How do legs change in response to running?

Question

Background Information:

I recently began a running/walking regime that lasts for 30 minutes. I think I run about half the journey and walk the other half of the journey. There are 2 very steep hills, and numerous medium hills on the journey. I tend to walk up the 2 very steep hills.

Question:

On my walk I noticed that some other people walking had very large/bulky (although doesn't look fat) looking legs. My observations of endurance athletes are that they have quite lean legs. I am weather my regime will turn my legs bulky, or if they will remain lean looking. (I would prefer if they don't become bulky, how can I prevent this?)

Answer 1

I run. Half marathons, 5ks 10k, and trail runs. building legs muscles are a lot like building other muscles. You can develop slow twitch and fast twitch muscle fibers. For running you are going to need both. The short answer is your legs muscles are going to take on your own unique genetic shape. Simple answer, keep up the endurance and run on flat surfaces if you want lean looking legs. Hills are going to make your muscles bulk up because it requires more strength. Eat light and lean and remember to train in your lactate zone so yo burn fat to keep trim. Most important have fun and allow your legs to be.

Answer 2

In general, runners tend to have more slender, leaner looking legs than other athletes. This is because low weight, high repetition exercising such as distance running (pretty much anything other than sprints, so anything above 400 meters, really) does not really lend itself to building bulky muscle, and is in fact counterproductive because of the extra weight. It's the wrong kind of stress in the muscle to produce bulk.

I would venture a guess that a lot of the "bulky" runners you see are doing weight training and simply running/walking for fitness, or they are multisport athletes such as triathletes or duathletes. This segment will have bulkier legs because of the bicycling that they are doing, which will cause greater hypertrophy in the calves and upper legs.