Genotypes affecting muscle power
Heterogeneity of muscles is crucial concerning their functions. The combination of histo chemical ATP painting, antibody staining and electrophoresis resulted in the separation of mammals’ four type skeletal muscle. They create a slowly shrinking – (1 type) and the muscle fibre-form (IIA, IIB- and IIX types) of three quick v nets. The isolated mammal ‘slow-twitch’ (ST) and ‘fast twitch’ (FT) muscle fibres and the differences of the mechanical and energy processes of their motor units/apparatus are known. Basically the ST muscles are slower with lower performance, but they are more economical when generating power than the FT muscles. The peak performance of ST muscles can be observed in case of slower shortening velocity in contrast to FT fibres. Motor tasks demand this heterogeneity in relation to muscle contractility to minimize fatigue and tiredness. Endurance can be connected to the dominance of ST fibres while in case of FT fibres power and speed are crucial. It is proved that strength athletes and sprinters have a higher percentage of low oxidative FT muscle fibres in contrast to endurance athletes having higher percentage of ST muscle fibres.
It is evident how important the strength of muscles and their performance are for sprinters and aerobic-anaerobic athletes. Several gene variants affect muscles working capacity under intensive physical loading. The phenotypes of muscles as well as their endurance capacity are affected by genes which influence muscle oxygen uptake and energy use.
The creatine kinase isoenzime MM (CK-MM) gene encodes those cytosolic CK isoforms which are responsible for the rapid re-synthesis of ATP during high muscle contraction. It was also observed that mice whose CK-MM gene was knocked out showed lower skeletal muscle fatigue and higher aerobic capacity of cellular adaptation. At the presence of the enzyme muscle tiredness occurs normally by increasing the inorganic phosphate concentration of local cell-components. Examinations carried out in humans have found close relationship between gene polymorphism and the increase of cardio-respiratory endurance while focusing on the variability of CK-MM gene-sequence. These outcomes were proved by examining the changes of maximum oxygen uptake after a 20 week long training as well as peak-performance and fatigue. In trainings the A/G polymorphism of CK-MM 3’ in the non-transferable region may affect the endurance of running. This gene variant decreases the power of muscle construction during a 60 second long test after physical activities lasting an hour and half. The outcomes of further researches and studies have not backed up the relationship between CK-MM gene polymorphism and the performance of muscles. But it has become clear that there is a relationship between Ncol A/A genotype and physical activity rhabdomiolysis.
ACTN3, α actinin-3 gene is an extremely preserved component of contractile mechanism/ apparatus in mammals’ fast skeletal muscle fibres. This protein can be found only in FT fibres and it is responsible for sprinters’ and cyclists’ performance. ACTN3 is present almost in every elite athlete’s body, while the R577X polymorphism (in exon 16 in 1747 position C> T exchange results in stopkodon) with ACTN3 deficiency – total protein deficiency- occurs more often in endurance athletes (e.g. marathon runners and rowers). Alpha -actinin-3 protein deficiency due to the C>T Base Exchange affects 18 per cent of the world’s population in case of homozygous XX genotype. ACTN3 deficiency does not cause musculoskeletal diseases, myopathy as ACTN2 compensates its deficiency. There are functional differences among ACTN3 gene variants. This perception is emphasised by the functional manifestation of XX genotype.
It has been shown that the diameter of fast fibres decreased in the muscles of ACTN3 ‘knockout’ (ko) mice, while the activity of several enzymes participating in aerobic metabolism improved, contractility qualities changed, and regeneration lasted shorter after fatigue. In contrast to the decrease of muscles built up by II type fibres as well as energy and power, the running performance of ko mice increased by one-third compared to those of the controlled animals. It can be stated that by increasing the metabolic activity of slow fibres of XX genotype it also enhances endurance. This phenomenon brought about by protein deficiency causes the change of activity of enzymes which occur in carbohydrate- and lipid metabolism. The reason for this was also the positive change of aerobic energy use. There is a shift from the characteristics of fast fibres towards those of slow fibres. (Resisting tiredness, more effective oxidative metabolism).This phenomenon can be explained by the influence of R577X nonsense polymorphism. Meanwhile the deficiency of ACTN3 protein negatively affects the skeletal contraction through the activity of lactate dehydrogenase as well as the decrease of the stored carbohydrate mobilisation. It is evident then that it adversely affected physical activities which require rapid force. On the basis of the latest studies it turned out that ACTN3 XX genotype characterises the inactive individuals’ muscle and the sprint performance of athletes having different ACTN3 genotype falls short. The women with XX genotypes significantly ran a short distance over a longer period than those of R alleles. The outcomes of examination carried out on high achievers were similar. ACTN3 wild type R allele supporting muscle fibre contraction can be detected in a higher proportion in sprinters and strength athletes than in athletes with X allele. The truth is that there are studies which have not proved the significant relationship between R577X polymorphism and extreme sports performance. Nonetheless ACTN3 gene is considered one of the most important markers regarding sport performance.
Out of PEP-s the polymorphism of angiotensin-converting enzyme (ACE) were examined in relation to sprint and endurance sport performance. ACE plays a crucial role in the so called rennin-angiotensin system (RAAS) which controls liquid-electrolyte household as well as blood pressure. ACE enzyme is an important vasoconstrictor in the process of transforming angiotenzin 1 form into angiotenzin 2 form. The two frequent alleles of ACE genes are insertion (I) brought about by knocking out a 287 nucleotide long sequence which consists of intron 16, and deletion (D). The D allele of ACE gene produces higher ACE activity in tissues and in serums. The higher frequency of I allele as well as II genotype which is accompanied with the decrease of activities were revealed in, for example, marathon runners, triathletes and rowers. Similarly higher frequency is observed in case of 1 allele mountaineers. When endurance was examined it became evident that ACE II genotype is related to I type (ST) muscle fibres which are present in a greater proportion and they eventuate higher VO2max and peripheral tissue oxygenisation. By contrast the presence of D allele is more intensive in case of strength oriented sports, such as, short and long distance swimmers. It is accompanied with higher angiotenzin II level which may favour of hypertrophy. It is also proved by the data of observations that the power and strength of quadriceps muscle with D alleles were increased by physical activities. Angiotenzin II leads redistribution of blood to fibres of II types which can also explain the relationship of D allele of ACE with power sports. By contrast I allele affects endurance performance through nutrient transport and the improvement of skeletal muscle effectiveness. Similar to ACTN3 the conclusions in relation to ACE gene examinations are not always unambiguous. Researchers found that D allele affects VO2max both positively and negatively. The examinations of Jamaican and American sprinters could not find any relationship between the allele and short distance runner status. Similarly, concerning the significantly different frequency of I allele no evidence was found in a sport endurance study which focused mainly on a mixed group of Caucasian athletes. There was no proof either of the difference in the process of oxygen uptake compared to the same geographical control population. Another examination within a Caucasian population appointed that there is no relationship between I allele and the elites’ physical performance. In case of Israelis and Koreans it is the D allele which relates to endurance performance. Despite the several ambiguous results ACE gene is also considered a candidate marker regarding the influence of performance and efficiency.
Muscle function is closely related to the genes affecting muscle energy metabolism during intensive physical activities. In the skeletal muscle the adenozin-mono-phosphate-dezaminaz 1(AMPD1) is an enzyme which actively participates in the catabolism of adenine nucleotide. In case of loading the decrease of ATP/ADP ratio results the activation of AMPD which with the hydrolysis of AMP supports the ATP formation. The C34T polymorphism of AMPD1 gene (nonsense mutation resulting stopkondon) is associated with the deficiency of AMPD in TT genotype individuals. Due to this phenomenon the decrease of physical activity and that of the cardio-respiratory response was observed among physically inactive people. Besides this fact, the breathing phenotype of T allele carriers under maximum load as well as its sub-maximum aerobic capacity was also restricted. The deficiency of the enzyme caused spasms, tiredness and muscle pain after trainings. This fact is proved by the outcomes of studies focusing on cyclists and runners. Here the frequency of T allele was lower that in the control population whose participants did not do sports.
Myosin light-chain kinase (MLCK) must be also mentioned which is calcium-calmodulin-dependent multifunctional enzyme. This kinase has an important role in controlling the contraction of smooth muscle. The polymorphism of protein coding gene (C37885A) was related to power loss after trainings: the heterozygotic polymorphism goes with more significant power loss than that of the homozygotic wild type (CC).
The mutation which was caused by the lack of myostatin (MSTN) protein in cows was described and detailed in 1997. Those animals that carried mutation in homozygotic form being present in MSTN gene had bigger muscle size. Myostatin is an important regulatory of the proliferation of myoblasts limiting muscle growth. This was also confirmed by researches carried out on MSTN ko mice. The increase of muscle fibres of knocked out mice resulted bigger muscle size. The role of MSTN gene variants concerning sport performance was first reported by observing greyhounds who participated in races. The greyhounds whose MSTN in its 3rd exon gene containing homozygous deletion were much faster that that of the wild types.
The removal rate of lactic acid was one of the factors of fatigue after intensive trainings. The gene variant of MCT-1 affects lactate transport thus the intensity of performance.
The gene variant of DIO1 dejodinaze-jodoironin-1 has also positive impact on anaerobic training, it enhances muscle power.
Figure 2. Gene variants concerning muscle power and power practice.