Steady improvement in exercise

I had mentioned that I am using our cross-trainer's estimate of calories burned as a proxy for measuring my progress. Since my first workouts on it I have more than doubled in its calories estimate while also recovering more easily afterward. I've been working on both duration and resistance: for instance, I was starting out on more like resistance level eight for twenty minutes, and this morning did resistance level eleven for thirty-two minutes.

One surprise has been that while I am not very regimented in how I do the workout - some days I might not feel so great, maybe I'll go at a slightly different speed, decide to adjust the resistance part-way or something - my overall calories burned increases surprisingly reliably given the small median difference between consecutive workouts. I had expected rather more non-monotonic noise around the trend line. Perhaps my variations over the course of a single workout tend to average out.

It is not as if I work out to the beat of a reliable drummer: the cross-trainer creaks and clatters enough in use that I don't attempt accompanying audio. Though, this made me curious about drummers. I expect that if I were to attempt to keep a beat myself then I would vary significantly over the course of a song. I wonder how much professional drummers vary and how much of their ability to keep the frequency constant is innate or acquired. I also wonder if they are actually driving the beat of the song or if they are also benefiting from feedback through listening to the other musicians and adjusting time somewhat to fit them too.