So, for my exercise plan, Here is exercise 1 from the April 1920 Good Housekeeping:
Position - The body should be perfectly flat on the floor, face up, hands clasped behind the head. Raise the trunk to an erect sitting position while the legs remain still as in figure 1. Lower slowly. Repeat four more times.
Breathing - Inhale as the trunk raises. Exhale slowly when hovering trunk