On 5 June 2022, Blummenfelt became the first person to complete an Ironman-distance triathlon in under seven hours during the Pho3nix Sub-7 Sub-8 event at the Lausitzring race track in Germany.

Despite competing in the ITU World Triathlon Series for a number of years, his highest finish was second place until 31 August 2019 when he took the gold at the Grand Final in Lausanne.

A similar feat was achieved at the 70.3 Middle East Championships in Bahrain in 2018, with Blummenfelt finishing first ahead of Iden with Stornes in third place.

[5] As a track runner, he represented the clubs Fana IL and TIF Viking and competed in the junior race at the 2011 European Cross Country Championships.

Blummenfelt raced the 70.3 Ironman Middle East Championships 2018 for the second year running, finished in the top spot and in doing so set a new world record for the distance of 3:29:04.

[11] In 2019, Blummenfelt achieved his first career gold at ITU World Triathlon Series level at the Grand Final in Lausanne on 31 August.

Blummenfelt raced the 70.3 Ironman Middle East Championships 2019 for the third year running, beating his previous world record time to win and set a new mark of 3:25:21.