Leg Muscle from Running


Jason, my question is about running. Let me start by saying that I have always had a problem with leg development.

I have squatted heavy, squatted light and my quads tone up nicely, but my hamstrings never develop (even though I have good glute development).

About 12 weeks ago I began a running program. I run with a high intensity for around 2-3 miles (at 6:30-7:00 pace) about 6 times a week. I charge the hills (to feel a burn) and I also try to do a day of explosive sprint work (the sprints I have been doing for about a year).

I was not expecting this because it goes against what i have been told about running, but my legs have increased in size dramatically. They look more dense, and for the first time i have some real hamstring development.

Overall I have put on 10 lbs in the 12 weeks. I am still lean so I know most of this has got to be leg muscle. A few friends of mine (a soccer player, a cross country runner, and a triathlete) have experienced the same. I have read a few running forums where there seems to be no shortage of the same experience.

However, I also read about people saying that they lose leg size. I guess my question is about the science behind this.

Does it come down to calories in-calories out? Can size be gained by any strenuous exercise (despite the load level) as long as the food is there?

Because here we can have two individuals with the same exercises but with different results. Is it muscle fiber composition? very confusing! Thanks for taking the question.

Answered by:
Jason Spencer, CSCS

Jason Spencer Online Personal Training

The fact that you have been able to build muscle from your running most likely comes from your sprinting and hill running activities.

These activities incorporate much more of a strength requirement from your muscles, which turns the running into an anaerobic type of activity. The stress on your leg muscles caused by the hill resistance and power activity of sprinting has stimulated muscle growth, which makes sense...

Especially since you mentioned your hamstrings in particular... Running inclines such as hills engages your hamstrings more due to the increased need to keep your hips extended and hold your posture as upright as possible.

No muscle size cannot be gained by just any strenuous activity. It must be of the intensity necessary to stimulate growth, which is heavy and challenging resistances like what the hills gave you...

For another person to run as actively as you do or even just run less intensely but consistently and lose muscle, this most certainly comes from lack of caloric energy as you mentioned. They are burning more than they are putting back into their body...

Lastly, muscle fiber composition is the end result of either situation. In your case you have been able to build more bulkier fast twitch muscles fibers through your hill and sprint training, which produce the power and strength you need to do so...

In the case of the person who is losing muscle, they are training there body to use its slower twitch fibers that are more conducive to endurance and are less bulky and powerful.

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