Exercise-induced muscle damage (initial phase)
The presence of certain genetic variants could explain why some people are less likely to be injured than others, as well as having an easier time recovering from prolonged and strenuous exercise. Knowing how someone will respond to a particular type of exercise can guide us in personalizing our workouts, while reducing the risk of injury associated with muscle overload.
Exercise can produce muscle damage through a series of two types of alterations, some of early onset and of mechanical origin, while others are a consequence of the previous ones and are due to the inflammatory process triggered.
Eccentric exercise training is one of the most commonly used models. Eccentric exercise is that in which the muscles are stretched while maintaining their contraction, such as, for example, squats.
This type of exercise is successfully included in the training of different sports contexts, improving muscle strength, coordination and performance. Changes in the elastic properties of muscles and connective tissue are known to occur. However, containing an eccentric exercise phase, it is highly associated with muscle damage and soreness.
As older people appear to be more susceptible to exercise-induced muscle damage than younger adults, older people with a genetic predisposition to increased muscle damage may be at increased risk of developing muscle and tendon injuries.
There is evidence to indicate that early phase muscle damage, produced by mechanical damage, prior to inflammation, may be associated with several genetic variants. In the first phase or stage of muscle damage, alterations occur in the muscle structures responsible for the contraction of the myofibrils, which are the contractile structures found inside the muscle cells. Damage occurs in the proteins that form the myofibrils (such as collagen, actin, myosin, desmin, titin) and other proteins that interact with the cell cytoskeleton and the extracellular matrix.
Two polymorphisms associated with muscle damage produced in this first phase after exercise have been identified. These markers are found in the ACTN3 and MYLK2 genes.
The ACTN3 gene codes for a muscle-tendon interaction protein, and the marker analyzed has implications for the risk of muscle injury. Individuals carrying two copies of this mutation are unable to produce the alpha-actinin-3 protein and this hinders recovery. The absence of alpha-actinin-3 does not result in disease due to the compensatory effect of the alpha-actinin-2 protein, but it does affect fitness.
The MYLK2 gene, on the other hand, is responsible for producing the enzyme "myosin light chain kinase 2" which is expressed in adult skeletal muscle, in muscle fibers, and variants affecting its production may be related to muscle strength and blood levels of creatine kinase, a marker of muscle degradation.
Both markers, in turn, have been linked to increased risk of rhabdomyolysis (breakdown of muscle tissue that releases the contents of muscle fibers into the blood).
13.5 million variants
Baumert P, Lake MJ, Stewart CE, Drust B, Erskine RM. Genetic variation and exercise-induced muscle damage: implications for athletic performance, injury and ageing. Eur J Appl Physiol, 2016; 116(9):1595–625.
Ben-Zaken S, Eliakim A, Nemet D, Rabinovich M, Kassem E, Meckel Y. ACTN3 Polymorphism: Comparison Between Elite Swimmers and Runners. Sport Med, 2015;1(1):13.
Deuster PA, Contreras-Sesvold CL, O’Connor FG, Campbell WW, Kenney K, Capacchione JF, et al. Genetic polymorphisms associated with exertional rhabdomyolysis. Eur J Appl Physiol, 2013; 113(8):1997–2004.
Pimenta EM, Coelho DB, Cruz IR, Morandi RF, Veneroso CE, de Azambuja Pussieldi G, et al. The ACTN3 genotype in soccer players in response to acute eccentric training. Eur J Appl Physiol, 2012; 112(4):1495–503.