The one part of our bikes we probably neglect the most is our saddle. Most of us are meticulous (or should be) about cleaning and lubricating our chains and drive train; are nutty about checking and double-checking our tires for wear and cuts; and are passionate about clean, neat, and shock absorbing handlebar tape. While all these basic maintenance items are critical for both the good working order of your bike and for conserving your energy stores by limiting resistance due to friction, the saddle is one thing most of us never take into consideration. Who really pays attention to their saddle before the cover starts to peal away or until it is so warn that you can't remember if it was white or dirty brown to begin with?
If you consider how critical proper positioning is on your bike you should also consider how important a fresh saddle is. As a saddle ages there are a number of ways in which it fails to provide the support for which it was intended. The most visible wear on a saddle will reflect in the cover, but really it's what's underneath the cover that enables a saddle to do what it was designed to do: maintain and support your position. The decidedly modest foam padding under a saddle's cover provides only a few millimeters of cushioning, but even this minimal amount of padding breaks down over time. Furthermore, the more the cushioning a saddle has the faster it will break down. A change of even a millimeter in saddle height means you are moving lower and more forward on the bike. Add 4 millimeters by way of material breakdown and suddenly you're half of a centimeter lower and drastically further forward. This change in your position forces your body to adapt to a new and probably a very inefficient pose which will cause you to fatigue faster and work less efficiently.
It's not only the foam padding that breaks down. The plastic substrate under the foam will also fatigue and sink. This sinking where the greatest amount of pressure is applied becomes exponentially greater over time as the material becomes more and more pliable. Couple the break down of the foam with the sinking of the substrate and you could be riding 1, 1.5, or even 2 centimeters lower than optimal! And, as this break down occurs fairly gradually over a span of weeks, months, or years-depending on how often you ride-you may not even notice that you are riding considerably lower and further forward than you should be. In addition to causing fatigue and poor pedaling efficacy, a lower and more forward position caused by the degeneration of your saddle's integrity can lead to a number of physiological problems including knee pain, lower back pain, shoulder and neck pain, constricted blood flow, reduced oxygen intake, and improper breathing.
Research conducted by Cyfac in conjunction with the French Institute of Sport in Lyon, France has indicated that in general racing saddles should be replaced every 5,000 miles. Saddles which break down the quickest, e.g., the Fizik Arione, have a typical life span of around 3,000 miles. That may seem like a significant amount of mileage for many riders, but for others that may only be 3 months' worth of training. (Note that saddles will break down faster for heavier riders.) To make sure your saddle is in good working order periodically reconfirm your saddle height. Measure your saddle height from the center of your bottom bracket along the angle of your seat tube to ensure consistency. To safeguard against seat post slippage, which would falsely indicate that your saddle is breaking down, wrap a piece of tape around the seat post where the seat clamp stops.
Saddles are to our bodies what tires are to our bikes. The proper function and safety of our bikes depends on fresh, reliable, and structurally sound tires. The proper functioning of our bodies depends upon a supportive and properly positioned saddle. And just as our tires have limited life spans, so also do our saddles.