The aim of this study was to clarify the relationships between muscle power and bone mineral density (BMD) and the α-actinin-3 (ACTN3) R577X polymorphism in Japanese female collegiate athletes participating in sports with various mechanical-load characteristics. This study included 260 female collegiate athletes involved in 10 competitive sports and 26 controls (mean ages, 19.2 ± 1.2 and 19.7 ± 1.3 years, respectively). The sports were classified into 3 categories (low-impact, multidirectional, and high-impact) based on the exercise load characteristics. Data on sports participation and competition experience were obtained through a questionnaire-type survey. The maximum anaerobic power (MAnP) test was performed to measure muscle power. The total body BMD was measured using dual-energy X-ray absorptiometry. The ACTN3 R577X polymorphism (rs1815739) was analyzed using a TaqMan® assay. The multidirectional sports participants with the RR genotype of the ACTN3 R577X polymorphism had a higher BMD than those with the RX and RX + XX genotypes (P = .018 and P = .003, respectively). The RR genotype was also associated with a higher MAnP than those with the RX + XX genotypes (P = .035). No other variables related to BMD and MAnP were significantly different. Our results suggests that the RR genotype may confer high trainability for BMD and muscle power in Japanese female collegiate athletes participating in multidirectional sport types. However, these associations were not found in the athletes participating in the low- and high-impact sport types.

Background/Objectives: Monocarboxylate transporters (MCTs) comprise 14 known isoforms, with MCT1 being particularly important for lactate transport. Variations in lactate metabolism capacity and aerobic performance are associated with the T1470A polymorphism in MCT1. We aimed to investigate the frequency of the T1470A polymorphism and compare relevant physiological parameters among long-distance runners, wherein these parameters are fundamental to athletic performance. Methods: We included 158 Japanese long-distance runners (LD) and 649 individuals from the general Japanese population (CON). The frequency of the T1470A polymorphism was compared between these groups and across athletic levels using the chi-square test. Additionally, physiological data were collected from 57 long-distance runners, and respiratory gas measurements were obtained using the mixing-chamber method during a graded incremental exercise test. Results: We observed a significant difference between the LD and CON groups in the dominant model and between the sub-28 min group and 28 min or above group in the recessive model. As the competitive level increased, the frequency of the AA genotype also increased. When comparing physiological parameters between the AA genotype and T allele, subjects with the AA genotype showed significantly higher values for oxygen uptake at lactate threshold (p = 0.001), oxygen uptake at onset of blood lactate accumulation (p = 0.01), maximal oxygen uptake (p = 0.005), and maximal blood lactate concentration (p = 0.038). Conclusions: These results suggest that the AA genotype of the T1470A polymorphism of MCT1 is an effective genotype associated with athletic status and aerobic capacity in Japanese long-distance runners.

Background: Blood lactate concentration and muscle oxygen saturation (SmO₂) are widely used indicators of endurance performance, reflecting the balance between oxygen delivery and utilization during exercise. To date, no studies have examined how the rs1049434 polymorphism of the SLC16A1 gene (the polymorphism) influences SmO₂ referenced to blood lactate thresholds in long-distance (LD) runners. This pilot study aimed to investigate the association between SmO₂ referenced to blood lactate concentration during maximal and submaximal exercise and the polymorphism in male collegiate LD runners. Methods: Overall, 15 Japanese male collegiate LD runners participated. Physiological parameters, including respiratory gas data, were measured during a graded incremental exercise test using the breath-by-breath method. SmO₂ was recorded from the right vastus lateralis muscle. Participants were genotyped for rs1049434, and comparisons were made between the AA genotype and T-allele carriers (AT + TT genotype). Results: Runners with the AA genotype exhibited significantly higher %$\stackrel{·}{\mathrm{V}}$O_2max at the lactate threshold (p = 0.044) and at the onset of blood lactate accumulation (OBLA) than T-allele carriers (p = 0.023). For SmO₂ measurements, those with the AA genotype displayed shorter t1/2_{reoxygenation} (p = 0.043) and higher SmO_2max (p = 0.045). Furthermore, SmO₂-OBLA was significantly higher in the AA genotype than in T-allele carriers (p = 0.029). Conclusions: These findings suggest that runners with the AA genotype may have greater oxygen utilization efficiency and potentially improved muscle oxygen delivery during high-intensity exercise. However, these are preliminary results, and further studies with larger and more diverse cohorts are needed to confirm these observations.

This study aimed to investigate the effects of resistance training (RT) experience on bone mineral density (BMD) and stress fractures (SFs) in female collegiate athletes. Overall, 492 female athletes from 16 competitive sports were included. Sports were categorized into four groups based on exercise load. Data on sports participation, RT experience, and SF history were obtained using a questionnaire. Total body and lumbar spine BMD were measured using dual-energy X-ray absorptiometry. Athletes with RT experience in both senior high school (ages 15–18) and university (ages 18–22), as well as those with experience from junior high school (ages 12–15) through university, had significantly higher BMD than those with no RT experience or RT experience only in senior high school (p < 0.05). Logistic regression analysis revealed that athletes with RT experience had significantly lower odds ratios for SFs compared to those with no RT experience. In the adjusted model that included sport type and university year, athletes with RT experience in junior high school, senior high school, and university had a significantly lower OR for SFs compared with no RT experience (OR = 0.06, 95% CI: 0.01–0.59, p = 0.016). No significant BMD differences were found between athletes with and without SFs (p > 0.05). The study findings suggest that initiating RT in junior high school may be associated with a reduced incidence of SFs during university.