Workouts (according muscle fibers concept)

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In the previous article , we commented on the characteristics of muscle fibers according to the stimulus we give them.

Again with the collaboration of writers / coaches, Pete Magil and Tom Schwartz, we have been able to visualize more easily the creation of exercises according to the type of muscle fibers specific to each type of work


Understanding muscle fibers allows us to design workouts that target specific fiber types, train them at the correct intensity and for the proper duration, and ensure maximum adaptation. This example are from running sessions, but all of this knowledge can be applied on the others disciplines.

long runs

FIBER: Slow-Twitch, Intermediate

WORKOUT: The long run is the backbone of our endurance training. Run once or twice per week, its length varies depending upon the runner’s fitness, philosophy and race goals.

We should keep in mind that many desirable adaptations occur after the 90-minute mark. The pace is generally conversational, with an emphasis on quantity, not quality.

EFFECT: By running long, we provide the necessary stress to ensure maximum adaptation of our slow-twitch fibers. We weed out weak myofilaments, replacing them with stronger ones. And as fatigue sets in, we begin recruiting intermediate fibers, improving their endurance capacity and coordinating their use alongside the less force-generating slow-twitch fibers.

extensive intervals

FIBERS: Slow-Twitch, Intermediate

WORKOUT: These repetitions range from 2 to 5 minutes  and can be run on the track, road, or trail. The pace mimics race efforts from 3K to 15K. Recovery can equal the duration of the repetition during early sessions, then is shortened as we get more fit.

EFFECT: Strength is increased in both slow-twitch and intermediate fibers as weak myofilaments are replaced with stronger ones. Slow-twitch fibers are forced to work at top contraction speed. And since all our slow-twitch and intermediate fibers are recruited, we develop a more efficient working relationship between the two fiber types.

intensive intervals

FIBERS: Intermediate, Fast-Twitch

WORKOUT: These shorter repetitions last from 30 to 90 seconds and can be run on the track, grass, or trails. Pace is based upon race times at distances from 800m to 3K.

EFFECT: Both intermediate and fast-twitch fibers are strengthened. Our two fastest fibers learn to interact more efficiently by reducing activation of unnecessary fibers.

long hill repeats

FIBERS: Slow-Twitch, Intermediate workout: Lasting from 30 to 90 seconds, these repetitions are performed on a moderately steep hill. Four to 10 repetitions are sufficient, with at least 2 minutes recovery for shorter reps and up to 5 minutes for longer ones. Schwartz suggests that the pace should be equivalent to what we could run all-out for 3 minutes up the hill. Athletes should hypothetically be capable of running an additional one to two reps if the workout called for it.

EFFECT: Since it’s force — not speed — that builds strength, this workout is more effective than intervals on the track, trails, etc., at strengthening intermediate fibers. By keeping our effort at the correct level, we create maximum stress on our slow-twitch and intermediate fibers. Running too fast recruits the big boys — our fast-twitch fibers — to do the heavy lifting, which in turn leads to rapid fatigue, less work for the targeted fibers, and a longer recovery period before we can train hard again.

short hills repeats

FIBERS: Fast-Twitch workout: Short, steep uphill repetitions lasting less than 10 seconds. Our effort should reach 90-95 percent of maximum — not an all-out sprint, but close. Two to three minutes is a good recovery period.

EFFECT: This workout strengthens all our fiber types, but we use it to focus on fast-twitch, which requires a 90-95 percent effort to become activated. Because the range of motion required to sprint up a hill is greater than on the flat, we recruit a fuller complement of all fiber types. This is also one of the best workouts for reducing inhibition, as it curtails the activation of fibers that don’t contribute to our speed.

tempo run

FIBERS: Slow-Twitch, Intermediate

WORKOUT: Über coach Jack Daniels has described tempo as a “comfortably hard” effort — about 25 to 30 seconds slower than 5K race pace — for 20 minutes.

EFFECT: Slow-twitch fibers reach maximum recruitment and contraction speed at about 80 percent VO2 max — in other words, at tempo pace. This means that all slow-twitch fibers are strengthened. Intermediate fibers will also be recruited, helping our bodies establish recruitment patterns for the two fiber types at half marathon and marathon paces.


FIBERS: Slow-Twitch, Intermediate

WORKOUT: We begin the run at an easy effort, then drop our pace 10-15 seconds each mile until we can’t lower the pace again without achieving a race-type stress. Most runners top out at about 5K race pace.

EFFECT: As with tempo, progression runs achieve maximum activation of slow-twitch fibers. They incrementally recruit intermediate fibers, improving coordination between the fiber types. Some fast-twitch recruitment during the last miles might aid fiber conversion.

FIBERS: All Fibers

WORKOUT: Also called “form drills,” this workout involves variations of skipping, bounding, marching, springing, fast knee lifts, quick foot movement, and any number of activities meant to mimic, exaggerate, or strengthen our running motion. For best effect, 60m-80m strides are run between drills, and a short distance run is completed afterward.

EFFECT: Drills like skipping and butt kicks mimic the effects of dynamic stretching. Bounding and springing are more plyometric, affecting both recruitment patterns and strength. Marching and fast knees reduce inhibition. Alternating each drill with a stride helps to integrate the desired effect into our running mechanics. A short run of 5 to 7 miles after the drills further hardwires these neuromuscular gains into our stride.

Adding up the benefits

Training specific fiber types to achieve greater strength, recruitment coordination, and race-specific conversion leads to many running benefits, including:

  • Muscle fibers that can produce more force;
  • Muscle fibers that can fire at a faster rate;
  • Improved stride efficiency;
  • Improved energy efficiency;
  • Improved speed;
  • Improved endurance.But there’s more. By training our muscle fibers, we also trigger increases in VO2 max, muscle glycogen storage, mitochondrial density, and energy (ATP) production.

By building the trainings that way, you will gradually see how necessary a coach’s presence is. It is up to him, to understand all these concepts and know the best time to apply them in your training plan.