For decades, exercise biologists have focused on the mechanisms in which our musculoskeletal system, specifically the skeletal muscle, functions, acts and responds both inside and out, all the way to the bottom layer that addresses the very specific individual muscle cells. This foundation of knowledge has provided us with many clues as to what’s best for ensuring optimal health and performance. As a result, we’ve come to understand that there’s a range of hypotheses and theories that benefit the skeletal muscle, such as a set amount of protein to support optimal growth and repair and a sufficient training stimulus.
The same thing applies to our bone tissue, also part of the musculoskeletal system, where scientific research has led to recommendations such as opting for a sufficient amount of Vitamin D and calcium from our diet, as well as sufficient exercise, all favoring the optimization of bone health.
There is no doubt that both nutrition and exercise play a pivotal role in supporting these parts of the musculoskeletal system. Yet there is something in the musculoskeletal system that hasn’t received the proper attention that might be warranted. It is mostly associated with sports injuries and is known to take quite the effort to recover from. You’ve also possibly encountered it on a piece of bone like chicken and had trouble tearing and cutting it with your teeth. I’m talking of course about the tendons and ligaments, something we often refer to as our connective tissue. But before we jump into what tendons and ligaments are, what do we mean if we refer to our ligaments and tendons as connective tissue?
Fundamentals of connective tissue
Connective tissue is a type of tissue that serves a structural purpose, like keeping your organs in place and preventing your eyes from popping out during a 1RM record attempt squat. It’s the difference being a structure that is both strong, flexible and that can withstand an impact, compared to being a loose blob of curry on the ground. To answer why we refer to our tendons and ligaments as our connective tissue and what prevents us from being a loose blob on the ground in the first place is to also understand what makes connective tissue unique.
First, there are three things that all connective tissues have in common that set them apart from other tissues in our body. The first is that they all originate from the mesenchyme, a loose fluid of embryonic tissue that can transform into many different tissues. Think of this tissue fluid like the layers of paint being applied to a skeleton in a Sci-Fi movie or TV show (like Westworld, the cover photo of this article) where eventually the layers add up to transforming the skeleton into a real human being. The second difference is that these cells originating from the mesenchyme, called the mesenchymal cells, can be situated any-which-way and are able to move from place to place. The third and final thing that separates connective tissue from other tissues is that literally all of it is composed of non-living material, called the extracellular matrix (ECM). In this particular case, the cells that reside in the matrix are actually LESS important than the matrix itself. You can think of the matrix as representing a piece of dessert jello with flowing pieces of goodies inside that are protected.
To expand on the analogy of the jello, the jello can be considered to be build up of two components: The first is the ground structure, which fills up the space between cells and acts as a form of protection. It is flexible because it consists of tons of starchy protein molecules mixed with water. The anchors of this framework are made up of proteins called proteoglycans. These anchor points have long starchy strands connected to them like ropes called glycosaminoglycans, or GAGs, that clump together in water like the gluten in flour that makes it firm and stretchy. The second part and running throughout the jelly are the fibers, which provide support and structure to an otherwise shapeless ground structure.
Elastin is one of those fibers and as the name slightly implies, has the property of being elastic. It allows tissues to ''snap back'' to their original shape after being stretched or contracted like your skin, or pulling on your ear. Another good example of where to find elastin is silverskin, that is the white fibrous tissue that you sometimes find on the surface of a muscle. Elastin can mostly found in the artery walls, lungs and intestines, not forgetting the skin.
Another class of fibers are the reticular fibers. Reticular fibers are sponge-like fibers that form delicate sponge-like networks that cradle and support your organs.
Lastly, collagen is by far the strongest and most abundant type of fiber in our body making up for up to 35% of our total body protein stores [1]. Collagen differs from elastin in a way that it is slightly less stretchy and can actually be softened and melted away if its cooked in something like a muscle-part of an animal - which makes the muscle taste moist.
Taking these different fibers into consideration, the distribution of fibers determines if they’re considered a form of loose connective tissue that is characterized with having less fibers, more cells and more ground substance, or dense connective tissue, which is characterized by being either more tight, irregular and/or flexible tissue. Our focus in this article is going to be on the dense connective tissue, that is the regular type, which is characterized by tight bundles of collagen running parallel and relate to our central question about tendon and ligament health.
The composition of tendons and ligaments
Now that we’ve got a general understanding of connective tissue and what characterizes the different tissues, we can start taking a closer look at the composition of tendons and ligaments. Although they differ in functionality, they share a basic framework and molecular composition, making them suitable for concerted discussion. [2] As discussed earlier, what makes up the ECM largely characterizes their structure and thus their function. Embedded in the ECM are the fibroblasts that are responsible for synthesizing the ECM’s components (collagen, elastin, proteoglycans) and by that, determining its composition. Furthermore, the fibroblasts are interconnected across the tendon/ligament via gap junctions [3], allowing the cells to communicate and respond in an uniform fashion to internal stimuli like growth factors and external stimuli like loading.
Collagen is the major type of fiber found in the ECM, making up around 80% of dry weight of ligaments and tendons [3][4], and is responsible for most tensile strength in this particular connective tissue. Just like type I, IIa and IIb muscle fibers, collagen comes in different isotypes as well. The vast majority of collagen is composed of collagen isotype I molecules that are arranged in a parallel, wave-like fashion and form composites within the ECM, allowing the tendon/ligament to withstand tension [5.]. Another similarity between muscles and tendons/ligaments is their hierarchical structure, starting at the smallest functional unit and forming increasingly large composites all the way to the complete muscle/tendon/ligament.
Other components of the ECM synthesized by the fibroblasts include elastin (2%) which we’ve addressed earlier and proteoglycans (1-5%)[6], which are proteins with attached sugar groups, that are responsible for the crosslinking of collagen fibrils [7].
Now that we’ve come to understand what makes up tendons and ligaments and how these characterizations shape the ECM, we can now understand the crucial role collagen synthesis plays in providing structural integrity for tendons and ligaments.
Collagen synthesis and recovery
As discussed earlier, the fibroblast are responsible for synthesizing the ECM including collagen, the main component of tendons and ligaments. Collagen synthesis can be considered a classic protein biosynthesis mechanism and thus also being concordant in its basic sequence with muscle protein synthesis. When stimulated, peptide chains called ‘’preprocollagens’’ are synthesized by ribosomes inside the fibroblast. Preprocollagen is mostly comprised of the repeated amino acid sequence glycine-X-Y, resulting in glycine being the predominant amino acid of collagen. This abundance of glycine makes collagen a notable exception to the rest of the proteins inside the body, which usually contain only small amounts of glycine. Inside the ribosome, proline, the second most common amino acid in collagen, and lysine are hydroxylated by enzymes that require Vitamin C as a cofactor.
Besides hydroxylation, further modifications like cleaving and glycosylation take place, allowing the peptide chains to form a triple helix (procollagen) that gets secreted into the extracellular matrix. Outside the fibroblast, procollagen gets cleaved another time, resulting in the finished triple helix collagen molecule (tropocollagen). Lastly, the lysine and the hydroxylysine parts of the collagen molecule are oxidated by lysyl oxidase, allowing the collagen molecules to aggregate to collagen fibrils.
Now that we understand how collagen is formed, we can start addressing the way in which tendons adapt to internal and external stimuli - but in order to do so, we have to understand their function first.
Tendon and ligament function
Ligaments connect bone to bone and are key structures for joint stability by blocking certain displacements of the joint and restrict movements within their physiological range [8]. While the function and properties of ligaments are pretty basic in nature, the functionality of tendons is a little more intricate and requires thorough explanation.
The main function of a tendon is to transmit forces exerted by the muscle to the skeleton and shows two distinct mechanical properties: non-linear elasticity and viscoelasticity [9]. The tendon’s non-linear elasticity, which differs depending on the tendon, can be observed in its non-linear stress/strain curve as shown in the top image. The toe region represents the „straightening“ of the wave-like collagen structure, leading to a non-linear slope. With increasing stress, the tendon’s collagen fibrils orient themselves in the direction of the mechanical load and stretch, thus leading to the linear part of the stress/strain curve. This linear part of the stress/strain curve can be considered a representation of the tendon’s elasticity, which means that when the loading is discontinued, the tendon will revert back to its original length. When the applied stress on the tendon results in tendon strain that exceeds approximately 4%, plastic deformation of the tendon starts to occur and the tendon is lengthened irreversibly due to failure of crosslinks between collagen fibrils, consequently damaging the tendon. This irreversible lengthening of the tendon continues with increasing stress until the applied stress causes a strain of 8-10%, the point at which the tendon ruptures [9].
The tendon’s second distinctive mechanical property is its viscoelastic behavior, which means the strain of the tendon is not exclusively dependent on the amount of stress that is applied to it but also on the rate at which the strain occurs, resulting in a non-constant relationship between stress and strain of a tendon. This behavior can be illustrated by comparing a slow, near maximum squat to a depth jump. In general, tendons at low strain rates, like those during a slow squat, are more deformable and less likely to rupture but absorb more mechanical energy and thus are less effective in carrying mechanical loads. In contrast, depth jumping exposes the tendons to a tremendously high rate of strain, resulting in the tendon being less deformable, more prone to injury but also more effective in transmitting high forces from muscle to bone [9].
Tendon and ligament adaptation
For a long time, tendons and ligaments were considered static tissues that show no adaptation to loading and act merely as structural components of the musculoskeletal framework. This widely held assumption among scientists and practitioners alike lead to the disregard of tendon strengthening protocols as a reasonable approach to injury prevention and rehabilitation. As more research on tendon health and development was performed, it turned out that these connective tissues are in fact highly dynamic and adaptable to training stimuli [10]. While the optimal training stimuli to elicit tendon adaptation are still not convincingly specified, the adaptations themselves and the adaptation process have been well established [10].
Research has currently established two possible mechanisms that allow a tendon to adapt to increasing mechanical demands: the first is an increase of the tendon’s cross sectional area (i.e. hypertrophy), with the second being a change of the tendon’s mechanical properties (i.e. an increase in tendon stiffness). The first postulated mechanism is tendon hypertrophy induced by load-induced strain of the extracellular matrix [10]. This load-dependent strain is transmitted to the cytoskeleton of the embedded fibroblast, activating a signalling cascade that ultimately leads to an up-regulation of collagen and matrix protein synthesis, allowing the tendon to increase in size. Furthermore, research demonstrated a second adaptive mechanism: mechanical loading increased the production of enzymes that are responsible for collagen crosslinking, thus leading to an increase in tendon stiffness associated with a lower electromechanical delay, greater rate of force development and jump height [10]. It is noteworthy that although tendons can adapt to mechanical loading via an increase in stiffness, healthy tendons are variable in their mechanical properties along their length. This makes sense, considering that the connection of two mechanically different tissues, like muscle and tendon or bone and tendon, can cause high stresses at the interface, possibly leading to injury. In order to align the mechanical properties of the connecting tissues, collagen crosslinking along the length of the tendon from bone to muscle decreases, leading to a stiffer tendon towards the bone and a more pliable tendon towards the muscle [11]. What happens when this mechanical variability is lost can be observed as a result of immobilization: preventing a joint to move causes an increase of tendon stiffness in the pliable region and an increase in ultimate tensile strength, likely due to increased collagen crosslinking [12]. Although ultimate tensile strength of the tendon increases, this reduction of pliability near the muscle increases the probability of damaging lengthening contractions. These damaging contractions are a result of the tendon’s stiffness exceeding the isometric strength of the muscle, thus increasing injury risk post-immobilization [11]. Although an adaptation of tendon stiffness can be considered a good thing for dealing with higher mechanical loads, it is of vital importance that the tendon remains mechanically variable.
Now that we have established the mechanisms by which tendons adapt, we can start taking a look at the temporal dynamics involving tendon adaptation compared to muscle tissue.
Temporal dynamic of tendon adaptation
Tendon tissue is characterized by a lower cell to overall dry mass ratio, vascularization, and metabolism compared to muscle tissue and research shows that the half-life of tendon collagen is almost tenfold higher compared to actin and myosin part of muscle tissue [10]. Furthermore, it has been postulated that tendon remodeling almost exclusively occurs in the outside regions of the tendon with the core of the tendon showing no significant collagen turnover [10]. These tendon properties combined with findings of heavy resistance training intervention studies, where changes of muscle morphology and architecture occurred as early as 3-4 weeks with no significant alterations of the tendons[10], can lead to the assumption that meaningful tendon adaptation occurs with a significant delay compared to muscle morphology and strength. That assumption is substantiated by exercise intervention studies that observed a 1-2 month delay in tendon adaptation in comparison to gains in muscle strength. What further underpins these findings is the fact that an increase in muscle strength can be achieved by neuronal adaptations that precede morphological changes of the muscle [10]. In contrast to that, adaptations in tendon resilience rely exclusively on the adaptation of the tissue structure, which tends to be a slower process due to the lesser rate of effective tissue renewal compared to muscle[10]. As a result of these hypotheses, it’s possible that imbalances between muscle and tendon development might occur during the training process, which brings us to our next aspect of the tendon’s adaptive process: which loading strategy is optimal for tendon health and development?
How different loading patterns influence tendon development
First off, this aspect of tendon adaptation has not been conclusively researched and needs further investigation. That being said, research and the aforementioned mechanism of fibroblast stimulation via deformation suggest that slow repetitive high-magnitude (at about 90% isometric maximum voluntary muscle contraction) tendon strain might be the best approach to elicit the greatest adaptations in healthy tendons [10]. It is noteworthy that the specific muscle contraction type (isometric, concentric, eccentric) seems to be of little relevance for triggering the adaptation process. Research that incorporated other loading schemes like plyometric loading (i.e. a high-magnitude, high-frequency tendon strain loading protocol) failed to elicit significant adaptive changes in tendon structure, although improving muscle strength [10]. This finding might provide at least some insight concerning the high prevalence of tendon overuse injuries in sports with a plyometric loading profile like basketball or athletic jumping and warrants additional research. Furthermore, research suggests that fatiguing training with moderate loading, like classic muscle hypertrophy training, effectively triggers adaptations in muscle strength and size, yet doesn’t provide sufficient stimulus for meaningful tendon adaptations to occur [10]. This lack of tendon adaptation could result in an increase in tendon strain as a result of increased muscle strength without the appropriate tendon adaptations, causing a possible risk for injury[10]. With that in mind, a compelling case might be made for implementing strength focussed training phases from time to time, even for athletes that exclusively train for muscle size.
While collectively these findings might indicate an appropriate strategy to promote tendon strength in healthy tendons, a different approach might be necessary for promoting recovery in injured tendons and ligaments. Research that used an in vitro tendon/ligament model, which properties more closely resemble developing/recovering tendons/ligaments (i.e. higher cell count, less matrix, higher expression of developmental collagen isotypes), provides findings that deviate from the findings concerning healthy tendons. Study of those engineered ligaments showed that the molecular response was independent of loading intensity and frequency [13]. Interestingly, it could be observed that the duration of the applied loading played a significant role in determining the molecular response. After about ten minutes of loading, the molecular response reached its maximum and additional time under load did not increase the molecular response any further. Moreover, it took six hours for the engineered ligaments to become responsive to loading again. These findings suggest that short bouts of lightly loaded exercise with potentially limited range of motion and extensive breaks between bouts might be the best way to aid tendon/ligament recovery.
Hormonal influence on tendons and ligaments
Lastly, although the specifics are not understood yet, hormonal status plays a role in influencing tendon and ligament integrity. One hormonal effect that has been well established is estrogen’s influence on ligament laxity [11]. Research showed that the degree of knee laxity and higher incidence of ACL rupture in female athletes compared to their male counterparts seems to be related to circulating estrogen levels [11]. In an attempt to confirm this, the researchers using the engineered ligaments exposed those ligaments to a physiologically high estrogen level that mimics the estrogen surge leading up to ovulation [14]. After 48 hours of exposure, they observed a decrease in ligament stiffness although the collagen collagen content did not decrease, which hints at a decrease of collagen crosslinking. To test this hypothesis, the researchers measured the activity of the primary collagen crosslinking enzyme, lysyl oxidase, under the aforementioned estrogen exposure of the ligaments. They observed that the activity of lysyl oxidase dropped as much as 80% after 48 hours of physiologically high estrogen exposure. Consequently, it seems reasonable to consider estrogen an influential factor for tendon and ligament integrity, especially in female athletes.
In contrast to estrogen, little is known about the effects of testosterone on tendon and ligament properties. Research only suggest that the use of androgenic and anabolic steroids in supraphysiological doses stimulate collagen synthesis and tendon stiffness, yet reduces tissue remodelling ultimate stress and strain, which might warrant some implications for long-term drug users [10]. That being said, little is known about the effects of physiological levels of testosterone on tendon and ligament development.
Another interesting observation was made when engineered ligaments were grown in media that was infused with isolated sera from human test subjects pre- and post exercise. The ligaments that were grown in the media containing post-exercise sera showed a significant increase in collagen content and mechanics compared to the ligaments grown in pre-exercise sera [15]. Furthermore, the same study showed that this stimulation of connective tissue was not mediated by growth hormone and IGF-1 but used the mTORC1 pathway, hinting at a global signal that improves connective tissue integrity in response to exercise. Finally this study showed that the treatment of engineered ligaments with high doses of recombinant growth hormone had no effect on collagen content or ligament mechanics. Yet, IGF-1 dose-dependently stimulated collagen synthesis and affected ligament mechanics. This observation substantiates the idea that physiological levels of growth hormone have an indirect effect on tendons and ligaments via regulation of IGF-1.
Now that we have briefly elaborated on the physiological and mechanical properties of tendons and ligaments and how they respond to loading and hormonal status, it‘s time to discuss how we might improve tendon and ligament development via nutrition and supplementation.
Nutrition and supplement considerations for optimizing tendon and ligament health
Regarding everyday nutrition, consuming a leucine-rich diet seems to be beneficial for improving tendon and ligament health. Researchers observed that consumption of whey protein, which is rich in leucine, can increase tendon hypertrophy in response to strength training. This observation could possibly be explained by the fact that leucine activates the mTORC1 pathway, a pathway that was also activated in engineered ligaments after treating them with sera that were collected from human subjects post-exercise. In spite of this hypothetical connection, it is not clear whether the study‘s result is based on a direct effect of whey protein intake on tendons or a byproduct of increased muscle hypertrophy and strength gains caused by whey protein consumption [16]. With no conclusive evidence for a direct effect of whey protein on tendon health and the fact that the diet of most fitness enthusiasts is rich in leucine for muscle building purposes anyway, we can take a look at a more interesting aspect: intake of actual collagen and its processed derivatives.
Research suggests that ingestion of collagen peptides has a plethora of effects on the human body. Besides their potentially beneficial effects on skin, osteoporosis, the immune system and precursor cell differentiation to only name a few [17] [18], research also suggest that ingestion of collagen peptides has beneficial effects on both collagen synthesis and tendon mechanics [19]. While measuring the plasma concentration of amino acids after oral collagen peptide ingestion, researchers observed high concentrations of oligopeptides, like proline-hydroxyproline and hydroxyproline-glycine, two hours after ingestion [18]. With collagen molecules heavily featuring the repeated amino acid sequence glycine-X-Y, with X and Y frequently occupied by proline and hydroxyproline, collagens high bio-availability and the fact that oligopeptides containing hydroxyproline are highly resistant to blood proteases [17], this observation seems comprehensible. Aside from collagen peptides providing the necessary amino acids for collagen synthesis, several studies also suggest that these stable hydroxyproline containing oligopeptides act as signalling molecules and thus being partly responsible for mediating the effects of collagen peptide ingestion[18]. Although the actual mechanism hasn’t been established yet, this might make a compelling case for increasing collagen intake considering the fact that hydroxyproline is almost exclusively found in collagen as a nutritional source
What further substantiates these hypotheses is a study on engineered ligaments [20]. During this double-blind crossover study, the researchers administered different doses(0g, 5g, 15g) of gelatin, a hydrolyzed form of collagen, to human test subjects along with a small dose (48 mg) of vitamin c, one hour prior to six minutes of jumping rope. The researchers collected blood samples of the participants at different time points and added the sera to the growth media of the engineered ligaments. They found a dose-dependent increase in collagen deposition with 15 g of gelatin doubling the collagen synthesis rate in engineered ligaments.
In another study performed on osteoarthritis patients, around 10 grams of collagen hydrolysate a day was significantly able to thicken the cartilage [21]. The same 10 grams of collagen hydrolysate in another study led to improvements in joint pain in athletes over a 24-week period [22].
Having these promising findings in mind, we have to take a look at actual collagen intake. Since collagen is the single most abundant class of proteins of the vertebrate body making up about one-third of an animals total protein content, it can’t be found in non-animal products [17]. Despite this abundance of collagen in vertebrates, the average collagen intake is presumably pretty low among non-meat-eaters and meat-eaters alike.
One of the reasons for low collagen intake might be that collagen is missing an essential amino acid, tryptophan, thus being considered a low-quality protein that doesn’t get much attention. Further possible reasons include that cuts of meat high in collagen, like pork chitterlings or chicken gizzard [18], tend to be less desirable to the general population’s palate or that the more chewy, fibrous parts of meats get trimmed off.
Caption: Beef vs. fish and shellfish (adopted from [24] and modified from [18]
That being said, there are alternatives to eating fibrous meats to reap the beneficial effects of nutritional collagen. Collagen can be extracted from collagen-rich animal tissues like skin, bone and tendons. After extracting the collagen, it gets processed via hydrolysis. Depending on the degree of hydrolysis, you either get the partially hydrolyzed collagen product gelatin or the fully hydrolyzed collagen hydrolysate. While both being tasteless and available in powdered form, the main differences between the two products are price, availability, molecular weight and usage. Gelatin is higher in molecular weight, relatively cheap, found at any convenience store and can be dispersed in liquids or used as a gelling agent for jellos and such. Collagen hydrolysate on the other hand is more expensive, can not be used as a gelling agent due to its lower molecular weight and is usually purchased at supplement stores.
At this point in time, there are no studies demonstrating a meaningful difference in bio-availability although collagen hydrolysate is claimed to be easier to digest. Both products seem to be sufficiently absorbed by the intestines as free form amino acids and oligopeptides [17] [18][23], making them equally suitable for increasing your collagen intake.
Putting it all together – a proposed protocol for tendon and ligament prehab and rehab
Preface: With research on influencing tendon and ligament development still in its infancy, these recommendations should be considered speculative and non-definitive. If you suffer from tendon or ligament injuries, please consult with your physician or physiotherapist first before implementing such a protocol.
Protocol for strengthening healthy tendons
This protocol should be used for strengthening healthy tendons and ligaments that are particularly stressed during your preferred movements in order to reduce their chance of injury. First, pick a movement that targets the tendon or ligament you intend to strengthen. You can either choose an eccentric-concentric movement, like the squat for strengthening the patellar tendon, or opt for isometric exercise like knee extension against a non-elastic band. Research suggests that the chosen exercise should be performed for 5 sets of 4 repetitions with each repetition consisting of three seconds of high intensity contraction (85-90% iMVC) followed by three seconds of relaxation and two minute inter-set rest intervals [10]. It is important that these exercises are performed at a joint angle that is close to optimal for force production, for example 60° knee flexion for patellar tendon training, in order for high tendon forces to occur. While performing isometric exercises at a certain angle is relatively easy to achieve, eccentric-concentric movements like the squat move through a wide range of angles during its full range of motion. To account for that and allow for sufficient time at which high tendon forces occur, the duration of a repetition is doubled from three to six seconds for dynamic movements [10].
This proposed set and rep scheme should be implemented three times per week along with your regular training for at least twelve weeks and can be applied to multiple exercises to strengthen different tendons and ligaments concurrently. To optimize training results, athletes are encouraged to ingest 15 g of gelatin or collagen hydrolysate with a small dose of vitamin c one hour prior to tendon training [11]. This can be done by dispersing the collagen product in a liquid that contains vitamin c (like juice) or by preparing a jello made from gelatin that also contains vitamin c. Moreover, it might be worth mentioning why the collagen product should be consumed one hour prior to training: while blood flow to inactive tendons is limited, suggesting limited nutrient uptake into the tendon post exercise, glucose uptake into active tendons is increased during exercise [25]. Thus, in concordance with the absorption rate of collagen peptides, taking the collagen product one hour prior to exercise seems reasonable to optimize nutrient uptake into the tendon.
Lastly, leucine-rich protein should be consumed as part of training to reap the potential benefits of mTORC1 activation on tendon and ligament development[11].
Protocol for accelerating the rehabilitation process after tendon and ligament injury
This protocol can be implemented to potentially speed up the recovery process after tendon and ligament injury. While the recommendations for collagen supplementation and leucine-rich protein remain the same, this protocol follows a different approach to training and is inferred from the observations regarding engineered ligaments, as they more closely resemble regenerating ligaments and tendons. Following injury, athletes should start their recovery training protocol as soon as possible by picking movements that target the injured tendon or ligament. Depending on the severity of injury, these movements can consist of weight supported exercises with limited range of motion if necessary. To maximally stimulate collagen synthesis, training bouts can be performed multiple times per day but should not exceed ten minutes of activity per single session. Furthermore, each training bout should be followed by at least six hours of rest to allow the connective tissue to become responsive to loading again and yield optimal results [11].
Training and supplementing for tendon and ligament health - the verdict
Although research provides some insight regarding training and supplementing for tendon and ligament health, these observations are far from warranting definitive protocols and should be treated as such. To close in on best practices for tendon and ligament health, extensive research has to be conducted, including the role of hydroxyproline oligopeptides, overall training volume, rest intervals and in vivo studies of recovering tendons and ligaments. It also remains unclear to what degree the total amount of protein matters in a diet that already contains the required contains sufficient protein to stimulate maximum protein and if adding additional protein with specific amino acids might yield more optimal results on top of muscle growth. Despite this rudimentary understanding of training and supplementing for tendon and ligament health, the proposed protocols represent our “best guesses” and might be worth a shot since they can be considered time- and cost-effective plus offering a desirable risk-reward ratio.
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