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.

Effect of citrulline on post-exercise rating of perceived exertion,muscle soreness,and blood lactate levels:A systematic review and meta-analysis

Background:Citrulline is one of the non-essential amino acids that is thought to improve exercise performance and reduce post-exercise muscle soreness.We conducted a systematic review and meta-analysis to determine the effect of citrulline supplements on the post-exercise rating of perceived exertion(RPE),muscle soreness,and blood lactate levels.Methods:A random effects model was used to calculate the effect sizes due to the high variability in the study design and study populations of the articles included.A systematic search of PubMed,Web of Science,and ClinicalTrials.gov was performed.Eligibility for study inclusion was limited to studies that were randomized controlled trials involving healthy individuals and that investigated the acute effect of citrulline supplements on RPE,muscle soreness,and blood lactate levels.The supplementation time frame was limited to 2 h before exercise.The types and number of participants,types of exercise tests performed,supplementation protocols for L-citrulline or citrulline malate,and primary(RPE and muscle soreness)and secondary(blood lactate level)study outcomes were extracted from the identified studies.Results:The analysis included 13 eligible articles including a total of 206 participants.The most frequent dosage used in the studies was 8 g of citrulline malate.Citrulline supplementation significantly reduced RPE(n=7,p=0.03)and muscle soreness 24-h and 48-h after post-exercise(n=7,p=0.04;n=6,p=0.25,respectively).However,citrulline supplementation did not significantly reduce muscle soreness 72-h post-exercise(n=4,p=0.62)or lower blood lactate levels(n=8,p=0.17).Conclusion:Citrulline supplements significantly reduced post-exercise RPE and muscle soreness without affecting blood lactate levels.

Caffeine Increases Rate of Torque Development Without Affecting Maximal Torque

Purpose The purpose of this study was to examine the effects of caffeine on peak torque(PT),rate of torque development(RTD),and muscle activation in college-age men.Methods Fifteen men(23.3±2.2 years,177.6±8.7 cm,90.3±19.1 kg)volunteered to participate in this study.During each of two test sessions,maximal leg extension PT and RTD were determined and electromyographic(EMG)and mechano-myographic(MMG)signals were collected to examine electrical and mechanical aspects of muscle activation,respectively.Participants also performed the Wingate Anaerobic Test(WAnT)for the determination of peak power(PP),mean power(MP),and fatigue percentage(FP).For the first test session,participants were randomly assigned to ingest either a caffein-ated drink(6 mg/kg)or a placebo 1 h prior to testing.The second test session was identical to the first,but the drink not previously administered was ingested prior to testing.Results The results indicated there were no significant effects of caffeine on PT,PP,MP,FP,or EMG and MMG measures.However,RTD was positively affected by caffeine(856.4±246.4 Nm/s)compared to the placebo condition(710.9±267.9 Nm/s).Conclusions These results suggest that caffeine can be an effective aid for sport activities requiring maximal rates of force or torque development during very short time periods.