We hear talk about “lengthening” muscles, But you really just...
Fred Duncan@Fred__Duncan
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Dec 10, 2025
~1 min read
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We hear talk about “lengthening” muscles, But you really just change what happens inside it.
Every muscle is made up of fascicles…bundles of fibers lined with contractile units called sarcomeres.
When you train at high velocity or under eccentric load, the muscle adapts by
Every muscle is made up of fascicles…bundles of fibers lined with contractile units called sarcomeres.
When you train at high velocity or under eccentric load, the muscle adapts by
1:31
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adding sarcomeres in series, the fascicle gets longer.
Longer fascicles mean a faster contraction speed and a wider range to produce force.
That’s why elite sprinters consistently show longer hamstring fascicles than comparators.
It’s not just genetics, it’s years of
Longer fascicles mean a faster contraction speed and a wider range to produce force.
That’s why elite sprinters consistently show longer hamstring fascicles than comparators.
It’s not just genetics, it’s years of
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exposure to sprinting and high speed eccentrics.
Sprinting is the best stimulus.
High-speed and traditional eccentrics help support it.
Heavy lifting builds the base.
Put them together and you get muscles that are strong, fast, and resilient.
That’s exactly what I built
Sprinting is the best stimulus.
High-speed and traditional eccentrics help support it.
Heavy lifting builds the base.
Put them together and you get muscles that are strong, fast, and resilient.
That’s exactly what I built
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the Project Speed Bundle for, to show you how all these pieces connect. In it I discuss isometrics, eccentrics, plyometrics, and how to develop explosive athletes.
• The Art & Science of Sport Preparation - 10 week program, 50 pages.
• Speed Kills for mechanics, sprint
• The Art & Science of Sport Preparation - 10 week program, 50 pages.
• Speed Kills for mechanics, sprint
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