Does ergogenic effect of caffeine supplementation depend on CYP1A2 genotypes? A systematic review with meta-analysis

Background:The ergogenic effects of caffeine intake on exercise performance are well-established,even if differences exist among individuals in response to caffeine intake.The genetic variation of a specific gene,human cytochrome P450 enzyme 1A2(CYP1A2)(rs762551),may be one reason for this difference.This systematic review and meta-analysis aimed to comprehensively evaluate the influence of CYP1A2 gene types on athletes’exercise performance after caffeine intake.Methods:A literature search through 4 databases(Web of Science,PubMed,Scopus,and China National Knowledge Infrastructure)was conducted until March 2023.The effect size was expressed as the weighted mean difference(WMD)by calculating fixed effects meta-analysis if heterogeneity was not significant(I^(2)≤50%and p≥0.1).Subgroup analyses were performed based on AA and AC/CC genotype of CYP1A2.Results:The final number of studies meeting the inclusion criteria was 12(n=666 participants).The overall analysis showed that the cycling time trial significantly improved after caffeine intake(WMD=-0.48,95%confidence interval(95%CI):-0.83 to-0.13,p=0.007).In subgroup analyses,acute caffeine intake improved cycling time trial only in individuals with the A allele(WMD=-0.90,95%CI:-1.48 to-0.33,p=0.002),but not the C allele(WMD=-0.08,95%CI:-0.32 to 0.17,p=0.53).Caffeine supplementation did not influence the Wingate(WMD=8.07,95%CI:-22.04 to 38.18,p=0.60)or countermovement jump test(CMJ)performance(WMD=1.17,95%CI:-0.02 to 2.36,p=0.05),and these outcomes were not influenced by CYP1A2 genotype.Conclusion:Participants with the CYP1A2 genotype with A allele improved their cycling time trials after caffeine supplementation.However,compared to placebo,acute caffeine supplementation failed to increase the Wingate or CMJ performance,regardless of CYP1A2 genotype.

Effects of 12 weeks of back-squat training program on jump performances and bone markers in female students

Background:The training program promoted improvements of jump abilities throughout the musculoskeletal system including bone markers.The aim of this study is to examine both the acute and chronic response of bone markers to resistance training program.Methods:Ten female students(age:18±0.7 years,body mass:63±3.6 kg;height:164±5.2 cm)participated in this study.They were recruited for a back-squat training program for 12 weeks,two days/week.The full-back squat protocol consisted of 3–5 sets×3–8 repetitions at 45–55%one repetition maximum.Testing sessions included a 5 jump test(5JT),standing long jump(SLJ),drop jump(DJ),and vertical jump(VJ).Results:Substantial improvements in all testing jumps(5JT:∆10%;P=0.000;ES=1.72;SLJ:∆7%;P=0.000;ES=1.33;DJ:∆11%;P=0.000;ES=0.72;VJ:∆20%;P=0.000;ES=1.84)were found during post program in comparison to pre-program results.Moreover,a significant change(P≤0.05)of bone markers during post-exercise compared to pre-exercise either before or after the training program.Only collagen type I carboxy-terminal peptide(CICP)levels elevated after the training program(pre-exercise only)compared to former levels.Conclusion:12 weeks of back-squat training program resulted greater acute improvements of jump abilities with adaptation in all musculoskeletal system including bone formation.

Temperature-Dependent SRS Behavior of 316L and Its Constitutive Model

The strain rate sensitivity（SRS）and temperature sensitivity（TS）of 316L austenitic stainless steel were investigated by constant strain rate test（CSRT）and strain rate jump test（SRJT）under four temperatures（293,373,473 and 573 K）and four strain rates（5 ×10^-4/s,1 × 10^-3/s,5 × 10^-3/s and 1 × 10^-2/s）.The results show that temperature sensitivity（TS）indexes at different strain rates are coincidence to be negative,related to temperature softening.On the contrary,SRS indexes change from positive to negative with the increase in temperature associated with dynamic strain aging（DSA）.Moreover,based on the comparison between CSRT and SRJT,SRS and TS indexes obtained by two methods agree well.It proves that the SRJT can describe the SRS and TS phenomenon of 316L efficiently.Furthermore,the effects of tem-perature and strain rate on fracture mechanism were discussed.At last,an improved Johnson-Cook model was proposed to consider the temperature-dependent SRS behavior of 316L.

Analysis of High Frequency Data in Finance:A Survey

This study examines the use of high frequency data in finance,including volatility estimation and jump tests.High frequency data allows the construction of model-free volatility measures for asset returns.Realized variance is a consistent estimator of quadratic variation under mild regularity conditions.Other variation concepts,such as power variation and bipower variation,are useful and important for analyzing high frequency data when jumps are present.High frequency data can also be used to test jumps in asset prices.We discuss three jump tests:bipower variation test,power variation test,and variance swap test in this study.The presence of market microstructure noise complicates the analysis of high frequency data.The survey introduces several robust methods of volatility estimation and jump tests in the presence of market microstructure noise.Finally,some applications of jump tests in asset pricing are discussed in this article.