New Zealand blackcurrant extract has no effect on physiological and cardiovascular responses during low-intensity sustained intermittent isometric contractions in men.

Purpose: Intake of anthocyanin-rich supplements such as New Zealand blackcurrant (NZBC) extract for 7 days showed beneficial effects on cardiovascular function at rest and during moderate and high-intensity exercise. The effects of 4- and 7-day intake of 600 mg of NZBC extract on cardiovascular function, femoral artery diameter, muscle force, muscle activity and muscle fatigue during low-intensity sustained intermittent isometric contractions were examined.

Methods: Fifteen healthy males (age: 25 ± 6 years, height: 180 ± 7 cm, body mass: 82 ± 8 kg) visited the laboratory on five occasions (familiarisation, days 4 and 7 of placebo (PLA) or NZBC extract intake). Each visit required the participants to hold the isometric contraction of the m.quadriceps femoris at 10% of their isometric maximal voluntary contraction (iMVC) for 5 bouts of 2-min. At the end of each 2-min, an iMVC was performed with subsequent 20 s rest before starting a subsequent bout. Electromyography, isometric muscle force, hemodynamic and ultrasound data were recorded.

Results: At days 4 and 7, there were no effects for NZBC extract on systolic blood pressure, diastolic blood pressure, heart rate, cardiac output, stroke volume, total peripheral resistance and femoral artery diameter. Although the isometric contraction protocol resulted in fatigue, there were no differences between PLA and NZBC extract conditions for isometric muscle force and muscle activity at days 4 and 7 (P > 0.05).

Conclusion: NZBC extract had no effect on cardiovascular function and exercise-induced fatigue during repeated bouts of low-intensity sustained intermittent isometric contractions of the m.quadriceps femoris, maybe due to the low demand of the exercise model.