Podcast #150: Achilles and Patellar Tendons with Gaspar Epro

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Study with older adults: “I trained the calf muscles three times a week over one and a half years with the Berlin method with 90 % of MVC with older adults… Five times four repetitions. And yeah, they improved their muscle strength and tendons stiffness. ⁓ But it stopped at one point. So there was no improvement after, I don’t know, at 20 weeks or 18, I can’t remember.”

Why it’s harder to grow calves: “It’s less economical to have a large muscle mass in extremities or further away from your centre of the body, because it’s then hard to move. You use more energy and that’s why when you look at animals also… when you look at horses also and quadruped animals, they have all really thin legs, all the masses up there. ⁓ And the main reason, researchers have also thought is this, that it’s less economical when it’s further away. It just will use more energy.”

“Tendon is a biological tissue. It can adapt to some stresses and the stress which we have in tendons is the strain it experiences, or how much stretch is put on it. And the stretch comes from a mechanical load. And the mechanical load in this case is how much the muscle is pulling from the tendon.”

“The tendon is basically like a rubber band between the muscle and the skeletal system. So when you activate the muscle, the muscle shortens, the tension causes a shortening there and this pulls from the tendon and then the tendon stretches. If the stretch of the tendon or the strain is high enough, it causes some damage in the tendon, so your body naturally wants to regenerate. Because otherwise when it would not regenerate, it would rupture at one point and then you wouldn’t be able to transmit those forces to the skeletal system and we wouldn’t be able to walk because there’s no tendon in between.”

“Tendon is like a transmission, a link between muscle and the skeletal system.”

“The more force or muscle we activate, the more force we generate, the more the tendon stretches, basically exactly like a rubber band.”

“Muscle adapts also to mechanical load or metabolic stress as well, but muscle usually needs a bit less load. So you can adapt the muscle with a really wide range of percentages from MVC when you would train… You train with 20 % of your maximum, you still get some muscle adaptation… But tendons, to get this 4.5 or 6.5 percent strain in the tendon, you usually need higher loads and those loads are somewhere at least above 80 percent and of your MVC in an isometric contraction.”

4.5-6.5% strain: “At this 80 or 90%, you can be more or sure that at least these strains are reached.”

“If there’s some damage already in the tendon, tendinopathy or something, then the tendons usually strain more. There’s more elongation in the tendon and the tendon strains more. That means when you would use this 90%, you would be much more forward as let’s say sweet spot for the tendon adaptation.”

“We know that tendon, almost independent of any species, any animals or humans, has its ultimate strain where it ruptures. It’s more or less fixed and when you get them closer to this then it becomes more dangerous to destroy a bit more tendon than you actually want and you be a bit more risk under risk for any injuries.”

“When you need to actually push with 90 % and you have a feedback from a force sensor, then you see that you can’t hold this level so long. It starts to drop at one point. And then you may reach to the area where it’s not beneficial anymore.”

Holding at 90%: “I may be able to hold 10 seconds, but I have also athletes who are not able to hold that so long even (5 seconds)… But usually a normal person should be able to hold 10 seconds, I think. But I can’t give you a certain value there. So that’s why doing this 3 seconds hold, then you can assure that in total you have the volume which you need for Tendon to adapt.”

“So all those creep studies, they’re done on those mechanical testing devices where you can type in there, okay, pull now with 2000 Newtons and, yeah, pull it unlimited. And then you can always get this 2000 Newtons. There’s this constant load on the tendon. But humans, obviously, we can’t hold a constant muscle strength or generate so much muscle strength or newtons of force there for the tendon to experience this strain… It’s what typically is the muscle, the joint moments which a muscle can generate will drop off and then you will not see really a elongation there or that the tendon would get longer and longer and then rupture at one point… I don’t even think that you would be able to get that when you would use electrical stimulation on the muscle. Because it’s still a biological tissue and it’s still, even if you constantly try to get this at one point, it will still reach its fatigue and it not really end at this stage.”

“When you have a dorsiflexed leg, you typically also feel that yeah there’s some passive tension in your calf muscles and the tendon is also not like a soft rubber band if you touch it but when you put your ankle in a plantar flex position then your tendon looks like it’s a soft or it’s like a cushion there.”

“The tendon is slack in this plantar flex position or when you look at knee extension then when the leg is completely straight and there’s no pull on the tendon, then firstly in order to for the muscle when you generate muscle force, first the tendon needs to overcome the slackness.

“You don’t really find much strain also in this slack position. Mainly because in the slack position for the tendon, calf and knee extensor muscles or quads, they are in a really short length. And when we look at the force length relationship, which is a relationship between the muscle or sarcomere length actually, in relation to how much force or tension it can produce, there seems to be an optimal range. it’s more like a parabola where there’s an optimal length of the muscle to produce force. And in the plantaflex position it’s in a less optimal position. So the muscle fibers are a bit too short. If you look at basic sports science and you remember the muscle contraction, you have the myosin and actin filaments in a really short length they are a bit let’s say cramped together and then to make the muscle shorten which it does in contraction there’s nowhere to go almost.”

“In the plantar flex position, it’s the weakest position for ankle to produce force. Even if you willingly push 100,% you still get maybe one third in the plantar flex position comparison to the dorsiflex position, depending on the person. And this determines directly how much strain does the tendon get.”

Adaptation: “The tendon still lags a little bit behind to the muscle… Tendon always adapts a bit slower. It’s a bit less responsive to mechanical loading.”

12 days in a row Berlin Method. Straight leg calf raise. One leg, every day. Other leg 3x per day.

“Half of the guys had also pain.”

“We saw that the tendon strain had increased, especially in this leg, which we train three times a day.”

“And we saw also in the blood also some biomarkers which showed that the damage in the tendon was bigger than tendon could regenerate basically.”

“So it was more like a mechanical damage in the tendon and it remained also when we stopped in the training, the 3 days after this 12 days of training, the tendon strain remains still higher. So it was more long lasting. So that means if you use high volume, well too high volume, the tendon tendon tendon can also reach those areas. So we reached, I think partly where the tendon would have gone towards the tendinopathy.”

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“How many sessions or how many contractions do we actually need in a week? in the end, it wasn’t much about how much time you have between, but you had to have in a week a certain load in total. If you went much over it, you didn’t gain much more. And if you did just enough, you could do even once a week, if the volume is high enough, it would be already enough for the tendon to adapt the same.”

“I would, generally, because I’m a coach as well, I usually keep it in also the typical way two, three times a week.”

“If somebody is coming back from tendinopathy, two to three times a week seems to be quite optimal.”

“Tendon needs a bit time to recover from training… It lags a little bit behind the muscle… If you just look at the protein synthesis. In the muscle it kicks in already, let’s say, less than a day or a day max. In tendon it can take up to two days.”

“The long contractions, I’d use them mainly only in cases when the tendon is already maybe in the first stages of trying to recover from an injury or tendinopathy. Then slowly return back when everything is healthy or closer to healthy, then towards to something like Berlin method or similar types of training.”

“If you’re in a dorsi flex position, you almost reach the optimal length of the sarcomere or the fiber to produce force so you’re more or less all the time on the ascending limb of this parabola curve.”

“The quads however, they are the muscles where the range of motion is so big that you go over this whole curve. So in the middle and optimal area you have the knee when it’s more or less at 120-130 degrees.”

“The tendon is a little bit curved, Achilles tendon. And depending on the measurement or the movement you’re doing, this curvature can play a big role in the strains, or what you calculate. If you take then a straight, measure the length of the tendon as a straight point from this point where you have the ultrasound probe and you’re here where it attaches, then you can easily overestimate the axial strains which occur in the tendon because it’s a little bit curved.”

Maximal strains in isometric contractions: “For Achilles tendon, I typically have seen, I think, six, seven is just a higher range… patellar tendon is typically a little bit a little bit higher.”

Sweet spot of strain: “Men are usually, let’s say, four or five. Females can be five, six.”

Why the patellar strains more than the Achilles: “I’m not sure. Firstly, maybe the overall muscle can be bit stronger and the tendon is also quite short compared to the Achilles tendon. I think it comes down to the strength levels, probably. Because there’s more load there and it elongates more due to this. But I’m not so sure really. To be honest.”

“There’s a high likelihood that with tendinopathy when you go directly at 90 (percent MVC), you’d probably be at a higher level than this sweet spot (for strain), so to say… 90% in this case, will be usually those people are training maybe too high. And then when measuring exactly how much strain is in the tendon using this 90% MVC then you can determine, okay, yeah, this 90 is maybe causing there already 7, 8% (strain). Okay, we measure them now, or we train them now at 60 % and this causes around 5 % strain. Then this could be for this person, let’s say individualized load where they need to train to cause adaptation in a tendon. Because otherwise they would train, get directly into the risky areas and they would just cause more damage than is needed.”

“I coach track and field and if you jump directly in after let’s say a season into jumps and really high loads directly in the start, it just takes two, three weeks when everybody will have tendon pain.”

“In adults, we see like 20, 30 % of adaptation and then we hit the ceiling effect. You don’t get much more there. If the whole tendon would adapt, then we would usually, there wouldn’t be a ceiling at one point. So the tendon should be able to adapt more than what we see, even if we do longer interventions.”

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