Controlling Regressive Joint Angles: A Missing Key in Training

Updated: Nov 30, 2020

What’s going on all! My name is Trevor Merritt and I am honored to be asked by one of my best friends and colleagues, Mikael Ruffin, to write for the Nerdy Athlete Blog. A little background about myself, I graduated from Central Washington University in 2018 with my Bachelor of Science degree in clinical physiology and a minor in physical rehabilitation. After that, I attended Eastern Washington University from 2018-2020 where I obtained my Master of Science degree in athletic training. As far as field experience goes, I’ve had the pleasure of working an externship with the University of Washington Huskies football program, a summer athletic training internship with the Seattle Seahawks, and am now working as a seasonal athletic training intern with the Seahawks for the 2020-21 season.

When I first had my experience with the Seahawks, I noticed the use of specific angular loading when it came to rehabilitation. The concept coming from Dr. Spina and Functional Anatomy Systems (FAS), illustrates maintaining or expanding active motion in joints of the body by placing specific load (force) demands on the tissues that interact with that joint. I could turn this blog post into a novel because this stuff is so awesome to learn and Dr. Spina and his group at Functional Anatomy Systems do an amazing job of teaching these concepts (Check out Andreo Spina on Youtube!).

Quick disclaimer: I am not affiliated with Functional Anatomy Systems and some of the information in this post originated from Dr. Spina and his group at FAS. Other information is pulled from literature cited at the end of this article. This article acts as a brief summary of my interpretation of the information from the authors I have obtained it from. The information in this article is not professional medical advice. Before implementing these concepts, individuals should consult their medical and/or fitness professional beforehand.

For today, I want to focus on regressive angular loading and the mechanical mechanisms and some of the physiological adaptations that occur because of it. In another post in the future, I want to touch on the neuromuscular adaptations and how regressive angular training increases movement efficiency, enhances your brain’s 3D map (or schema) of your body, and how it can decrease chronically tight musculature. For now, to dive into the physical mechanics of regressive angle training we must first understand the force-length relationship muscles have in respect to the joints they act upon. Below is a graph of a typical force-length curve of, for the sake of this post, the majority of all skeletal muscle (Figure 1).

As seen in Figure 1, the majority of the force a muscle produces comes from more or less the middle 80% of our joint’s range of motion. From an evolutionary standpoint this makes sense as most of our activities happen with our joints at or near this range of motion. Additionally, it is well documented that the strength of our tissues (muscles, tendons, ligaments, etc.) is what gives us the resiliency to injury. The more strength our tissues have, the more force they can tolerate before being compromised.

Now the regressive angle refers to the closing angle of the joint in action (i.e. the top position of our knee after flexing our hip towards our chest or the top of a bicep curl when our hand is near our shoulder). In other words, its muscles acting on joints when they are in a shortened position (beginning of the curve in Figure 1). Now why the hell would we want to care about these closing angles if most of our activities happen in our middle ranges? Whether its sports, weightlifting, recreational activities, or regular daily activities we sometimes get ourselves into positions or deal with a force we were not planning on being in or dealing with. Referring back to resilience to injury, injuries happen when the load placed on our tissues from a particular action exceeds our tissue’s capacity to produce force in that position. The more we can “smooth out” this force length curve and train ranges in which we are weak in (raising our ability to produce force at/near our end ranges), the more our tissues will adapt and become resilient in these vulnerable positions.

How do our tissues adapt to contracting and producing force in a shortened position? Well, the majority of the force our muscles produce does not happen in a straight in-line pull or longitudinal manner. In other words, all of the muscle fibers in our bicep do not directly pull on our biceps tendon to flex our elbow. Some of you are asking what the hell do you mean?? This came as shock to me as well when I started diving into the literature. But in actuality our muscle fibers interface with multiple layers of connective tissue in, on, and around our muscles that uses a lateral pathway in distributing force. Let’s dive into some quick muscle anatomy.

Let’s take our bicep for example, our bicep is covered with connective tissue called the epimysium or deep fascia. Inside are groups (fascicles) of as many 150 muscle fibers and the fascicle is covered by the perimysium [1]. Each muscle fiber inside a fascicle is covered by the endomysium which is adjacent to the fiber’s membrane or sarcolemma [1]. A muscle fiber is a collection of myofibrils and inside each myofibril lies myofilaments which contain actin and myosin. Actin and myosin make up what we call sarcomeres which are the basic contractile unit of a muscle. All of the connective tissue (epimysium, perimysium, and endomysium) is continuous with the muscle’s tendon [1], but not all muscle fibers directly attach to the tendon [2]. Some muscle fibers run the length on the entire muscle connecting linearly with the tendon and exerting a longitudinal pull. Other muscle fibers do not have a direct relationship with the tendons, instead they insert themselves on the intramuscular connective tissue or adjacent muscle fibers exerting their forces on them. In addition, multiple bridges of connective tissue including costameres bind parallel sarcomeres laterally and transversely and provide a sort of 3-dementional scaffolding framework [2,3].

This lateral connective tissue framework increases our muscles ability to produce force. One review article looking into multiple studies investigating these lateral pathways found that 30-40% of the force generated by the muscle is not directly transmitted to the tendon, but rather to the connective tissue outside of the muscle [2]. Another review found that 75% of the muscle’s force production was carried out through the sarcolemma along lateral pathways to the tendon [3]. In short, this connective tissue framework provides multiple additional pathways for force to be distributed throughout the entire muscle increasing its ability to produce force while simultaneously acts as a protective mechanism by increasing the muscle’s resiliency to injury because of its increased capacity to withstand force.

So how does all this muscle anatomy talk relate back to why contracting muscles in a shortened position is beneficial?? It turns out that these lateral connections increase in tension as our muscles contract and become shorter and wider. In the perimysium, researchers found that:

“in the middle layer fibers are arranged to form an average angle of 55 degrees in respect to the resting muscular fiber; if the fiber is recruited, the angle increases up to the value of 80 degrees and decreases to 20 degrees if it is stretched. The direction of the collagen fibers therefore changes according to the state of the muscle, confirming how much this part of the intramuscular connective tissue is related to the activity of the muscle itself” [2, 4, 5].

This quote shows us that the angle of pull of the connective tissue in our muscles becomes more perpendicular to the muscle fibers (more lateral stress) as the muscle contracts which just makes sense that if you make a muscle shorter and wider then it would stress out the stuff that connects it laterally. I like to think of this as if you took a bundle of Red Vines licorice, grabbed them on each end, then tried to bring the two ends together in a straight line, you would see the middle of the bunch separate from each other laterally.

This last point here is a cool one, we can strengthen the connective tissue in our muscles! In physiology they call this Davis’s Law which states soft tissue (muscle, tendons, ligaments, etc.) will remodel itself based on the mechanical stresses placed upon it. This isn’t something that happens after a few sessions, but with multiple mechanical stress inputs over time will allow this connective framework to reinforce itself thus becoming stronger and more resilient to injury.

Okay, I know this was a lot for some, so here are some highlights from what we’ve talked about so far:

  • Force-length relationship of a muscle illustrates the ability to actively produce force is typically strongest in its middle 80% range.

  • Resiliency to injury means having the capacity to produce specific forces in specific ranges of motion.

  • Muscles are not one unit of tissue, rather composed of subdivisions of muscle tissue of different lengths densely interlaced with connective tissue and it is the connective tissue that is continuous throughout the muscle to the muscle’s tendon.

  • The connective tissue interlaced within the muscle provides a lateral pathway which force can be transmitted through the muscle and eventually to the muscle’s tendon.

  • This lateral pathway increases the muscle’s ability to produce force and protects the muscle tissue by dissipating force throughout the muscle’s connective tissue framework.

  • Tensile load is increased on this lateral connective pathway in the muscle as the muscle is actively contracted into a shortened position.

  • We can increase the tensile strength of the connective tissue by therapeutically dosing load in these specific positions in order for the connective tissue to remodel itself along the mechanical force demands placed upon it (Davis’s law).

I know this was a lot, and I appreciate you all for taking the time to read this post. This was honestly an awesome experience for me writing this for you all! Please let me know what you think about this topic! Like I said there is more to this concept than just the physical mechanics and later I want to talk about the neural adaptation and eventually ways to apply these concepts to your training. I wanted to write this piece to open up a discussion of what it means to train your body, that our body is beautifully complicated, and how we can give it the right inputs to adapt to what we want it to do. Appreciate you all.

- Trev


1. Haff, G., & Triplett, N. T. (2016). Structures and Function of Body Systems. In Essentials of strength training and conditioning (p. 4). Champaign, IL: Human Kinetics.

2. Turrina, A., Martínez-González, M. A., & Stecco, C. (2013). The muscular force transmission system: Role of the intramuscular connective tissue. Journal of Bodywork and Movement Therapies, 17(1), 95-102. doi:10.1016/j.jbmt.2012.06.001

3. Bloch, R. J., & Gonzalez-Serratos, H. (2003). Lateral Force Transmission Across Costameres in Skeletal Muscle. Exercise and Sport Sciences Reviews, 31(2), 73-78. doi:10.1097/00003677-200304000-00004

4. Trotter, J.A., Purslow, P.P., 1992. Functional morphology of the endomysium in series fibered muscles. Journal of Morphology 212 (2), 109e122.

5. Passerieux, E., Rossignol, R., Chopard, A., Carnino, A., Marini, J.F., Letellier, T., Delage, J.P., 2006. Structural organization of the perimysium in bovine skeletal muscle: junctional plates and associated intracellular subdomains. Journal of Structural Biology 154 (2), 206e216.

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