Career
Groenendaal began to ride as a junior in 1987. The following season he joined the Amateur category which he stayed until the 1993-1994 season when he turned professional. Early in his career he showed promise as a road rider by finishing in the top ten in the 1992 Tour de l"Avenir, the year he also took part in the Summer Olympics road race.
At the start of Groenendaal"s career he was often compared to his father Rein and one commentator in Belgium sometimes referred to him as Reintje.
However after two seasons, Groenendaal had stood on more international podiums than his father and the comparisons stopped. In 1996 Groenendaal joined the newly formed Dutch cycling team Rabobank which he would stay with until the end of the 2006-2007 season when he choose to ride for an individual sponsor.
In the following season, Groenendaal dominated cyclo-cross with wins in the Superprestige series and the World Cup as well as being number one UCI ranked rider. Groenendaal started as a big favourite for the World Championships but suffered a crash during the race and did not recover and as a result lost his Rainbow jersey.
Groenendaal finished fourth and as best non-Belgian.
Foreign the 2003-2004 season, Groenendaal suffered from a knee injury at the start of the season. In an unexpected finale, Groenendaal took the 2003-2004 World Cup classification after the final event of the season. Groenendaal finished in twelfth place.