Ah, the long run. The sacred weekend ritual of the distance runner. The indispensable cornerstone of any training cycle. The long run.
Long runs do so many amazing things for us. Why do we do it? What do we get out of it?
Well, in terms of the ol' "practice makes perfect" mentality, long runs seem to make perfect sense for someone training for a long race like a marathon or half marathon. If you want to get good at running a long way, you should practice running a long way.
But that's clearly not all there is to it. Nearly all of us run all or most of our long-run miles considerably slower than race pace. Marathoners don't even run their full race distance, mostly topping out at a couple of runs in the low twenties per training cycle. And what of 5K & 10Kers? If they're only racing 3 or 6 miles, why do runs in the 10+ range? When you dig a little deeper, suddenly "practice makes perfect" doesn't actually hold up all that well.
I dug into this a while back when I was helping to coach long distance high school runners as part of my first teaching job. It seemed to me that if we were going to ask kids racing 1-3 miles to run an easy 10K once a week (which, for most high school kids, is REALLY FAR!), I needed to be able to justify it to them.
So, miler or marathoner, what are the physical effects of running long that will help make you a stronger, faster runner? If it hadn't been for my inquisitive kiddos, I may never have learned that long runs give you...
Tougher bones. As strong and hard as bone tissue is, bones are still prone to injury from repeatedly absorbing force. Gradually increasing the amount of time you continuously ask them to do it stimulates your bones to produce more tissue and become denser. The denser your bones become, the more resistant they will be to injury.
Tougher muscle & connective tissue. Just as with bones, muscles, tendons, & ligaments are prone to injury from absorbing force and moving in extreme or unexpected ways (as with sprains and tears). Long periods of easy running stimulate all of these tissues to become denser and stronger, making them more resistant to injury.
A stronger heart. Just as with skeletal muscles, increased periods of aerobic exercise stimulate cardiac muscle to become denser and stronger as well. The stronger your heart, the higher your stroke volume (how much blood your heart is able to pump out to your body with each beat). This means that your heart has to do less work to get more oxygen to your muscles.
More red blood cells. Red blood cells carry oxygen. On long runs, muscle tissue needs a lot of oxygen for an extended period of time, which stimulates your body to produce more red blood cells. More red blood cells mean more fuel sent to your cells more quickly.
More capillaries around muscle fibers. Capillaries are the tiny blood vessels that transport blood to your muscle fibers. Running long stimulates more capillaries to grow around your muscle fibers, which means more oxygen (and hence more energy) more quickly.
Increased myoglobin concentrations. Once the capillaries get the oxygen to your muscle fibers, myoglobin is the substance that carries the oxygen to the cells. The more myoglobin in your muscles, the more quickly more oxygen can get to your cells.
More and larger mitochondria. Mitochondria are the parts of your cells that use oxygen to transform fat and carbs into energy. When you run long, you send your body the message that you need access to a LOT of energy, so your body creates more & larger mitochondria in your cells, which means your body can generate more energy more quickly.
Increased aerobic enzyme activity. Mitochondria contain enzymes that speed up energy production; going long increases the activity of these enzymes, helping your mitochondria to create energy more efficiently. (Also, all the business with the mitochondria & enzymes is what helps increase your lactate threshold.)
The physical effects above are likely to help out ANY runner, regardless of what distance they're training for. In addition to all that, there are some particular advantages for folks shooting for the longer stuff:
Fast twitch muscles acting like slow-twitch muscles. Slow-twitch muscles are the ones that help us out the most at long distances. When you continue running past the point where your slow-twitch muscles become fatigued, your body learns to recruit fast-twitch fibers and use them more like slow-twitch fibers to keep you going.
Increased glycogen storage. Glycogen is how your body stores carbs, which you go through a LOT of when you run long. Your body can only store a limited amount of glycogen (about twenty miles worth, more or less, for most people), but running to the point of near-depletion stimulates the muscles to store more glycogen in the future.
Increased reliance on fat for fuel. For all intents & purposes, your body has an unlimited amount of fat it can use for fuel. However, burning fat is a slow process, so when you’re active (ie, running), your body prefers to burn more glycogen. Running to the point that we deplete our glycogen stores helps train our bodies to rely more on fat for fuel than they really want to. The more your body burns fat, the longer your glycogen reserves will last.
Better form for longer. When your form is good, you're a more efficient runner. Most of us can keep up reasonably good form for a while, but the more exhausted you get, the harder it is. Going long gives you a chance to practice keeping up your form when you're really, really tired and helps to make good form more automatic.
The best part is that you get ALL these benefits running at an easy, relaxed pace. In fact, one of the biggest (and easiest to rectify) mistakes that distance runners make is running their long, easy runs too fast. While we should definitely do some race pace, tempo, & speed runs when training for something specific, those have a different purpose. In fact some of these changes (like teaching your body to burn more fat & spare glycogen) won't occur or won't occur as effectively if your heart rate is too high. (Running too hard too often also means your body will need more time to recovery and be ready to run again, so save those efforts for your hard days.) Love your long, slow runs, and they will love you back!
Next up -- the psychological & logistical benefits of long runs.