According to the Houston Chronicle, the elliptical machine does work the abs. The muscles in the abdomen are used to stabilize the body while exercising on an elliptical similar to how they stabilize the body during everyday activities such as walking, sitting, standing, reaching or lifting.
To increase the effectiveness of an elliptical workout, trainers should play close attention to posture. The Houston Chronicle advises that people stand up straight and tighten their core while working out on an elliptical. Additionally, It's better for trainers having a hard time maintaining posture to slow down than to sacrifice stance. Increasing resistance on the elliptical while maintaining proper form places additional stress on the abdominal muscles.