Grundmanis won a gold medal at the 1935 EuroBasket competition, becoming the first European champion.

He was also a member of the Latvian Christian Youth Society, and graduated from a four-year physical education program at the University of Tartu.

In late 1930s Grundmanis played for the military team Rīgas ASK, and became a two time Latvian champion (1939-1940).

During Nazi occupation of Latvia during World War II, Grundmanis was conscripted into Latvian Legion.

He committed suicide on 30 November 1944 at the German POW camp in Sarkandaugava, Riga.