[1][2] Shortly after, he set a new personal best of 45.25 at the Swiss Championships and also finished in first place at the event, securing his second national title.

Lionel remains with Adliswil Track Team, but his trainer is Alex Hautle from LAC TV Unterstrass in Zürich.

[8][9] Spitz made his international debut at the 2017 European Youth Olympic Festival in Győr, Hungary and finished in fourth place in the 400 metres.

He was supposed to run the anchor leg of the race, however, a commotion caused his teammate to trip before Spitz could be passed the baton.

The same year, he attended the 2022 European Championships in Munich, Germany and qualified for the final rounds in the 400 metres.

He competed in the mixed 4 x 400 metres relay and ran the first leg of the race, however, he and his teammates failed to advance to the final rounds.

[16] Previously, he and the entire mixed 4 x 400 metres relay team—comprising Ricky Petrucciani, Giulia Senn, and Julia Niederberger—broke the Swiss record in the category at the 2023 European Team Championships with a time of 3:14.22.