Linear, sigmoidal, arc and exponential.
I'm certain you can find career paths of biomedical research PIs that can be so described. You can think of the dependent variable as a conglomerate measure of lab size- people, funding, space, collaborations and vigor.
I used to see a lot of sigmoids in my subfield peers.
A slow start, struggling to land that first major funding. Hard to find or hard to fund postdocs so making do with techs, undergrads and maybe a grad student who don't know any better.
Eventually things click, the grant clouds pour down direct costs rain and the postdocs come a-running.
A successful career launch.
It feels as though I'm seeing a lot more interruptions lately. Peeps who I thought were, and should be, on the steep part of the curve suffering an interruption of some sort. Not always sure why...after all it's kinda rude to front your colleagues about perceived slowdowns. Unless you are the Chair, I suppose. I tend to assume it is because the grant dice just aren't coming up. And there is very little room for error in the current funding environment. Very different from when I was just getting started in my independent phase.
Watching the people that I like take a hit in what should be a time of scientific vigor in their career path is unpleasant.