New Study Shows CurraNZ Targets “Endurance Engine” Muscle Fibres to Boost High-Intensity Running Performance

A new exploratory human trial has found that New Zealand blackcurrant extract (CurraNZ™) can significantly improve high‑intensity intermittent running in athletes whose muscles are rich in endurance‑type (Type I) fibres - offering powerful new evidence that the proprietary berry extract alters how muscles fuel and fatigue under pressure.

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 show that the running performance benefits of CurraNZ depend on an athlete’s muscle‑fibre profile.

CurraNZ delivers impressive double‑digit performance gains in muscle fibre Type I–dominant runners

Participants in an exploratory study completed an exhaustive high‑intensity intermittent treadmill protocol after seven days of CurraNZ (210 mg anthocyanins/day) or placebo, in a double‑blind, crossover design. Participants’ results were separated based on their fibre type.

Key findings:

• Individuals with high levels of endurance fibres (Type I muscle‑fibre profile) improved performance with CurraNZ.

In these Type I-dominant individuals, CurraNZ delivered large effect sizes across all performance measures, increasing:

• Total running distance by an average 17% (526m)
• High‑intensity running distance by 15% (308m), compared with placebo

Athletes could run harder and longer at the same heart rate and lactate, suggesting no additional cardiovascular and metabolic strain.

Mark Willems, Professor of Exercise Physiology who led the study at the University of Chichester, says: “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.”

“It is possible that athletes adopting finishing kicks in competitive endurance running may benefit from the ergogenic effects by New Zealand blackcurrant extract. But more work needs to be done.”

Builds on earlier CurraNZ evidence: Glycogen storage and Type I fibre protection

The new paper strengthens a growing body of CurraNZ research showing that New Zealand blackcurrant extract-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.

Additionally, CurraNZ study 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 tap into fat stores more effectively 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 reach far beyond the lab:

Team‑sport and racket‑sport athletes (football, rugby, basketball, hockey, tennis) rely heavily on high‑intensity repeat efforts under fatigue. For players with more endurance‑dominant muscle profiles, CurraNZ may provide a meaningful edge in repeated sprints and late‑game performance.

Endurance athletes (distance runners, triathletes, cyclists) with a high proportion of Type I fibres could see performance benefits in sessions and races that include surges, hills and intermittent high‑intensity efforts.

Everyday active people may experience improved “engine durability” - being able to hold pace longer in intervals, group classes or match play - without feeling more drained.

The authors note that larger, confirmatory studies are needed, but their data directly link CurraNZ’s well‑established performance benefits to fibre‑type–specific effects in human muscle, moving the field 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, thanks to its pioneering evidence‑based approach to sports nutrition.

This latest study adds a critical new piece: who responds best and why - showing that athletes with Type I‑dominant muscles can expect sizeable gains in high‑intensity intermittent performance, supported by improved glycogen storage, enhanced IMTG use, and reduced fatigue in those fibres.

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