Increasing physical education in high school students: effects on concentration of circulating endothelial progenitor cells - Walther, C; Adams, V; Bothur, I; Drechsler, K; Fikenzer, S; Sonnabend, M; Bublitz, B; Körner, A; Erbs, S; Busse, M; Schuler, G (Eur J Cardiovasc Prev Rehabil, 2008)