Blackcurrant extract does not affect the speed-duration relationship during high-intensity running.

Anthocyanin-rich blackcurrant extract (BC) has been shown to ergogenically aid high-intensity exercise. Capacity for such exercise is evaluated by the hyperbolic speed-tolerable duration (S-D) relationship. Therefore, in double-blinded and cross-over randomised controlled trials, 15 males underwent treadmill running incremental exercise testing and were assessed for S-D, quantified by critical speed (CS) and ' (distance), and assessments of time to exhaustion performance to empirically test the limits of the S-D relationship, after daily supplementation of 300 mg/d BC (105 mg/d anthocyanin) or placebo. Supplementation with BC did not change CS (placebo 12.1 ± 1.0 km/h vs BC 11.9 ± 1.0 km/h, >.05) or ' (placebo 918.6 ± 223.2 m vs BC 965.2 ± 231.2 m,  > .05), although further analysis indicated ' increased in 60% of subject (=.08), indicating a trend toward cohorts potentially benefiting from BC supplementation. BC supplementation did not change time to exhaustion at or above CS, maximal oxygen uptake (VO), lactate threshold (LT), submaximal running economy (C), or substrate utilisation during exercise (all >.05). In conclusion, we could not detect any beneficial effect of BC supplementation during high-intensity running exercise, including the determining factors S-D relationship, VO, LT or C. Hence, no ergogenic effect was observed.