To successfully complete a marathon, we need to sustain ourselves over a long period of time (measured in hours) and distance (26.2 miles)—and doing this requires that our bodies have adequate energy sources of glycogen, fat and muscle.
The primary, and most efficient, energy source in our bodies is glycogen, produced by carbohydrates in our diet and stored in our muscles and in our liver. The second most efficient energy source in our bodies is fat, another essential component of a well-balanced diet.
We have enough fat stored in our bodies (even those skinny elite marathon runners) to run hundreds of miles—honestly, “fat” is not a problem.
But we only have enough glycogen stored in our bodies to last 20-22 miles. Once we have depleted our bodies of glycogen, our performance suffers. ‘Racing’ or running fast (a relative term) uses glycogen in short order to fuel our muscles. This is our ‘flight or fight’ syndrome where we use our most efficient energy source quickly. Once depleted of glycogen, we suffer muscle fatigue, soreness and cramping-- commonly referred to as ‘hitting the wall’ in a marathon, and can also occur if we run too fast in our training runs.
We don’t always have to suffer glycogen depletion and we won’t always ‘hit the wall.’ By learning how to consume more fat and less glycogen, we can stave off glycogen depletion. We learn this during properly executed long runs.
Instead of running too hard (i.e., ‘fast’) during our long runs, we should be Running on LSD℠. This LSD is not a hallucinogenic (even on those 20 mile runs when our minds wander), nor is it Lake Shore Drive along Chicago’s beautiful lakefront path. Running on LSD℠ means running Long, Slow Distance (“LSD”) runs. LSD’s are also referred to as ‘fat burning runs’—when we burn fat and glycogen simultaneously, with a higher proportion of fat to glycogen, rather than primarily glycogen. This helps build our endurance levels in training and allows our bodies to replace glycogen stores quicker between hard workouts.
While many of us often want to run faster, long runs are not the workouts to run hard and fast each week. Our body uses glycogen, then fat, then muscle (protein) when participating in endurance events. When we run our long runs too hard (i.e., too fast), our bodies use our glycogen stores in a higher ratio, resulting in earlier muscle fatigue. Recovery is also affected since it takes time to replenish our glycogen stores after a hard workout. A slower pace allows our bodies to burn a lesser proportion of glycogen and a higher proportion of fat with quicker recovery after the workout.
A marathon requires endurance more than speed, regardless of our finishing time or goals. In training, endurance is built first, speed comes later.
Endurance is developed over time--by gradually increasing the length of time we’re on our feet, and by learning how to burn fuel most efficiently throughout the many weeks of marathon training. Long runs (LSD's) serve both purposes - building endurance and teaching our bodies how to burn fuel efficiently.
The correct pace of these long slow distance runs is approximately 70% of our 5K racing pace. For those training for a first marathon or unsure of current ‘marathon pace’, a good measuring stick is the conversation test. While running your long runs, you should be able to talk in complete sentences without gasping for breath while running. If you are unable to maintain a conversation with your running partner (or with yourself), you are running the long run too fast. Slow down - your body will thank you.
Yes, it seems counterintuitive to run slower in order to run a faster marathon, but that's how the science works. By running slower on training runs, our endurance and our fitness improve. Our recovery between long runs is shorter, meaning we are able to run more miles later in the training season. As fitness improves, we will run faster and longer.
If you know your marathon pace based upon previous experience, your estimated LSD pace should be 1 - 2 minutes slower per mile than marathon pace. If you do not know your marathon pace, monitor your run by the talk test. You will have a better performance on marathon day.
“Good form will carry you through”®