Originally Posted by Tutt
@Kyrpa
Was just reviewing an interesting study that affirmed a couple interesting points.
(1) Elongation was confirmed to be the result of 3 mechanisms; inter-fiber relaxation, inter-fibril relaxation, and intra-fibril relaxation. But they all happen on different time scales in respective order; 0.3-1.0 seconds, 3-90s, and >200s. The indication being that the fibers will slide quite quickly to accommodate acute strain. Over about 90s, the fibrils begin sliding, and then if the stress remains, after about 200s the molecular bonds begin to break down.
(2) As it turns out there is a distinct difference between tendon and ligament. Tendon was shown to have a positive relaxation relationship to initial stress. That is, high initial stress results in faster relaxation. Ligament is shown to have an inverse relationship. Higher initial stress results in slower relaxation.
As we are discussing something more akin to ligament and not tendon, this supports the mindset of starting with low loads and very slowly increasing.
Tutt,
1) The time spectrum sounded familiar and I went through some sources.
To me, it appears as a result of a collagen gel study produced with different stages of cross-linking.
If the results have been emulated in actual ligaments, that I did not know.
Would you be kind and lead us to the source.
About the different mechanisms, not only do they happen in different time scales they do happen in different length scales as well.
As your previously shared study prevailed already.
The inter-fibrillar slipping is the major source of elongation no matter the scales.
At low strain rate applications, it means 6% if the total strain percentage being 10%.
If the maximized inter- fibrillar relaxation is proportionally analogous to inter-fibrillar sliding, I can´t say for sure.
The mechanism beyond >200s surely is very different when operating under influence of therapeutic heat.
What is described as breaking of the molecular bonds, which resembles as a result of forceful disassembly, is happening in a more controlled smoother fashion under heat.
The bonds do get under denaturation processes but by mechanisms that allow significantly less all-level damages, and are quickly reconstructed once the temperature drops back to resting temperature.
2) Tendons are build to cope with loads and stresses greater than ligaments.
So different behavior should be expected.
I would still not rush to claim the there being all inverse relation with the stress level only.
We need to understand that ligaments do have strain-related stress relaxation properties, which might be the major contributor to different stress-relaxation relations to initial stress levels.
Ligaments have been found to show greater stress relaxation properties at low strain and inverse at larger strain percentages. Although the authors do speculate the differences between species and even different ligaments for the very same donor.
Surely we can confirm the TA behaving as a ligamentous element. Which most of the literature suggests as well.
And yes, the classic low force long-duration stretch scenario is the basis.
The evolution should be the low strain rate, low increment loading application.
Did you see this yet?
The characteristics of the tunica albuginea revisited
There are some hints on what should be deemed as low-force applications.
To me, it seems clear operating under or slightly above 0.17Mpa stress threshold can be labeled as low force applications. That is the point we enter to the elastic region with TA.
Just posted the initiative, there is more to follow as you might suspect.
I am really convinced that the optimal stress levels can be determined with the tools introduced.
Hopefully, you could join in and collaborate on this particular thread and help to bring the knowledge in the present time, and beyond.