What could be the cause of bulging below the sternum and between the navel in an adult with moderate to high physical activity level while doing abdominal exercises?

Abdominal Bulging During Exercise: Diastasis Recti

The bulging you're observing between the sternum and navel during abdominal exercises is most likely diastasis recti—a separation of the rectus abdominis muscles along the linea alba—which becomes visibly prominent when intra-abdominal pressure increases during core muscle contraction.

Understanding the Mechanism

The phenomenon occurs due to increased intra-abdominal pressure during abdominal exercises, which causes the abdominal contents to protrude through the weakened connective tissue between the separated rectus abdominis muscles 1. This is distinct from exercise-related gastrointestinal issues, which involve internal organ dysfunction rather than structural muscle separation 2.

Key Distinguishing Features

• Visible ridge or bulge: The bulging appears specifically along the midline (linea alba) between the two sides of the rectus abdominis, running vertically from below the sternum toward the navel 1
• Exercise-induced appearance: The bulge becomes prominent only during abdominal muscle contraction (such as during crunches, sit-ups, or planks) and may disappear when muscles are relaxed 1
• Location specificity: The bulging occurs in the infra-umbilical and supra-umbilical regions, not in the flanks or lower quadrants where other pathology would manifest 1

Clinical Significance and Risk Assessment

This condition requires proper assessment before continuing intensive abdominal training, as inappropriate exercises can worsen the separation and potentially lead to complications.

Potential Complications if Unaddressed

• Progressive muscle separation: Continuing traditional abdominal exercises (particularly sit-ups with foot fixation and bilateral straight leg raises) can compound the separation and create further muscle imbalance around the pelvis 1
• Lumbar spine stress: Exercises that increase intra-abdominal pressure without proper muscular control can hyperextend and hyperflex the lumbar spine 1
• Functional impairment: The separated abdominal muscles lose their ability to effectively stabilize the lumbar spine and control pelvic tilt 1

When to Seek Immediate Evaluation

While diastasis recti itself is not a medical emergency, certain presentations warrant urgent assessment:

• Acute onset with severe pain: If the bulging is accompanied by sudden, severe abdominal pain, this could indicate abdominal wall muscle injury with rhabdomyolysis, which can mimic an acute abdomen 3
• Associated swelling or discoloration: Visible swelling, bruising, or skin changes suggest potential muscle trauma requiring imaging 3
• Systemic symptoms: Fever, nausea, or dark urine alongside the bulging may indicate more serious pathology 3

Recommended Management Approach

Step 1: Immediate Exercise Modification

• Discontinue traditional exercises: Stop performing sit-ups with foot fixation, bilateral straight leg raises, and any exercises that cause visible bulging 1
• Avoid Valsalva maneuvers: Refrain from holding your breath during core exercises, as this dramatically increases intra-abdominal pressure 1

Step 2: Assessment Protocol

A musculoskeletal assessment should be performed before prescribing any abdominal exercise program to evaluate the degree of separation and identify any muscle imbalances around the pelvis 1. This assessment should include:

• Palpation test: Lying supine with knees bent, perform a small head lift while palpating along the linea alba to measure the width of separation (typically measured in finger-widths) 1
• Functional movement assessment: Evaluate control of pelvic tilt and lumbar stabilization during basic movements 1

Step 3: Corrective Exercise Prescription

• Pelvic tilt re-education: Begin with exercises that train muscular control of pelvic tilt before progressing to more challenging movements 1
• Trunk curls without foot fixation: These engage the infra-umbilical portion of the rectus abdominis without excessive hip flexor involvement 1
• Avoid exercises that increase separation: Do not perform exercises where the abdominal wall visibly domes or bulges outward 1

Important Caveats

Traditional abdominal exercises without external resistance do not significantly improve abdominal strength in healthy adults, so the focus should be on quality of movement and proper muscle recruitment rather than high repetitions of ineffective exercises 4. The trunk curl and modified sit-up (without foot fixation) are safer alternatives to traditional sit-ups, as they minimize lumbar spine stress while still engaging the abdominal muscles 1.

Common Pitfalls to Avoid

• Continuing high-intensity core work: Exercises that cause visible bulging will worsen the condition rather than strengthen the core 1
• Ignoring hip flexor dominance: Many individuals compensate for weak abdominals by overusing hip flexors, which can be identified during assessment 1
• Assuming all core exercises are equivalent: Exercise specificity matters—some movements exacerbate diastasis while others promote healing 1

The mechanical stress from improper exercise technique, similar to how repetitive impact causes tissue damage in runners, can progressively worsen abdominal wall integrity if not addressed 5. Therefore, proper assessment and exercise modification are essential for both symptom resolution and prevention of long-term complications.