Single leg standing with resisted obliques ("Crunch, oblique" Core/abdominal strengthening, with band, overhead, standing)

Stand holding the resistance band with one arm above your head.
Take a step forward on the same leg as the arm holding the band, and lift your other knee towards your chest.
At the same time, twist your body and bring your elbow down towards your raised knee.
Make sure the movement is smooth and the twisting is mainly through your upper spine.
Control the movement as you step back and simultaneously de-rotate your body.
Repeat.