Speed or how fast you run is determined the both the length and number steps you take per unit of time. Research has shown that most elite distance runners have a stride rate (SR) of about 180 strides per minute (spm). Although it is not a magic number that applies to everyone, determining what your SR is, either at long-run training pace or at marathon race pace and finding that "optimal" rate can be beneficial in improving running economy and lessening potential for injury.
When your SR is slower than optimal it translates into spending longer time off the ground and in the air, and the longer you're airborne, the higher displacement of your body mass and the harder you hit the ground when your foot lands. Considering that most running injuries are a result of landing shock, its something worth looking into to see if you have room for improvement.
The 180spm is equal to 90-steps of one foot and equivalent to the 90 rpm cadence that serious bicyclists strive for. Although it can be tricky to find your "optimum" SR if it deviates from the average of 180, the first starting point in evaluating this is learning how to measure it. You can do this easily on any run by counting the number of foot-strikes for one leg over 1-minute and multiply that by 2. Do this at various times throughout one of your runs to get an idea of what your SR is.
Some treadmills have functions that monitor the number of steps you take for the duration of your run. My treadmill has this function and I use it to asses what my SR every time I run on it. Last week I did a 5-mile pace run on the treadmill, the first mile a gradual speed-up from 12:00 to 8:00 pace, then 8:00 for the next 4-miles. The resulting SR came out 179.4 and that's a pretty good place for me to be. I know from past experience that I am running most effectively with a feeling that it is controlled and comparatively easy (in terms of breathing), and feeling I can sustain it for far longer duration at an SR ranging between 178-180.
Of course, at other times when I run slower training or recovery run paces in the 9:00 to 10:30 pace range, the SR will be much lower, somewhere between 168-174. I have experimented at times trying to increase the turnover and maintain the slower speed, but it always seems like I have to shorten the length of each step so much that if feels awkward to sustain it for any length of time. I don't have a clear explanation for this phenom yet, and I am concluding at slower speeds it is just best to go with what feels "natural."
But if you are an Intermediate or a more experienced marathoner intending to run the marathon at your maximum aerobic capacity, or close to it, then assessing your SR and training to find and sustain that turnover rate may go a long way to helping you finish your race at target time.
For Novices that are not trying to run at maximal capacity, but simply finish a marathon, it may or may not be beneficial to strive for a 180 SR. You are likely running far-less than your maximal potential capacity, so in your case we just might want to try to "tune" into whatever SR seems to reduce impact shock and leads to a nicely, controlled breathing intensity that feels easy. But, the first step in trying to find whatever that SR sweet-zone is, starts with measuring it.
I will post more down the road on this subject giving some tips to help you find what your optimal SR might be if it differs from the 180 magic number, plus some routines or drills you can try to help you find it and train to run it consistently. Meanwhile, just start doing some counts on your runs and make a note of the pace you are running, as well as how it feels in terms of intensity, breathing and footfall dynamics.
Coach Frogger
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