Grünenfelder first competed in an international cross-country skiing race for Switzerland in 1982. He finished 20th in freestyle over 15 kilometers. His first Olympic participation was in 1984 in Sarajevo . The best individual result was sixth place over 50 kilometers. In the relay race he reached fifth place with his teammates Joos Ambühl , Giachem Guidon and Konrad Hallenbarter . In the following four years he was still active, but could not achieve any international medals or podium finishes. It wasn't until the 1988 Winter Olympics in Calgary that Grünenfelder was able to win his first medal - bronze over 50 kilometers. With the season he, Guidon, Jeremias Wigger and Jürg Capol narrowly missed another podium and finished fourth. After the Winter Games, Grünenfelder withdrew from active sport.