Learn How You Stand
The body likes to relax. This can sometimes be a good instinct for a karate-ka to nurture: far too many earnest young students tense their shoulders furiously during basics, from opening kiai to closing bow, and their technique suffers from exhaustion for the instructional (the author was one of those students.) Relaxing can save you from a full-nelson headlock and from a fall out a window. However, relaxing is not always good.
Sensei Jim Landon taught me long ago that there are only two circumstances in which one's knees should be allowed to lock: while stretching, and during the utmost extension and snap of a kick. Yet most of us, standing in front of a gym locker or at a bank counter, will straighten one leg to lean on the lock of the knee joint -- resting on the bone to give our muscles a break. After a minute or two, we will switch to the other leg. This is a poor habit, and teaches our muscles to be lazy. Indeed, the consequences can be immediate. In a middle school choir some years ago, the singer next to me passed out cold, mid-verse, because she locked both knees and limited blood flow to her upper body.
Shihan Mike Susulka reminds me that the body likes to make things easier for itself, and we must train our muscles to behave how we want them to. It takes effort to remind the legs to stand on two, with knees slightly bent, where each leg may bear an equal burden of the body and the muscles may strengthen over time. So, too, does it take effort to push our arms to execute crisp technique at the end of a long class -- but that moment is when precision is most important. Muscles learn best when tired, and the memory will stick around for next time.