The decline started in the late 1800s, accompanied by the long gradual rise in temperature. (realclimate.org)
The question that raises in my mind is what changed back then to start the long gradual decline and by inference the long gradual rise in temperature? (realclimate.org)
The rectus femoris remains more active than these single - joint knee extensors, with gradual rise and decline. (stretchcoach.com)