When you start running after not being active you will definitely develop muscles in your legs. They’re going to probably get a bit larger through the initial — stepping into running — phase.
Additionally, if you concentrate on running with a fore-foot or mid-foot strike you will be putting more stress in your calves (than middle school heel striking) and certainly will cause these to harden.
The key muscles you will notice growing will be the quadriceps, hamstrings, calves (especially because of the strikes i have mentioned), and glutes.
Your upper legs and glutes can get larger, also, if you focus on speed and hills.
You’ll basically be engaging your fast twitch muscle fibers a tad bit more in the beginning. After the initial phase you will probably have lost some weight, but even although you have not, muscle and neurological system have adapted into the weight and motions you have practiced.
Your fast twitch muscles will not develop from running, however your slow twitch groups of muscles will continue to develop. At that point your legs will likely not grow larger from running anymore and you will instead start working on the muscular endurance…
I say start here — but really, you have been working on muscular endurance the whole time.
Muscle will continue to harden and develop, but you probably won’t experience hypertrophy from running unless you are doing weighted runs, sprints, or hill workout routines (or all of the above).
Even then you’ll have diminishing returns in terms of building pure strength. Olympic middle to long distance runners generally have next to no one fat and incredibly visible, not huge muscles:
This really is Galen Rupp, 2012 Olympic silver medalist when you look at the 10k. Notice how developed his hamstrings and quads are, but he still remarkably skinny looking.
This is Actually The US Mens 4×100 Sprint Relay Team:
These guys are much more muscular, but the majority of this is not from running, it’s for running. They are doing plenty of weight training exercise and explosive lifting to develop their fast twitch muscles in order to explode and keep their legs pumping past what their body weight would normally let them train.
They still train for sprinting, of course, and their muscles are made up for this, but most of the muscle they have is from cross training. From the other far end for the spectrum, listed here is Ryan Hall, US Marathoner:
There clearly was muscle there, but much less type II fast twitch muscle fiber. Don’t get me wrong, he could be incredibly fast, averaging faster than 4:45 mile inside the marathon ( I can’t even do that in a single mile), but his build is set up for endurance and there’s very little waste weight or energy expenditure there.
Running will mostly build up your cardio vascular system, inform your joints to carry on to develop lubrication and maintain your bone relative density up. It does build muscle tissue initially, but isn’t a sensible way to do so if you wish to get larger.