Will Running Make My Legs Bigger

As a runner myself, I’ve often been asked whether running will make your legs bigger. It’s a common concern, especially for those who are worried about adding bulk to their lower body. In this article, I’ll delve into this topic and provide you with some insights based on my experience and research.

Understanding Muscle Growth

Before we can answer the question, it’s important to understand how muscles grow. When you engage in strength training exercises, like weightlifting, you create tiny micro-tears in your muscle fibers. The body then repairs these tears by building new muscle tissue, resulting in muscle growth and increased size.

Running, on the other hand, is primarily a cardiovascular exercise that focuses on endurance and aerobic fitness. It doesn’t involve the same level of resistance as weightlifting, which means it’s less likely to cause significant muscle growth in the legs.

The Role of Genetics

Another factor to consider is genetics. Some individuals naturally have a predisposition for developing more muscle mass, while others may struggle to do so. This genetic variation plays a significant role in how our bodies respond to exercise, including running.

If you have a genetic tendency to develop larger leg muscles, then running may contribute to some muscle growth. However, for most people, the increase in leg size due to running will be minimal compared to dedicated strength training exercises.

Types of Running

It’s also important to differentiate between different types of running. Long-distance running, such as marathon training, primarily focuses on cardiovascular endurance and fat burning. This type of running is less likely to result in substantial muscle growth.

In contrast, sprinting and interval training involve short bursts of high-intensity running, which can stimulate muscle growth to a greater extent. These exercises engage fast-twitch muscle fibers, which have a higher potential for growth. However, even in these cases, the increase in leg size may not be significant unless combined with strength training exercises.

Balancing Cardio and Strength Training

If your goal is to increase leg size, it’s essential to strike a balance between cardio exercise like running and strength training exercises that target the leg muscles. Incorporating exercises such as squats, lunges, and calf raises into your routine can help stimulate muscle growth in the legs.

Remember, though, that muscle growth takes time and consistency. It’s unlikely that running alone will cause your legs to bulk up significantly. Instead, aim for a well-rounded fitness routine that includes both running and strength training to achieve the desired results.


In conclusion, running is an excellent cardiovascular exercise that can improve endurance, burn calories, and promote overall health and fitness. While it may contribute to some muscle growth in the legs, the increase in size is usually minimal unless paired with dedicated strength training exercises.

Ultimately, whether running makes your legs bigger depends on various factors, including genetics, the type of running you do, and your overall fitness routine. If you’re concerned about leg size, it’s best to consult with a fitness professional who can provide personalized guidance based on your specific goals and body type.