The aim of this study was to investigate the prevalence of the ACTN3 rs1815739 polymorphism and to study its association with athletes' level of competition and lower-extremity power. Method Time-of-flight mass spectrometry (TOFMS) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) techniques were employed to identify the ACTN3 rs1815739 genotypes and allele frequencies in 108 elite sprinters and 206 untrained controls. Questionnaires were then used to assess subjects' 100 m sprint, standing jump (SJ) and standing triple jump (STJ) personal best record. Results (1) The RR, RX and XX genotype distribution of the ACTN3 rs1815739 polymorphism is 42.6%, 49.1%, 8.3%, respectively. R and X alleles frequency is 67.1% and 32.9%, respectively, which comply with Hardy Weinberg equilibrium (HWE) through Chi-square (χ 2) tests (χ 2 = 0.661; df = 2; P = 0.718). (2) Significant differences were found in R allele frequency between the elite sprinter group and controls. (3) The athletes' 100 m sprint, SJ, and STJ personal best records were better in those with RR and RX than XX genotype. A significant association was observed between the R alleles and 100 m sprint, SJ, and STJ results of male and female athletes. Conclusion The present results indicate that ACTN3 rs1815739 polymorphism has a significant association with speed and lower-extremity power in sprint/power athletes.

Objectives: This study aimed to examine the relationship between vertical jumping at forces of specific time phase and sprint performance in teenage sprinters. Methods: Fifteen male teenage sprinters (age: 14±2 years, height: 168±2 cm, weight: 61±1 kg) participated in the study. The subjects performed the following bilateral/unilateral jumps on a force platform: a) squat jump (SJ), b) unilateral SJ (USJ), c) 40cm drop jump (DJ), and d) 20cm unilateral DJ (UDJ). The 60m sprint test was administered on the second day. Brower split timers were positioned to record subjects’ 5m, 10m, 50m and 60m split times. The variables for inclusion were vertical jump height, maximum force, and force output at 120ms in all jumps and sprint time measures. Results: The results of the Pearson Product Moment Correlation analysis showed that SJ120ms was correlated to 5m and USJ120ms was correlated to 10m. UDJ120ms showed a stronger correlation with 50m than DJ120ms. Although significant correlations using maximum force and height were observed, there were inconsistent results between bilateral and unilateral jumps. Conclusion: Our results highlighted that jumps that have similar form with certain force outputs at specific event timing could more precisely predict sprint performance in teenage sprinters. USJ120ms and UDJ120ms could better predict the acceleration (10m) and high-speed phase (50m) in sprint performance, respectively. Moreover, coaches and practitioners should be cautious when using only jump height or maximum force to predict sprint performance, since the results could be inaccurate when specific movement variables are not thoughtfully considered. Level of evidence III.

RESUMO Objetivos: Este estudo teve como objetivo examinar a relação entre o salto vertical e a força em tempo específico e o desempenho de sprint em velocistas adolescentes. Métodos: Quinze adolescentes velocistas do sexo masculino (idade: 14 ± 2 anos, estatura: 168 ± 2 cm, peso: 61 ± 1 kg) participaram do estudo. Os indivíduos realizaram os seguintes saltos bilaterais e unilaterais em uma plataforma de força: a) squat jump (SJ), b) SJ unilateral (USJ), c) drop jump (DJ) de 40 cm e d) DJ unilateral (UDJ) de 20cm. O teste de sprint de 60 m foi realizado no segundo dia. Os cronômetros rastreadores para treinos fracionados foram posicionados para registrar os tempos fracionados de 5 m, 10 m, 50 m e 60 m. As variáveis para inclusão foram altura do salto vertical, força máxima e saída de força a 120 m em todos os saltos e medidas de tempo do sprint. Resultados: Os resultados da análise da correlação produto-tempo de Pearson mostraram que o SJ de 120 m foi correlacionado com 5 m e USJ de 120 m foi correlacionado com 10 m. O UDJ de 120 m teve correlação mais forte com DJ de 50 m do que de 120 m. Embora tenham sido observadas correlações significativas com força e altura máximas, alguns resultados foram inconsistentes entre os saltos bilaterais e unilaterais. Conclusões: Nossos resultados destacaram que os saltos com forma semelhante a certas saídas de força no tempo específico do evento podem prever com mais precisão o desempenho no sprint em adolescentes velocistas. O USJ de 120 m e o UDJ de 120 m podem prever melhor, respectivamente, a aceleração (10 m) e a fase de alta velocidade (50 m) no desempenho no sprint. Além disso, treinadores e praticantes devem ser cautelosos ao usar apenas a altura do salto ou a força máxima para prever o desempenho no sprint, uma vez que os resultados podem ser imprecisos quando variáveis específicas do movimento não forem consideradas com precisão. Nível de evidência III.