The ability to perform aerobic or anaerobic exercise varies widely among individuals, partially depending on their muscle-fiber composition. Variability in the proportion of skeletal-muscle fiber types may also explain marked differences in aspects of certain chronic disease states including obesity, insulin resistance, and hypertension. In untrained individuals, the proportion of slow-twitch (Type I) fibers in the vastus lateralis muscle is typically around 50% (range 5–90%), and it is unusual for them to undergo conversion to fast-twitch fibers. It has been suggested that the genetic component for the observed variability in the proportion of Type I fibers in human muscles is on the order of 40–50%, indicating that muscle fiber-type composition is determined by both genotype and environment. This article briefly reviews current progress in the understanding of genetic determinism of fiber-type proportion in human skeletal muscle. Several polymorphisms of genes involved in the calcineurin–NFAT pathway, mitochondrial biogenesis, glucose and lipid metabolism, cytoskeletal function, hypoxia and angiogenesis, and circulatory homeostasis have been associated with fiber-type composition. As muscle is a major contributor to metabolism and physical strength and can readily adapt, it is not surprising that many of these gene variants have been associated with physical performance and athlete status, as well as metabolic and cardiovascular diseases. Genetic variants associated with fiber-type proportions have important implications for our understanding of muscle function in both health and disease.
Ildus I. Ahmetov, Olga L. Vinogradova and Alun G. Williams
Olga N. Fedotovskaya, Leysan J. Mustafina, Daniil V. Popov, Olga L. Vinogradova and Ildus I. Ahmetov
In red skeletal muscle, monocarboxylate transporter 1 (MCT1) is required for lactate to enter the myocytes for oxidation. The A1470T polymorphism (rs1049434) in the MCT1 gene was shown to be associated with lactate transport rates in human skeletal muscles. The aim of the study was to compare genotype and allele frequencies of the MCT1 gene polymorphism in 323 Russian athletes and 467 nonathletic controls and to investigate the association of the MCT1 gene A1470T polymorphism with maximal oxygen consumption and maximal lactate concentration in rowers (n = 79).
Genotyping for the A1470T MCT1 polymorphism was performed by PCR-RFLP method. Physiological measurements of 79 Russian rowers of national competitive standard were determined during an incremental test to exhaustion on a rowing ergometer.
Frequencies of the A allele (71.8% vs 62.5%, P < .0001) and AA genotype (59.8% vs 39.4%, P < .0001) were significantly higher in endurance-oriented athletes (n = 142) than in the control group. Mean blood lactate concentration was higher in male rowers with the T allele (AT+TT 10.26 ± 1.89 mmol/L, AA 8.75 ± 1.69 mmol/L, P = .005).
MCT1 gene A1470T polymorphism is associated with endurance athlete status and blood lactate level after intensive exercise.
João Paulo Limongi França Guilherme, Ekaterina A. Semenova, Hirofumi Zempo, Gabriel L. Martins, Antonio H. Lancha Junior, Eri Miyamoto-Mikami, Hiroshi Kumagai, Takuro Tobina, Keisuke Shiose, Ryo Kakigi, Takamasa Tsuzuki, Noriko Ichinoseki-Sekine, Hiroyuki Kobayashi, Hisashi Naito, Oleg V. Borisov, Elena S. Kostryukova, Nikolay A. Kulemin, Andrey K. Larin, Edward V. Generozov, Noriyuki Fuku and Ildus I. Ahmetov
Purpose: To replicate previous genome-wide association study identified sprint-related polymorphisms in 3 different cohorts of top-level sprinters and to further validate the obtained results in functional studies. Methods: A total of 240 Japanese, 290 Russians, and 593 Brazilians were evaluated in a case-control approach. Of these, 267 were top-level sprint/power athletes. In addition, the relationship between selected polymorphisms and muscle fiber composition was evaluated in 203 Japanese and 287 Finnish individuals. Results: The G allele of the rs3213537 polymorphism was overrepresented in Japanese (odds ratio [OR]: 2.07, P = .024) and Russian (OR: 1.93, P = .027) sprinters compared with endurance athletes and was associated with an increased proportion of fast-twitch muscle fibers in Japanese (P = .02) and Finnish (P = .041) individuals. A meta-analysis of the data from 4 athlete cohorts confirmed that the presence of the G/G genotype rather than the G/A+A/A genotypes increased the OR of being a sprinter compared with controls (OR: 1.49, P = .01), endurance athletes (OR: 1.79, P = .001), or controls + endurance athletes (OR: 1.58, P = .002). Furthermore, male sprinters with the G/G genotype were found to have significantly faster personal times in the 100-m dash than those with G/A+A/A genotypes (10.50 [0.26] vs 10.76 [0.31], P = .014). Conclusion: The rs3213537 polymorphism found in the CPNE5 gene was identified as a highly replicable variant associated with sprinting ability and the increased proportion of fast-twitch muscle fibers, in which the homozygous genotype for the major allele (ie, the G/G genotype) is preferable for performance.