[3][4] He represented Sweden at the 1928 Summer Olympics in Amsterdam and nearly qualified for the final, placing third in his semi-final.

[1] Wennström reached his peak in 1929, consistently running under 15 seconds and winning another Swedish national title;[3][4] finally on 25 August, in a dual meet against Norway at Stockholm, he broke the world record with his time of 14.4.

[4] Although a number of other athletes, starting with Earl Thomson in 1920, had run the slightly shorter 120 yd (109.7 m) hurdles in 14.4, Wennström was the first to do so over the metric distance.

[4] There were some doubts about the validity of Wennström's mark, with wind assistance and unreliable clocks cited as possible factors in it,[4] but the International Amateur Athletic Federation, responsible for officially ratifying world records, found no problems with the time and accepted it.

[4][5] Wennström lost his best shape after the 1929 season and never regained it,[4] although he did become Swedish champion for a third and final time in 1931.