1) A contraction or shortening of a specific muscle or muscle groups, followed by:
2) A controlled or voluntary lengthening (eccentric contraction), of the same muscle(s) under load/resistance.
This is similar to an isolytic contraction.
Feel free to follow along; however, you'll want to explore these movements MORE SLOWLY than I am demonstrating. Also, this is a limited example of what is possible. Keep exploring and find what else works for you!