Effect of New Zealand Blackcurrant Extract on Force Steadiness of the Quadriceps Femoris Muscle during Sustained Submaximal Isometric Contraction

Intake of anthocyanin-rich New Zealand blackcurrant (NZBC) can alter physiological
responses that enhance exercise performance. In two studies, we examined the effects of NZBC
extract on force steadiness during a sustained submaximal isometric contraction of the quadriceps
femoris muscle. With repeated measures designs, male participants in study one (n = 13) and study
two (n = 19) performed a 120 s submaximal (30%) isometric contraction of the quadriceps femoris
muscle following a 7-day intake of NZBC extract and placebo (study one) and following 0 (control),
1-, 4- and 7-day intake of NZBC extract (study two). Participants for both studies were different. In
study one, NZBC extract enhanced isometric force steadiness during the 120 s contraction (placebo:
6.58 ± 2.24%, NZBC extract: 6.05 ± 2.24%, p = 0.003), with differences in the third (60–89 s) and
fourth quartile (90–120 s) of the contraction. In study two, isometric force steadiness was not changed
following 1 and 4 days but was enhanced following 7-day intake of NZBC extract in comparison
to control. In study two, the enhanced isometric force steadiness following 7-day intake did occur
in the second (30–59 s), third (60–89 s) and fourth (90–120 s) quartiles. Daily supplementation of
anthocyanin-rich NZBC extract can enhance force steadiness of the quadriceps femoris muscle during
a sustained submaximal isometric contraction. Our observations may have implications for human
tasks that require postural stability.