@book { MentalSkillsTestforGymnastics,
    title = "Mental Skills Test for Gymnastics",
    author = "Axel {Schulze}",
    year = "2009",
    publisher = "Diplom.de",
    address = "Hamburg, Deutschland",
    doi = "10.3239/9783836637336",
    url = "https://m.diplom.de/document/227290"
}