The consumption of blackcurrants has previously been shown to increase blood flow to the hands and eyes in humans at rest via vasodilatory mechanisms attributed to polyphenolics. While an increase in blood flow to the hands at rest may have health related benefits, such as improving resting circulation, it is unclear whether there is a benefit during fatiguing exercise. An increase in blood flow to contracting skeletal muscle during exercise may, in theory, delay the onset of fatigue by improving oxygen and nutrient delivery to the muscle while additionally increasing the rate at which metabolic waste products and biochemical agents of fatigue are removed.
PURPOSE: To investigate the effects of New Zealand blackcurrant extract on peripheral (forearm) blood flow and muscular performance.
METHODS: Ten healthy males participated in two trials during which they ingested either blackcurrant extract (BC), delivering 1.87 mg anthocyanins/kg bodyweight, or a placebo powder (PP) containing equivalent amounts glucose, fructose and sucrose to BC; treatment allocation was randomly allocated in a balanced fashion and participants were blinded to the treatments. Participants sat at rest and measures of forearm blood flow (FBF), using venous occlusion plethysmography, heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP) were made prior to and every 30 min after treatment ingestion, for 2 h. After 2 h participants completed intermittent isometric handgrip exercise to volitional fatigue. Differences within and between trials for all criterion measures were analysed using two-way repeated measures ANOVA.
RESULTS: A treatment effect (p = 0.014), time effect (p = 0.05) and a treatment x time interaction (p = 0.005) were observed for FBF. FBF decreased over the 2 h period with PP only (90 min = - 35.8 ± 28.8 %, p =0.047; 120 min = - 39.4 ± 29.1 %, p =0.028), no change was observed with BC. HR, SBP and DBP changed over time (all p < 0.001) however no difference between treatments was found. The number of repetitions completed during hand grip exercise did not differ between treatments (BC = 73.6 ± 28.8 repetitions vs PP = 77.2 ± 44.5 repetitions, p = 0.68).
CONCLUSIONS: New Zealand blackcurrant extract maintains peripheral blood flow during a period of prolonged sitting, however this effect does not alter fatiguing hand grip performance.