Nutrition for Soft-Tissue Training, Recovery, and Injury Prevention

This article is an ongoing project, and published early for the sake of the reader, and to gain some search engine mojo. Scandalous I know.

Now doubt the article will continue to evolve, hopefully become more cogent, and I will announce larger updates on Facebook, Twitter, and Instagram, so please do bookmark this page for a future visits.

Do let me know if there is anything more you want clarity on, have any further questions, or believe anything needs correcting. tom@useful.coach

Page Updated: 25/08/2017

UPDATE: Since this is pertinent to the article, do see my video: How to fix and prevent "climbers elbow" inside elbow pain from climbing - Medial Epicondylitis.

Contents

The Preamble

I have worked with a number of climbers, and quite often their nutrition practices are body-composition, budget, ethically (vegan / vegetarian), or perhaps "assumptive" (vegan / raw-food / low-carbohydrate high-fat) focused over supporting climbing performance and training recovery. And though these focuses are not mutually exclusive, there are ways to optimise food choices and eating habits to better support climbing longevity, particularity that of soft-tissue (muscle, tendon, ligament) health.

Since your life is literally hanging from your soft-tissues, providing optimal nutritional support for their performance, and recovery is essential.

Research data is also beginning to show that not only might we augment their adaptations via specific nutrition and training, but there may be things we are consuming and doing that are hindering their growth and repair.

This article provides a background overview of soft-tissue, the impact of specific training and loading modalities on their properties, thoughts on common injury recovery and prevention, and practical nutrition guidance to support and augment their development, injury resistance, and recovery.

I use the collective-term "soft-tissue" for muscles, tendons, and ligaments; and "connective-tissue" more specifically for tendons, ligaments, and the inter-/intramuscular collagen containing tissue matrix (ECM).

Cocktails and Connective-Tissue

Since all good stories start at the bar…

Earlier in October (2016) I contacted Professor Keith Baar, Ph.D. of the Functional Molecular Biology Laboratory, UC Davis in regards to his work on collagen synthesis. The email thread was in regards to the differences between muscle and collagen protein synthesis, and how training and nutritional timing differ in optimising each respectively.

This article circles our conversation, and so I would like to thank Dr. Baar for sharing his lab's work, and I look forward to the future data, especially how it could be applied to the climbing community.

So to begin, here is a tale of two cocktails…

The Exercise-Induced Biochemical Cocktail

First up, a 2015 published paper titled: The exercise-induced biochemical milieu enhances collagen content and tensile strength of engineered ligaments.1

The purpose of this study was to determine the effect of the human exercise-induced biochemical milieu on collagen turnover using ligaments engineered from cells obtained from the human anterior cruciate ligament (ACL). We used a within-subject design whereby culture medium was enriched with serum obtained at rest and after exercise from the same individual.1

The scientists grew donated knee ligaments in the lab, and then bathed them in blood serum drawn from individuals 15 minutes after doing multi-set resistance (leg super-set) training. They then compared the knee ligaments to those bathed in blood serum drawn from the same subjects at rest.

They wanted to investigate whether the exercise-induced circulating hormones and nutrients would aid in the collagen remodelling of the ligament.

What did they find?

In summary, we report that ligament constructs treated for 7 days with serum obtained post-exercise exhibit enhanced collagen content and tensile strength compared with constructs treated with serum obtained from the same individuals at rest. Thus, our data suggest that one biological function of the exercise-induced biochemical milieu may be to support connective tissue remodelling.1

From an applied standpoint, our findings suggest that changes in the physiological milieu may provide a signal to stimulate collagen turnover in tendon, ligaments and skin (Crane et al. 2015) to maintain or improve tissue function.1

They also tried subjecting the ligaments to two isolated typically elevated post-exercise hormones: GH (growth hormone) and IGF-1 (Insulin-like growth factor 1), but this did not work as well as the blood serum.

From a 2016 commentary paper:

Given that recombinant IGF-1 and GH showed no benefits for collagen beyond resting levels, the data presented by West et al. (2015) highlight the apparent importance of the complete physiological ‘cocktail’ of the post-exercise milieu, which ultimately contains additional (unidentified) exercise-induced metabolites, hormones, binding proteins, etc. that may synergistically aid in remodelling of collagen tissue.2

The results from the present study … would suggest that it may be beneficial for athletes or the elderly aiming to rapidly and effectively recover from musculoskeletal injuries (e.g. strains, sprains, surgeries) resulting from damage to collagenous tissues to engage in exercise with the uninjured tissues in an effort to induce transient increases endogenous anabolic hormones.2

Resistance training outside of climbing useful?

The Nutrition-Induced Biochemical Cocktail

Second, a 2016 paper titled: Vitamin C-enriched gelatin supplementation prior to intermittent activity augments collagen synthesis.3

The background and objective of the research:

Musculoskeletal injuries are the most common complaint in active populations. Greater than 50% of all injuries in sports can be classified as sprains, strains, ruptures, or breaks of musculoskeletal tissues. Nutritional and/or exercise interventions that increase collagen synthesis and strengthen these tissues could have a significant effect on injury rates. This study was designed to determine whether gelatin supplementation could increase collagen synthesis.3

The scientists continued in a similar vein as the previous study using engineered ligaments, but this time they subjected the tissues to blood drawn from subjects who were supplemented with various amounts (placebo, 5g, 15g) of gelatin, equal amounts of ascorbic acid (vitamin C), one hour before completing 6 minutes of rope-skipping. This protocol was then repeated 3 times a day for 3 days.

We intend to test the hypothesis that consuming gelatin (a food derivative of collagen) and Vitamin C combined with exercise may increase collagen synthesis. To test this hypothesis, eight healthy males will complete a randomized cross-over design protocol where they will consume either a drink containing a isocaloric placebo, 5, or 15 grams of gelatin at a constant level of Vitamin C. Measurements of amino acid appearance in the blood over the first 3 hours will be measured in each condition and a larger blood draw will be taken at 1 hour to determine the effect of the nutritional supplement on engineered ligament collagen and mechanics.3

They found that the comprising amino acids of gelatin (glycine, proline, hydroxyproline, hydroxylysine) increased in the blood in a dose-dependent manner (highest with 15g) peaking one hour after consumption. They also found that the engineered ligaments treated with serum showed a corresponding (gelatin dose-dependant) increase in collagen content, density, and tendon mechanics.

2016 interview transcript with Prof. Baar:

We then take a large amount of blood at one hour and we put it into our engineered ligament model just to see whether the blood from a person taken before they've taken the gelatin or after they've taken the gelatin, can we see any difference in the function of the ligaments that we get from these? And sure enough, what we see is that if you make the ligament and you feed it media that contains the serum of the people after they've had the gelatin supplement, you get more collagen in a step-wise response, whereas at the 5 grams of gelatin you get more collagen than the placebo and at the 15 you get more collagen than you do at either the 5 or the placebo group. And then what we look at is we look at the mechanics and sure enough, the mechanics are improved. They are stronger. They're stiffer than they were without the supplement.4

The scientists then asked the subjects to supplement with the gelatin and ascorbic acid one hour before jumping-rope for 6 minutes, and repeating this protocol twice more with a minimum of 6 hours between each exercise bout.

The subjects will perform six minutes of rope-skipping to stimulate collagen synthesis. This short bout of exercise will be repeated every six hours for the next three days and will be preceded by one hour with the appropriate drink containing placebo, 5, or 15 grams of gelatin. Over the 3-day training period, blood will be taken for the analysis of the amino-terminal propeptide of collagen 1 (PINP), a byproduct of collagen synthesis.3

More interview transcript:

And so they jump-rope for six minutes and then they take a six hour rest, they then drink whatever supplement they're supposed to drink again, and then an hour later they jump-rope and they keep doing this three times a day for three days. And what we find is that anybody who jumps rope, those people who jump-rope show a doubling in their collagen synthesis and most of this collagen is synthesized from the bone, from the impact of the jump-rope. When we add the gelatin, the low dose of gelatin wasn’t enough to get a significant effect of the supplement, but when we increased the gelatin content in the supplement to 15 grams of gelatin, what we see is a further doubling of collagen synthesis.4

So the study data supported their hypothesis that starting an exercise bout one hour after consuming 15g of gelatin (with Vitamin C) resulted in greater collagen synthesis in the recovery period following exercise.

Now it is important to point out that data reflected bone collagen synthesis in the subjects (in vivo), but there was a similar response in the engineered ligaments (in vitro) treated with the serum.

UPDATE: Since writing this article, the ever brilliant Adel Moussa from SuppVersity wrote the following summary: 100% Increase in Exercise-Induced Collagen Synthesis With Cheap, Yet Effective 15g Gelatin + 200mg Vitamin C Stack.

The Muscle-ECM-Tendon Complex

If I ask you to jump, you dip first. Why?

Dynamic movement is triphasic: firstly a counter-directional eccentric (lengthening) phase where the working muscle (agonist) stretches, an isometric (no length change) intermediary phase, and finally the concentric (shortening) phase.

The shortening concentric contraction of the agonist muscle after the eccentric counter-movement stretch is known as the stretch-shortening cycle (SSC).

In a stretch shortening cycle, the viscoelastic characteristics of the muscle-tendon complex play an important role in enhancing both the effectiveness and efficiency of human performance. Of particular importance is the ability of these tissues to store energy when deformed (stretched) by external force and to recoil after being stretched.5

By improving an athlete's ability to absorb force eccentrically, the concentric, power production aspect is maximized, leading to improved sports performance. It becomes clear the elite athlete has an advantage based on their ability to absorb and produce force in a much more rapid fashion, while also working more efficiently with a higher percent of this power coming from the elastic components of the SSC.6

Muscle recoil ability is possible because muscles are composed of more than just contractile fibers. The SSC produced by the muscle-tendon complex, could be defined and understood more holistically as being produced by the "muscle-ECM-tendon complex".

The images they obtained suggest that sheets of perimysial collagen join and become continuous with tendon. It is interesting to note that tendon and perimysium both contain primarily type I collagen, and the primary proteoglycan (PG) for both structures is decorin. In contrast, epimysium and endomysium are made up of almost equal amounts of types I and III collagen and contain other PGs. The structure of perimysium is also different from the mesh-like structure of endomysium. This evidence supports the hypothesis that perimysium is continuous with tendon.7

The viscoelastic tendon does not truly end at the muscle, but rather runs right through it via the perimysium end-to-end. See: Figure 1. Gillies, 2011.7

The Ubiquitous Extracellular Matrix (ECM)

The bundled structures that comprise skeletal muscle are each individually bound together by an extracellular matrix (ECM) of collagenous viscoelastic soft-tissue.

The ECM of skeletal muscle is composed of three interconnected layers. The outermost epimysium layer surrounds each muscle and is connected to the tendons that join the muscle and bone. The intermediate perimysium layer surrounds muscle fascicles and extends further to the myotendinous junction where it joins the tendon. Endomysium is the inner connective tissue layer that surrounds muscle fibers within fascicles.8

The collagenous extracellular matrix (ECM) wrapping individual skeletal muscle structures.

The ECM contributes to the muscle's structural stability, passive stiffness, tensile strength (resistance to breaking under tension), and the lateral force transmission across muscle fibers and fascicles.

Cross-linked collagen fibres within the ECM form an irregular lattice, which in the case of the outer-most epimysium, become denser and align unidirectionally to form tendon attaching muscle to bone.

Muscles develop force longitudinally by the shortening (sliding filament theory) of the contractile elements (sarcomers) within individual muscle fibres (myocytes), with 80% of that force transmitted laterally into the surrounding ECM. The function of this transfer is to allow the working fibers to continue shortening, and to join adjacent fibers together to protect them from individual injury.

Based on the fact that muscle fibers within a motor unit do not extend the length of a fascicle and the observation of an intimate interaction between tendon and perimysium, a current structural model for muscle tissue is one in which muscle fibers are embedded within a matrix of ECM that forms discrete layers that are mechanically interconnected. Thus, muscle fiber force generated by actin-myosin interactions will be transmitted to the ECM at multiple focal adhesions along the muscle fiber itself. Once force is transmitted to the ECM, there would be nearly infinite paths of force transmission to the external tendon.7

Muscular strength and power is then determined by the optimal transfer of the generated force out and through the ECM and tendon, leading to movement across the joint. The structural properties (i.e. collagen type, alignment, density, cross-linking) of the muscle-ECM-tendon complex is then essential to efficient force transfer.

You could think of connective-tissue like climbing rope. The rope is designed to transfer the force of a fall optimally, and its properties: length, width, elasticity, and tensile strength are all essential to its proper function. If its health is compromised—a flaw or exaggeration of any of these properties—performance (safety) is compromised.

Fascial connective-tissues differ in terms of their density and directional alignment of collagen fibers. (Schleip, 2013)

The ECM spreads wider still. Fascia, has been described a body-wide interconnected network of collagenous tissue.

This continuous network envelops and connects all muscles and organs. Elements of this fibrous network include muscle envelopes, joint capsules, septi, intramuscular connective tissues, retinaculae, aponeuroses, as well as more dense local specifications such as ligaments and tendons.9

Some would argue that we should think less of the body as a continuous stacked compression structure (head sits on the neck, neck sits on the torso, etc), but rather the bones "float" inside the soft-tissue with everything interconnected to form a tensional structure—everything effecting everything else.10

'ECM' is not quite a substitute for our new expanded definition of fascia, because the ECM does not include the cells, and 'fascia' would definitely include the fibroblasts, mast cells, and various other cells (like osteoblasts, chondroblasts, osteoclasts, etc.) that create, maintain, and break down the ECM. Put the body in a vat of solvent and dissolve away all the cells to see that ECM in its singular organic unity. ECM + connective tissue cells = fascia. One parallel that may help to see this is an orange: the rind, pith, and the walls between the sections would all be like the fascia of the body, organizing the ‘juice’ into discrete but interconnected compartments.11

Do read Does Fascia Matter?, a detailed critical analysis of the clinical relevance of fascia science and fascia properties.

Some fascia research is truly intriguing. What many researchers are saying about fascia is reasonable. Many are not reaching awkwardly beyond the data. Unfortunately, many therapists fascinated by fascia are reaching beyond—way beyond—what the science can actually support, or probably ever will. 12

The ECM is also an important site for mechanotransduction signalling, that is converting mechanical stimulas into electrochemical activity, allowing the muscle to dynamically adapt to the mechanical stress received.

Among others, one notable proprioceptor is the Golgi Tendon Organ (GTO) located between the muscle and its tendon (myotendinous junction), in ligaments (called Golgi End Organs), and joint capsules. GTOs function to provide feedback information about dynamic force changes during muscle contraction.13

In order to handle the extreme antigravity balancing challenges as a biped, our central nervous system can reset the Golgi tendon receptors and related reflex arcs so that they function as very delicate antigravity receptors. This explains that some of the leg’s balancing reactions in standing occur much quicker than it would take for a nerve impulse from the brain to the leg.13

When the muscle contracts the GTO is activated and responds by inhibiting the contraction (reflex inhibition), and by contracting the opposing (antagonist) muscle group. This process is called autogenic inhibition and plays an important role in overstretch protection and flexibility.14

Extracellular Matrix (ECM) Composition

This ubiquitous inter–/intramuscular extracelluar matrix is composed of two major classes of biomolecules: glycosaminoglycans (GAGs) which link together to proteins to form larger proteoglycans, and fibrous glycoproteins: elastin, fibronectin, laminin, and collagen. Glycosaminoglycans are negatively charged so they attract cations (i.e. sodium ions) which cause water to be pulled into the matrix. 90% of the ECM is water, allowing the diffusion of molecules, movement of cells, resistance to compressive forces, and viscoelasticity.15

One notable proteoglycan found in the ECM is "decorin", a small leucine-rich proteoglycan (SLRP), composed of a repeating amino acid chain rich in leucine, to which a single GAG (chondroitin/dermatan sulfate) attaches. Decorin is involved in cellular signalling, ECM integrity, collagen fibrillogenesis, collagen fibril binding, and interacts with the glycoprotein fibronectin responsible for cell adhesion, migration and differentiation. In muscle tissue decorin is found in the perimysium and involved in muscle cell growth and differentiation.

Decorin is known to modulate TGF-beta (transforming growth factor-beta) and has been referred to as a "guardian from the matrix" as it regulates cellular processes including (but not limited to) angiogenesis, myocardial infarct, innate immunity, inflammation, diabetic nephropathy, fibrosis, wound healing, and autophagy.16

Overall, a predominant theme that emerges from studying the decorin interacting network appears to be related to reducing tumorigenesis by several different mechanisms. These mechanisms include altering signaling pathways in tumor cells themselves as well as by reducing tumor angiogenesis, partly through modification of the tumor secretome and possibly also through the induction of autophagy in vascular cells. Additionally, the secondary, but imperative, theme of maintaining extracellular matrix structure by decorin cannot be pushed to the wayside, as this subject is where the significance of decorin in vivo began. … We have just hit the tip of the iceberg regarding understanding the vast signaling capabilities of decorin.16

Connective-tissue (tendons, ligaments, bone, cartilage, haemopoetic, blood, adipose) contain various specialised cells (e.g. fibroblasts, osteoblasts, chondroblasts, hemocytoblasts) which synthesise various forms of ECM.

The fibroblasts produce fibrous proteins (e.g. fibronectin, elastin, collagen) which provide the unique structural properties of skeletal muscle, tendons, and ligaments.

Fibronectin functions in tissue repair, blood clotting, cell migration, and cell adhesion anchoring cells to collagen or proteoglycans. Elastic fibres are composed of elastin and other glycoproteins such as fibrillin. Elastin provides tissues the ability to recoil and prevent overstretching. Collagen which is the most common fibrous protein in the ECM and the bulk protein in connective-tissue, provides tensile strength.

The tensile strength, stiffness, and elasticity of connective-tissue is determined by the total collagen content, type, alignment, and the chemical cross-links that bind together the varying composing structures of collagen to form fibrils, which form fibres, which form a collagen matrix.

Collagen, Cross-linked

Collagen is the most abundant protein in the body, making up 25% of total protein mass. 45 distinct genes in the genome code for 28 different collagen types I–XXVIII. 80-90% of the collagen in the body is Type I, II, and III, yet all serve to provide tensile strength and prevent overstretching.17

Type I is the most abundant collagen, primarily found in tendons, ligaments, joint capsules, cartilage, skin, bones, sciera, and dentin. Type II makes up more than 50% of cartilage. Type III supports the walls of intestinal tract, uterus, and blood vessels.

Collagen proteins consists of three coiled peptide chains each 1050 amino acids long, wound around each other forming a right-handed triple helix. This coiled structure arises from the abundance of three amino acids: glycine, proline, and hydroxyproline, which repeat hundreds of times in a sequence of glycine-proline-X or glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline, hydroxyproline, or tryptophan.18

All proteins are composed of specifically twist-folded chains (peptides) of amino acids. Amino acids are both the building blocks of peptides (the building blocks of proteins), but also act as signalling molecules. For example the amino acid leucine activates other key signalling proteins (mTOR pathway) responsible for synthesising new proteins. A low protein (low varied amino acid) diet is then sub-optimal for growth and recovery.19

Type I collagen molecules pack side-by-side and cross-link at their ends to form fibrils which have incredible tensile strength when stretched. Fibrils then pack side-by-side in cross-linked bundles to form collagen fibers. Gram for gram, type I collagen is stronger than steel.

Hierarchical structure of tendon spanning from the single collagen molecule up to fibrils, fascicles, and whole tendon. (Connizzo, 2013)

Mature collagen cross-links are formed by the amino acid lysine aided by the copper-dependant enzyme (lysyl oxidase) to which ascorbic acid (vitamin C) is a co-factor, or non-ezymatically by glycated proteins called AGEs (Advanced Glycation Endproducts).

AGEs are proteins (or lipids) which when exposed to sugar, attach themselves to the sugar molecule. The most abundant AGEs found in collagen are pentosidine (formed from ribose), and glucosepane (formed from glucose). Glucosepane is also the most prevalent AGE found in skin collagen, and part of the reason our skin becomes less elastic as we age.

AGE accumulation is particularly high in long-lived proteins, such as collagen. Indeed, collagen half-life varies between tissues but remains generally large, from 1–2 years for bone collagen to about 10 years for type I in skin. The low biological turnover of collagen makes it therefore susceptible to interaction with metabolites, primarily glucose. Aside from protein longevity, another factor that influences the formation of AGEs is the glucose level in the blood stream. Hyperglycemia related to diabetes is suspected to strongly predispose tissues of these patients to accumulation of AGEs.20

From these reports, it is possible to hypothesize that a dietary regimen with a high AGE content may promote a sustained low-grade inflammatory state. In fact, AGEs may induce the expression of inflammation markers such as cytokines and adhesion molecules via reactive oxygen species production and nuclear factor KB activation, properties which are also exhibited by dietary AGEs. These highly reactive molecules, could, together with hyperglycemia, contribute to the inflammatory state associated with pre-diabetes and related cardiovascular disease.21

AGE cross-links increase the stiffness of connective-tissues, which is why musculoskeletal injuries are statistically greater in diabetic individuals. Their higher basal blood sugar provide ample opportunity for AGE formation.

You may actuallly have heard of AGEs before in relation to browning foods during cooking…

AGEs are created through a nonenzymatic reaction between reducing sugars and free amino groups of proteins, lipids, or nucleic acids. This reaction is also known as the Maillard or browning reaction. The formation of AGEs is a part of normal metabolism, but if excessively high levels of AGEs are reached in tissues and the circulation they can become pathogenic. The pathologic effects of AGEs are related to their ability to promote oxidative stress and inflammation by binding with cell surface receptors or cross-linking with body proteins, altering their structure and function.22

In the past few years, the potential role of dietary AGEs in human health has largely been ignored, however, recent studies with the oral administration of a single AGE-rich meal to human beings as well as labelled single protein-AGEs or diets enriched with specific AGEs such as carboxy-methyl-lysine (CML) and methyl-glyoxal (MG) to mice, have clearly shown that dietary AGEs are absorbed and contribute significantly to the body’s AGE pool.21

AGEs in the diet represent pathogenic compounds that have been linked to the induction and progression of many chronic diseases. This report reinforces previous observations that high temperature and low moisture consistently and strongly drive AGE formation in foods, whereas comparatively brief heating time, low temperatures, high moisture, and/or pre-exposure to an acidified environment are effective strategies to limit new AGE formation in food.22

Carbohydrate, Glycation (AGE) and Connective Tissue

Though I would hesitate to directly connect (no pun) dietary intake of AGEs and endogenous AGE formation in connective-tissue, there is some warrant for monitoring your habitual diet in effort to reduce both.

In relation to dietary AGEs, just be aware of the amount of fried, grilled, and roasted foods you consume. No doubt tasty, but seemingly less healthy. In relation to endogenous AGE formation, we generally maintain a circulating blood-glucose level of 5g in total, and this rises in relation to the glucose content of foods consumed and their speed of digestion. Your ability to clear excess blood-glucose is limited by activity levels (glucose use), tissue stores (glucose absorption), and hormonal (insulin) sensitivity which control the former two.

Chronic pulsing of carbohydrate (i.e. sugary snacks / drinks) throughout the day "may" provide greater opportunity for endogenous AGE formation during those blood-glucose peaks.

I find no reason to disagree that AGEs are harmful to the tendons; we know they’re harmful in general, and it wouldn’t be surprising to learn that they also affect tendons or other connective tissues. Where I disagree is with his nutritional recommendation to decrease the carbohydrates in your diet. … Without evidence that carbohydrates—outside of hyperglycemia—can increase AGE production, there’s no meat to the argument. Carbohydrates themselves have no other known deleterious effect on tendons, and there’s no impetus to go low-carb.23

Tendons and Ligaments

ECM collagen distribution, density, and alignment varies in relation to the function of the particular muscle, and the need for stability, control, tensile strength, and force transfer.8

The muscles of the hands have the greatest collagen content compared to any other muscle region. This higher density provides greater structural stiffness during high velocity movement, and allows for fine motor control. The axial muscles (trunk, head) have higher collagen content than that of the appendicular (arm, leg) regions to provide support. The muscles of the forearms and lower legs have almost identical collagen content. The upper arms which outside of resistance training do not experience high loads have lower collagen content, and the shoulders have high collagen content to provide stability and control of the glenohumeral joint.

  • Collagen: Most abundant protein found in the body—tendons, ligaments, skin, cartilage, intervertebral discs, bones, blood vessels, corneas, teeth, and ~2% of muscle tissue. See video: Collagen: The fabric of life. Enter the Matrix!
  • Tendons: Tightly packed longitudinally running high density collagen fibres which connect muscles to bones. Less elastic than ligaments, but have higher tensile strength. Withstand tensile forces whilst retaining flexibility. Conserve elastic energy. Relatively avascular (have poor blood flow) and slower to heal.
  • Ligaments: Randomly weaved patterns of low density collagen fibres which connect two bones, cartilages, or joints together. Hold more "ground substance" and thus water. More elastic than tendons, but have less tensile strength.

Where the muscle ends and the tendon begins is called the myotendinous junction. Where tendons attach to bones is the osteotendinous junction. Tendons attach to muscles with finger-like projections (invaginations), and this junction is at its greatest strength with a large surface area, and a correct orientation. It is strongest when pulled (loaded) in-line with the projections, but weakest when pulled apart, a bit like how Velcro works.

The over-stressing, and poor recovery of this osteotendinous junction is the problem behind lateral (outside "tennis" elbow pain) and medial (inside "golfers" elbow pain) epicondylitis—tendonitis or tendonosis. I will discuss this in more detail later.

UPDATE: See my video: How to fix and prevent "climbers elbow" inside elbow pain from climbing - Medial Epicondylitis.

A healthy tendon transfers force optimally from the muscle to the bone when it is compliant (laxer) nearer the muscle, and stiffer nearer the bone. This is accomplished by increasingly greater collagen cross-linking along the length of the tendon as it approaches the bone.

Tendons can become stiffer nearer the muscle with disuse, say in the case of immobilisation due to injury. This is caused by the increase in collagen cross-linking both enzymatically (lysine) and non-enzymatically (AGEs). Movement keeps things more compliant by breaking the cross-links, and this makes sense. The tendon attaching to the muscle stays more compliant to receive the generated force, and becomes increasingly stiffer as it approaches the bone to drive movement.

The body adapts to use and disuse. Muscles atrophy when not used, bones become brittle if not bearing weight, and joints and their connective-tissues become weaker, stiffer and less flexible when not loaded and moved through their range of motion. For this reason keep moving, but do take care when loading your your shoulders, fingers, or knees (fall-landing) after long periods of rest, injury, or perhaps after a month on the International Space Station.

Is there warrant for wanting to increase overall tendon stiffness, would this lead to more efficient force transfer?

TO BE CONTINUED…

I have loads more content still in disconnected paragraphs which I will publish as soon as I have the time. I apologise for merely wetting your appetite.

References

  1. West, D. W. D., Lee-Barthel, A., Mcintyre, T., Shamim, B., Lee, C. A., & Baar, K. (2015). The exercise-induced biochemical milieu enhances collagen content and tensile strength of engineered ligaments. J Physiol The Journal of Physiology, 0, 1–11. http://doi.org/10.1113/JP270737  2 3 4

  2. Abou Sawan, S., Mazzulla, M., Brooks, J., Williamson, E., & Hirsh, D. (2016). “Engineering physiology” to understand the post-exercise biochemical milieu: mixing it up with anabolic hormones. The Journal of Physiology, 594(2), 263–264. http://doi.org/10.1113/JP271857  2

  3. Shaw G. (2016). Vitamin C-enriched gelatin supplementation prior to intermittent activity augments collagen synthesis. http://doi.org/10.3945/ajcn.116.138594  2 3 4

  4. SNR #143: Keith Baar, PhD – Tendon Stiffness, Collagen Production & Gelatin for Performance & Injury. http://sigmanutrition.com/episode143/  2

  5. Fukashiro, S., Hay, D. C., & Nagano, A. (2006). Biomechanical behavior of muscle-tendon complex during dynamic human movements. Journal of Applied Biomechanics, 22(2), 131–47. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/16871004 

  6. Dietz, C. Van Dyke, M. (2015). Supramaximal Slow Eccentrics and the Safety Bar Split Squat. http://vandykestrength.com/pages/supra_eccen 

  7. Gillies, A. R., & Lieber, R. L. (2011). Structure and function of the skeletal muscle extracellular matrix. Muscle & Nerve, 44(3), 318–31. http://doi.org/10.1002/mus.22094  2 3

  8. Lin, E. Y. H. (2011). Collagen Quantification Across Human Skeletal Muscles. University of California, San Diego. Retrieved from http://gradworks.umi.com/15/02/1502084.html  2

  9. Schleip, R., & Müller, D. G. (2013). Training principles for fascial connective tissues: Scientific foundation and suggested practical applications. Journal of Bodywork and Movement Therapies, 17(1), 103–115. http://doi.org/10.1016/j.jbmt.2012.06.007 

  10. Myers, T. What is Tensegrity. Youtube. https://www.youtube.com/watch?v=BzgxYpDyO0M 

  11. Fasica. Anatomy Trains. Accessed 06/11/16. https://www.anatomytrains.com/fascia/ 

  12. Ingraham, P. (2017). Does Fascia Matter? A detailed critical analysis of the clinical relevance of fascia science and fascia properties. https://www.painscience.com/articles/does-fascia-matter.php 

  13. Schleip, R. (2003). Fascial plasticity - A new neurobiological explanation. Part 2. Journal of Bodywork and Movement Therapies, 7(2), 104–116. http://doi.org/10.1016/S1360-8592(02)00076-1  2

  14. Hindle, K. B., Whitcomb, T. J., Briggs, W. O., & Hong, J. (2012). Proprioceptive Neuromuscular Facilitation (PNF): Its Mechanisms and Effects on Range of Motion and Muscular Function. Journal of Human Kinetics, 31(March), 105–13. http://doi.org/10.2478/v10078-012-0011-y 

  15. Connective Tissue. The Histology Guide. Faculty of Biological Sciences, University of Leeds. Accessed 08/11/16. http://www.histology.leeds.ac.uk/tissue_types/connective/index.php 

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