Kazumoto Tanaka Takayuki Kataoka Makoto Hasegawa Virtual Sport System for Optimum Exercising Based on a User Model. 283-290 2009 Edutainment http://dx.doi.org/10.1007/978-3-642-03364-3_34 conf/edutainment/2009 db/conf/edutainment/edutainment2009.html#TanakaKH09