The intestines themselves are smooth muscle, however, there is a large involvement in straining thoracic and abdominal muscles whilst defecating. The abdominal muscles act to increase the pressure within the abdomen following contraction to prevent mechanical damage to the spine during dynamic movements, assist posture etc but also this can assist in the movement of a stool.
The mechanism of excretion is an intrinsic reflex that is stereotyped to produce a certain intensity and speed if intestinal contraction called a mass movement. So, your defecating won’t be ‘faster’ as they travel through the intestine, but you will have more force available to you to move very dry, compact stool, or large stools out of the bowel which may require your assistance.
In short, no, having a six pack will not mean you have super charged defecating that fly out of your rectum, but you will be able to increase the pressure available to you to push stool out. Careful though, don’t use those gains for a grade 3 rectal tear…
Know that bathroom posture affects your health – we’re not meant to sit on the toilet seat. Squatting is the natural position for our body to poop (and give birth for that matter).
Fun Fact: The “Poop Splash” is actually called a “Worthington Jet“. Yes, some guy out there thought it so fascinating, that in 1895 he did the science on it.