Some days you just want to run easy, while other days it may seem impossible to hold yourself back. Slower and faster running both have their places in every runner’s training arsenal, and knowing how and why to implement each type is essential to your success.
At the physiological level, our muscle fibers play an essential role in our ability to sprint and also run long and easy. Developing both types of skills is beneficial, whether you’re training to run a fast mile or an ultramarathon. Different types of workouts can be used to target each group of muscle fibers.
SLOW- VS. FAST-TWITCH MUSCLE FIBERS
We are all born with slow- and fast-twitch muscle fibers. On average, we start with about 50% of each, but we can improve their function and efficiency with training. Here are the types:
- Type I: The slow-twitch fibers. They are primarily responsible for longer, sustained efforts of endurance-based training. They fire less forcefully than fast-twitch fibers but also require less energy.
- Type IIx: These are the super fast-twitch fibers responsible for explosive movements like sprinting. They can only be used for short periods of time as they are larger and less efficient.
- Type IIa: These are considered intermediate-fast twitch fibers. They are a blend of slow- and fast-twitch and have greater aerobic capability than Type IIx but also fire more forcefully than Type I.
Although the composition of muscle fibers that you’re born with plays an important role in your development as a runner, they’re responsible for less than half of your performance! Your long-term training affects how you refine and improve the fibers you start with, along with other nonphysiological factors like mental tenacity.
SLOW OR FAST? IT’S ALL IMPORTANT!
No matter what you’re training for, it’s most effective to include workouts that target each kind of muscle fiber. Incorporating speed sessions into your endurance training allows you to increase neuromuscular coordination, making you more fluid and efficient at any pace. Speed work specifically targets your fast-twitch fibers, so your stride becomes more explosive with less effort.
These workouts target specific types of fibers:
- Long runs: Slow twitch
- Tempo runs: Both slow and intermediate
- Short repeats: Both intermediate and fast twitch
- Strides and hill sprints: Fast twitch
As a general rule, it’s ideal to run about 75–80% of your mileage at an easier effort and 20–25% of your time on faster sessions. This will vary to some degree depending on your training age, what you’re training for, as well as what phase of training you’re in.
What you don’t want to do is spend all your time training in the gray zone, somewhere in between fast and slow, which isn’t hard enough to stimulate improvement but not easy enough to allow for recovery. You have undoubtedly heard it before, but keep your hard days hard and your easy days easy!
THE BEST OF BOTH WORLDS
Both easy days and speed sessions are critical to your running success. When scheduling challenging runs, don’t try to cram in too much — and definitely allow for recovery time in between. Hard workouts should always be sandwiched on either end of an easier effort — and some workouts may require several recovery days.
Easy running can be done by feel, tracking heart rate or monitoring pace. If you’re watching your pace, know that weather conditions and fatigue (among other factors) can significantly impact how easy a run really feels. Without these recovery runs, your body won’t have time to process harder workouts, and you won’t gain as much from them.
Some types of speed work can be done on your easier days, including strides and hill sprints. Because these are short efforts that don’t generate a great deal of fatigue, they can be done more frequently than longer track sessions and tempo runs.
If you’re new to speed work or are recovering from an injury, strides and fartleks are an excellent way to ease back into faster running.
While it’s fun to get out there and push yourself, make sure you strike a balance with slower, easier miles. You’ll get the most out of your running when you strategically incorporate a variety of workouts into your training plan.