Constipation affects 4% of adults in the United States (U.S.). An estimated half of constipated patients are unable to relax pelvic floor muscles during defecation, a type of constipation called pelvic floor dyssynergia (PFD). Biofeedback has been recommended for the treatment of constipation because uncontrolled studies over the past 10 years suggest that these treatments are as effective as medical or surgical management and involve no risk. However, placebo-controlled trials are still lacking. The aims of this study are: