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Which do runners lose first, speed or endurance?
Technically, speed goes first, but the outcome for distance runners is a loss of endurance.
First off, before I explain more, don’t get mad. Every time I address age-related performance decline in running, some readers get upset. Age is just a number, they write. Fifty is the new forty. Yadda yadda yadda. I agree with all that. But I also believe that the more we explore the issues facing aging runners, the better equipped we are to meet them head on with smart, effective training.
I’m an aging runner myself. And, like everyone else, my age 55–59 record (15:42) is slower than my age 45–49 record (14:34)—over a minute slower. I don’t know about you, but I want to know why I’m slowing down so that I can put on the brakes of that process. Which brings us back to the question: speed or endurance?
Let’s start by looking at American records for speed and endurance in three different age groups. That’ll give us an idea of who gets hit hardest by the aging slowdown. The following table shows age group records, then lists the percentage of slowdown for athletes in the older age groups (versus the age 39-and-under record):
It appears that sprinters slow down more than distance runners by mid-40s. Then the pendulum swings in the opposite direction post-40s. So common sense dictates that speed goes first, but endurance goes worse. As is often the case, common sense doesn’t tell the whole story.
First, let’s look at speed. As early as our mid-20s, we start to lose fast-twitch and intermediate fast-twitch (speed) muscle fibers at a rate that can reach 1% per year, a process called sarcopenia. On the other hand, our slow-twitch (endurance) muscle fibers are resistant to age-related atrophy. So right off the bat, we get slower because we lose the muscle fibers responsible for running fast.
Our nervous system control of the remaining muscle fibers also starts to break down. Individual nerves control between a very few (e.g., 10) and a very many (e.g., 2000) muscle fibers. As we lose muscle, nerve-muscle fiber groups (know as “motor units”) reorganize, become less efficient, and produce less force. Since speed requires lots of force, we get slower.
Next, let’s look at endurance. A 2014 study in Sports Health estimated a loss in endurance capacity of 10% per decade. This is based on measurements of VO2max, which is the amount of oxygen your body uses each minute to create aerobic energy. A 2013 study in Molecular and Cellular Biology puts the blame for this decline on age-related loss of mitochondria (microscopic, aerobic-energy producing power plants inside your muscle fibers). But the study also points out that loss of mitochondria is directly correlated with (drum roll please) sarcopenia.
Makes sense. When we lose muscle fibers, we lose the mitochondria within them. And here’s the important part for distance runners: While we use mostly slow-twitch fibers for distance and tempo runs (our favorites), we use almost all our faster fibers in races like the 5K—so loss of “speed” fibers also affects both the force we generate for our stride during races and the aerobic energy we can produce to fuel that stride. With a shorter stride and less energy, we run slower.
Now for the good news: Smart, well-rounded training that targets faster fibers can prevent, delay, and even reverse the decline in both speed and endurance. That’s because training faster fibers slows the rate of muscle fiber loss and preserves force production, nervous system function, and aerobic energy production at faster paces.
Including these five types of training is a good start:
- Resistance training: Focus on lower-body exercises (e.g., squats and step-ups) and use enough resistance to limit each set to 5-10 reps.
- Hill repeats/hill sprints: Running up a hill fast engages all your muscle fibers.
- VO2max repetitions: Reps at 3K to 5K pace stimulate mitochondrial gains in faster muscle fibers.
- Form drills: Drills improve nervous system control of muscles and strengthen muscles through their full range of motion, improving dynamic flexibility.
- Diet: Keep your protein intake high to improve tissue repair post-workout.
For distance runners, it’s not important whether speed or endurance goes first. It’s important that they’re flip sides of the same coin. Where one goes, the other follows.