Stretching and Arthrofibrosis

Sebastiano Nutarelli interviews Nikos Apostolopoulos, author of Stretch Intensity and Inflammatory Response: A Paradigm Shift (2018). Watch the full video below at the bottom of this blog.

Sebastiano: Arthrofibrosis is a fibrotic process involving joints. Today, the focus is on knees, but it can happen in any joint. This can happen for multiple reasons, but what the patient experiences is a loss of range of motion—flexion and/or extension—and quite often a combination of the two. There is also restricted patellar mobility and, ultimately, this sensation of having a stiff knee. This obviously leads to a significantly reduced level of function and independence, impacting daily life in a very relevant way. Biologically speaking, this occurs due to a range of causes, but to summarize: we see unregulated healing. What happens in the final stage is that myofibroblasts—cells that should stop producing scar tissue after healing has occurred—don’t shut off. Instead, in arthrofibrosis, it's like a healing loop that never ends. This results in fibrosis inside the joint, outside the joint, and sometimes even involving the capsule itself, effectively gluing everything down.

So, Nikos—why do you think stretching is helpful overall for patients with arthrofibrosis, and when is it done appropriately?

Nikos: Thank you, Sebastiano. The book I wrote is actually based on my PhD thesis, which looked at gentle stretching. That’s really what microstretching is all about. So why is stretching helpful? Well, I believe that when done properly, stretching can improve range of motion, balance, and posture. It can lead to improvements in movement efficiency and muscle coordination, and to some extent, reduce the risk of injury. The key is relaxation. The other key phrase is “done properly.” What I’ve noticed is that when stretching is aggressive and not supported—meaning it causes pain and discomfort—it can increase inflammation and hinder the body’s recovery and regeneration. This is something I’ve also found through my research, which we’ll discuss later.

When stretching is aggressive and not supported—meaning it causes pain and discomfort—it can increase inflammation and hinder the body’s recovery (see Fig. 1)

Fig. 1: Numerical Rating Scale (NRS) – based on perceived tension

Sebastiano: Yeah, the research background underpins all the material you present today. For us at the IAA, I want to stress that this is crucial. We aim to promote and share knowledge that has scientific research behind it. That’s very important.

Do you think the principles of stretching apply in the same way when considering the health status of different joints?

Nikos: I specifically looked at the parameters involved in stretching: intensity, duration, frequency, and volume—as well as the technique of stretching. I think those are very important. In my work and research, what I noticed is that intensity and technique are the two most critical variables to consider. I’ve worked with professional, elite, and amateur athletes, as well as people suffering from osteoarthritis, rheumatoid arthritis, fibromyalgia, and chronic fatigue. What I found through my research is that if the stretch is held very gently, around a 3 or 4 out of 10 in terms of intensity (tension, not pain intensity), the body responds in a way that doesn’t cause an inflammatory response. As you know, inflammation is something that needs to be reduced to help the joint recover properly.

The key takeaway from my work is that stretching needs to be very gentle. The technique used must also support the body during the stretch.

Sebastiano: So, what do we mean by scar tissue? And also, how does it react to stretching?

Nikos: I define scar tissue as an excessive accumulation of fibrous connective tissue. So, with scar tissue we see an excessive accumulation of fibrotic connective tissue due to myofibroblast activity. In particular, there's an accumulation of collagen as a consequence of chronic inflammatory response. So what’s very important here is how we actually deal with the inflammation in the body—and how we try to help the body recover from what it’s dealing with, whether it’s a disease or an injury.

In excessive scar tissue, there's an accumulation of collagen as a consequence of chronic inflammatory response.

Sebastiano: Can you explain how scar tissue is connected to cells? And also, what are we actually provoking in the body when we provide appropriately prescribed stretching?

Nikos: We need to look at stretching as a mechanical force. The body gains information from its environment—both mechanically and chemically. Here, we’re focusing on the mechanical response: it’s the means by which cells recruit, proliferate, and undergo changes in response to mechanical stress. More importantly, it’s about what’s happening at the cellular level—how the cells interpret the mechanical force and then trigger a biochemical response, which can be inflammation or an inflammatory cascade. Mechanical stress, I believe, leads to fibroblast accumulation. And this is part of an interplay with inflammatory cells.

Excessive mechanical stress—like aggressive stretching—can contribute to the progression of fibrosis by modulating (stimulating) immune pathways

What I’ve looked at is how these immune pathways stimulate the cells to lay down fibrotic tissue. I believe there is a discrete (therapeutic) window—early, specifically the middle phase of wound healing. You have the innate immune phase, then the proliferative phase, and then remodeling. In that second proliferative phase, I think that’s when, if we introduce proper therapeutic interventions (very gentle stretching), it can actually aid in the recovery and regeneration process. Because we’re trying to ameliorate further inflammation in the body. If we apply excessive mechanical stress, it further activates the inflammatory response.

If we apply excessive mechanical stress, it further activates the inflammatory response (see Fig. 2)

Fig. 2: Connection of scar tissue to cells. If we apply excessive mechanical stress, it further activates the inflammatory response.

Nikos: First, we need to understand that the mechanical force from stretching depends on both the magnitude and the rate of the stretch. These two factors can influence the body both macroscopically and microscopically. The key here is comfortable—meaning there's no strain on any other part of the body while you're performing the stretch. That body positioning is essential because it allows the nervous system to stay calm, which directly supports the effectiveness of the stretch and minimizes the risk of triggering protective muscle contractions. This is especially critical when dealing with individuals who are already compensating or have chronic conditions like fibrosis. The second core principle is something I refer to as parasympathetic activation; essentially trying to engage the body's rest-and-recovery mode. Most traditional stretching approaches, especially those done at high intensity or in dynamic formats, can activate the sympathetic nervous system—the “fight or flight” mode. With microstretching, we’re deliberately doing the opposite: trying to bring the person into a calmer, more relaxed physiological state. Because tissue recovery, anti-inflammatory signaling, and proper remodeling of the extracellular matrix all happen more effectively in that relaxed state.

Summary of Microstretching Principles

• Intensity: Low (3–4 out of 10 perceived stretch tension, gentle, like placing your hand in lukewarm water).

• Duration: Each stretch held for 60 seconds.

• Frequency: Performed once per day

• Volume: Three repetitions per muscle group per session.

• Principle 1 – Stability & Control: The body must be positioned to feel safe, supported, and relaxed.

• Principle 2 – Parasympathetic Emphasis and Stretch Sequence: Aim to calm the nervous system and encourage healing by avoiding pain and strain.

This is the concept of mechanotransduction, where the mechanical inputs you're giving (through the stretch) translate into cellular responses—ideally shifting them away from a fibrosis-promoting state toward a regenerative, functional tissue state. The goal is eliminating as much muscle contraction as possible.

For example, if a person is trying to stretch their calves by hanging their heals off the edge of a step (while standing), that, to me, is not a proper calf stretch because the calf muscles are also active at the same time in order to support the body. So you're now trying to stretch a muscle that's active—and that to me is counterproductive. However, with microstretching, you place the body in a position where you offload the muscle that you want to stretch in order to have more control and, more importantly, be able to feel the proper gentle stretch.

Nikos: The second principle looks at stretch sequencing. So when you stretch the origin and the insertion indirectly, then you go into stretching the hamstring muscle, which then becomes a more effective hamstring stretch.

Sebastiano: Can we apply these principles with patients suffering from arthrofibrosis? It’s not a healthy joint; there are a lot of structures that can be fused together: tendons, muscle, capsule, there's scarring, adhesions.

Nikos: Most certainly, you can apply microstretching. Because with microstretching the stretch is very, very gentle, aimed at minimizing any pain in order to eliminate the inflammatory response. If you're supporting your body, you’re relaxing the supportive structures of the joint—the ligaments, the tendons, and the muscles. So when all those are relaxed, the joint actually is less compressed. And compression, I think, is something that we need to look at. So if you’ve got a very tight joint, you’ve got compression in that joint—and how does that affect the cartilage and the cartilage cells? So if you release that compression in the joint by relaxing all the other muscles, you're more likely to help that joint heal.

Sebastiano: Is this all passive stretching? Active stretching? And what is the difference between the two? What do you think is mostly helpful?

Nikos: Very good question. First and foremost, I want to make a distinction between active stretching and passive stretching. In the first diagram, the person is doing an active stretch—basically, they are stretching themselves; it’s performed by them.

With passive stretching, you are allowing somebody or some machine to do the work for you. The leg is supported, which then means the person is less likely to create any contraction in their body.

Sebastiano: It’s a matter of spreading the volume throughout the day and making sure that it’s not too much all of a sudden, but “little and often”—which is the way we frame this out. Not too much of an insult. We just need to convince your tissues to give up progressively.

Nikos: Oh, exactly. It's something that you don’t have to put yourself through pain and discomfort for. Because when you do that, it’s a sympathetic nervous system response. You might be doing something where you're blocking pain out because you believe that if you stretch aggressively, to the point of pain, that means you're going to get better and get the range of motion you want. No, you're not. What you're doing is fighting your nervous system. Your nervous system is designed to sense pain. When it senses pain, the sympathetic nervous system becomes activated, which then increases tension in your body.

And what is the purpose of the sympathetic nervous system? To protect you. Pain is a stimulus that says, "Hold on, this is way too much, and if you continue, you're going to get injured. I'm going to try to prevent that."

A classic example I give to my athletes: if you put your hand on a hot stove, are you going to leave it there? Of course not. So you remove it. The body is no different when you're stretching. It knows pain and no pain, discomfort and no discomfort.

Sebastiano: Thank you for going through this. The overachievers, the athletes, in particular—when they get injured in a way that is handicapping, like arthrofibrosis—they try to do more and more. They feel like they have to make it happen. So having effective strategies, including how to explain what we're trying to do, is really important.

Can you please explain to us, what is the effect of different levels of stretching intensity? What happens if we overstretch or use excessive intensity (force)?

Nikos: I’ve always believed that intensity is the key factor we need to look at. Through my doctoral research, I was able to critically examine this issue. The results confirmed that stretching needs to be done gently. We defined aggressive stretching as an 8 out of 10 intensity—high intensity, great pain, strong awareness of muscle pull. What we examined was something called high-sensitivity C-reactive protein (HSCRP). It's very important because any time you cause a local injury, the body attempts to heal it locally but also releases IL-6 (interleukin-6), a pro-inflammatory cytokine. For IL-6 to be expressed, it requires tumor necrosis factor-alpha and interleukin-1 beta to be released at the site. So, we measured inflammation markers post-aggressive stretching. We had a therapist aggressively stretch the glutes, hamstrings, and hip flexors of participants. We used a randomized crossover trial design—so the participants acted as their own control. What we found is that aggressive stretching resulted in an increase in HSCRP immediately after and 24 hours later. The first study showed that aggressive stretching increases inflammation. The second study asked whether stretch intensity had a dose-dependent association with inflammation. We tested stretching at 30%, 60%, and 90% of maximum perceived intensity (force). Again, using a randomized crossover design, we measured HSCRP. And we found that at 9 out of 10 on the intensity scale, we saw inflammation. So as stretch intensity increased—from 30% to 90%—we saw a higher likelihood of inflammation, both immediately and 24 hours after.

Sebastiano: When you talk about stretching at 3 out of 10, you mentioned intensity—but many clinicians use a pain scale. Is pain a good indicator for excessive stretch intensity?

Nikos: Personally, I tend not to use a pain scale. If I tell someone to stretch at 3 or 4 out of 10 on a pain scale, they may think, "I need to feel some pain—otherwise, it’s not doing anything." Instead, I focus on tension—not pain. But pain is important. According to the International Association for the Study of Pain, pain is "an unpleasant sensory and emotional experience associated with actual or potential tissue damage."

So, when we develop excessive mechanical force during stretching—if it causes pain—it increases the likelihood of sustained tissue damage.

As we've discussed, excessive force in stretching causes inflammation, and it's associated with the release of pro-inflammatory cytokines and an immune response. And if you're activating pain, you're also activating the sympathetic nervous system. The whole purpose of the sympathetic nervous system is to limit the stimulus of pain—it prepares the body to fight, flee, or freeze. So if your patient is visibly generating pain, you can bet you're activating the sympathetic nervous system—and with that, inflammation increases.

Sebastiano: Thank you. So, to wrap up: out of your experience and research, what is the most effective method of stretching that you would recommend?

Nikos: So, based on my research, I believe gentle stretching is the most effective method. It reduces sympathetic nervous system activation, which in turn minimizes inflammation and supports healing and regeneration.