Endurance performance depends on the integration of several phenotypic traits influenced by multiple environmental and genetic factors. Objectives of the study were: (1) to examine the genotypic frequencies of the ACE I/D, ACTN3 R577X polymorphisms and endurance performance-related phenotypes, (2) to evaluate the dynamics of endurance performance parameters during a 5-year period in relation to ACE I/D and ACTN3 R577X genotypes in Estonian young skiers. Determination of VO2peak was performed in 58 skiers aged 15-19 years (41 males, 17 females) during a 5-year period. The control group consisted of 322 healthy non-athletic subjects (145 males, 177 females). The study groups were genotyped for the ACE I/D and ACTN3 R577X variants. Frequencies of the ACE ID and ACTN3 RR genotypes were significantly higher (p = 0.047 and p = 0.003, respectively) and the RX genotype was lower (p = 0.008) in young male skiers compared with controls. A significant relationship was found between change (Δ) of training volume and ΔVO2peak (mL·kg-1·min-1) (r = 0.475, p = 0.002). No significant main effect was detected between VO2peak (mL·kg-1·min-1) dynamics (comparison with the previous age group data) and ACE I/D and ACTN3 R577X genotypes interactions (F = 0.571, p = 0.770 and F = 0.650 and p = 0.705, respectively) in all young skiers. Study results indicated a significantly higher frequency of the ACE ID and ACTN3 RR genotypes among Estonian young male skiers compared with the male control group. Significant genotype-related differences in dynamics of VO2peak during a 5-year period were not found. In the future, longitudinal research including different gene variants may contribute to a better understanding of the nature of endurance performance
