Ever notice top-heavy "muscle dudes" at the gym? Lots of upper-body muscle and little scrawny chicken legs? Beach muscles (the pecs, biceps, and that six-pack) often get all the attention in a workout. That's all and fine, but doesn't do a runner much good. Actually it doesn't do the average person much good either.
Focusing so much on the "mirror muscles" (you know, the ones you see when you're posing in front of the bathroom mirror in your fruit-of-the-looms) 0ften creates muscle imbalance. This can spell I-N-J-U-R-Y. Ever see big muscle dudes that are hunched forward and have hardly any shoulders? That's because so much focus has been given to the pecs and very little attention has been paid to the trapezius, rhomboid, and lat muscles of the back as well as the shoulder muscles (the deltoids).
Muscle dudes aren't the only ones guilty of muscle imbalance. Runners will often hit the leg extension machine to pump-up those quads and will completely skip working out the hamstrings. Actually more time should be spent on hamstring exercises than quads. Some experts say three times as much. (Note: the leg extension machine is very bad on your knees. Lunges are a much better quad exercise.)
My best advice to help prevent this imbalance and at the same time strengthen your body for running is to take a little time while posing in that mirror to check out your backside. Yes, I said it. Take a look at that toosh...and your back...and hamstrings...and calves. Everyone, (especially runners) need to focus more on the muscles of their posterior chain which includes the erector spinae muscles, glutes, hamstrings, and calf muscles. One of the best ways to prevent injury, improve your posture, and increase your capacity to have more power is to focus a large portion of your workouts on the posterior chain. Check out the clips below from Kinetic Health Online and Expert Village for some great posterior chain exercises.