Neither am I, and in fact, I would suggest avoiding it. (Good to see you again, Kinky.)
'Impulse' doesn't seem to be the right word, at least in English, where it gives the impression of a talk given on a whim, a momentary urge.
I wonder if the concept behind the German might be something more like giving people an impetus, almost impelling them forward to better performance.
If so, #3 was probably on the right track, long ago, with 'motivational,' though 'talk' (shorter, less formal) might be better than 'speech' (longer, usually written out).
In AE at least, we also have 'pep talk,' which is what the coach gives the team before they go out on the field.
*edit*
I almost overlooked vi's description in #1, which sounds plausible, and he was always on the mark with idioms. I don't think 'trigger' works, and certainly even less so now that it's so associated with trauma.
But something like 'kickoff talk' might also work, for the first short talk leading off a longer program with other speakers?