Runners come in all different shapes and sizes and their muscle fiber does too. On average, humans have roughly 50 percent endurance muscle fibers and 50 percent explosive muscle fibers. The actual distribution varies significantly within each individual. Some may have a 60/40 endurance to explosive muscle fiber ratio, while others may have a 40/60. This distribution can make a significant difference in the performance of each runner, predisposing one runner for speed and another runner for endurance. The distribution can make an even bigger difference for outliers with an 80/20 ratio.
For a simple example, a runner may find that she loses to a competitor every time in a 10k, but then she effortlessly defeats the same competitor every time in a 5k. As the difference in distances increases, the results become even more pronounced.
Determining the disposition of a runner shouldn’t be too hard, and the gained knowledge can have a tremendous impact on training when leveraged properly.
Some of the key areas where differences occur include the utilization of aerobic and anaerobic metabolisms, the distribution and use of muscle fibers, and the strength of the fuel systems. The way an endurance-type and a speed-type of similar skill levels utilize their bodies can vary greatly. Try a few different routines on your treadmill to determine which type you are.
The endurance-type often has more strength in the middle portion of a race and has lots of staying power. Oftentimes—but not always—they are drawn to longer distance events, like marathons, because they are naturally better at them.
Long, slow distance runs are home for the endurance-type. They run longer at a good pace and may even have some aerobic energy left towards the end of a run. Oftentimes, this type of runner will have developed a superior aerobic metabolism. This means they will be able to keep a steady pace for longer without building up lactic acid. They may be interested in developing their anaerobic metabolism with strength exercises.
Tempo runs with a 15K–half-marathon pace are ideal and will feel very comfortable.
The speed-type will usually excel on a final sprint and will be more comfortable switching gears throughout a race. Again, oftentimes—but not always—they are drawn to shorter, speed events.
In many cases, this type will also develop a stronger anaerobic metabolism. This will provide them power and speed, but at the sacrifice of distance. They can develop this system to build their strength or they could do lactic threshold trainings to build their aerobic system.
In a long race, they may benefit greatly from varying the pace or even taking quick breaks.
What Does This Mean For You?
As you’re looking to go further with your running, what is your goal? Are you aiming for speed or are you more comfortable increasing your distance? By paying attention to this natural comfort zone, you can train to excel at something you’re biologically programmed to do. Or, you can focus on training where you struggle a bit more to make yourself a more well-rounded runner.