The Ultimate Guide to Achilles and Patellar Tendinopathy

A scientific(ish) review of literature, adapted for parkour training

Author: Kosta Krunić

Video version:


1. Introduction

1.1. Tendon function, stress, and strain

1.2. Tendinopathy Diagnosis

1.2.1. Risk Groups

1.2.2. Pain & function

1.2.3. Training history

1.2.4. Differential diagnosis

1.2.5. Imaging

1.3. Structure

1.4. Pathogenesis

1.4.1. Stress-Strain

1.4.2. Collagen Turnover

1.4.3. Matrix & Cells

1.4.4. Pathology Cycle

2. Rehabilitation

2.1. Treatments

2.2. Mechanical Loading

2.3. Exercise Protocol

2.3.1. Isometric training

2.3.2. Heavy slow resistance training

2.3.3. Energy-storage and release

2.3.4. Return to sport

2.4. Rehabilitation Advice

3. Prevention

4. Parkour Specific

5. Recap & Conclusion

6. Bibliography

1. Introduction

Jumps are a crucial part of most sports and are one of the most attractive and fun activities to perform. It’s no wonder a great jump is a sensational feat. It’s a display of power like no other. Not only that you need strong muscles to perform these feats, but also strong tendons, and arguably their role is even more important in such activities. With all that power comes a great cost, an immense stress on the body, and if it’s not properly addressed, planned, and programmed for, it can lead to overuse injuries and in severe cases ruptures. Tendinopathy is a term describing pain and disfunction of a tendon. It’s a major problem for some of the more traditional sports like basketball, volleyball, football, and athletics (1–3), and maybe even a greater one for the newer sports like parkour (4,5) and tricking due to not fully developed training methodology and coaching system. If untreated correctly, it can end the athlete’s carrier because this condition doesn’t get better by itself. Times heals a lot of things, but not tendinopathy. It is treatable though, but there isn’t an overnight cure, the recovery takes time. In this article, I will explain what tendinopathy actually is and how it occurs, as well as how to fully diagnose, recover, and prevent further pathologies from recurring. The focus will be on patellar and Achilles tendinopathy, but the approach is somewhat relatable for the other ones.

Understanding what’s going on in a tendon on a cellular level, how the damage occurs, and how a tissue adapts is a must when considering a recovery strategy. On top of that, understanding the forces at play in different activities helps us choose the optimal training load for the best rehab results. That is what separates the “copy-paste” programs you can find online that can be a hit or miss, and the “tailored” programs that have consistently high success rates across all patients.

1.1. Tendon function, stress, and strain

For those who don’t know, tendon is an organ that connects a muscle to the bone. It has a purpose of transmitting a force that a muscle generates onto a bone its attached to, which is causing the body to move. (6) They have the role of storing and releasing elastic energy during fast movements, kind of like stretching a rubber band before you send it flying, or compressing a spring before it bounces back. (7,8) That process is called the stretch-shortening cycle, and it enhances the force we produce in our fast movements. It occurs every time we squat down before a jump or swing an arm back in order to throw a ball. During slow movements, less elastic energy is being stored, and even more energy is being lost in the process compared to fast movements, which is one of the reasons they are not as stressful for the tendon. Fast movements, and especially the ones with high load as well, store a great amount of energy and are more stressful for the tendon, and jumps fall in that category. (9,10) To put in perspective, during a barbell squat the peak ground reaction force is around (3-5) times bodyweight depending on the relative weight you’re able to lift. (11) However, during the triple jump, the step phase to be more precise, peak ground reaction force reaches astonishing 15+ times body weight. (12) Knee joint is the main contributor here for dispersion and production of force. Having said this, it’s only natural that the majority of athletes suffering from patellar tendinopathy are involved in jumping activities, though different activities will be hazardous for different body parts. Running for instance is not as stressful for the tendons of the knee, but it is for the Achilles tendon since that’s where the highest load is in that type of movement. (13,14) Something like hockey where an athlete is bent in the hips will be detrimental for hamstring tendon (15), and so on.

1.2. Tendinopathy Diagnosis

How do we diagnose tendinopathy? To answer that we need to look at the pain, function, and training history. To start off, it’s important to note that pathology pain. Many athletes who have pathology don’t actually have pain. Furthermore, a lot of athletes, if not most of the athletes involved in plyometric activities have some level of tendon pathology already present. Just because you don’t have pain doesn’t mean you have perfectly healthy tendons, therefore you should all care about the loads you place your tendons under (16).

1.2.1. Risk Groups

Patellar tendinopathy seems to be a condition developing in adolescence. It’s reported that the majority of male athletes who had pathology at the age of 15 & 16 still had it in adulthood, but only a few athletes developed it from scratch as adults.(17,18) Patellar tendon only fully matures post-puberty, which means we should be quite careful about how we train kids in their early teens. Unfortunately, this is also when training raises in intensity and transitions from play to more serious sports training, thus, this time frame is when the majority of pathology in patellar tendon develops. (19–21) This is not the case with the Achilles tendon though, where the most affected group seems to be middle-aged men. (22) When it comes to sex differences, females, in general, have a lower risk of tendinopathy, probably due to higher estrogen levels which seem to act as a shield, however, after menopause, the risk increases significantly. (23,24) Girls also enter puberty sooner than boys, finishing their growth a few years earlier. By the time training raises in intensity their patellar tendons are fully developed, which altogether makes girls more protected from the early development of patellar tendinopathy. (25)

1.2.2. Pain & function

Pain is probably the worst during stretch-shortening cycle activities. It also increases with load, which means you can squat down slowly without pain, but if you try to jump following a fast squat or load the squat substantially, the pain will arise. Warming up eases the pain, however, if you continue with activity despite that pain, it will increase the following day. It also results in a feeling of “tightness” in the tendons when resting, which is especially true early in the morning (you feel a bit like walking on stilts, especially when walking up and down the stairs). The pain is almost always localized to an area of 1-2 centimeters (1/2 inch), and it does not spread. For the knee joint, it’s mainly at the attachment of the patella tendon, just below the knee cap. It can occur above the knee cap as well, and at the attachment to tibia, although those cases are not as frequent. For the Achilles, the pain is usually in the middle of the tendon, and seldom at the attachment to the heel bone.

1.2.3. Training history

When it comes to training history, if you have practiced too much, too soon, too often, this is a likely scenario. High storage and release of elastic energy, and high loads on the tendon over an extended period are some of the red flags. The most affected groups are jumpers and runners (which includes team sports like basketball, football, etc.), but non-athletes can also be affected. (26) If you suddenly picked up a new sport, changed the type of physical activity from something slow like yoga to a faster one like dancing, this is a risk factor. The tendons are not used to that type of load they develop a pathology. The same goes with changes in surface stiffness, if you’ve been training on grass or in a gym, and suddenly move to concrete. If you’ve switched from a running shoe to a barefoot shoe but kept similar intensity. If you’ve suddenly shortened ground contact time in all of your jumps. In my case, I switched from parkour to athletics suddenly, and even though both are jumping activities, parkour involves much slower ground contact times. That change put a lot of stress on my Achilles tendon which is insufficiently trained in that regime and caused tendinopathy. Tendinopathy also often creeps up on you and appears suddenly. It often arises after a prolonged break that followed an intensive training cycle. If you’ve been away from a sport because of an illness or some other injury, or whatever the case is, and got back with the same intensity, that could’ve resulted in the manifestation of pathology. All of these are risk factors that have to keep in mind.

1.2.4. Differential diagnosis

Now, let’s say you’ve been just lifting weights slowly and get knee pain. It is unlikely it’s patellar tendinopathy, since there we no large load spikes in the tendon, no storage and release of energy. If we exclude all of the aforementioned red flags, we should look at the other conditions and see if they fit the narrative. Likewise, if you’ve been cycling a lot and get Achilles pain, it’s unlikely it’s tendinopathy since there we no high loads on the tendon. It’s possibly a different condition, presumably a peritendon problem caused by the irritation due to tendon gliding. That is why differential diagnosis is important, which means excluding all of the other conditions that similar symptoms might respond to. For example, a large percentage of patients diagnosed with patellar tendinopathy actually have patellofemoral pain syndrome, and its rehabilitation procedure is indeed different. Lastly, there are questionnaires VISA-A and VISA-P for Achilles and patellar tendinopathy respectively, that can be used when evaluating the severity of tendinopathy, as well as tracking the effectiveness of a rehab program. They are useful tools to have even for someone who cannot see a therapist, since low scores on that test most certainly point to tendinopathy.

1.2.5. Imaging

What about imaging, do we need it? Well, no, not really. Even though we have really good tools like ultrasonography and UTC, which are one of the best for tendon properties to date, results aren’t going to be of much use when it comes to treatment. Why? In a scenario where imaging shows you have pathology in patella tendon, but your pain is actually caused by, let’s say patellofemoral syndrome (because pathology ≠ pain), then your rehab would be on the wrong track. That is why clinical assessment might be a better option when we talk about diagnosis. On the other hand, monitoring the pathology through imaging can be a waste of time and money since pain and function are our primary indicators and not the clinical image. If the pain and function are improving, so will the clinical image (27,28).

1.3. Structure

When it comes to structure, there are 3 main components: the cells, collagen, and the matrix. The majority of the tendon is made up of water, but the dry portion is predominantly made of type I collagen. Collagen molecules form small fibers that then bundle together into greater ones and so on, and they reside in the tendon matrix (Figure 1).

Figure 1 - Schematic of tendon structure, taken from Costa-Almeida et al. 2019

Tendon cells (tenocytes) are the ones producing the matrix as well as the collagen. (6,29) They have ways of communicating with each other, and with the surrounding matrix as well. If we load a tendon, the cells will get that information from the matrix via integrin switches and communicate with each other to give a response based on the load type, magnitude and duration (30–32). This mechanosensitivity is not exclusive to tendons, but to bones, muscles, and other connective tissue as well (33). This is the key to tendon rehabilitation from a microscopic perspective. If we load the tendon properly, it can create new tendon material as a response.

One area of a tendon that is of particular interest to us is the attachment to the bone – the enthesis. Muscles and bones have different mechanical properties, there’s an obvious difference in hardness and malleability, so joining the two is always a difficult task. The enthesis tries to make that transition smooth by gradually stiffening the tendon. It is, however, still the most vulnerable section, and most tendinopathies occur at these insertions (34), with some exceptions like Achilles tendinopathy.

1.4. Pathogenesis

1.4.1. Stress-Strain

Tendons have a characteristic stress-strain curve. Elongation of a tendon in sports usually is above 5%, which is a point where microfailures occur (Figure 2). (35)

Figure 2 - Tendon Stress-Strain curve, Jarvinen et. al. 2005

As previously mentioned, vertical load in jumping sports can reach 15x BW in a single leg in the case of the triple jump, or 8-9x BW in basketball and volleyball. With basketball players jumping ~50 times per average during the game (36), and volleyball players ~100 times (37), it’s clear how that can pose a risk for overuse injuries.

Another important role in tendinopathy development is the distribution of load, i.e., not every collagen fiber is under the same tension. That is more exaggerated in patellar tendon, and especially in deep knee flexion. The anterior part of the tendon is under more load than the posterior which is being “stress shielded” (38). Great joint angles also introduce compressive loads on a tendon, which can locally reduce tendon’s tensile strength making it more prone to injury (39). Performing at great muscle-tendon lengths will also increase tensile load substantially (39).

This is why an activity like weightlifting where an athlete catches a barbell in deep knee flexion, with very little room for dampening the impact is posing a risk for pathology. Almost the same goes in parkour for landings in a deep squat.

Figure 3 - Stress-Strain curve of a pathological tendon (orange) vs healthy control (blue), Scott 2015.

When we scan a pathological tendon and examine its properties, it will almost always have lower tendon stiffness (Figure 3) but it will be larger in diameter, thicker (40). In healthy individuals, a thicker tendon means higher stiffness, but since this is not the case it implies that structural changes occurred (i.e., collagen fiber structure becomes disorganized, unaligned). That means that for the same load, the pathological tendon will stretch more, further increasing the risk of tear and contributing to the pathology, but not providing more energy storage because the quality of the tissue has worsened.

1.4.2. Collagen

Loading a tendon triggers an increase in collagen synthesis and collagen degradation for the next 3 or so days (41,42) , and degradation is happening a tad quicker (Figure 4).

Figure 4 - Time course of synthesis and degradation of collagen following an intensive plyometric training session, Magnusson 2010

If the period between these heavy loadings is too short, or the load is too great, the degradation will overtake synthesis of collagen protein, and the net balance will be negative (43). This degradation causes a deterioration in collagen quality, from Type I to Type III, which has weaker mechanical properties, it has less tensile strength so it’s more prone to rupture (44).

How collagen is structured is almost as important as net synthesis (Figure 5). (45) Highly aligned collagen is preferred over more randomly distributed one (46).

1.4.3. Matrix & Cells

Figure 5 - Microscopic image of (A) healthy collagen fibers, and (B) collagen fibers in disarray (yellow arrows) of a pathological tendon. Taken from Khan 2002.

In addition to collagen, other matrix proteins also respond to load, and they are responsible for organization and development of a tendon (47), so the whole matrix starts falling apart in the end.

Karim Khan used this analogy of matrix as a cement holding bricks together, with bricks being the cells. So you can think of this oozing of cement as a matrix losing its structure, and the wall (being the tendon) losing its stability and strength.

Figure 6 - A brick wall (representing tendon) with oozing cement failing to keep bricks (cells) in place thus impairing function of the wall

What happens to cells? Aren’t they regulating both matrix and collagen? Well, this is the issue underlying the whole pathology. Tendon cells die. This is believed to be the main cause of tendinopathy (48–50). They die in an organized and tidy fashion called apoptosis, which is contrary to inflammatory death you might see in a muscle rupture or something. This is leading to the matrix breakdown and the absence of cells is lowering the rate of collagen synthesis thus reducing the rate at which the tendon can heal (51,52).

1.4.4. Pathology Cycle

In summary, these are the hypothesized stages in the cycle of tendon pathology development (Figure 7). Overuse causes apoptosis that leads to degradation of collagen resulting in loss of tensile strength which may lead to rupture if the issue is unaddressed (53). However, rupture is unlikely due to an increase in thickness, and that seems to be the tendon’s way of adapting to pathology (54).

Figure 7 - Proposed stages in cycle of tendon pathology, taken from Murell 2002.

2. Rehabilitation

2.1. Treatments

Rehabilitation of tendinopathy has its set of challenges and it has certainly come a long way over the years. Before the 90s, tendinitis was the general term used for describing this pathology. The suffix “itis” of course denounces inflammation, because the inflammation was thought to be the leading cause (55,56). The problem is, you treat inflammation with resting, anti-inflammatory therapies, corticosteroid injections, and more (57), all of which are quite detrimental in the case of tendon pathology we know of today. Some of these therapies do seem to help because they affect pain rather than function and tissue itself, while others straight up don’t work (58–60). The predicament is that it's uncertain what exactly causes the pain, and we don’t know the exact moment at which the pain goes away. Nevertheless, treating pain without treating tissue is obviously not the best idea because it just masks the underlying problem and can potentially worsen the pathology. On top of that, it is only a short-term solution. However, it can be completely justified if an athlete needs to perform despite q injury, or a patient has a low tolerance to pain and can’t commit to a rehabilitation program.

A couple of non-invasive treatments for tendinopathy that don’t revolve around inflammation seem to have promising results, but there is insufficient evidence for strong conclusions for now.

My own advice would be to stay away from these treatments since it’s a gamble in a way (and costs a lot of money), and to focus your time and attention on what we have almost conclusive evidence on > exercise.

2.2. Mechanical Loading

Now that we know that cells are the key to pathology, and we know about their mechanosensitivity, mechanical loading is our main tool in the treatment. It’s debatable whether or not it’s actually possible to cure the pathology. So far, the evidence for that is weak. However, don’t let that discourage you. We can build new tendon material around pathological tissue, which will be just as strong, if not stronger. A pathological tendon seems to have more healthy material than a normal tendon, although less functional (61,62) That means we don’t have to worry about “bad” tissue, and the priority is not just on generating a new one, but on distribution of collagen within it, thus improving mechanical properties which will restore its function.

Figure 8 - Ultrasound image of a crossectional area of a healthy tendon (A), a tendon with reactive tendinopathy (B), and a degenerative tendinopathy (C). Docking 2015.

To achieve this, the tendon needs to be placed under the optimal load. High enough and long enough to cause adaptation, but not to increase strain and cause further damage. (63)

An increase in tendon thickness (tendon hypertrophy) is the greatest in a region where tendon is under the most load (64–66). That seems to correspond with the regions where pathology occurs. It seems, however, that most likely an increase in tendon thickness, and in tendon’s mechanical properties takes a lot of time, which would explain why rehabilitation of tendinopathy takes so long (66,67).

The first step in rehabilitation is to identify and minimize the load that is causing you pain. That can be something like big jumps and drops, heavy landings, fast change of direction or accelerations & decelerations. Figure it out, remove it or reduce it as much as you can. (68) The second is to figure out the optimal load to use in our rehabilitation. That answer lies in the pain and our knowledge of tendon loads in different exercises. Having some pain during the rehabilitation is completely fine, as long as it is minimal (up to 2-3 / 10 on a subjective scale). Pain the day after the workout is our way of monitoring the intensity, as it peaks around 24 hours post-exercise. To have consistent results, load response tests should be introduced, where you load the tendon the same way every day and see how much pain you feel. The tests should vary depending on the current state of pathology. For the patella tendon, it can be a simple squat, a single leg squat with an elevated heel, or a squat jump. For the Achilles, it can be a heel raise on 1 or 2 legs or a single leg hop. The pain should never be increasing, it should either stay the same or decrease as we increase the load in our training. The increase in pain means the load was too high and you should decrease it for the next session. Remember to change only one thing at a time, whether it’s an increase in load, a change in exercise speed, or an introduction of a new exercise. This incremental progression allows you to optimize the load, and recognize and deal with potential issues if they arise.

2.3. Exercise Protocol

The third step is choosing the exercise protocol. To change tendon properties, the type of muscle contraction doesn’t matter all that much, but what’s important is the overall magnitude of the load.63 Tendon needs to be placed under sufficient load for a certain amount of time. Therefore, something like slow concentric, slow eccentric, and isometric (static) training should induce a positive change in tendon properties.

Eccentrics have been a staple in tendinopathy rehabilitation for two decades, especially for Achilles tendinopathy (69,70). It was one of the first protocols to show great long-term improvements in pain and function, although rehab protocols progressed since then. Both heavy slow resistance training and isometric training were indeed shown to have similar or greater effects than eccentric training in tendinopathy rehab, mostly due to patient satisfaction (71,72). People need to actually stick with the program and do the prescribed loads, and that is more difficult if the program is uninteresting and/or takes a lot of time.

To get an athlete back to their sport, the tendon needs to be prepared for high storage and release of elastic energy and high peak strains. You can’t get that with isometric or heavy slow resistance training. That is when eccentrics and plyometrics (jumping) come into play. Therefore, it is not about which loading you should use, it’s when you use it, and for what purpose.

In line with this, Malliaras and colleagues formulated a 4-stage rehabilitation program.(73) Isometric>Heavy Slow Resistance>Energy Storage and Release>Return to Sport.

I, personally, am in favor of this strategy for both Achilles and patellar tendinopathies. Other strategies work or may work as well (74) and you’re free to try them. There is a great paper titled: “Diagnosing Achilles tendinopathy is like delicious spaghetti carbonara: it is all about key ingredients, but not all chefs use the same recipe”. (75), and I think it sums up this topic nicely. I added my personal touch to these protocols, but you can see the original ones in citations of the blog post.

Table 1 - Different tendinopathy rehabilitation protocols, Taken from Malliaras 2013.

2.3.1. Isometric training

Probably the best at reducing pain both immediately and long term (76,77). It loads the tendon at a steady, constant rate, and it excels at building tissue and improving its properties (78–80). When it comes to load and duration, 4-5 sets of 30-45s isometrics should be performed almost every day in this first rehab stage. Some authors even endorse 2-3 sessions per day. I Recommend doing this 5-6 days a week depending on your activity levels, and maybe performing an additional session 3-4 more days per week if you’re very inactive. Those 30-45 seconds of exercise duration should be near your maximum for that isometric hold. Having a muscle tremor can be a sign of too much load if it’s not a balancing issue. Of course, a little warmup in the form of 2-3 isometric holds of 10-15s should precede the session.

Table 2 - Isometrics for Achilles and Patellar Tendinopathy. *If the leg extension is not available. **Should not be performed at great joint angles as it strains the tendon substantially

These daily isometric exercises should continue throughout the rehabilitation process. -Walking up the stairs every 2nd step is one of my favorite exercises, and I also use it to test pain 24h after the workout. Since it’s purely a concentric exercise I’m mentioning it here as I feel it can be implemented before heavy slow resistance exercises.

2.3.2. Heavy slow resistance training

Its purpose is to build strength throughout different ranges of motion used in the actual sporting activity. You should transition to this stage when more difficult isometric exercises can be performed with minimal pain. Regarding intensity and volume, 3-4 sets of 15RM progressing to 6RM performed every second day are recommended (3 times per week) (72). Progression can lead to the inclusion of multiple exercises thus an increase in volume. Isometrics should be continued on the “off” days to manage pain. During this phase it’s advisable to work on every locomotion deficiency, strengthening antagonist muscles as well. Hamstrings and glutes have an important role in jumping tasks and they should be strengthened accordingly (81,82). Calves take most of the load during jumping exercises, so even if you’re dealing with patellar tendinopathy, you should improve calf strength and function. For Achilles, the function of the soleus muscle could be important in the management of tendinopathy (83).

Table 3 – Proposed exercises for stage 2 of the tendinopathy rehabilitation protocol for both Achilles and Patella tendon

2.3.3. Energy-storage and release

Stretch shortening cycle activities by themselves don’t cause morphological changes (changes in size) in tendons, simply because the time tendons spend under load is too short, compared to isometric training for instance (63). However, plyometrics can most likely cause a change in the tendon mechanical structure, since it can cause an increase in stiffness despite causing no changes in the thickness of a tendon (an increase in Young’s Modulus) (67,84–86). This is a sign of change in collagen organization (87,88).

Reintroduction of these types of exercises is therefore mandatory for athletes looking to return to high energy storage and release activities. Transition to this phase should happen when you can tolerate plyometric exercises (no increase in pain 24h after), as well as when you get sufficiently strong, and that is difficult to quantify. Authors of these recommendations are mentioning single-leg press 4 sets of 8 reps with 150% body weight. Even though leg press is great for scientific purposes since it’s easy to measure and quantify the load, I would have to argue about its efficacy in the athlete’s actual training. Therefore, I suggest the back squat (or front squat if you prefer) for 4 sets of 6 reps with 1.5 times BW, however, the exact numbers depend on an athlete, and may vary significantly.

The exercise choice in this stage is the most important & challenging so far, and should be individualized for every sport, based on the athlete’s movement intentions. Progression should happen from the slower SSC movements of different joint angles and low intensity, to exercises that mimic the joint angles, ground contact times, and forces an athlete is performing at. For example, if we take a look at the knee joint, in athletics it usually operates in the upper range, and seldom reaching 90°, while in parkour most of the jumps are initiated from that 90° angle, but they also go into deep flexion when landing. Exercise choice should correspond to these demands.

This stage of the protocol should not be performed more than 2 times per week at first, as that is the time necessary for the collagen synthesis to complete, and you should carefully progress towards 3 times per week as you adapt.

Stage 1 and 2 of this rehab protocol should still be performed, 2 times per week.

The volume should increase gradually, as tolerated. An increase in volume should happen before an increase in intensity, and both should progress incrementally. Exerted effort can be a regulator of intensity more than a choice of exercise performed; e.g., light hops and maximal hops have drastically different tendon loading rates even though they’re the same exercise. Accordingly, you should exert minimal effort in jumps when transitioning to the 3rd stage, and increase it gradually over time before the introduction of new, more demanding exercises.

The transition from low intensity to higher intensity exercises should happen gradually over a course of a few months.

Table 4 – Proposed low intensity exercises for early phase of stage 3 of the tendinopathy rehabilitation

Table 5 – Proposed high intensity exercises for late phase of stage 3 of the tendinopathy rehabilitation

2.3.4. Return to sport

Getting back to sports training should technically replace the 3rd stage of rehabilitation, which means 2-3 sessions per week should be adequate. This of course depends on a level of demand. The highest loads should be undertaken not less than 3 days apart. This of course should essentially apply to all athletes, not just symptomatic ones. The increase in load should be gradual again. In parkour, since a great part of the sport is plyometrics itself, this is when you introduce greater jumps. Introduction of elevation difference precision jumps, moderate running precision jumps, catpass-precisions, etc. Focus should be on technique and control, with again, raise in volume before a raise in intensity. That means not just a progressive increase in distance, but doing jumps on elevated obstacles first, and progressing towards lowered ones.

Phase 1 of this protocol can still be practiced whenever the timeframe allows it and can be incorporated into this 4th phase as well, either before or after the training session. Phase 2 should be practiced twice per week.

Table 6 - Proposed weekly planning in stage 4 of the rehabilitation protocol

2.4. Rehabilitation Advice

The literature presents this protocol in a very strict, systematic manner, where it’s divided into these 4 stages, strict reps, etc. It has to be, it’s easy to gather data that way, and it’s replicable. However, the adaptation doesn’t happen in stages. The athletes are also not robots that can do everything by the book and researchers know that, so don’t be afraid if you’re not following it faithfully. Sometimes you get sick and don’t train, you go to a party or a concert and jump and dance even if you’re “not supposed to”, or you just decide you want to play or train despite your pain just because you feel like so. Other times, a professional setting might require you to perform movements not favorable for your condition. What you have to keep in mind though is the overall magnitude of load, so if you went wild on couple occasions, just dial it back a bit with intensity and everything will be fine. There is also a factor of technique degradation when you step down from a sport to focus on rehabilitation. In a professional environment this can have terrifying consequences. This is why you must continue to train every aspect of your sport that is not harmful for your tendons (shooting, ball control, flexibility, balance, etc.).

The stages of this protocol are there to give structure, but they are not strict. I don’t advise jumping straight from strict isometrics to squats, or straight from squats to plyometrics. Do some transitional work. If you’re transitioning from stage 1 to 2, try adding one very low intensity exercise to your sessions that has both concentric and eccentric portion. Then gradually raise the load, volume, and number of exercises. Start barbell squats with a pause at the bottom and very slow eccentric for example. You won’t be able to do that for 15 reps as prescribed, but it will be way more effective if you start from that point, gradually increase the speed of the lift, and then adjust for reps according to your level of exhaustion. The same is with plyometrics, first increase the speed of your lifts. Try adding 1-2 low intensity plyometric exercises at the start of each session, and continue increasing the volume until you decide to do plyometric training separately. Do everything gradually!

3. Prevention

Throughout rehabilitation, as soon as we’re done with managing pain in 1st phase, we’re constantly preventing the recurrence of symptoms. The rehabilitation follows guidelines the same way a general training should. The only difference is, in my opinion, that training doesn’t have to be as precise when it comes to load management, meaning you can “push” the intensity up with asymptomatic athletes without having an immediate backlash as you would with someone dealing with tendinopathy. That being said, you can only “push” so far, minding the overuse injuries of course, but more room for “error” makes the athlete’s and coach’s life much easier.

The recurrence of tendinopathy is quite common (89), and reportedly more prevalent in athletes who return to sport sooner (athletes who take longer to rehab have less chance of reinjury). Taking your time with tendinopathy treatment, being patient and trusting the process will definitely pay off in the end.

The key to tendinopathy prevention is of course the optimal loading of the tendons. In regards to that, you need to know the following:

1. The time it takes for collagen to repair after each intensive training session (42,90,91). As we already mentioned, collagen degrades and synthesizes after exercise, and net synthesis is set 36+ hours after. Not respecting this time frame will lead you towards tendinopathy. If the magnitude of the load was moderate, the net synthesis will take place sooner and the risk of overuse injury will lessen. This leads us to our 2nd point.

2. Tendon loads (or at least ground reaction forces) for each frequently performed movements. You have Baxter et. al. (92) tier list for Achilles tendon loads in various movement tasks. For patella tendon we don’t have such a list, but we have various data on loading in horizontal vs vertical jump.

Table 7 - Achilles tendon peak forces and loading rates in various exercises. Taken from Baxter et al. 2020.

Table 8 - Peak forces and loading rates in patella tendon for horizontal and vertical jumping tasks, across multiple studies

From this we can conclude that horizontal jumps are way more tasking on the patellar tendon than vertical jumps, and sudden stops will increase loading rates drastically.

A study titled “Jumper’s knee or Lander’s knee?” (93), a systematic review of landings from both vertical and horizontal jumps and their influence on tendinopathy, found exactly that. Landings are the most concerning part of the jump, especially if you have forward momentum as well.

Figure 9 - Pain monitoring model, taken from Silbernagel & Crossley 2015.

Overall, it seems that quick ground contact or fast change of velocity (be it stiff landing, deceleration, acceleration, or change in direction) will result in a higher loading rate of a tendon. It goes without saying that both vertical and horizontal displacements are major contributors as well, just be a bit more cautious with horizontal ones. Some of the exercises performed in sports are so demanding that some athletes can’t perform them well. If the athlete yields too much or is too slow off the ground the stress is too great for the current level of athlete, and they need to address muscle-tendon strength and/or coordination before attempting to perform at that intensity. Those exercises definitely cause excessive strain of the tendon and place an athlete in the high risk zone (94) (Figure 9) which should be avoided as much as possible. Being moderate with the selection and dosage of high loading rate exercises brings us to our 3rd point.

3. Quantifying weekly volume of intensive movements. Some coaches started counting the number of jumps (using various tools) their players are making during the training/game and it had positive results in a reduction of overuse injuries.(95,96) You don’t have to go that far of course, but the subjective level of exhaustion and performance levels are good enough indicators. If you feel tired, replace an intensive exercise with a less demanding one, or stop completely. Likewise, if your performance in intensive plyometric exercise drops, that is the point where you’ll probably get diminishing returns, and that should be the signal to halt.

4. The time it takes for tendon properties to deteriorate following detraining (97,98). This should concern anyone who took time off training for whatever reason.

Figure 10 - Stress-strain curve of a tendon before, during and after training period (A), and before, during, and after detraining period (B). Taken from Kubo 2010.

Just a month of detraining reduces tendon stiffness by a huge margin (Figure 10) while the neural component of muscle strength stays the same. This means when you get back, you have almost the same power, but your tendons are now weaker and can’t follow up. If you do high intensity exercises at this point it’s a recipe for injury.

4. Parkour Specific

Parkour covers a vast variety of movement tasks: jumping, climbing, vaulting, balancing, rolling, etc. It has both a structured coaching system (parkour classes, workshops) and is free for individuals to train by themselves. Views on what parkour is and how should be trained vary even within a single community, based on the training history of individuals, personal preference, cultural factors, etc. It varies between different communities, and from nation to nation, continent to continent. Because of this great diversity, it’s very difficult to present statistics that should represent the whole sport. However, those statistics are necessary in order to identify issues within a sport and remove the risk of bias.

We have two papers so far that looked at injuries in parkour, and both reported tendinopathy being quite common amongst practitioners (Figure 11). (4,5) To address the possible causes, I will of course make a few assumptions, so take everything I say from now as just a hypothesis.

Figure 11 - Occurrence of injuries in parkour practitioners for Ankle and Knee joint respectively, Grospretre & El Khattabi 2022

Parkour revolves mostly around horizontal movement when we talk about jumping. Vertical leaps are most of the time unnecessary as we use every trick in a book to gain height (we push off the wall, grab a ledge, tic-tac of a pole, etc.). Parkour also introduced “sticking” a jump, which became the golden standard for everyone.

Every catpass must be stuck, every precision jump, every tic tac, every flip.

Most of the jumps in parkour are heavy for the patella tendon, and rarely would you see someone suffering from Achilles tendinopathy, though it’s not impossible.

My guess would be that people who practice tumbling and flipping are more likely to suffer from Achilles tendinopathy due to the quicker ground contact times that are required to perform these feats. That is achieved by calf muscles primarily, and knees are then almost fully straight, which is in contrast to classic parkour jumps where knee extensors are the ones working harder.

From those few studies, we’ve seen that horizontal jumps, especially the ones with sudden stops, are producing much greater loading rates in the tendon. I would really like to know the forces developed when sticking a running precision, or a standing one with a hefty drop. It’s needless to say that these are the jumps that are most demanding for the patella tendons, and the amount of those jumps should be monitored.

The mindset of doing the same big jump 20, 50, or 100 times until you make it is understandable from a “spirit” perspective, but very unwise from the perspective of your poor suffering tendons. My advice would be: Have those excursions with smaller and more technical jumps that are not as stressful and prioritize your health with the bigger ones.

Don’t train big jumps more than 3 times a week. Of course, if you’re only doing a few big jumps per training it won’t be an issue, but try to have a rough idea of how much jumping you did in a week and take proper rest. You can’t improve if you’re injured.

Work on your conditioning! If you don’t have time to train it separately, do it after each training session just a bit. Exercises that were quite popular in the early days of parkour are often criticized for not being specific enough. Even with that, they somehow survived the test of time be it by pure luck or some extraordinary gut feeling traceurs had. Whatever the case is, for some of them I now see the real benefits. Quadrupedal movement is one of those exercises. It seems useless at first, but it works your quads in quasi-isometrics, so it ends up being a great exercise for building patella tendon resilience. It can be argued it does the same thing for shoulders, providing the same benefits for those who do dive kongs for example. Balancing on a rail does the same with calf muscles, traversing does the same for the rotator cuff, and so on.

Gym training has been rising in popularity amongst athletes and I’m a huge proponent as well. Lifting weights has a variety of benefits and I highly suggest everyone to incorporate a bit of lifting into their training. Obviously, training outside can be almost as effective, just requires a bit more out of the box thinking and a lot more training knowledge & dedication to pull off.

Lastly, take it very slowly when you’re coming back after a prolonged break from training (>2 weeks). This is something I see way too often, people want to come back, they start jumping, they get hurt, stop.

Take it very slowly, the first few months should be prioritizing technique and control, and strength and conditioning. I know it can be boring for someone but just think long-term. This can all be avoided if you just never stop training!

5. Recap & Conclusion

Tendinopathy develops due to overuse of tendon tissue if the intensity (tendon loading rates) and volume are too great. Various jumping activities are the biggest contributors to this pathology. Patellar tendinopathy most likely develops in adolescence, so mind training intensity for kids in puberty. Achilles tendinopathy is most prevalent in middle-aged men. Women are less likely to get tendinopathy (before menopause).

A localized pain in the tendon during stretch-shortening cycle activities is an indicator of tendinopathy. The pain increases with load and decreases with warm-up.

Training history can tell us a lot: too much training, training after a long break, and sudden change in training methods are some of the indicators.

Imaging is not that important for diagnosing tendinopathy, as asymptomatic tendons can have pathology present.

The death of tendon cells is most likely what’s initiating tendinopathy, which leads to collagen & matrix degradation. Degraded tissue most likely cannot be repaired, however, creating new one is possible. Tendon cells can sense mechanical loads, so if the stimuli are there, they will create new tendon material. Tendons must be loaded in order to recover, and this is where exercise protocols come into play. Alternative treatments are not a wise option, in most cases it’s a waste of money & time.

What drives tendon adaptation is the overall magnitude of the load, and contraction type is less important. Every contraction type has its purpose though. Isometric excels at building new tendon tissue and relieving pain. Slow resistance training excels at building strength and tendon mechanical properties. Eccentric training excels at building strength at greater muscle-tendon lengths and prepares the tendon for high strains. Plyometric training builds up tendon energy storage capacity, improves muscle function, and prepares the body for the return of high intensity jumps.

In order to avoid recurrence of tendinopathy don’t rush with recovery. Collagen takes 3 days to finish synthesizing, so do high intensity training only 2-3 times per week.

If you took a break from training, return slowly, with a lot of conditioning and only low intensity plyometrics. The tendons will lose a lot of mechanical properties in just a month of detraining, and that is when they’re most prone to injury. Be wary of the overall intensity and volume of jumps, especially horizontal ones. If you want to push repetitions in training, do so with resistance training, not with intensive jumps.

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