I often wonder at the details of meridian theory. Proven with GSR measurements.

How though did the ancient Indians and Chinese discover or sense the Nadis/meridians

In my personal experience I have come closest to this while practising extreme isometric tension exercises.

For example holding two 24kg kettlebells in the hands in a standing stance for as long as possible I will swear I can feel the meridians in my arms and microcosmic circuit

Have others had similar experience with isometric exercises ?

In meditation though I feel that I am only imagining the meridians.