you hear how excited people are that ARX allows for safe, perfectly-loaded, quantifiable eccentric contractions, now you know why!