He competed in the 400 m, 1500 m and 4 × 200 m events at the 1956, 1960 and 1964 Olympics and won four silver medals; he also helped Japan win a bronze relay medal in 1964 by swimming in the heat, and placed fourth in the 4 × 200 m relay in 1956 and in the 1500m in 1960.

At the 1960 Olympics, he swam the fastest leg in the 4 × 200 m relay, yet his team lost to the United States.

[1] Yamanaka studied in college at the University of Southern California, where he broke the 200 m world record three times within two months in 1961.

He set two more records over 200 m earlier in 1958–59, but unfortunately for him this distance was not an Olympic event in those years.

Yamanaka graduated from Waseda University and later headed the Itoman Swimming School in Osaka.