Sport Specialization
Health,  Rants

Should you test your kids muscle fiber type for sports specialization?This article is a 7 min read

Sports specialization has dramatically increased with youth as free play has decreased. Sports specialization is defined as year-round training in one sport with the exclusion of other sports (Jayanthi, Pinkham, Dugas, Patrick, & LaBella, 2013). In the British Training of Young Athletes Study researchers found that generally parents drove initial interest in a specific sport, however it was coaches who influenced the drive for intense training (Baxter-Jones, Maffulli, & TOYA, 2003). Further, a study of high school athletic directors also suggested that coaches were a strong influence on athlete’s decision to specialize in a sport and engage in intensive training (Hill & Simons, 1989). According to Jayanthi et al, this may unintentionally have deleterious effects for the student-athlete. The parent fosters initial interest, the student-athlete has success, the coach encourages sports specialization and intensive training which in turn increases the risk of injury during critical growth periods (2013).

As stated above parents have a great influence on sports participation. In the Training of Young Athletes Study, it was demonstrated that youth with potential for sports success that did not have active parental support were less likely to participate. As parents make the decision for their child to enter sports most do based on the desire for recreation. However early sports specialization may be driven to give their child a competitive edge (Malina, 2010).

Competition, muscle fibers, and sports specialization

The competitive edge has not only influenced onset on sports specialization, but also a focus on the evolving science behind genetics and muscle typing. We have two major types of muscle fibers, slow and fast twitch. Fast twitch can be further subdivided into three sub-classifications, type IIa, IIx, and IIb. This typing of muscle fibers are based on how they produce adenosine triphosphate (ATP), the type of nerve innervations, and the type of heavy myosin chain expression (McArdle, Katch, & Katch, 2015). Slow twitch fibers are associated with slower contraction times, greater resistance to fatigue, and are the main muscle fiber type activated during long endurance steady-rate activities (McArdle, Katch, & Katch, 2015). High distribution of slow twitch fiber types are found in elite distance runners and cross-country skiers (McArdle, Katch, & Katch, 2015). Strength and power athletes demonstrate higher distribution of Type IIa fibers (Beardsley, 2017), for example, soccer, lacrosse, and ice hockey (McArdle, Katch, & Katch, 2015).

According to researcher Chris Beardsley regarding testing muscle fiber type “Currently, all current gold standard methods are invasive and involve taking muscle biopsies” (Beardsley, 2017). There are three methods Myosin ATPase histochemical staining, MHC isoform identification, and Biochemical identification of metabolic enzymes (Beardsley, 2017). Each test makes the assumption that the limiting factor of what speed the cross-bridge cycling can occur is the rapidity of ATPase at the myosin head hydrolyzing ATP to energize the process (Beardsley, 2017).  If a parent is not inclined to have their child biopsied there is an alternative.  Atlas Sports Genetics has marketed a saliva test that looks for the ACNT3 gene. Some research has linked the RR gene variant with type II muscle fiber development and the type XX variant with type I fibers (Peterson, 2008). One problem with these tests is that over 220 genes have been identified and linked with athletic performance. To look at one expression is questionable at best.

There are three ways that fiber type cross-sectional area (CSA) can be measured, proportionate CSA, absolute CSA, and relative CSA. Some of these may be susceptible to change with training. For example, the absolute measure will increase for all fiber types with strength training due to hypertrophy (Beardsley, 2017).  However, we may see a decrease in type IIx fibers with strength training and endurance training with an increase of the proportion of type IIa fibers (Beardsley, 2017).

At extremes, muscle fiber type may enhance an athlete’s ability to participate in a sport. However, both slow and fast twitch fibers are involved for many sports such as middle-distance running or in “stop and go” sports such as soccer, hockey, and basketball (McArdle, Katch, & Katch, 2015). Independent of fiber type other factors play into athletic success. These include other physiologic, biochemical, neurological, and biomechanical supports (McArdle, Katch, & Katch, 2015). For example, individual differences in a muscle fiber-motor unit ratio may contribute to variations in skills development (McArdle, Katch, & Katch, 2015). Practicing a movement creates a neuromuscular “groove” that embeds a learned pattern of movement – whether it is learned correctly or not. This further supports the importance of neural aspects in sports training.

Faulty reasoning and risks

In my opinion, the reason for obtaining information regarding information about muscle fiber typing of children to guide them into sports is faulty. Outside of using muscle biopsy testing for medical purposes it has no place in youth sports for predicting future success. Using it to see which sport or sports a child should specialize in to give them the time needed to gain the skills necessary to compete at high levels is unwarranted. Research has suggested that early diversification is more beneficial to future athletic success (Caruso, n.d, Jayanthi, Pinkham, Dugas, Patrick, & LaBella, 2013, Rusin, 2017). According to Robert Malina in an article on sports specialization, he wrote: “Risks of early specialization include social isolation, overdependence, burnout, and perhaps risk of overuse injury” (2010). Injury during essential periods of growth and development can prove catastrophic as extended periods of inactivity during this period are at best counterproductive and worst can increase health risks (Rusin, 2017). Interesting, a simple test to assess athletic prowess is the finger test. It requires a simple measure of lengths of the index finger and ring finger. You divide the index finger by the ring finger and if the ratio is closer to .90 than 1.0 you may have a future elite athlete. It is based on analysis of exposure testosterone while in the womb. According to the theory the greater exposure to testosterone during fetal development the greater chances for enhanced physical and motor ability (Peterson, 2008).

Rethink why

For youth, participation in athletics is about fun and should be building self-esteem (Rusin, 2017). However, with sports specialization we see a different picture, one of competition based performance (Myer et al., 2015, Rusin, 2017), increased injury potential (Myer et al., 2015, Rusin, 2017), decreased free play (Myer et al., 2015, Rusin, 2017) and possible physical and emotional abuse (“Best Practice for Youth Sport: Specialization in Youth Sport,” n.d.). Options other than biopsies or saliva testing exist in developing elite talents such as an emphasis on the ABCs — agility, balance, coordination, speed and the paradigm of long-term athlete development (LTAD) which has been used successfully since the 1990’s (Brenner, 2016).


Baxter-Jones, A. D., Maffulli, N., & TOYA, G. R. (2003, June). Parental influence on sport participation in elite young athletes. Retrieved October 4, 2017, from

Beardsley, C. (2017, April 12). Muscle fiber type. Retrieved October 4, 2017, from

Best Practice for Youth Sport: Specialization in Youth Sport. (n.d.). Retrieved October 4, 2017, from

Brenner, J. S., & Council On Sports Medicine And Fitness. (2016, September 01). Sports Specialization and Intensive Training in Young Athletes. Retrieved from

Caruso, T. (n.d.). Early Sport Specialization Versus Diversification in Youth Athletes. Retrieved October 4, 2017, from

Hill, G. M., & Simons, J. (1989). A Study of the Sport Specialization on High School Athletics. Journal of Sport and Social Issues, 13(1), 1-13. doi:10.1177/019372358901300101

Jayanthi, N., Pinkham, C., Dugas, L., Patrick, B., & LaBella, C. (2013, May). Sports Specialization in Young Athletes: Evidence-Based Recommendations. Retrieved October 4, 2017, from

Malina, R. M. (2010). Early Sport Specialization. Current Sports Medicine Reports, 9(6), 364-371. doi:10.1249/jsr.0b013e3181fe3166

McArdle, W. D., Katch, F. I., & Katch, V. L. (2015). Exercise physiology: Nutrition, energy, and human performance (8th ed.). Baltimore: Wolters Kluwer Health/Lippincott Williams & Wilkins.

Myer, G. D., Jayanthi, N., Difiori, J. P., Faigenbaum, A. D., Kiefer, A. W., Logerstedt, D., & Micheli, L. J. (2015). Sport Specialization, Part I. Sports Health: A Multidisciplinary Approach, 7(5), 437-442. doi:10.1177/1941738115598747

Peterson, D. (2008, December 15). How to Pick Athletic Superstars at Age 1. Retrieved October 4, 2017, from

Rusin, J. (2017, July 10). Early Sport Specialization Is Killing The Health of Our Kids. Retrieved October 4, 2017, from

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