[1] He represented Germany at the 2016 Summer Paralympics in Rio de Janeiro, Brazil and he won the gold medal in the men's shot put F41 event.

[1] He also represented Germany at the 2020 Summer Paralympics in Tokyo, Japan and he won the bronze medal in the men's shot put F41 event.

At the 2015 World Championships held in Doha, Qatar, he won the silver medal in the men's shot put F41 event.

[2][3] In 2016 and 2017, Kappel won the German Sportspersonality of the Year award in his category (male athletes with a disability).

[4] Kappel competed in the 2024 Paris Paralympic Games and won the silver medal in the men's shot put F41 event.