Irritable Bowel Syndrome (IBS): This condition is characterized by chronic abdominal pain, bloating, and alteration of bowel habits in the absence of any mechanical, inflammatory, or biochemical abnormalities. The symptoms of fecal urgency and diarrhea, especially triggered by long runs, align with IBS, particularly the subtype IBS-D (diarrhea-predominant).

Gastrointestinal Infections: Infections such as gastroenteritis caused by viral, bacterial, or parasitic pathogens can lead to acute onset of diarrhea and fecal urgency. The physical stress of long runs might exacerbate symptoms.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic diarrhea, abdominal pain, and urgency. Physical activity might worsen symptoms due to increased bowel motility.
Food Intolerances: Lactose intolerance, fructose malabsorption, or other dietary intolerances can lead to diarrhea and urgency after consuming specific foods, potentially exacerbated by physical activity like long runs.

Ischemic Colitis: Reduced blood flow to the colon can cause sudden onset of abdominal pain, diarrhea, and potentially bloody stools. While less common, it's critical to consider, especially in older individuals or those with vascular disease, as it can be precipitated by intense physical activity.
Infectious Colitis: Certain bacterial infections (e.g., Clostridioides difficile, Salmonella, Shigella) can cause severe diarrhea, abdominal pain, and urgency. These conditions require prompt diagnosis and treatment to prevent complications.
Colon Cancer: Though less likely in younger individuals, new onset of diarrhea and fecal urgency, especially if accompanied by weight loss, blood in stool, or iron deficiency anemia, warrants investigation for colorectal cancer.

Microscopic Colitis: Characterized by chronic, watery diarrhea without visible inflammation on endoscopy but with microscopic changes in the colon lining. It's more common in older adults and can be exacerbated by physical stress.
Eosinophilic Gastroenteritis: A rare condition involving eosinophilic infiltration of the gastrointestinal tract, leading to symptoms like diarrhea, abdominal pain, and urgency, potentially triggered or worsened by food allergies or physical activity.
VIPoma: A rare pancreatic tumor secreting vasoactive intestinal peptide (VIP), leading to severe, chronic diarrhea (often >3 liters/day), hypokalemia, and dehydration, known as Verner-Morrison syndrome or pancreatic cholera.