Well it’s fantasy football season for me, which means I have my eye on the injury list. Some players get the unfortunate label of being “injury prone” which got me thinking. Is there such a thing? Does it depend on the position, how good the defense is, or is there something going on with the athlete? Is it a strength deficiency, movement error, or dumb luck?

I talked to one of my colleagues, Scott McNulty of Naples Sports and Spine Therapy (another doctor of physical therapy), and he suspected there is something going on at the connective tissue level. Perhaps ligamentous laxity or something of that nature. 

Before we dive into it, we have to have a basic understanding of collagen. Collagen is the main protein found in connective tissues. Connective tissue is all over the body, and is in bones, skin, tendons, muscles, ligaments, organs, etc. Depending on the mineralization, it can be rigid or compliant, and anywhere in between. Fibroblasts are cells that create collagen. Gene expression influences the activity of fibroblasts and collagen formation. There are several types of categories of collagen. For now, all we need to understand is types 1-3. Type 1 has tensile strength meaning that it is found in tendons and things that need to stretch. Type 2 has compressive strength and therefore is found in cartilage. Type 3 provides structural integrity of arterial walls and mutations in the gene that express type 3 production (COL3A1) have been implicated in aneurysm formation and vascular Ehlers Danlos Syndrome (Kuivaniemi & Tromp, 2019).

The COL1A1 gene produces type 1 collagen, the tensile one that forms tendons and ligaments. There is a polymorphism that affects the way the gene expresses itself. About 20% of people have a mutation that causes an increased expression of this gene, which may increase the tensile strength of tendons and ligaments. About 4% of athletes carry a two-fold propensity for this gene expression and have significantly decreased risk for ACL ruptures and achilles tendinopathy. There are other polymorphisms of the COL1A1 that are associated with decreased injuries in shoulder dislocation and muscle strain severity (Goodlin et al., 2015). 

There is an association between type 1 and type 3 collagen. We know that in wound healing, type 3 collagen helps repair the injured site, then in the later stages of maturation, the type 3 collagen is replaced by the stronger type 1 collagen. A study by Stępień-Słodkowska in 2015, found a correlation between overexpression of the COL3A1 gene (for type 3 formation) and increased risk of ACL tears amongst Polish skiers. This may explain why things like ACL tears, achilles tears, and rotator cuff tears seem to run in families. 

There are genetic tests that may help with injury risk assessment, but it may be easier than that. Since connective tissue is determined by gene expression, the young athlete may only look to her mother with osteoporosis to know that she may be at risk for fracture. However, this brings up a huge philosophical question. How much information is too much? Are we just invoking more fear? Will the athlete with a mother who has osteoporosis opt out of sports? Perhaps she doesn’t even have the gene. 

Or, with mutations in the COL3A1 gene, cardiac arrest can spontaneously occur. So now we are talking about death. At what point does legislation intervene and create mandates? In 2012, Pennsylvania adopted the “Sudden Cardiac Arrest Prevention Act”. This means that an athlete has to be removed from play if they are “known to have exhibited signs or symptoms of sudden cardiac arrest at any time prior to or following an athletic activity”. They cannot return to play until cleared medically (Wagner, 2013). Genetic counselors are currently not on the list of practitioners that can clear the athlete, but what happens if they are allowed to be involved? Will this young athlete never be allowed to play sports? 

At the end of the day, muscles hold the skeleton together, as do ligaments and tendons. This is why I am a strong proponent of emphasizing strength rather than flexibility for our athletes. Although I think that an athlete should be able to fully express the positions required by their sport, they also have to have active control in the extreme end ranges of these positions. There are certainly cases where an athlete is missing range of motion and will need to mobilize, but more often than not, they are missing strength at the end ranges of motion where injuries occur. This is where sport specific strengthening is paramount. So for the hypermobile athlete, I do not think the answer is to stop playing their respective sport to avoid injury. I think the answer is to get as strong and resilient as possible. 

References:

Kuivaniemi, H., & Tromp, G. (2019). Type iii collagen (col3a1): Gene and protein structure, tissue distribution, and associated diseases. Gene, 707, 151–171. https://doi.org/10.1016/j.gene.2019.05.003 

Goodlin, G. T., Roos, T. R., Roos, A. K., & Kim, S. K. (2015). The dawning age of genetic testing for sports injuries. Clinical Journal of Sport Medicine, 25(1), 1–5. https://doi.org/10.1097/jsm.0000000000000158 

Stępień-Słodkowska M, Ficek K, Maciejewska-Karłowska A, et al. Overrepresentation of the COL3A1 AA genotype in Polish skiers with anterior cruciate ligament injury. Biol Sport. 2015;32(2):143-147. doi:10.5604/20831862.1144416

Wagner JK. Playing with heart and soul…and genomes: sports implications and applications of personal genomics. PeerJ. 2013;1:e120. Published 2013 Aug 1. doi:10.7717/peerj.120