Effects of New Zealand Blackcurrant Supplementation on Exercise and Cognitive Performance in Resistance-Trained Adults

Background and Rationale Polyphenol‐rich supplements have attracted growing interest insports nutrition research, largely because of evidence that anthocyanins can influenceseveral physiological processes relevant to exercise. These include improvements invascular tone and blood flow, reductions in exercise‐induced oxidative stress, changes insubstrate utilization during activity, and improvements in fatigue tolerance. New Zealandblackcurrant (NZBC) extract has emerged as one of the more studied anthocyanin sources inthis area, with prior research documenting benefits in high‐intensity cycling,intermittent running, and fat oxidation during exercise.Despite this growing body of evidence, nearly all existing research on NZBC has focusedon endurance or aerobic exercise contexts. Whether NZBC could influence maximal strength,total lifting volume, or barbell power output in resistance‐trained individuals had notbeen previously examined. Additionally, the potential for NZBC to influence cognitivefunction during resistance training is biologically plausible given its monoamine‐relatedbioactive profile, but had not been rigorously tested in this population. This study wasdesigned to address both gaps using a well‐controlled crossover design.Study Design This was a randomized, double‐blind, placebo‐controlled, four‐periodcrossover trial conducted in the Exercise Physiology and Nutrition Laboratory atJacksonville State University. The four conditions were a no‐capsule control, a placebo,a low‐dose blackcurrant condition (250 mg/day), and a high‐dose blackcurrant condition(600 mg/day). Each capsule condition lasted seven consecutive days, with laboratorytesting on day seven. The no‐capsule control was always administered first; the threecapsule conditions were assigned using a balanced 3×3 Williams design to minimizecarryover effects. Randomization was computer‐generated by an investigator independent ofdata collection. All capsule conditions were separated by washout periods, and capsuleswere identical in appearance and mass to maintain blinding.Interventions The placebo capsule contained 600 mg of maltodextrin per day. The low‐dosecondition contained 250 mg of NZBC extract plus 350 mg of maltodextrin per day, providingan estimated 87.5 mg of anthocyanins daily. The high‐dose condition delivered 600 mg ofNZBC extract per day, providing approximately 210 mg of anthocyanins daily. Capsules weretaken once daily, timed two hours before training on workout days or at noon on restdays. On laboratory testing days, the final capsule was taken on‐site two hours beforetesting, with staff present to confirm ingestion.Dietary standardization was implemented throughout the study. Beginning two weeks beforethe first test session, participants discontinued all dietary supplements andover‐the‐counter medications. In the 72 hours preceding each laboratory visit,participants abstained from structured exercise, caffeine, alcohol, dietary nitrate,polyphenol‐rich foods, and antibacterial mouthwash. Dietary intake was monitored usingfour separate three‐day recording windows via MyFitnessPal to verify consistency acrossconditions.Statistical Analysis Each outcome was analyzed using a repeated‐measures general linearmodel with treatment (four levels) as the within‐subject factor and sex as thebetween‐subject factor. The model tested the main effect of treatment and thetreatment‐by‐sex interaction. Sphericity was assessed using Mauchly's test, withGreenhouse‐Geisser corrections applied where needed. Significant overall treatmenteffects were followed by pairwise comparisons using estimated marginal means with theleast significant difference procedure. Effect sizes for pairwise comparisons werecalculated as Cohen's d_z and interpreted as trivial, small, moderate, or large. Allanalyses were conducted in IBM SPSS Statistics, version 31.