The pattern nobody explains
Sitting isn’t the villain.
Not changing position is.
The common advice is that sitting is bad for your back. It is more accurate to say that staying in one position is, whatever that position happens to be — which is why people who switch to a standing desk often find the ache simply relocates rather than disappears.
What is actually happening by mid-afternoon is straightforward. Tissues held at a constant low load for hours become uncomfortable, and the muscles that should be quietly sharing that load have gradually stopped contributing. The pain arrives late in the day because it takes hours to accumulate, not because anything is damaged. That is also why it clears overnight and starts again the next afternoon. It is a capacity pattern, and capacity is trainable.
"Most Reformer Pilates studios focus on fitness. We focus on how your body actually moves — and why it moves the way it does."