I have a distinctly shaky tone when I play. It's obvious when I warmup, but it happens even on the first few notes and occasionally goes away. I do a few minutes of long tones through the whole warmup session, through the low to high range. My whole practice session, minus music that I need to know: warmup long tones; slurs (mid to high range); long tones (I play two or three scales several times; eight counts each note; double octave if lower than a C scale). If I'm tired or very shaky, I will rest then continue at whatever I note I left. I rest a lot more often between scales, long tones, exercises, etc. than I used to. Previously, when I felt a burning/achiness, I would continue playing just to the end of the scale if doing long tones, but by that point, I was already on the lower octave if I were doing a two octave scale.