2.2. Study Design
POLAND
The study was designed as a double-blind randomized controlled trial with parallel groups. The supplementation protocol involved a 90-day (7 times per week) supplementation program with 6 g of lyophilized black chokeberry extract in semi-professional football players of the MUKS Zawisza Bydgoszcz Soccer Club (Bydgoszcz, Poland). During the initial study visit, the subjects’ ages, body compositions, and heights were recorded. All participants were examined by a professional physician and were healthy. Before and after 90 days of supplementation, the participants completed the maximal multistage 20-m shuttle run test. Further, before and after the supplementation period, venous blood samples were taken four times for serum analysis. Before the study, the lyophilized black chokeberry extract used during the supplementation was analyzed by antioxidant testing (