missed a beat.

[keannu]

I found its dictionary definition, but how come it means "experience stopping something"? What does "beat" here mean?

st35)In Europe, the downward trend in work hours has hardly missed a beat. Unlike the United States, organized labor in Europe has kept the issue of shorter working hours at the top of its agenda...

 

[JMurray]

not a teacher

In Europe, the downward trend in work hours has hardly missed a beat. Unlike the United States, organized labor in Europe has kept the issue of shorter working hours at the top of its agenda...

I'm not sure if the "beat" necessarily refers to that of a heart or of music, possibly both. It's a very common informal phrase. To "miss a beat" means to falter or stop for a short period, as a heart or drummer might if either missed a beat. So the European trend did not falter because the unions kept the issue prominent.
It's often used in the negative and frequently refers to a transition of some sort.
"She was a little nervous about going from office-worker to boss, but she managed it without missing a beat." i.e. She made the transition very smoothly.