What are the potential causes and recommended course of action for an adult with no significant medical history experiencing sharp subcostal pain during exercise?

Sharp Subcostal Pain During Exercise

The most likely diagnosis is exercise-related transient abdominal pain (ETAP, commonly called a "side stitch"), which presents as sharp subcostal pain during activities involving repetitive torso movement and typically resolves with rest or cessation of exercise. 1

Primary Diagnosis: Exercise-Related Transient Abdominal Pain (ETAP)

ETAP is extremely common, affecting approximately 70% of runners annually and one in five participants in any single running event. 1 The pain characteristics match your presentation:

• Location: Most commonly occurs in the lateral aspects of the mid-abdomen along the costal border (subcostal region) 1
• Quality: Sharp or stabbing when severe; cramping, aching, or pulling when less intense 1
• Timing: Occurs during exercise, particularly with repetitive torso movement in extended positions 1
• Resolution: Typically transient and resolves with rest 1

The current leading theory suggests irritation of the parietal peritoneum as the mechanism, though the exact etiology remains incompletely understood. 1

Critical Red Flags Requiring Immediate Medical Evaluation

Stop exercising immediately and seek medical consultation if you experience: 2

• Upper body discomfort (chest, arm, neck, or jaw) during exercise—any intensity of aching, burning, tightness, or fullness 2
• Fainting or feeling faint during exercise (not just brief lightheadedness after vigorous exercise) 2
• Severe shortness of breath where conversation becomes an effort or wheezing develops 2
• Symptoms persisting beyond 5 minutes of rest 2

These symptoms may indicate cardiac ischemia rather than benign ETAP and require urgent evaluation before continuing exercise. 2

Important Differential Diagnoses to Consider

While ETAP is most likely, other conditions can present with subcostal pain during exercise:

Gastrointestinal Causes

• Exercise-induced gastrointestinal syndrome (EIGS): Affects 30-93% of endurance athletes, caused by splanchnic hypoperfusion (up to 80% reduction in gut blood flow during maximal exercise) 2
• Median arcuate ligament syndrome: Rare but causes severe exercise-related abdominal pain from celiac artery compression 3
• Gastrointestinal ischemia: Results from blood shunting away from viscera to working muscles 2

Musculoskeletal Causes

• Rib stress fractures: Present with localized tenderness and pain with movement, diagnosed by bone scan 4
• Intercostal muscle strain: Causes tenderness between ribs 4
• Costochondritis: Pain around 2nd-5th costochondral joints with point tenderness 4

Heat-Related Causes

• Heat exhaustion: Headache, dizziness, nausea, cramps accompanying the pain when exercising in temperatures >80°F 2, 5

Evidence-Based Prevention Strategies

Dietary modifications (strongest evidence):

• Avoid large volumes of food/beverages for at least 2 hours before exercise, especially hypertonic (high-concentration) drinks 1
• Avoid high-fructose beverages exclusively containing fructose; fructose-glucose combinations are better tolerated 2
• Avoid high-fiber foods on the day of or days before intense exercise 2

Hydration management:

• Start exercise euhydrated (normally hydrated), as both dehydration and overhydration worsen gastrointestinal symptoms 2
• Avoid excessive pre-exercise fluid loading (>1134 mL immediately before exercise increases abdominal pain) 2
• Maintain euhydration during exercise with ad libitum fluid intake rather than forced programmed intake 2

Training modifications:

• Improve core strength to support abdominal organs 1
• Correct thoracic posture during exercise 1
• Consider wearing a supportive broad belt during activities 1
• "Gut training": Gradually increase tolerance to fluid/food intake during exercise over 28 days 2

Environmental considerations:

• Exercise in early morning or late afternoon when temperature >80°F 2
• Avoid exercising in high heat and humidity which increases core temperature and gastrointestinal perturbations 2

Medications to Avoid

Do NOT use NSAIDs (ibuprofen, naproxen) or aspirin before or during exercise if you experience gastrointestinal symptoms. 2 These medications:

• Increase gastrointestinal permeability 3-5 fold 2
• Aggravate exercise-induced intestinal injury 2
• Significantly increase risk of upper gastrointestinal bleeding and perforation 2

When to Seek Medical Evaluation

Obtain medical consultation before continuing exercise if: 2

• Pain persists beyond typical ETAP pattern (should resolve within minutes of stopping)
• Pain occurs at rest or awakens you at night
• Associated symptoms develop: severe shortness of breath, chest discomfort, fainting
• Pain progressively worsens over multiple exercise sessions
• Inability to complete usual training sessions with reserve 2

Immediate Management During an Episode

• Stop or significantly reduce exercise intensity at first symptom onset 2
• Alter breathing pattern: Try deep, controlled breathing
• Change posture: Straighten thoracic spine if hunched
• Apply manual pressure to the painful area (anecdotal relief)
• Resume exercise gradually only after complete symptom resolution

Common Pitfalls to Avoid

• Do not "push through" severe pain—this may indicate a more serious condition requiring evaluation 2
• Do not assume all subcostal pain is benign ETAP—cardiac causes must be excluded in adults, especially those >40 years 2
• Do not exercise within 2 hours of eating, as the postprandial state significantly exacerbates ETAP 1
• Do not rely on NSAIDs for prevention—they worsen gastrointestinal integrity during exercise 2