Will long-distance running slim the legs or build muscle?

Generally speaking, long-distance running helps slim the legs without building muscle mass. The detailed explanation is as follows:

Long-distance running is an aerobic exercise that promotes fat burning and metabolism. During prolonged aerobic activity, the body primarily draws energy from fat stores. With consistent long-term running, overall body fat—including fat in the legs—can gradually decrease, resulting in leaner, more toned leg contours. Additionally, long-distance running is a low-resistance, endurance-based form of exercise. Compared to high-intensity, low-repetition exercises such as weight training, running provides less stimulus for muscle growth. This is because sustained aerobic activity and low-resistance joint movements (such as those involving the hip and knee) primarily develop muscular endurance rather than muscle hypertrophy. Therefore, long-distance running typically slims the legs without causing significant muscle gain.

It should be noted that running is not the only factor affecting leg shape; other forms of exercise and diet also play important roles. For those aiming to slim their legs, it is advisable to control dietary intake and develop a comprehensive exercise plan.