@article{ref1,
title="Children injured during physical education lessons. nine hundred and eighteen cases",
journal="Journal of sports medicine and physical fitness",
year="1981",
author="Hammer, A. and Schwartzbach, A. L. and Paulev, P. E.",
volume="21",
number="4",
pages="423-431",
abstract="<p>[Abstract unavailable]</p> <p>Language: en</p>",
language="en",
issn="0022-4707",
doi="",
url="http://dx.doi.org/"
}