We are taught that if your straining then your not doing the technique correctly. the idea beind the techniques is that one shouldn't have to strain. Now Im sure there are times when you can toss a little more "Umph" into a technique and get diffrent results. Rexlaing body and mind and using Ki flow is what makes the techniques dynamic.
We are also taught to use our whole body, not just one part of it. So if you use your entire body and entire mind and entire spritual self in a technique the results would be heavenly.
There is more to it than just relaxing your muscles. relax your mind, and extend your ki. I think all Aikidoka strive not to master just the technique, but to master harmony with ones entire being, body, mind, and soul.
This link you may find useful. Check out the unbendable arm as an example.