Tendinopathy in an athletic population
An in-depth review of, and a 6-step protocol for, tendon rehab
In the following article, I will delve into the injury and rehabilitation of tendons in an athletic population. The article represents a collection of all the information I have gathered over the last few years researching tendons, trying to uncover the mechanisms of injury, recovery, and training. I don’t claim to provide an exhaustive review of all available research. Rather, it is a compilation of the info and practices I have gathered and experienced to be most practical and effective.
There is quite some conflicting information and a lot of unknowns surrounding tendons and tendon injuries, however, there actually is some consensus amongst the leading researchers and practitioners regarding fundamental and effective interventions and protocols. This is what I have based my approach on. Additionally, I do use a few protocols that rely more on anecdotal evidence or individual case studies (N=1) but have proven successful in aiding individuals, including myself, in their battle against tendon injuries.
When we look at tendon injuries in an athletic population, there are 2 primary categories: those that result from acute (major) trauma and chronic tendon injuries. While there are various other factors that can lead to tendon injuries such as degenerative disease and the like, in this article I will mainly discuss chronic tendinopathy, which either results from overuse, repetitive overuse without a distinct traumatic incident, or unresolved (minor) trauma. It's worth noting that the rehabilitation of tendons following injuries like full ruptures shares similarities, but these cases often have additional complications like surgery or other damaged tissues making these much more complex processes.
I do want to state that I’m not a medical professional. If you suspect you have a tendon injury, be sure to find a medical professional and get a proper diagnosis before randomly applying the techniques discussed later. Tendon rehab is, unfortunately, a lengthy process and some of the techniques will be inefficient at best for treating other injuries and might elongate your recovery.
In the article I will discuss what a tendon and tendon injury is, how the injury and recovery process look and lastly I’ll discuss a 6-step rehab protocol that I often use with my clients. To me, having a somewhat thorough understanding of the mechanisms behind injury and healing has been a massive help in rehabbing tendons. However, for those more interested in the practical applications, feel free to skip to the last part where I explain the general methodology I use.
We will delve deeper into the particulars of tendon injuries and their various stages shortly, but first let’s have a quick look at what a tendon is.
What’s a tendon?
A tendon is a specific type of connective tissue that plays a major role in human movement by connecting muscle to bone. The tendon is primarily made up of strains of collagen (type 1) and liquid. Its primary function lies in the transmission of force. When the muscle contracts the tendon will pull on the bone and make it move in space or the other way around. The tendon pulls on the bone when the muscle moves and pulls on the muscle when the bone moves. Additionally, it can work like a spring that stores and releases energy from movement.
Delving into the specifics anatomy of a tendons is obviously out of scope for this discussion but there are a few factors that are worth noting for further discussion. Firstly, for optimal functionality, a tendon needs a delicate balance between rigidity and elasticity. The rigidity, or stiffness, is a measure of the tendon’s resistance to deformation this is crucial for transmitting force efficiently. The elasticity, its ability to stretch and return to its original form without permanent deformation, this is essential for accommodating sudden impact without breaking. The rigidity results from the inherent strength collection of collagen fibres that make up most of the extracellular matrix of the tendon, as well as the water stored within the tendon that makes the tendon resist deformation under sudden impact. The elasticity on the other hand comes from the organization of the fibers. When viewed under a microscope in an unloaded state, these fibers have a somewhat crimped appearance when unloaded and they can spring back after stretching under load. Additionally, because these fibres have different lengths the tendon will become stiffer the more it’s lengthened because more and more of the fibers reach their end range.
The presence of fluids within the tendon, as previously mentioned, creates an interesting dynamic. When loaded quickly the fluid has no time to leave the extracellular matrix of the tendon thereby increasing the stiffness by resisting deformation because the fibers have less room to stretch due to increased internal pressure. However, when loaded slowly and over a longer period of time the fluids are pushed out of the tendon, lowering the internal pressure and allowing the fibers to stretch much further. Consequently, the tendon exhibits viscoelastic properties, combining aspects of viscosity, resistance to deformation, and elasticity. Which makes a tendon behave differently under different conditions, i.e. fast loading vs slow and long loading. This can be utilized in training to purposely either work at short and stiff tendon lengths or closer to end-range.
Let’s get into stiffness a bit more. In this context stiffness, as just mentioned, refers to the tendon's capacity to resist lengthening or deformation. Which determines how fast and how much energy the tendon returns after being stretched by movement of either the bone or the muscle. Stiffness assumes a key role when considering tendons from a functional and athletic perspective. A stiffer tendon is better equipped to act as a spring, efficiently storing and releasing energy, essentially adding some free energy on top of what’s created by the muscle. Stiffer tendons often result in a higher movement efficiency, for instance when running or bounding, the tendon will absorb some of the energy from the impact of the body against the ground and will return this to propel the athlete forward. The stiffer the tendon, the more energy is returned, therefore less additional energy is required for the movement. Changing tendon stiffness is one of the qualities we can aim to impact with training.
More isn’t always better, however. As mentioned earlier the tendon also acts as a shock damper, helping to soften the impact of sudden forces on the body by lengthening and absorbing the impact. When the tendon becomes stiffer, its ability to deform and absorb force diminishes. This means the muscle is stretched more, increasing the risk of muscle tears. This relationship works in both directions, if the muscle is too strong relative to the stiffness of the tendon likelihood of tendon ruptures increases. Balancing these factors is critical in optimizing athletic performance while minimizing the risk of injury.
Types of Tendon Injuries
As previously mentioned, the primary focus of this article lies in the discussion of chronic tendinopathy. This often results from an unresolved (minor) previous injury or, more commonly, an overuse injury. Overuse injuries account for more than half of tendon injuries in an active population and are the result of a disbalance between load balance and recovery. Factors like ageing, poor mechanics, muscle imbalance and trauma to the tendon or other parts of the chain can often increase one’s risk for overuse by either increasing the demands placed on the tissue or by lowering one’s loading tolerance.
Before delving into the mechanics, it’s necessary to clarify some of the terminology frequently used when discussing tendon issues: tendinitis, tendinosis and tendinopathy. Now often these are used interchangeably but they have distinct meanings. Tendinitis refers to an injury involving an inflammatory process, indicating an increased level of inflammation in the tissue. In contrast, tendinosis implies an absence of inflammation, and is more indicative of tissue degeneration. Lastly, tendinopathy signifies the broader condition of tendon injuries in which 3 general stages can be distinguished: the reactive stage (or acute stage), the disrepair stage and the degenerative stage. This is a more useful distinction because in an injured tendon we often simultaneously observe inflammatory and degenerative processes. So, let’s look at these stages.
The reactive (or acute) stage is the initial phase immediately after the injury. The stage is marked by the presence of inflammatory cells, and often goes along with swelling and tenderness. It often lasts for about 2-3 weeks, this is the stage that corresponds with the term tendinitis. In overuse injuries, there often isn’t a clear trauma moment, yet we do observe a reactive stage at some point where the “abuse” of the tendon seems to cross a threshold and a sudden flair-up of symptoms is noticed.
If the tendon doesn't undergo sufficient healing during this initial inflammatory stage it will regress into a stage of disrepair or degeneration. These are essentially two points on a continuum of tissue degeneration, with disrepair representing the earlier phase. Both are often referred to as tendinosis. This occurs when the athlete continues to push a reactive tendon, or degenerated tendon past it’s loading capacity. In this stage inflammation doesn’t play a very meaningful role anymore yet can still be present in minimal amounts.
While in these stages there is some remodelling of the tissue, the deposition of collagen often occurs in an erratic pattern along with unwanted nerve in-growth and increased vascularity, increasing the sensitivity of the area.
Understanding the distinction between these stages is crucial for rehabilitation. A tendon in the reactive stages will, more or less, resolve over time if proper rest is taken. Loading a tendon in the reactive stage is often not advised apart from doing some very light movement to stimulate some bloodflow. However, in the case of a degenerative tendon, loading becomes a vital component to restore full functional capacity.
Before we move on to discussing how to incorporate this knowledge, I want to underscore the significance of receiving an accurate diagnosis from a medical professional. Muscular- and other joint injuries can easily be misdiagnosed as tendon injuries, which can lead to slow and ineffective rehab at best but can also aggravate the current injury.
Having said that there are a few telltale signs that can be indicative of tendinopathy in the stage of disrepair or degeneration:
- The pain is felt consistently in the same specific spot (on the tendon) and can often be pointed out quite specifically
- The pain is often only felt when the tendon is in a loaded state
- The pain, initially, becomes worse with increased loading
- The pain decreases once the tendon is warm
- The pain is most noticeable in compressed or lengthened positions
Recovery mechanisms
In this section I’ll expand on some of the key mechanisms behind tendon healing. Whenever we’re dealing with a reactive tendon it is imperative to remember that the inflammation is a critical part of the healing and (unless out of control) shouldn’t be disrupted with icing or anti-inflammatory medication. Additionally, we should keep in mind that the tendon at this point has a decreased loading capacity and needs rest. During the first 3 weeks after injury, or in response to an overuse moment, the body puts down new collagen of a weaker type (type 3) that can tolerate a lot less stress. Which is why its loading capacity is so much less at that point. After 3 weeks this collagen will be replaced by the type 1 collagen which is stronger but needs to go through remodelling before being at optimal strength. During the initial few weeks, light exercises can be utilized to stimulate blood flow, but the main concern is giving the tissue a chance to recover and avoid re-injury. If this stage is executed properly, the athlete should be able to slowly start progressively loading the tendon again after about 3 weeks.
When the new collagen fibers are laid down, they’re not optimally aligned to deal with the forces yet. This takes time, repetition and (heavy) loading. In response to mechanical force being placed on the tendon, the new fibers will align along the direction of the force, approaching a more optimal orientation to resist and transfer force in the future. This alignment is one of the most crucial factors that determine strength in a tendon.
Knowing this explains why rest does not fully restore the tendon. Because rest sometimes decreases sensitivity and therefore pain, it can actually give the athlete false confidence in its loading capacity. We see this often where someone takes a big rest break after a tendon injury, comes back pain-free, and then “re-injures” or to the same degree or even worse than before. A tendon needs load to restore to full capacity because that’s how it aligns its fibers to optimally deal with future forces.
If however, the athlete continues to push an injured tendon, it will go regress into a stage of degeneration. We distinguish 2 phases on a continuum of degeneration. The earlier stage is called the disrepair stage and the later stage is simply called degenerative stage. A tendon in the disrepair stage often has a random pattern of disformated fibers and formation of blood vessels and nerves where previously none were located. This is due to the constant “chaos” of injury and repair. Because these tissues don’t add to the structural integrity of the tendon and increase the sensitivity of the tissue, this is an unwanted situation. Often at this stage, there is still a possibility of full recovery, as long as the negative cycle is broken and the body is given a chance to recover and create new healthy tissue.
If the overuse continues and the injury exacerbates the tendon goes into a degenerative stage. At this point parts of the tendon are completely disrupted, scar tissue has formed and the tissue is structurally weakened. Additionally, the already limited blood flow is reduced even more. Regaining full functionality from this stage is often still possible, however there is some ongoing discussion about whether the damaged tissues can be fully repaired and restored. Historically, the prevailing idea was that the tendons’ slow turnover rate, stemming from their limited blood supply, severely impeded their ability to heal from injury. This led to rehab being focussed on strengthening the healthy tissue, not repairing the injured tissue. More recently however, there has been some evidence that, with proper training and nutritional interventions, tendons may indeed have the capacity to heal and produce new tissue. Practically speaking, apart from putting a bit more emphasis on isometrics, this doesn’t change much with regard to the approach of rehab.
Regardless of the ongoing discussion about the specific mechanisms involved, both camps agree that with proper rehab, nutrition and dedication most tendons can regain functional capacity after injury. Like with any injury however, there is always a possibility of it staying a “weak-spot”.
Before delving into the mechanisms of recovery, I’d like to quickly touch upon the notion of pain and pain sensation, nociception. It’s a curious phenomenon because we see that tendon pain sensation isn’t always directly correlated with actual tendon damage. Understanding this can be crucial for directing the treatment methods.
There are cases in which even after recovery, pain is still experienced. This happens even though there is no damaged tissue anymore. The persistence of pain potentially can be attributed to the brain becoming hypersensitive to any stress in the area that was previously injured, leading to a pain sensation even when there’s actually nothing going on. Additionally, as a result of the old injury there might be lingering alterations in the inhibition or excitability of nerves in and around the previously injured area, changing mechanics and loading. If either of these are case, then part of the treatment should also focus on desensitizing the affected area. The use of auditory feedback during training has been a tool I’ve used to address these issues, which I’ll discuss in the next section.
Rehabilitation
Alright, so let’s get into the nuts and bolts. Rehabilitation of tendinopathy follows a logical and progressive structure. For simplicity, we can categorize the rehab into six different stages that all have a specific goal that builds upon the capacities gained in the previous phase. I’ll go through those phases shortly and highlight a few training tools that match up with the goals of the specific phase. Throughout I will give some example exercise prescriptions with each of the phases. The examples revolve around someone recovering from a patellar tendinopathy.
From a birds-eye perspective, we see there’s somewhat of a chronological order to the rehab process. Initially we’ll focus on stimulating the healing and decreasing pain by removing any excess stress on the tissue. Then we’ll move to re-integrating functional movement patterns and regaining the necessary loading capacity. Once we’ve built up some general capacity we start working on becoming more powerful, fast and sport-specific again. Throughout the steps the objectives will change, however, improving qualities like increasing loading tolerance and movement capacity obviously stays relevant throughout. Therefore it is good to realize that some of these stages might overlap and certain training tools or progressions might be used in multiple stages. The actual rehab mainly happens in stages 1-4, once the athlete moves into the point of power development and sports-specific training, the training process doesn’t differ much from the training of regular athletes that need to develop in these capacities with the remark that load and intensity management needs to be heavily monitored given the athlete’s previous overuse.
It’s crucial to note that we need to start this process slowly and minimize the reaction of the tendon throughout. Having said that a bit of reaction is often unavoidable because the line between under- and over-stimulating is still quite thin. Therefore, I tend to stick to the following rule: some reaction and sensitivity is okay. On a pain scale of 0 (no pain) to 10 (worst pain ever) the pain shouldn’t be more than a 2-3 AND, the tendon should be back to or below pre-exercise pain-levels after about 24 hours.
Lastly, it’s always good to set some expectations. Tendon recovery takes a while. Moving through all stages of recovery can take anywhere from 3 weeks up to 2 years. On average, most people take about 4-6 months to complete the whole rehab cycle. Having said that, some can already resume group training or even competition before the cycle is over and just need to add some extra care throughout their training week. Lastly, although some might never get a 100% back to pre-injury levels of individual tendon strength, it’s imperative to emphasize that there is a difference between full repair, without any traces of injury, and regaining full functionality. Full functionality can be obtained while there are still some minor traces of the injury.
Phase 1: Reduce pain & stimulate healing
The major objective of this crucial phase is to stop aggravating the injury and give the body a chance to start healing. This often means a drastic reduction in training volume. We need to see a decrease in that spike in reactivity and sensitivity of the area. Now as stated previously, this doesn’t always mean completely deloading the tendon. However, this is not the point where we look for strengthening yet, essentially everything that aggravates the tendon at this point is too much. Some movement to stimulate blood flow, or light isometrics, can be appropriate but sometimes a brief break is necessary. Athletes with more chronic conditions often don’t need this break because the tendon isn’t highly reactive and can start with isometrics or move to the second phase right away.
The number one go-to tool in this phase and something that plays an important role throughout the whole process is mid-range isometrics. Not only does it often have an analgesic (pain-reducing) effect but, if executed long enough, it is effective in loading damaged portions of the tendon that thereby get triggered to start healing.
Due to a phenomenon called stress-shielding, the tendon normally diverts forces around the injured area when loaded quickly. The result of this is that the injured area hardly receives any mechanical load which is necessary for its recovery. Isometrics can overcome this by leveraging what we call stress relaxation. As earlier discussed, due to the viscoelastic properties of the tendon discussed earlier, the prolonged application of force makes the tendon relax and lengthen until it reaches a steady state at which all fibres are essentially at full length. This forces some of the load to also pass through the injured part of the tendon, which triggers healing and restructuring.
This is why isometrics are such a great tool for tendon recovery: it allows prolonged stress on the tendon. Getting to the tendon to its maximum length on average takes about 30 seconds, which therefore seems to be a bit of a magic number for isometrics. Longer is fine, though not necessarily better, shorter seems to be less effective. Initially I have my athletes perform their isometrics in mid-range positions to take away any potential provocation of the tendon through compression at end-range positions. I would always prefer them to prioritize making it to the 30-second mark and adjust their position accordingly.
Technically, these isometrics can be done multiple times per day, as long as there is at least 6 hours of rest between other tendon-stressing activities. But I always start conservatively with once a day or even every other day, before increasing the volume. Often, I’ll stick with this protocol throughout the whole rehab process as it’s a very low-stress method that can still be a great supplement in later stages.
Example protocol:
Isometric single leg wall sit: 3 x 30 sec per leg, 90sec rest between sets.
Phase 2: Heavy Slow Resistance
Classically heavy slow resistance training has been the go-to when it comes to tendon rehabilitation. Often the emphasis is placed on the eccentric part but, if the weight is heavy and the movement slow, both the eccentric and concentric parts stimulate tendon healing and remodelling. The force through the tendon helps the tissue align its new and current fibers in the direction of the force and stimulates the creation of crosslinks, making it more resilient and stiffer.
Research suggests that working at approximately 70% of the 1-rep max (1RM) and higher is optimal for generating positive outcomes. Additionally, I tend to stick with about 6 seconds per rep and roughly 5 reps per set. At the proper loading, I wouldn’t expect an athlete to be able to complete more than 6-8 reps at this tempo and weight. If they can, it’s likely that the weight is a little on the light side and they might be understimulated. Obviously, in some cases, the athlete might not be resilient enough to move 70% of 1RM right away and would need some time to progressively build towards it.
There is some research indicating that higher rep ranges might be effective for tendon healing too although this might be explained by the fact that this mimics the stress relaxation effect due to the long time under tension. This might be suboptimal because this method might not provide the optimal force to effectively help the new fibers align, however, there is still a lot unknown around this topic.
Given that this modality of training is often introduced early in the rehab, there is still a risk of reactivity in compressed positions. So, while a greater range of motion is always preferred, if pain-free, initially it might be wise to focus on a shorter range of motion to avoid end-range compression. At this point, the main objective is to load the tendon and stimulate adaptations we’re not too worried about fixing or improving movement patterns, yet.
During this phase, I often prefer to do single joint movements as this allows you to more specifically target a joint and tendon without having to worry about other muscles taking over. Machines, in this case, can be very helpful. The leg extension, for example, is a great way to specifically target the quad- and patellar tendons. Additionally, for similar reasons, I prefer unilateral work at this point as it takes away the possibility of the uninjured or less injured side taking over. For all functional-training fetishists: we’re not too worried about movement yet, heal the tissue first, then worry about movement.
Having said that, this is the perfect time to start addressing mobility, stability or strength deficits in other joints and muscles that might have contributed to the injury. At this point, the total training load is likely reduced anyway which makes it a good moment to start addressing those limitations and set the athlete up for success once we start introducing move sport-specific movement patterns again.
Lastly, along with tempo prescriptions I often utilize a metronome in this phase. Beyond serving the practical application of ensuring the athletes adhere to the prescribed tempo, there’s research suggesting that it aids in “rewiring the brain”. In certain cases, athletes still experience pain after the tendon is healed. This lingering pain might be attributed to the brain linking a specific movement to a previous pain sensation. Using an auditory cue, like a metronome, can assist in rewiring these neural patterns decoupling the pain stimulus from the movement. By synchronizing the movement to an external rhythm, new connections can be formed.
Exercise example:
Single-leg leg-extension, 3 x 5 per leg, 3121 tempo, RPE 8-9, rest 120seconds between legs.
Phase 3: Re-building “functional” strength and capacity
Once the athlete can comfortably load the tendon without any (major) reaction after training, we can start moving on to more sport-specific and full-range movements. At this point, we’ll address potential dysfunctions in these specific movements too. The goal is to re-introduce previously problematic movement patterns and build these up to where the athlete can execute them pain-free through the required range of motion. While there aren’t strict guidelines concerning readiness, a good rule of thumb is that the athlete should be able to execute the movements pain-free before increasing volume and intensity. If this is not the case yet, adding load and power is likely going to make it worse again. The emphasis during this phase is really on restoring volume tolerance more than strength or power. We want to rebuild a capacity base for the next stages.
Movement velocities should be kept relatively low still, and excessive use of the stretch-shortening cycle should be avoided. Keep in mind that tendons respond to force, which is the product of both mass (weight) and velocity (speed), so sudden turnarounds or accelerations increase the stress on the tendon, even at lighter weights. That’s why at this point we’re still cautious with things like bouncing out of the bottom or quick plyo’s. Again, staying with tempo work here can be a good call. Also, the idea of working in a triphasic structure where you move through phases of eccentric, isometric, and concentric focus can be a good tool.
Exercise example:
Barbell back squat, 3 x 10, 21x1, @50% of 1rm, rest 2:00
Stage 4: Build Strength, Power and Speed
Upon achieving pain-free movement and establishing a substantial training capacity we start focussing on rebuilding strength, power and speed. At this point, we can become a bit more aggressive with overloading certain movements and we can start adding speed and power to the training. Initially, I prefer to train concentric acceleration and eccentric deceleration separately before integrating them. Initially, this might mean box jumps and low box landings for instance. While later on this might progress to hang power cleans & high box landings. At this point though, I would start incorporating some lower-impact extensive plyometrics to rebuild some loading capacity in those qualities too.
This is often the point where the phases become much more overlapping. It’s very likely that the athlete can already start including some of these drills while they are still building their capacity back up to their previous levels. For instance, an athlete might be ready to start some lower-level bounding, but might not yet have the resilience to do heavy back squats.
Example exercises:
A1. Bottom-up explosive med-ball squat and throw 3x5
A2. Low box jump down, stick and hold landing 3x4
B. 3x 20 sec of pogo jumps
C. Barbell Back squat, 3x5, 10x1, RPE 9, rest as needed
Stage 5: Developing the Stretch-Shortening-Cycle
At this stage, we start more intensely loading the stretch-shortening cycle again by introducing more explosive plyometrics, lifts and change of direction drills. It’s crucial to recognize that this too needs a progressive build-up and we should continue to build capacity at lower intensities before increasing to more explosive or complex movements.
The requirements for this stage vary significantly between sports. A powerlifter, for example, might have minimal needs for plyometric work and focus their effort more on their capacity in the bottom of a squat, while field-sport athletes would need a much bigger variety of movement exposure.
The goal is to systematically develop the stretch-shortening cycle in a very similar way as we would train any other quality: In a controlled and progressive manner. This is often the phase in which athletes can start or fully or partially resume their training, often at lower volumes initially.
Exercise example
Initially, this might look something like
A1. 3x2 Hang squat cleans @40% 1rm
A2. 3x 20 skater jumps
A3. 3x 1.1.1 submaximal broad jumps
And later on, this might be turned into
A1. 4x2 Full squat cleans @70%
A2. 4x 1+1 depth jump
A3. 4x band-assisted high jumps
Stage 6: Return to sport
During this last phase, the athlete is gradually exposed to their sport at full intensity again. In an ideal scenario, this is done progressively both in intensity and duration. However, this part is often a bit fuzzy and might run somewhat concurrently with the previous parts depending on the severity of the injury and complaints. In sports, especially professional sports, you don’t always have the luxury of waiting until the athlete is completely pain-free. Despite not being ideal from a rehab perspective, athletes can, under careful monitoring of symptoms and load, attempt to concurrently rehab and still participate in their sport as long as it doesn’t exacerbate the injury. This approach may extend recovery time, but can sometimes be a good compromise when there are important competitions or times in the season coming up. In this case monitoring volume and reducing triggers wherever possible becomes crucial.
Objectives of the phase are obviously to get the athlete back to their pre-injury levels (or better) both in terms of physical capacities and competition performance. When running the rehab concurrently with training or competing I would try to bring the sport-specific training back to its core as much as possible and minimize training volume for the injured tendon, while trying to go through the above phases during the strength and conditioning sessions. Monitoring total training load, on- and off-field, is key in these situations. The use of isometrics and slow heavy lifting is, in this case, probably going to be the bulk of your training. As most sports are pretty dynamic already, I would advise to be hesitant adding much more explosive loading to the injured area. But this should be reviewed on a case-by-case basis.
As stated before, the stages often overlap to some extent and aren’t strictly sequential. The duration of each stage depends on the severity of the injury, individual differences, and the effectiveness of the healing process. Each rehabilitation process should be tailored towards the athlete, the injury and the sport for optimal healing and quick recovery.
If you’re interested in applying these techniques to your own training or have any comments or thoughts about tendon injuries. Click on this link, to get in touch!