Effects of Blackcurrant Extract During High-Intensity Intermittent Running: An Exploratory Study of Possible Muscle Fibre-Type Dependence

Intake of anthocyanin-rich blackcurrant extract showed muscle fibre-type specific force responses during fatigue development from combined use of voluntary maximal isometric contractions and electrically evoked twitch contractions of the <i>m. quadriceps femoris</i>. In the present exploratory study, we examined the fibre-type specific effects by blackcurrant extract on high-intensity intermittent treadmill running performance to exhaustion. Active males (<i>n</i> = 16, age: 23 ± 3 years, height: 179 ± 5 cm, body mass: 79 ± 3 kg, V˙O_2max: 55.3 ± 5.0 mL·kg^-1·min^-1) completed a fatiguing protocol with 16 voluntary maximal isometric contractions to predict muscle fibre typology. The high-intensity intermittent running protocol was completed twice following a 7-day intake of blackcurrant extract (210 mg anthocyanins per day) and twice following a placebo (PL) in a randomized, double blind, crossover design. Heart rate and lactate were recorded at exhaustion. Data were averaged for each condition. There were no significant correlations between the percentage force decline by the repeated isometric contractions (mean ± SD: 29.3 ± 12.4%) and total and high-intensity running distance. Participants were categorized into a predominant muscle fibre type I (slow-twitch, <i>n</i> = 3 with the lowest isometric force decline: 12 ± 9%) and type II typology (fast-twitch, <i>n</i> = 3 with the highest isometric force decline: 46 ± 10%). Only the individuals with a predominant type I fibre typology improved the total running and high-intensity running distance by 17 ± 12% and 15 ± 11%. At exhaustion, there were no differences between individuals with a type I or II fibre typology for heart rate and lactate. These exploratory results suggest that the ergogenic potential of anthocyanin-rich blackcurrant extract on high-intensity intermittent exercise may depend on muscle fibre type, though larger and more robust studies are needed to confirm this observation. Future work will establish whether our exploratory results contributed to our understanding of the underpinning of inter-individual responses to the intake of anthocyanin-rich nutritional ergogenic aids.