Most karate students will know that class begins from the moment they step across the threshold of the dojo door on the way in and does not end until they step across again on the way out. Arguably, training does not end when you walk out of the dojo and therefore, the next time you walk back in, it's not really another beginning, just a continuation from where you left off last time.
To some, the attitude appears to be that the karate training does not begin until the warm up has concluded. This is incorrect. Most instructors are aware of their students deficiencies; they are also keenly aware of their students attitudes by observing the way they carry and conduct themselves before, during and after class. There's not much that goes unnoticed.
To get the most out of taiso one needs to have a warm body so that the muscles are flexible and less prone to damage. So, getting warmed up before a class starts, for the graded student especially, is a matter of self-responsibility. Especially in winter when our muscles are cold and stiff.
Chapter Thirteen of Masotoshi Nakayama Sensei's Dynamic Karate covers Calisthenics and Exercises. I know that these exercises are fundamental to good Shotokan practice because they are the exact same exercises we were taken through as novice students when I began my studies, well before any of us even knew that the book Dynamic Karate existed.
The history of calisthenics is linked to Greco-Roman gymnastics. Taiso, a generic Japanese term for conditioning, literally means 'body (tai) hardening (so)'. As diligent karate-ka it behoves us to devote time and effort to overcoming the limitations and weaknesses taiso uncovers. All things being equal and, in relation to a perfectly fit and healthy body, these weaknesses usually manifest themselves as pain. And this pain is simply the body's way of letting go of that weakness. Or, in other words, we are becoming stronger.
Pay attention to what is going on for your body during taiso. Work on mastering the exercises that come difficult to you, as you would a kata. Be sensible about this. Don't injure yourself for the sake of looking good in class, but push a little bit more every time. And if an exercise does come easy to you, don't sit and relax in a pose, push that a little harder too. We are all different. Our bodies are all different. Yes, it is good to focus on and capitalize upon our strengths, but don't cherry-pick and neglect difficult exercises just because they are uncomfortable.
It's a domino effect. Good taiso enables good kihon; good kihon enables good kata; and good kata enables good kumite. It ALL counts.