Bar end levers.
Because of the increased desire of the time trialist for an aerodynamic position on the bicycle, a time trial bike uses triathlon bars, a different bar arrangement from a road bicycle’s drop handlebars.
The controls are mounted at the end of the triathlon bars and are called bar end levers or barcon, for bar control.
Bar end levers can also be used on the ends of drop handlebars, a set-up common on touring bicycles, as bar-end shifters are more robust than integrated shifters. (fig. 59).
This allows switching during a trial without moving the hands.
Constructive you can compare them with the indexed switches that can be mounted on the down tube.
For the mountain bike is also a special bar end shifter on the market.
This is until now only included on the most expensive bike.This shifter also includes a special thumb lever.