When riding a bike uphill or running you are working to overcome gravity. For the bike I’m sure that’s obvious. Riding up a hill means that gravity is trying to pull you back down. That’s what makes climbing on a bike so challenging. Running probably doesn’t seem as difficult because when running there is only a little bit of vertical movement occurring with each stride. While it’s not great it’s happening about 170 times per minute. That’s a lot of times. If the vertical displacement with each stride is only one inch (many age group runners bounce up and down much more than an inch with each step) that means you are lifting your body’s center of gravity 170 inches – 14 feet (425cm) – every minute. If running for an hour you’ve produced 283 yards (257m) of vertical displacement. That’s an 85-story skyscraper you’ve climbed. Huge!
Now imagine that you are riding your bike up a steep hill or running along a flat road as usual, only this time you’re wearing a backpack filled with 10 pounds (4.5kg) of rocks. It’s obviously far more difficult when wearing the backpack. But why is that? It’s because as the mass of an object (you, your equipment and the backpack with rocks) increases, the pull of gravity also increases. That’s why you have bathroom scales – to measure the pull of gravity on your body. We refer to that as your weight. So increases in weight result in your having to use more energy to lift it while riding uphill or running. Notice that there was no change in your power when you put on the weighted backpack; only a change in weight.
Now imagine the opposite. You’ve got a new bike that weighs 10 pounds less than your old clunker. It’s easier to ride up the hill, isn’t it? Or imagine that you’ve been losing excess body fat and your bathroom scales now say you are 10 pounds lighter. What will happen to your running? You’ll run faster at the same energy rate. Again, no change in power; only a change in weight.
Every extra pound (450g) added to your body and equipment “costs” you about one-and-a-half watts of power on a steep hill climb on your bike and about two seconds per mile when running. A few extra pounds one way or the other directly impacts how fast your race times are.
There’s no doubt that what your body and equipment combined weigh has a lot to do with how well you perform in triathlon. If we can reduce your weight without changing your power you will go faster. Or, conversely, if we can increase your muscular power with weight remaining the same you will also go faster. The best combination is to increase power and reduce weight. Much faster!
Here’s a simple guide for determining what your body weight means to performance. Divide your weight in pounds (kilograms) by your height in inches (centimeters). The typical, high-performance, male triathlete is in the range of 2.1 to 2.3 pounds per inch (0.38-0.41 kg/cm) with high-performance female triathletes generally being 1.9 to 2.1 pounds per inch (0.34-0.38 kg/cm). In road racing the best male climbers are typically 2.0 pounds per inch (0.36 kg/cm) or less. Top female climbers are under 1.8 (0.32 kg/cm). Of course, there are always exceptions such as Lance Armstrong who is about 2.1 pounds per inch (0.38 kg/cm). He overcomes his greater weight by having even greater power.
This doesn’t mean that you can’t excel if above these common ranges. It simply means that you must also have a higher-than-normal power output per pound (kilogram) to overcome the greater weight as Lance does.
Reducing your excess body weight and the weight of your bike and running shoes will potentially pay off with faster race times. But there’s risk associated with such weight reductions. If you lose muscle, especially the muscles that are used for swimming, biking or running, you are likely to be slower. Replacing heavy components on your bike with the lightest (and most expensive) equipment available raises the risk of that component failing during a race. For example, lightweight tires are one of the most effective weight reducing changes you can make since they lower rotating weight. The downside is that they are more likely to have a puncture. A super-lightweight saddle is more likely to break when you hit a pothole. Featherweight handlebars have been known to snap with a powerful rider is climbing out of the saddle. Running in racing flats may increase your risk of injury. Lowering your racing weight provides both reward and risk.
Of course, for riding a bike on a flat road or indoor trainer (regardless if the front wheel is raised or not) and for swimming, mass is not critical. The tug of gravity on your body and equipment is not as great. In fact, a big triathlete riding a bike on a flat course is generally faster than a small triathlete since being big usually means having more power. That’s why if your weight is above the pounds-per-inch ranges suggested above it’s best to select flat race courses when possible.