“Because it’s so hard to pinpoint each of the three muscles separate because the motor cortex area associated to the legs is deep in the motor cortex, we tested the triceps area as a whole. So we found that in runners with tendinopathy, they had increased inhibition. So if you have more inhibition, you have less input arriving at the muscle. And we found that associated with deficit in plantar flexor endurance.”
“People with Achilles pain on one side, we found deficits in endurance on both sides compared to controls. And there was no differences in peak isometric force.”
“We found that there was something happening (increase inhibition), and then we decided to go more specifically.”
“The way that the central nervous system modulates force is in two ways. You can think of as a… Imagine you have a car that you’re trying to pull and you have two people pulling this car and you just can’t move it. So the two people being motor units, the nervous system will have two strategies, either increase the firing rate or the frequency of the action potentials of those motor units or to recruit more motor units so we have more people doing the work and producing more force.”
“So looking at the motor unit firing rates gives us an idea of the neural drive, how much that nervous system is driving that muscle to contract. So that’s what we did in the second study. We looked at increments of force and how that modulation was changing with the increase in force because you expect to have a higher firing rate. And again, we looked at the soleus, the medial gastroc, and the lateral gastroc, and we found that the lateral gastroc didn’t change the firing rate as the torque increased, but we saw an increase in firing rate in both the medial gastroc and the soleus, and in both groups.”
“There was the second study showing that showed there was something wrong with the neural drive, but it was more specific to the lateral gastroc.”
“There was another study that was about force sharing strategies… I think it’s very, very relevant because the triceps surae is a synergist for plantar flexion… And what we know these days, on the newer strategies, is that the nervous system has a partial independent control of each muscle. So it can fine tune and adjust the amount of stimuli to each muscle to adjust for joint stability and control and to distribution of muscle force. And what this study found was that in people with Achilles tendinopathy, they had 28 % lower contribution of the lateral gastroc in force production.”
“As far as what we studied around soleus physiology and the nervous system playing a role in soleus force production, not only our study, but our other studies as well that looked at that, we can’t find anything that justifies the soleus having an altered capacity to produce force.”
“There could be other types of contractions that we didn’t measure, like explosive contractions, or maybe even during running, or other things that we didn’t actually test. But with the things that we tested, there appears to be no difference between the people with and without Achilles tendon pain in soleus neurophysiology.”
“When you bend your knee, you have less tendon stretch because the tendon of the gastroc gets less stretched. You have reduced neural drive to the gastroc and it might be that you have some compensation of the other muscles. It could be that the compensation is not great and maybe that’s why you see the deficits on bent knee positions.”
“It was the foundation of my PhD to say that there might be something else that we need to be looking at instead of just focusing on the soleus as the main driver of Achilles tendinopathy as we have been for a long time.”
“There was another interesting study that tested firing rates but with higher intensity contractions. And they didn’t find anything in the medial gastroc and soleus, and they didn’t find a lower reduction or a lower activity of the lateral gastroc. They found that at higher contraction intensities, the lateral gastroc was working harder. So again, I’m not saying the lateral gastroc is working less. We’re saying that there’s something wrong with it. So it might be that this modulation is altered and it’s impacting the control of the muscles.”
“This altered neural drive that we’re seeing in isometric contractions, we may be seeing this in other types of exercise, like running, for example.”
How the lateral gastroc deficit comes about: “We exactly don’t know that… but one of the hypotheses is that the soleus is a muscle with a huge endurance capacity. It’s a fatigue-resistant muscle. Running is an endurance exercise. With these independent coordination strategies, the muscle that will fatigue quicker will not be the one that is highly resistant to fatigue like the soleus, it will be either lateral gastroc, medial gastroc.”
“When one muscle gets less active, the nervous system has this capacity to readjust the input to maintain the same force. Because we didn’t find deficits in peak force, but there were deficits in neural drive. So it could be that there’s compensation. One muscle increasing to compensate deficits of another muscle.”
“Running is an endurance sport. If you have a muscle like the soleus that has a higher percentage of slow twitch fibers, higher resistant, fatigue resistant muscle, I see it as very hard to see that that muscle will be the most affected because it’s the strongest in the plantar flexors, it’s a high resistance to fatigue and running is an enduring sport. Whereas the lateral gastroc, the medial gastroc have less of that slow twitch fiber and will be more likely to fatigue before than the soleus.”
“Deficit in endurance is something that we’ve been seeing a lot in this population. So I asked clinicians how they address that in the clinic and they said, well, I don’t because they get that from running. So what I don’t understand is if they’re getting that from running, the endurance component, shouldn’t they not have endurance deficits if they’re getting that from running? So I feel that a lot of the interventions that are done for Achilles tendinopathy are tendon-based, like you want to improve function or structure…. So I think that different treatments focus on different things, but we might be failing to address those little things that we’re talking about, like the specific deficits of the lateral gastroc or the endurance deficits that we are seeing in this population.”
“Running doesn’t work the muscle the same way as a calf raise. Even your body weight single leg calf raise will work in a different way than running. You can run for two hours. You can’t do more than 40 calf raises with a single leg. You’re gonna get fatigued. So the muscle work in a different manner. And the environment that you’re working on might benefit your muscle in a different way.”
Training endurance: “One way that I think is easy to do and is being used more and more is a single leg calf raise. I like to do it off the floor instead of off a board or inclined board or a step or something because it’s easier for patients to do if they don’t have a board or you know some people might use a 10 degree board or a 45 degree board… And just do as many as you can. I think that the overall consensus is that we have a metronome to control pace, so patients are hurrying up to do it quickly.”
Endurance calf raise to failure: “I wouldn’t compare with the other side because this is something that has been observed not only in Achilles but in patellar tendinopathy, that sometimes the deficits are bilateral, even in unilateral presentations. So I think that’s a call for a normative data for athletes.”
In Achilles tendinopathy: “The deficits in peak force are a lot more conflicting… The deficits in endurance are a lot more perceived… But I think one of the issues as well is that a lot of the studies measured the peak isometric with the knee bent. So if you’re just measuring knee bent, you’re not working the full capacity because you’re biasing soleus.”
“In terms of muscle adaptation, the knee straight would work all three muscles more efficiently and you’re gonna have higher loads to to do your exercises.”
Minimizing strain early on: “You can also do a standing calf raise with no weight if that’s your starting point because you don’t want to load the tendon heavy, right? So I don’t see myself a specific reason for tendinopathy to do a seated calf raise. I would see it for a soleus strain, muscle strain. You’re trying to really make sure that you’re taking the gastrocs out of the equation so you don’t overload and be provocative with high load in this sense. But in terms of tendon adaptation, tendon strain and even in working the whole muscle, I really don’t see a point of the seated calf raise really.”
Achilles tendinopathy and calf atrophy: “There was one study, that saw a selective atrophy of the lateral gastroc… There was a reduced volume of the lateral gastroc.”
“With the foot position, we were able to selectively induce those changes in neural drive. Exactly as we talked about the foot position in increase the lateral gastroc, the foot position out increase the medial gastroc.”
Calf training study: “Foot position in induced a lateral gastroc hypertrophy ⁓ and the foot position out induced a medial gastroc hypertrophy.”
“One thing that might be good at addressing these deficits in the lateral gastroc could be adding a plantarflexion exercise with the foot in on top of your exercise routine.”
“Hops and jumps and different types of plyometrics work the tendon in different ways. You might be there one or two days a week adding a couple of exercises with the foot in.”
“We use the foot in position, but it’s sort of like you’re rotating your hips inward, not your foot. Your foot is positioned inward, but it’s a straight knee rotating of your whole leg inward and I feel that it’s easier to do on either standing or the leg press. I think the leg press, because of that compression of the leg press, some people might feel uncomfortable on the hips doing it.”
Foot pressure with toe in calf raises: “Trying to go towards the big toe because if you go out, you’re using your your inverters… so trying to make sure that you’re pushing off and your toes are on the ground and they’re not rolling out.”
“What we do see is that, even in healthy population, the lateral gastroc, when you’re doing ramped contractions, the recruitment of lateral gastroc is later than the medial gastroc and the soleus and that’s just how it is.”
Recruitment sequence: “Physiologically, in healthy people, it’s soleus, medial gastroc, and later you have your lateral gastroc coming on board, but we don’t know if that changes with tendinopathy.”
“Everywhere we look, the lateral gastroc is showing that there’s something that’s just not behaving as a control or someone with tendionopathy would behave. The neural drive or the activity or the contribution of force production is different somehow.”
“Another thing that has a good effect on reducing inhibition is eccentric contractions. And you might even explain why Alfredson’s had good success with his Achilles.”
“If the lateral gastric is the muscle with the deficit, the foot position would be enough to increase that activation.”
“The foot in, would increase the lengthening of the lateral gastroc and reduce the medial gastroc.”
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Paper (Selective triceps surae weakness in Achilles tendinopathy: it is time to look beyond the soleus): https://sportrxiv.org/index.php/server/preprint/view/633/1382?utm_source=ig&utm_medium=social&utm_content=link_in_bio&fbclid=PAZXh0bgNhZW0CMTEAc3J0YwZhcHBfaWQMMjU2MjgxMDQwNTU4AAGn5a-uyRWns7A2jHfVNnWCoehQ1PIgL7Ggya2Mz-kjgWM_jghd7BzybyM67D4_aem_62cdO-b2oHquLV5Ie8AmpA
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