Social media fitness myths discourage young women from healthy exercise

On any given day, thousands of young women scroll through TikTok and Instagram and encounter a simple, terrifying claim: jogging will widen your waist. Exercise will puff up your face. Lifting weights will make you bulky. These ideas have names now—'runner's waist,' 'cortisol face'—and they're spreading fast enough that health organizations have started to worry.

ExerciseNZ, a non-profit focused on physical activity, has flagged these trends as a genuine problem. The organization argues that appearance-driven fitness myths are actively discouraging young women from exercising at all. What's particularly troubling, according to the group, is that these claims have no scientific backing whatsoever. Yet they're being promoted by online influencers—many with no formal training in exercise, health, or biology—to audiences in the millions.

Take the 'runner's waist' myth. The claim is straightforward: regular running activates your oblique muscles, making them visibly larger and creating a wider, boxier midsection. Medical research tells a different story. Running does engage the core, but only at intensities far too low to actually build significant muscle mass. What running actually does is develop cardiovascular fitness, endurance, and core stability. As one medically reviewed analysis put it, the idea that jogging makes your waist bigger is "misleading and potentially dangerous." The physiology simply doesn't support it.

Then there's 'cortisol face'—the notion that exercise elevates stress hormones enough to cause facial puffiness and bloating. Medical experts from Ohio State's Wexner Medical Centre have examined this claim and found it has no basis in recognized medicine. While rare disorders involving abnormally high cortisol can change how someone's face looks, everyday exercise and normal life stress do not produce the dramatic facial transformations being showcased across social media. The condition doesn't exist in any meaningful medical sense.

The third persistent myth concerns weightlifting and bulk. The fear is that any strength training will automatically make you large and muscular. In reality, building substantial muscle mass requires years of progressive resistance training, carefully controlled nutrition, and often favorable genetics. It's not something that happens by accident.

Richard Beddie, chief executive of ExerciseNZ, expressed frustration that these trends are gaining traction now, after decades of work to build a healthier cultural relationship with exercise. For most people, he noted, the primary reasons for exercising are health and mental wellbeing. These new social media crazes reverse that entirely, replacing those motivations with appearance anxiety. "We've gone from celebrating what our bodies can do to worrying about whether our waistline or face fits the latest TikTok trend," he said. "That's a step backwards."

What concerns Beddie most isn't the myths themselves, but what they reveal about how young women have come to see themselves. The irony is sharp: the very activities most proven to improve health—running, strength training, regular exercise—are being weaponized as threats to appearance. Beddie's message to young women is direct: be skeptical of health advice from social media, and remember that your body isn't a trend. Exercise should be about building strength, improving health, and giving yourself the best chance at a long life. No viral moment should take that away.