>>394064
>>394102
Here's some studies that might be relevant.
https://www.ncbi.nlm.nih.gov/pubmed/12224475
https://www.ncbi.nlm.nih.gov/pubmed/11578974
https://www.ncbi.nlm.nih.gov/pubmed/8915619
>study #1
The electrical waves governing rectal motility are initiated from the rectosigmoid pacemaker, which is located in the rectosigmoid junction.
Damage to the rectosigmoid pacemaker (anesthetization in the case of the study) results in the loss of rectal contraction.
It could be concluded that repeatedly smashing massive long dildos and objects through the rectosigmoid junction could damage it, reducing or eliminating rectal motility. Which would make it hard to push out shit.
>study #2
Distention of the anal sphincter resulted in sigmoid pressure and rectal pressure increase.
Distention of the anesthetized anal sphincter resulted in no pressure increase of either the sigmoid or rectum.
This is probably why repeatedly flexing your anal sphincter helps you go.
>study #3
The sigmoid was filled up with gradually increasing amounts of liquid. At around 86ml the sigmoid contracted and expelled its contents. The anesthetized sigmoid did not contract at all.
Regarding enema dependence, maybe repeatedly filling up the colon (specifically the sigmoid) with large amounts of liquid and forcing it to be held in (those "high" enemas that people do) may over time "re-calibrate" the threshold for sigmoid contraction to a larger than normal volume. So a normal volume of stool isn't enough to make your sigmoid contract anymore so you become dependent on the enema liquid to inflate your sigmoid enough to make it contract and push everything out.
There's a lot of complex reflexes and interactions in the lower colon. So it's always best to be careful and use a lot of lube. As always pain means you're doing something wrong.