Quite interesting study at the nano-scale level of ligament tissue that I don’t remember discussing here. It sheds further light on how the tissue deformes within the elastic region.
First off it confirms that the tissue deformation does in fact occur within the elastic region, not past the elastic limit as was debated earlier in this thread. They were not ever able to realize a “plastic region”, but instead just instantaneous failure at the tissue level within the linear elastic region.
Their focus was primarily on strain rate and strain% at three different levels of observation; (1) macro tissue level, (2) micro fibril level, and (3) nano molecular level. At the smallest scales they literally measured the gap length between molecules at various strain rates. What is seen by us as tissue strain actually has many counteracting mechanisms at the smaller scales to ensure tissue viability. All of which relate to our objectives here in fascinating ways.
First off, their strain rates were within a more normal physiological range of 0.001/s to 0.05/s. My proposed optimal rate of 0.005/m is just 0.00008/s which is orders of magnitude slower than their tests. And many of the manual exercises on TP are much faster than their highest rate. But it seems to me that the methods Kyrpa and others use on this thread are actually within the rates of this study, especially given consideration for time under tension.
What is most interesting is the mechanism producing the strain at different rates. IOW, are the fibrils deforming, the cells elongating, the gaps enlarging, or the fibrils sliding past each other? The answer is maybe on all accounts purely depending on the strain rate.
It’s counterintuitive, but at the fibril level, the higher the rate the less proportionally is attributable to fibril strain. This is explained by the modulus reactions at the tissue level vs fibril level. At the tissue level, the modulus (stiffness) increases 3.5x from the slowest to fastest rate. But at the fibril level, the modulus increases 11.5x. IOW, at high strain rates, the individual fibrils are highly resistant to deformation. So at high rates, the fibrils effectively have a molecular defense making them rigid and strong. At these high rates, tissue deformation is driven by cross-linkages breaking and fibrils shifting independent of one another in an effort to preserve the fibrils. Importantly, this is shown in other studies to trigger a healing response as the tissue requires immediate reinforcement to remain viable. We would see this as “toughening” of the tissue; the TA gets thicker, stiffer, and stronger. So while the immediate result is a fair amount of permanent tissue strain, the long term result is the tissue fortifying itself against future deformation. Other studies show this toughening response to slowly begin within 1-2 weeks of onset of repeated stress and ramping up heavily at 6-8 weeks. Tissue level modulus decreasing near baseline within 6-10 weeks of stress elimination, but tissue density remaining elevated even past 12-16 weeks.
So if we strain fast it might be possible to effect more significant immediate residual elongation due to bonds breaking and fibrils shifting, but the tissue will dramatically and quickly ramp up its toughening mechanism starting around 10-14 days and by 42-56 days will pretty much eliminate any possibility of further gains without exponentially increasing load or prolonged decon break at least 4-6 months to reach baseline values. Slight progress might be made as soon as 2-3 months decon, but despite a recovery of low modulus at the cellular level allowing for these modest gains, reaplication of stress will continue thickening the tissue that will not return to baseline values for several more months. I postulate that this is the primary mechanism of the “plateau”.
Now let’s contrast the slow strain rate mechanisms from this study. At slow rates there is effectively zero deformation of fibrils until 5% strain. This is observed as the straightening of the crimps representing the toe-heel region of the load-strain curve. (Side note, the study did not see a toe-heel region at the highest rates. The fibrils stiffen so quickly that it’s all elastic region). At sufficiently slow rates, tissue deformation is observed at both the fibril and molecular levels. Crimps straighten in gap regions, tropocollagen molecules slide past each other, gaps widen, cells elongate, fibrils deform… A key distinction here is that there is minimal damage to tissue. As opposed to a healing/toughening response, we see a neocollagenesis response. At a molecular level, the tissue is triggering the chemical response that will allow for functioning within its new base state.
Basically, we want strain to be happening at the molecular level first, fibril level second, and preferably not ever at the tissue level. So what is the optimal rate at each level. To avoid tissue level deformation, we absolutely must stay below 1%/s. This is absolutely certain, so if you do manuals at all, keep them very slow and even because 1%/s is already so slow that it’s difficult manually to do things that slow. At the molecular level, I haven’t been able to see a benefit to going slower than 0.1%/s although this is not true of the fibril level. At that level, the fibril continues to benefit exponentially at even slower rates with only marginal benefit below 0.01%/s.
If we go slow enough under heat, we are able to realize significantly greater strain in a single session but it likely won’t be as permanent as the fast rates. However, if we reach rates as low as 0.01%/s we should be able to continue with far fewer decon and with virtually no toughening of the tissues.
I’m becoming even more convinced that our objectives here can only be facilitated by mechanical device capable of incredibly slow rates of strain. I know it is discouraging to many because of greater complexity of design, but any type of spring loaded or continuous load (hanging weight) mechanism would be very difficult to accomplish this. You might try something like a hanging device in which 2kg of water or sand very slowly fills a container on a pulley over a span of about 10 minutes.
Optimally a device like mine giving stress relaxation and micrometer adjust at very slow rates.