Sit-Up
Lie on your back with the knees and hips bent to place the feet flat on the floor—the feet can be anchored under or around a weight or rack. Hold the fingers at the sides of the head. Squeeze the abs to crunch the trunk and then sit up completely. Return to lying flat while maintaining tension in the abs and repeat.
To add resistance, hold a dumbbell behind the neck. This keeps the resistance for longer through the motion and requires less weight.
Purpose
The sit-up is a basic but effective trunk and hip flexion exercise for trunk stability and stamina.
Programming
Sit-ups should be done for sets of 10-30+ reps; weighted sit-ups can be done for sets of 8-15 reps.
Variations
The sit-up can be done with or without the feet anchored, with additional weight (ideally held behind the head/neck), with slow tempos, with pauses, with rotation, on a decline bench, in a glute-ham bench or Roman chair, and with pauses in a partially-sitting position.