I remember my junior year of track we got a new coach, he was a great coach, super motivated and super passionate about seeing us succeed. He introduced us to weightlifting and began teaching us all these crazy moves that he said would make us stronger and better runners. I remember thinking 'I'm a runner... why the heck do I need to be strong? I just need to be fast and be able to run a long time without stopping."
That was my less educated, and not willing to learn anything new teenager self. It also required a lot more effort, left me sore and made practices longer because we had to do that stupid weightlifting and our normal running practice. Then I got to college and one of the first things the track coaches did was have us lift. My first 6am lifting session was horrible, they not only taught us much more challenging lifts than I learned in high school but I STILL did not understand the purpose of it. Not once did any coach I had actually explain to me why lifting was important for runners and how it would help make me a better runner.
A year or so after I quit running college track, I got into my first real Exercise Physiology classes, where I learned so much about the human body and how it responds to exercise. Finally things started clicking and looking back I was like hey, that's probably why I had to learn the clean and jerk in track practice, so I could explode out of the blocks. And that's why I had to do so many lunges, because it helps increase my muscle endurance, which will help me to run further. Now, I know a lot more than I did when I was in high school, but if I didn't study Exercise Physiology I probably still wouldn't know why weight lifting was so important for runners, or ANY endurance athlete, mountain bikers included (that means you, Mom and Dad).
Effects of Resistance Training:
Decreases body fat percentage and increases fat-free mass
May help increase the strength of tendons and ligaments and increase bone density
Increases the amount of energy stored in the muscle (ATP, creatine phosphate and glycogen)
Improves sprint speed, anaerobic (without oxygen) power, vertical jump and muscular strength
Enhances muscular strength, power and muscular endurance
Basically a whole lot of good stuff that enhances our fitness and therefor will help us be better runners and of course make us look better.
How resistance training helps runners:
Prevention of injuries: Especially overuse injuries that are so common with runners! Increasing the strength of connective tissue (tendons and ligaments) is so important for those of us who like to run lots of miles, every day!
Reduce muscle imbalances: Strength training helps balance your body. Just running everyday is a great cardiovascular workout, but it doesn't work your muscles equally. Your legs get a good workout, but they need to be STRONG and you need to make sure you're working all the muscles in the legs, glutes, hamstrings, quads and hip flexors! Just running will not strengthen all of these muscles.
Also it is important to work the postural muscles. Running with good posture is so important because it ensures that you are filling your lungs to capacity. Strictly endurance training (running especially) often completely ignores the upper body. In order to make sure we are standing up straight we NEED to strengthen the muscles of the back
Increased strength helps with hill climbing, or "the final push" in a race, when you increase speed in hopes to catch another runner or improve time.
Overall, running and endurance sports are great for our cardiovascular system but often times they lead us to be imbalanced which can cause injuries or leave us not as strong as we thought we were. Adding in strength training to your every day running plan can help reduce injuries, improve muscle balance and posture, increase strength and performance of ever day activities AND improve running performance.
Much of the information in this post was obtained from The Essentials of Strength Training and Conditioning from the National Strength and Conditioning Association, a book I never wanted to read again after passing my CSCS, but here I go again reading textbooks and research in my free time.