Stride Rate and Ground Impact    By Rick Niles - Level 2 Triathlon coach
 
It may seem as if taking fewer steps to get anywhere might be easier, but this does not seem to be the case with running. A few more steps could lighten your load. Shorter strides reduce ground impact. Until now, that degree of reduction has been a bit vague. Research from Medicine and Science in Sports and Exercise has given us some specifics. It¹s more than you would think, and if you aren¹t a short stride believer, read on. There are some interesting things which relate to both your running economy, and injury prevention.
Energy absorption from the landing has to (or should) come from the knee, the hip, and the ankle. As you go faster, the impact rises. Running downhill increases landing stress, and so a greater contraction from the muscles crossing the above joints. It¹s long been supposed that an increased stride length also increases these stresses, and that is what this study is all about. If the lower body can¹t handle these stresses, then the back also gets involved. You don¹t want that.
One thing that makes this study particularly worthwhile, is that the subjects ran a 7 minute per mile pace. That is something that most of us can relate to much better than a bunch of thoroughbreds running under a 5 minute pace. Even if you run a 9 minute pace, a study dealing with 7 minute milers has much more relevance for you.
Everyone has a preferred stride length. In my experience, this is not necessarily the best one. It¹s just something learned along the way. Just one more thing that gets corrupted when we reach our teen years. Most small children will run with short strides, their feet landing underneath them. As teenagers, we somehow come up with the notion, that if we want to run faster, just reach out and grab more real estate. High school runners are notorious over striders. In any event, this carries into adulthood whether or not you were on the track team. Nearly everyone I¹ve coached starts out with some degree of overstride. It¹s almost universal.
So the study we are looking at, had the runners with their preferred stride length, 10% greater, 20% greater, 10% less and 20% less.
The single most important finding was that the overall impact of a -20% stride length was half that of a +20% and about 60% of the preferred stride.
That is a lot, folks. More than I ever thought. That means it takes 40% less energy to land from a short stride than your preferred stride. Most running fatigue is a result of the landing, and this is even more so in a triathlon. The quads, which are the largest impact absorbers, are already fatigued from the bike.
The forces at the knee represented most of the 60% above. Knee flexion also becomes greater as you increase stride length, which means that works it harder for longer. With a shorter stride, you nearly eliminate forces at the hip. This will make a difference in the stress on your back, in addition to your overall running economy. The
ankle forces are reduced the least at about 25% less than your preferred stride. It is during the support phase of running, when your ankle is flexed, when the greatest stress is placed on the achilles.
Because you land harder with a longer stride, it means that you have to go higher. So your push offs, rather than propelling forward, have to be pushing you up. So all your energy is spent going up and landing. Sort of like running in place.
It is well documented that running speed also increases impacts. It can be close to 20% increase for each minute per mile. Fortunately, you don¹t improve from an 8 minute mile to a 6 minute mile sustained pace overnight, so you gradually build up your landing strength as you improve.
What to Do:
So how can you tell where you are, without going out and measuring your stride length? The easiest way is to count strides by right feet. At anything faster than a 7 minute per mile pace you should be at 90-95 right foot strikes per minute. A good example of stride shortening comes from one of my recent camps. I had a guy
running a 6:40 pace at 72 strides per minute, which is actually 144 when you count both feet. (It¹s easier to count one side) The stride distance is 5.5 feet. After looking at the videotape, we worked on some techniques on shortening his stride. He then went out and ran the same pace at 95 strides (or 190). That brought his stride
distance down to 4.2 feet which is a 23% reduction. His response is that his new technique feels much easier, which indicates less force and less muscle involvement. If you run in that range and you are at 95 stride per minute, you most likely won¹t benefit from any stride shortening. All good things have limits.
At a 7:30 pace, your rate can slow to the high 80s, low 90s range. At an 8 minute pace and slower, an optimal stride rate would be in the mid 80s. If you are in those ranges then you are already there. If not, you could benefit from an increase in stride rate.
Form:
You want your foot to be landing underneath, not out in front. You can have a moderate heel landing, but it should be almost a mid-foot touch down. Landing on the ball of your foot is also fine. You¹ll need to experiment.
You want to run nearly upright with your hips drawn forward. Runs with short repeats of faster running get the motor patterns working for a shorter stride. You can do short, 20 or 30 second pickups during course of an easy run. On the track, 200 meter repeats, with a 200 jog work well. When you count strides, make sure count zero when the time starts. You don¹t want to have 1 stride when you are at zero time. Just count every time your right foot touches down.
When you start to feel comfortable with a shorter stride, try it on some downhill segments of a minute or less. Try to run the same stride as you do on a flat. If you can learn to land over your foot while going downhill, you¹ve got it.
Any change in running form will recruit new muscles. They may not be as strong as the ones you¹ve used in another form. Give the new ones time to gain strength. Pay close attention to the hamstrings. Because they too, will take less stress, another benefit is that your shoes will last longer.

About the Author
Rick Niles has been competing in triathlons for 18 years and have been coaching full time for 10 years.
He has a masters in exercise physiology, and has been on the USAT national coaching committee since it's inception 3 years ago. This Committee's function is to set the coaching certification program for USAT, and to assist in certification clinics for level 1 and level 2 coaches. As the program has been growing, all committee members will be the first group of level 3 coaches.
Rick has a book out called, "Time Saving Training for Multisport Athletes" (Human Kinetics 1997) as well as many other coaching tools including : coaching software, Performance Progress Plus, and a monthly newsletter, The Performance Newsletter. I'm currently working on a coaching video, which will be available this summer.
Check out his website at www.ranfit.com