I am telling this even though I expect you will have already heard about it in one of your economics lectures, but you know, you can’t always remember everything ... Graphically, this change is usually illustrated as follows: a line shows trend GDP growth over time, while actual GDP sometimes grows faster and sometimes slower, which is shown by a cyclical curve along the trend line.
If the potential output growth rate increases, the line becomes steeper, and if it decreases, the line runs flatter. The latter is what happens when demographic change takes hold.