Experts have dismissed the viral myth that running makes your waist bigger. Social media claims suggest that running builds thicker muscles in the midsection, creating a boxier torso and hindering an hourglass figure. However, science shows that regular running does not typically cause muscle gain in the waist area.
According to a medically reviewed article by Healthline, while running engages core muscles like the obliques, the aerobic exercise does not work them in a way that leads to bulkiness. Muscle hypertrophy requires specific, consistent work with heavy resistance, such as weightlifting, whereas running is a low-resistance, endurance-based activity focused on calorie burning.
A 2025 analysis found that internal obliques are active during running but within a normal range, not intense enough to trigger hypertrophy. Instead, a 2022 research paper indicated that regular aerobic exercise typically reduces waist size and total body fat, meaning running promotes fat loss, not gain.
The myth may stem from the trim appearance of elite sprinters or trained distance runners, but these athletes train very differently from recreational runners. Factors like fat distribution, rib cage width, and hip width vary among individuals and cannot be controlled. Temporary changes after running may be due to inflammation, bloating, or water retention.
Performance physiologist Francesca Bagshaw told The Independent that running heavily engages lower muscles and abdominal muscles, causing micro-tears that lead to adaptation and strength, not bulk. While long-distance running can build muscle elsewhere, it does not enlarge the waist.
