I've got a question for you: What do you see? Five pairs of shoes. Each a Nike. Each similar.

You've got a question for me: Why so many? Five pairs of shoes? Each a Nike? Each similar?

The first, on top of the shoe-star, silver & black with red, was my first pair of Nike's since kiddom. The Vomero 2 sold me on the company & this line the moment I put them on. Cushy & springy. Compared to the tanks I was retiring & the brand x mid-range shoes I was struggling in, this pair was a dream. I ran my first marathon in these: Lincoln, 2008. I proudly retired these to be my knocking around shoes near two years ago with 472 total running miles on them.

The second on top right, white & silver with lime green is the Nike Vomero 3. I ran my second marathon in these: Cowtown, 2009. I retired these with 451 running miles almost a year ago. Other than the colors, they are identical to the next pair.

The third, lower right, white & black with orange, are Nike Vomero 3s. I ran my third marathon in this pair just days after my 40th birthday: Cowtown, 2010. These are nearing retirement with 397 miles. They don't go any longer than six miles now lest I feel it in my hips & knees later.

The fourth, lower left, white & silver with blue, are Nike Vomero 4s. They are my current long run shoes. Going 12+ miles every Saturday while training for the 2011 Lincoln Marathon will elevate their mileage quickly. They have 157 miles after this morning's run.

The fifth, upper left, white with red & gray, are my newest pair, the Nike Vomero 5. I just got them this week through an amazing eBay deal. They've got the smell of new & zero running miles. I'll put about 30 miles on them with a long run of 12 before they serve to carry my 26.2 miles through Lincoln on race day, May 1st.

Why so many pairs? Experts say & my experience validates that the average shoe has a running life expectancy of around 400 miles. Give or take some miles given the shoe & the runner. As an example: take the second & third pair. Identical shoes other than the color. And. Other than mileage. Thats the key. With 250+ miles difference you could put one shoe from each pair on me while I was blind-folded & I could tell the difference. Just standing. On carpet. Not even walking or running. That noticeable.

Why is that? Simply put: the white, sometimes gray, squishy foam that makes up the midsole & majority of cushioning in running shoes is shot. That foam holds micro-bubbles of gas. The bubbles burst until the foam looses its spring. You loose energy return. You loose protection. You end up more tired or, worse, injured through the pounding running puts on a body.

You're thinking: Thanks for the pointers to track mileage & buy new shoes regularly, Aaron, but what's the point of this post?

Here it is: Well designed, properly chosen, thoroughly executed anything grows old & worn with time. Replacements. Upgrades. Progress. Change. These are healthy. These are part of life & growth.

And. As with my running shoes. Change can be safer & better for you than staying the same.