Raised in Starovičky, in the south-eastern Břeclav District,[1] Juška made his international debut for the Czech Republic at the 2012 World Junior Championships in Athletics.

Outdoors, he was the long jump winner at the Josef Odložil Memorial in Prague (the country's foremost track meet) with a personal best mark of 7.94 m (26 ft 1⁄2 in).

[1] Under the tutelage of Josef Karas (a former decathlete), Juška was encouraged to focus on both his athletics and his studies at the University of Economics, Prague.

[5] In the final he was spurred on by the home crowd and improved his personal best to 8.10 m (26 ft 6+3⁄4 in) to claim the silver medal behind Michel Tornéus.

[7] He was one of three Czech athletes to win medals on the first day of finals at the championships, alongside Ladislav Prášil and Eliška Klučinová.