Keage (“snap”) is what gives karate techniques their power. Well, not power per se, but impulse.
Impulse the change of an object’s momentum due to a force acting over some time interval; I = Δp =∫F dt . Since your strike stops, it delivers all of its momentum, so Δp is a constant. The only way to increase the force of the technique is to decrease the time interval which it acts over.
This is achieved by adding a whip-cracking or towel-snapping motion to all techniques. This “snap” is generated by switching from a relaxed state, completely tensing at the exact moment of impact, and back to relaxation as quickly as possible; this necessitates a short ibuki breath. This should be a total-body spasm-like reaction, similar to a sneeze. This is the trick behind Bruce Lee’s famous One-Inch Punch.
All Goshin-Jutsu Karate techniques snap to some degree, so you must keep practicing this forever. Constant practice is needed to make these motions automatic, and to maintain this skill.