A new exploratory human trial has shown that CurraNZ™ can significantly improve high‑intensity intermittent running in athletes whose muscles are rich in endurance‑type (Type I) fibres.
The findings provide powerful new evidence that our proprietary berry extract changes how muscles fuel and fatigue when the pressure is on - increasing the body's 'endurance engine'.
Published in the journal Muscles, the study, “Effects of Blackcurrant Extract During High‑Intensity Intermittent Running: An Exploratory Study of Possible Muscle Fibre-Type Dependence,” is the first to demonstrate that the running performance benefits of CurraNZ depend on an athlete’s muscle‑fibre profile.
CurraNZ delivers double‑digit gains in Type I–dominant runners
In this exploratory study, participants completed an exhaustive high‑intensity intermittent treadmill running protocol after seven days of CurraNZ (210 mg anthocyanins per day) or placebo, in a double‑blind, crossover design. Their results were then analysed according to their muscle fibre type profile.
The key finding: individuals with high levels of endurance fibres (Type I muscle‑fibre profile) improved performance with CurraNZ.
In these Type I‑dominant runners, CurraNZ produced large effect sizes across all performance measures, increasing:
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Total running distance by an average of 17% (an additional 526 m)
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High‑intensity running distance by 15% (an additional 308 m) compared with placebo
Importantly, athletes were able to run harder and longer at the same heart rate and blood lactate levels, indicating no extra cardiovascular or metabolic strain despite the higher workload.
Lead author Mark Willems, Professor of Exercise Physiology at the University of Chichester, (left) explains:
“These exploratory results suggest that the ergogenic potential of anthocyanin‑rich New Zealand blackcurrant extract for enhancing repeated high‑intensity exercise is muscle fibre‑type dependent and points to increased fatigue resistance in Type I fibres.”
He adds: “It is possible that athletes adopting finishing kicks in competitive endurance running may benefit from the ergogenic effects of New Zealand blackcurrant extract. But more work needs to be done.”
Building on CurraNZ evidence: glycogen storage and Type I fibre protection
This new paper strengthens a growing body of CurraNZ research showing that New Zealand blackcurrant–derived anthocyanins change how muscles store and use fuel at the fibre level.
A 2020 trial, “Effect of New Zealand Blackcurrant Extract on Isometric Contraction-Induced Fatigue and Recovery: Potential Muscle-Fiber Specific Effects,” reported that CurraNZ increased fatigue resistance and preserved force during repeated maximal isometric contractions, again pointing to preferential support of Type I fibres.
Further CurraNZ research has demonstrated greater muscle glycogen storage and increased intramuscular triglyceride (IMTG) utilisation in Type I fibres, indicating that the extract helps endurance‑type fibres stockpile carbohydrate and draw more effectively on fat stores during exercise.
Taken together, these findings support a powerful mechanistic story: CurraNZ appears to “upgrade” the body’s endurance engine – Type I fibres – by improving fuel handling (glycogen and IMTG) and delaying fatigue, which then translates into real‑world performance gains in high‑intensity intermittent running.
What this means for athletes and active people
While the current study focused on well‑trained men, the implications extend well beyond the lab:
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Team‑sport and racket‑sport athletes – Players in football, rugby, basketball, hockey, tennis and similar sports rely on repeated high‑intensity efforts under fatigue. For those with more endurance‑dominant muscle profiles, CurraNZ may offer a meaningful edge in repeated sprints and late‑game performance.
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Endurance athletes – Distance runners, triathletes and cyclists with a high proportion of Type I fibres could see benefits in sessions and races that include surges, hills and intermittent high‑intensity efforts, where finishing kicks and repeated bursts are critical.
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Everyday active people – Recreational runners, gym‑goers and participants in group classes may experience improved “engine durability”: the ability to hold pace longer in intervals, classes or match play without feeling more drained.
The authors emphasise that larger, confirmatory studies are needed. However, these data directly link CurraNZ’s established performance benefits to fibre‑type–specific effects in human muscle, moving the science beyond generic “antioxidant” explanations.
CurraNZ: leading the way in fibre‑level performance nutrition
With over 60 peer‑reviewed papers on New Zealand blackcurrant extract across performance, recovery and health, CurraNZ holds the highest level of evidence of any polyphenol‑based sports supplement. This latest study adds a crucial new piece of the puzzle: who responds best, and why.
For athletes with Type I‑dominant muscles, CurraNZ can deliver sizeable gains in high‑intensity intermittent performance, supported by improved glycogen storage, enhanced IMTG use and reduced fatigue in those endurance fibres.
As our research continues to uncover how CurraNZ blackcurrant anthocyanins work at the microscopic level, the brand remains at the forefront of fibre‑level performance nutrition – helping athletes and active individuals get more from every stride, sprint and surge.
References
1. Willems, M.E.T.; Blacker, S.D.; Perkins, I.C. Effects of Blackcurrant Extract During High-Intensity Intermittent Running: An Exploratory Study of Possible Muscle Fibre-Type Dependence. Muscles 2025, 4, 56. https://doi.org/10.3390/muscles4040056
2. L. A. Jones, L. Leung, J. S. Barrett, H. O. Fortis, J. A. Strauss, S. O. Shepherd, New Zealand blackcurrant extract augments muscle glycogen storage at rest and enhances intramuscular triglyceride degradation during prolonged exercise, 2025 European Journal of Applied Physiology https://doi.org/10.1007/s00421-025-05995-9
3. Mark E. T. Willems * , Megan Bradley, Sam D. Blacker and Ian C. Perkins Effect of New Zealand Blackcurrant Extract on Isometric Contraction-Induced Fatigue and Recovery: Potential Muscle-Fiber Specific Effects, Sports 2020, 8, 135; doi:10.3390/sports8100135