The butterfly crunch is a popular bodyweight exercise that targets the rectus abdominis, or "six-pack" muscles. It gets its name from the position of the elbows and knees, both of which are bent out like wings. It can be performed for time or reps as part of any abs-focused circuit or workout.
Serious core activation and burn
Glute activation from lower-body butterfly position
Butterfly position makes it harder to use the hip flexors