More than 70% of visits to the physio/doctor for sportsmen and women at every level of competition are the result of musculoskeletal injuries. These injuries to muscles, tendons, ligaments, bones and cartilage are often the result of weakness within the extracellular matrix (ECM). In bone for example, the ECM is like the steel bars in reinforced concrete that increase the strength and ductility of the material. Therefore, strengthening the ECM has the potential to decrease sporting injuries. Beyond the role in injury prevention, ECM plays a further role in performance; increasing the rate of force development (one of the best measures of speed and power).
The ECM has long been considered an inert gel that just holds tissues together. In the last ten years, this view has been challenged by a number of experiments that demonstrate that the ECM is in fact a dynamic tissue that is essential to proper musculoskeletal function. For an athlete, the ECM has two main functions: 1) transmit forces quickly to maximize speed and performance; and 2) absorb energy from impact to prevent injury. Central to the first role are the ECM of muscle and tendon, whereas the second role also includes the ECM in ligaments, cartilage, and bone as well. Below, I will discuss how exercise and nutrition can maximize both functions.
ECM function is determined by the amount and cross-linking of collagen and the water stored within the tissue. The amount of water within the ECM does not appear to change appreciably with training, therefore for the ECM to become stiffer and stronger requires an increase in the amount of collagen or the number of cross-links binding the collagen proteins together. Cross-linking can be increased enzymatically (lysyl oxidase and prolyl-4-hydroxylase) or non-enzymatically (glucose-derived cross-links). In general, the enzymatic cross-links are beneficial and are regulated by exercise and nutrition, whereas the glucose-derived cross-links are detrimental and lead to many of the negative secondary outcomes of diabetes (high blood pressure, increased risk of tendon rupture, cataracts, etc.).
To maximize speed and power performance, coaches use high velocity movements with a significant plyometric component. This type of training does two things to the ECM: 1) increases the collagen content and cross-linking within the muscle ECM; and 2) increases the cross-linking of the ECM in the muscle end of the tendon. The result is that force can be transmitted from muscle to bone faster resulting in an increase in speed and power.
To prevent muscle injuries, coaches and physical therapists use slow movements; either heavy weight training, slow eccentric movements, or heavy isometric holds. This type of training does two somewhat different things to the ECM: 1) it will still increase the collagen content and cross-linking within the muscle ECM; but unlike the fast movements this type of training will 2) decrease the cross-linking of the ECM in the muscle end of the tendon. Since the muscle end of the tendon functions as a shock absorber, decreasing stiffness in this region of the tendon will protect the associated muscle from injury.
Even though coaches have some tools improve muscle and tendon performance and injury rate, there are fewer tools to prevent injuries in ligaments, cartilage, and bone. This is largely because we haven’t really understood how these tissues respond to loading and nutrition. Recent advancements in this area provide hope for a new toolset to prevent stress fractures, and progressive ligament and cartilage degeneration
The first advance came from research in rodents and humans that showed that short loading protocols (5 and 40 loads) separated by >6 hours of rest were enough to maximize bone synthesis rates. Similarly, we showed that collagen synthesis in ligaments was maximized by short periods (5-10 minutes) of exercise separated by 6 hours of rest. These data suggest that, unlike muscle that continues to adapt as long as we exercise, our ECM only gets the signal to adapt for 5-10 minutes before the cells start shutting down. Everything after that is causing mechanical fatigue and damage without giving a further stimulus to adapt and get stronger.
This means that for our ECM we should be doing short periods of loading (5- minutes) that target the tendons/ligaments/bones/cartilage that we use in our sport (jump rope for runners, bench step ups for basketball players, rotator cuff exercises for baseball/water polo/cricket players). These training sessions should be performed at least 6 hours away from our other training (where possible). These protective sessions serve to stimulate ECM production and decrease the likelihood of repetitive stress injuries to bone, ligament, tendon, and cartilage.