The short answer to the question, "Does sprinting make your legs bigger?" is, "Probably, yes." However, the more accurate answer is, "It depends." While sprinting tends to favor muscular development in the legs, whether this translates into bigger legs depends on additional factors, such as genetics and starting body composition.
The SAID Principle
SAID stands for "specific adaptation to imposed demand." The SAID Principle is based on the observation that the body changes in ways that are very specific to the type of training being done. For sprinters, this often means bigger legs. When you look at a picture of an elite sprinter, you get the best example of how sprinting affects the physique. She has exceptionally muscular legs that most would consider to be big. While women with muscular legs may have a natural talent for sprinting, sprint training clearly develops the body in a way that favors better performance.
An article published in 2001 in the journal "Sports Medicine" describes the changes in leg muscles in response to sprint training. These changes include chemical changes, performance adaptations and structural changes. A primary structural change is "increased muscle cross-sectional area." That means that sprinting makes the leg muscles bigger. This sounds good if you're starting out with legs that you think are too skinny and could use a little muscle enhancement. If you already have big, muscular legs, sprint training will likely give you bigger and more muscular legs.
High-intensity interval training, such as sprinting, is recognized as being more effective than traditional aerobic exercise for fat loss. This was highlighted in a study published in 2008 in the "International Journal of Obesity." Women who participated in high-intensity intermittent exercises lost more body fat, including subcutaneous leg fat, than women who performed steady-state aerobic exercise. This is good news if you have large legs due to fat. The combined effect of muscle growth and fat loss from sprint training could actually net you thinner legs.
The combined effects of fat loss and muscle development will improve the tone and definition of the legs of a sprinter. Whatever your starting body composition, Sprint training will probably help you to firm up your legs. It is a great choice if you want to enhance your curves and reduce your jiggle.
Ron Rogers, a Washington chiropractor, has worked with local and national regulatory bodies in his profession and has provided consultation to the national chiropractic licensing board. He is recognized by the National Strength and Conditioning Association as a certified strength and conditioning specialist. Rogers' works have been published in several peer-reviewed professional journals, covering topics ranging from musculoskeletal diagnosis to research-based rehabilitation strategies.