Stretching: What its actually doing and its application
Stretching is a common form of physical activity people do to “lengthen” their muscles and attempt to increase their flexibility. People sometimes do see increases in flexibility, but it is likely not for the reasons they think. In this post, I want to go over what is happening during a stretch, why the perceived flexibility is not due to the muscle getting “longer,” and how stretching could really be applied despite its conventional application.
When a muscle is pulled on, it is being pulled into a relatively “lengthened” position. Intuitively, this would make sense as something somebody would do to increase flexibility. The problem here is what is actually occurring during the stretch. As you pull the extremity to its end position, you are causing the muscle itself to tense, acquiring a concentric orientation. Concentric orientation of muscle is associated with internal rotation (IR) and force production. A muscle that is concentric is a muscle that is contracting - the stretch that is being done is promoting more contraction in the muscle itself, and therefore promoting more of a concentric orientation. If we are stretching, we are trying to get the muscle to expand, not contract. Therefore, we can see that stretching is actually not promoting the behavior of muscle that is ideal for our initial goal of acquiring more flexibility. Essentially, if you are trying to improve flexibility by pulling on a muscle, you are likely not achieving flexibility in the muscle itself, but in other joint structures. True flexibility entails no tension on the muscle. If we have tension on the muscle, we are not actually gaining flexibility in said muscle. Think about the people who need to stretch all the time before getting out of bed, working out, or sitting for a long time because it’s the only thing they perceive as providing them relief. Do you ever realize that they never reach a point where they no longer have to do all of that stretching? They always have to do it to accomplish the given goal of increasing muscle length, but if they are stretching so devoutly, they would have improved flexibility in that muscle by now. They do not. Real world examples like this give us insight into what is truly happening with some of the things we do with our bodies and serve as overlooked proof as to the reality of stretching, in this example.
People do tend to see some improvement in flexibility with stretching. Why is that?
The improvement in flexibility we see with stretching is very likely because their skeleton is acquiring a specific position that is beneficial to the person in question. For example, let’s take a wide infrasternal angle (ISA) individual, who I have previously established holds a bias toward extension and internal rotation. This person tends to have tight quads, so they stretch their quads and see improvements in flexibility within a couple of weeks with daily stretching. One might believe that this improvement is because of the muscle having gotten longer, but the real reason this person saw improvements in their flexibility is because the joint acquired a more externally rotated position, something a wide ISA benefits from. When you bend the knee, the distal aspect of the femur will externally rotate relative to the proximal aspect of the tibia, which is internally rotating. A wide ISA that holds a bias towards internal rotation tends to have a bias toward having a distal femur that is internally rotated. Promoting movement in the opposite direction is more favorable for movement gains, and that is likely why the individual in this circumstance saw a benefit from stretching. The skeleton acquired a more favorable position relative to its starting conditions and that has led to improvements in relative motion (mobility) between the joints.
Another potential reason for the increase in perceived flexibility is the effect that stretching has on a tendon’s behavior. Some individuals, like our wide ISA example, have a bias towards stiffer tendons. It does not have much pliability and cannot store energy well. By stretching, the tendon is being elongated and this allows for more pliability of the tendon; it can store energy more effectively because it is more flexible. Stretching creates a yielding behavior of tendon because the tendon is giving way to the force being applied to it. Stretching to improve tendon pliability can be a viable strategy under this context. The problem here is that you are also creating more concentric orientation of muscles, which is something a wide ISA already has a bias towards. When choosing to include stretches in a program, whether it be for a wide or narrow ISA, you must be aware of what it will entail and assess whether this would align with the goals of your program going into things. Don’t do it just to do it.
Rectus Femoris muscle
Credit:
- Complete Anatomy app by 3D4Medical from Elsevier
- Mike Camporini for how he lays it out in his Substack
Muscle is shortening, tendons are lengthening
How to Apply Stretching
Building off of the aforementioned concepts, stretching can be very useful for acquiring the yielding behavior of tendons, or promoting more concentric muscle orientation. For example, the narrow ISA probably benefits greatly from stretching since their muscular bias is one of eccentric muscle behavior. Narrows, especially more active/athletic ones, may have some issues with allowing their tissues to yield, as they are easily compressible due to their pliability. This may result in having a lot of stiffness in their tendons. Stretching may alleviate this tension and give the tendons more freedom of movement, and an improved ability to absorb energy. A wide ISA may benefit from a small dose of stretching too, because of the effect on their tendons, but keep in mind that the concentric behavior associated with stretching may be interference to the goals you may have for a wide ISA trainee. Their initial bias is one of concentric muscle orientation already, so promoting even more of that may limit their ability to acquire a more relative eccentric position of musculature and can hinder their ability to lengthen and contract musculature.
Think about what muscles you would want to stretch (or what joints, rather). Being deliberate with what areas you choose to stretch can have positive effects on movement, and therefore could be useful to include prior to any speed/power work done, or as a potential recovery modality for areas that received heavy stimulus afterwards. For example, stretching the quads and shins with something like a couch stretch can be beneficial in restoring some tendinous qualities and optimizing muscular qualities in certain individuals, and would be useful if done prior to high-speed work. Examples like this are helpful to understand the contexts in which you would choose to pick one stretch over the other, or whether to even have someone stretch at all.
