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“You can get just the same benefit, if not slightly better, by going low volume, low frequency, but high intensity loading [compared to daily calf raises].”
“We want to see, if you improve function and capacity, does that take care of the pain response? And broadly speaking, it did, but not everybody responds at an individual level.”
“The muscle knows the difference but the tendon might not know the difference between a iso/con/ecc, it just senses tension and load.”
“Strain of between 4.5-7%, that seems to be the sweet spot for the tendon to improve its mechanical and material properties.”
“The force required to achieve that zone of strain may differ from person to person so somebody might have a super strong calf but have a tendon that hasn’t got good mechanical properties and their 90% of their maximal force might overshoot that zone and they might hit 9 -10% strain. Maybe that’s adaptive, they might get some adaptations. Whereas, somebody else, their maximal force may not be enough, they may not be strong enough to get that strain, it might be 4% strain. So they may need to prioritize hypertrophy and improving the force capacity of the calf first in order to hit that zone of strain. But, in terms of clinical symptoms, they may still get better by just doing some calf loading at least, to start the process. But if we’re dealing with competitive athletes that want to get back to competitive sport, we certainly want to improve the tendon mechanical and material properties as well as the force capacity of the whole unit.”
“I don’t think there’s been any study that’s shown there’s been an improvement in tendon stiffness from doing those long duration isometric holds [30-45 seconds].”
Isometrics: “Normally like 3-6 seconds is what I’m shooting for.”
“If you’re trying to adapt the tendon positively, each rep should take about 5 or 6 seconds if you’re going concentric-eccentric. Or if it’s isometric, at least, try to get a minimum 3 second hold.”
“If someone has an Achilles tendinopathy and they’ve got a low baseline, any bit of landing is probably gonna reset the tendon, reset the tenocytes, promote a healthier, more orderly inflammatory response (tenocyte-inflammatory cells-matrix interaction).”
Strain: “It’s 10% or more [in jogging]. If you’re sprinting, it’s probably 12-14%. If you just rely on running to adapt the tendon and you’ve got poor mechanical properties… it’s probably not gonna be the right stimulus to adapt it. It needs probably some support in the form of calf loading, if you’re dealing with a vulnerable tendon.”
“When you’re doing plyometrics, you’re getting double digits of strain as well. Plyometrics, on its own, doesn’t seem to be enough stimulus to improve tendon stiffness. It improves other qualities: coordination around the joint, muscle morphology, etc.”
Plyometric-tendon stiffness studies: “However, you do need good tendon stiffness to be good at plyometrics.”
“When you go from medial gastroc MTJ to calcaneus, it’s not a straight line because the tendon actually curves.”
“A healthy tendon is unlikely to rupture. There is underlying pathology there, silent tendinopathy. You have a heightened amount of collagen re-synthesis going on but the tendon isn’t sore or painful yet.”
Perfect storm for a rupture: “Poor tendon quality tissue, poor control of an explosive movement, poor mechanics and coordination of the foot/ankle complex.”
Achilles rupture: “They probably land slightly plantarflexed and they haven’t got the pretension and the optimal length-tension relationship of the calf muscle complex to put the brakes on properly.”
“When you do an explosive contraction of the calf muscles, you get muscle gearing, so you get a rotation of the fascicles, and that causes the muscle to bulge, and that might contribute to the transverse strain at the proximal area of the tendon. And if that happens as you hit the ground at the right time, that might be enough to pretension to whole muscle-tendon unit and maybe reduce some of the longitudinal strain at the mid portion area, which is the common site of rupture.”
Muscle gearing: “When it’s very very fast, the muscle fascicles, instead of just shortening, they tend to rotate… whereas, you get into more top end sprinting or steady state running, the muscle starts to behave more quasi-isometrically… But when it’s something very fast and explosive, you get that rotation of the fascicles. So basically the muscle itself shortens more than the actual fibers shorten.”
“If you’re jumping or accelerating, you get that [tendon] catapult response. When you do something cyclical (top end sprinting, running, repeated hopping), you get more isometric behavior and more energy storage in the tendon, and it’s more efficiency at that stage. When you’re doing some deceleration or landing work, you get a rotation of the fascicles the opposite way. The muscle will actually increase its length longitudinally, so the fascicles will rotate before they stretch. So the tendon stretches and then the energy is dissipated through the muscle and the fascicles will rotate longitudinally before they lengthen [in healthy circumstances].”
“With your medial and lateral gastroc, you’ve got a unipennate fiber arrangement. With the soleus, you’ve got a multipennate arrangement so the actual pennation angle varies throughout the region of the muscle. Distally, mid portion, and proximal.. It’s a lot more pennated as you get more towards the mid portion of the muscle belly. Less pennated maybe at the more distal region of it at the MTJs.”
“The anterior (deeper) compartment is designed a little bit more for excursion… whereas the posterior (more superficial) compartment, as a whole, is designed for high force, behaves a little bit more isometrically.”
“There’s a lot of independence within the soleus muscle among its compartments.”
“The soleus is a very clever muscle. Small fascicle lengths, very large physiological cross sectional area so it’s capable of producing massive forces. By far the biggest contributor of force of the lower limb muscles during any sort of athletic task.”
Soleus: “No matter what your task is, if you go slow or high, it’s able to adjust its fiber length in order to stay on its optimal region of the force-velocity curve. It’s not designed for fast contractions, it’s able to contract slowly.”
Knee going straight before rupture: “Certainly that could upset the uniformity of strain within the layers of the tendon…. A healthy tendon has a lot more displacement of the deeper layers that come from the soleus. Older people and people who’ve had a tendinopathy, that starts to reduce, so they have a lot less displacement from the soleus fibers and the tendon as a hole probably strains in a more uniform manner, which means there’s less variation and a lot more strain concentrated in the same area that’s repeated over and over again.”
Achilles repair: “When the surgeon repairs it, they can’t restore that rotation, they have to stitch it up where they can so it becomes a bit more linear so you probably lose that spiral formation… The medial gastroc tendons to suffer the most, you see the biggest amount of atrophy… we also see a big loss in soleus force output as well that takes a while to restore.”
Post rupture repair: “You have a big architectural adjustment, the tendon loses tension, the slack length from the medial gastroc increases and it doesn’t have that crossover to the opposite side (where a normal tendon inserts).”
“There is some force sharing within the triceps surae complex (gastroc and soleus) but there’s also some independence as well.”
“Given the complexity of architecture of the soleus, if you do the same calf exercise straight leg, whether you’re getting the same tissue loading across all regions of the muscle and whether maybe you get something different if you do a bent knee or permutations of knee angle and foot position, and also varying the strain and the shear between the subtendon fascicles and maybe the aponeurosis of the soleus and the gastroc.”
Seated calf raises: “It’s an exercise that can be prescribed and executed poorly.”
“If you do a seated calf isometric test on a force plate, competitive sport person will probably hit peak force of more than twice bodyweight, recreation might hit 1.5 times bodyweight.”
“Tendon is mechanically sensitive (very sensitive to mechanical loading) and metabolically active (sensitive to other things going on in the body, genetic, inflammatory conditions, etc.)”
“When someone gets a tendinopathy, you get maybe a non-resolving inflammatory response that alters the signature of the tenocytes. They become a lot more catabolic and degradative in nature. You get that mismatch of the MMPs and the tissue resolving MMPs.”
“Exercise can help to preserve fibril diameter as you get older and also help to control or slow down those non-enzyme cross-links that are not good for the tendon.”
Soleus: “We probably inadvertently or unwittingly train it anyway if we’re doing squats or any type of jumping, we probably underestimate how much we train it and give it a good stimulus doing normal S&C… but any off-axis movements, COD, track athletes going around the bend, it’s probably going to change the stress to different regions of the soleus.”
Biggest issues with Achilles rehab: “They probably are under-dosing their rehab. They’re probably not giving it enough of a stimulus when they’re loading. If they’re trying to get back to running, they probably haven’t spent enough time doing plyometrics to try and prepare it for the high loading rates and its ability to store and recycle elastic energy… also, I just don’t like the idea of daily calf loading. You can make a sore tendon sore and keeping making it sore, and also not give yourself a good window to recover and adapt properly… I prefer to load it heavy every 48-72 hours and let it recover and adapt.”
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