Fast Twitch Muscle Fibers: Angus Ross on Training Them

Based on Episode 36 of the Just Fly Performance Podcast, a conversation between host Joel Smith and sport scientist Dr. Angus Ross.

If you want to change your fast twitch muscle fibers, Angus Ross argues you are looking at the wrong end of most training programs. A physiologist and strength expert with High Performance Sport New Zealand, Ross has spent two decades studying one uncomfortable fact: ordinary heavy lifting tends to make muscle more fatigue-resistant and a little slower, not faster. The one modality he has found that pushes fiber composition the other way, toward bigger and faster fibers, is heavy eccentric training. In this episode he explains what that does to muscle, how to program it without blowing up an athlete, and where the whole strength project stops paying off.

Key Takeaways

• Eccentric training is the rare modality that shifts fiber type toward fast twitch. Ross says it can raise fast-twitch cross-sectional area and fiber type at the same time, which traditional lifting does not.
• Heavy concentric strength work can make muscle slower. The usual adaptation is a drift away from the fastest myosin toward more fatigue-resistant fibers.
• Eccentrics need a plan, not a trial. Program them in the preparatory period, expect a temporary performance dip, then taper and let the adaptation surface.
• There is a “strong enough” point. Past a reasonable strength reserve, more time under the bar buys less than technical and specific-strength work, especially for advanced athletes.
• Gym or bike power does not equal sprint speed. Concentric-only power tests correlate poorly with sprinting; specificity decides transfer.

What eccentric training does to fast twitch muscle fibers

Ross’s central claim is that eccentric resistance training is unique in what it does to muscle at the fiber level. Where most training pushes fibers toward fatigue resistance, heavy eccentrics push the other way.

It’s probably the one modality where you can, that we’re shown increases in fiber type or fast-twitch fiber and cross-sectional areas simultaneously. There’s no other training modality, and I’ve been looking at this stuff and the research for 20 years, that has offered that. Typically when we do resistance training, we get a shift away from the fastest myosin, the IIx myosin, and we get a shift towards a more fatigue-resistant IIA.

That is the whole argument for caring about eccentrics if speed is the goal. A sprinter does not want to trade explosive, fast-twitch tissue for tissue that is merely harder to tire out. Ross adds that most athletes, not just the genetically gifted, can improve their fiber composition with the right stimulus. The catch is that “the right stimulus” is demanding and easy to misuse.

How to program eccentric overload without wrecking the athlete

Ross is blunt that eccentric training does real damage and will temporarily lower performance, so it has to be planned. He puts it in the preparatory period and keeps it away from competition.

Eccentric training will also do damage and it will compromise other training units, and you need to build it into your periodization, allowing for perhaps a depression of performance initially, and allowing time for them to rebound, taper the training, and show some real positive adaptations down the track.

His warning is aimed at coaches who sample it once, feel worse, and quit.

One of the things I see is people will try it. “Oh, it got worse. That doesn’t work.” Well, you need to have a plan. If you haven’t got a plan, it’s gonna fail.

Because a fast, high-force eccentric contraction loads the muscle so heavily, soreness and recovery cost climb accordingly, and the damage can interfere with proprioception, technical work, and speed sessions. That is exactly why he confines it to blocks where a short-term dip is acceptable, not the competition phase.

Simple ways to add eccentric overload

None of this requires exotic machines. Ross uses purpose-built flywheel devices, but most of his overload comes from partners and creativity.

Kettlebell swings with a partner, throwing the kettlebell on the eccentric phase, you’re overloading that phase. You’re limited by your imagination, really. Somebody pushing down on the weight stack while they’re doing the eccentric phase, or somebody else pushing down with their leg on the weight stack, so you’re getting excessive overload.

The principle is constant: make the lowering phase harder than the lifting phase. A training partner adding force on the way down turns an ordinary machine or kettlebell into an eccentric-overload tool, which keeps the method accessible to programs without specialized equipment.

Fast twitch fibers, tendon stiffness, and the leg spring

The fiber-type story does not stop at muscle. Ross ties heavy eccentric and isometric work to the stiffness of the whole leg spring, which governs how well an athlete returns energy on the ground.

We know that eccentric training and even isometric training, high loads, do develop tendon cross-sectional area, and eccentric training will develop stiffness of the whole leg spring, which probably relates to fascial thickness and integrity as well as muscle adaptation. Because of the ability to get very high tensions, it is a very strong stimulus for that spring.

He is more skeptical of isometric-only tendon work in isolation, worrying it can build a strong but sluggish system. The point for a speed coach is that eccentric loading is doing double duty: changing the muscle fibers and stiffening the elastic tissues that let those fibers express force quickly.

The strength reserve: how much is enough

For all his interest in loading, Ross does not believe more strength is always better. He describes a strength reserve that matters up to a point, then stops paying transfer.

Having a bigger strength reserve tends to be good for greater force development. But at some point, doing boatloads of strength training, particularly traditional strength training, will give you a slower muscle rather than a faster muscle. You’ll end up being married to the weight room.

He is skeptical of the simple story that getting stronger makes you faster. Novices do get faster as they get stronger, he grants, but he suspects they mostly reached “strong enough,” and coaches read cause and effect into it. Once an athlete clears that threshold, Ross would rather spend the energy on technique and specific qualities than on adding weight to a lift that has stopped transferring.

Why bike power does not predict sprint speed

Ross uses a concrete example to show how weakly general power predicts sprinting. Take a group of athletes, test them on a Wingate cycle test, then sprint-test them, and the link is thin.

You’d expect that the powerful athletes on the bike would be the fast runners, right? As it turns out, the correlation is really, really poor. It’s something like R squared under 0.3 in quite a few of these studies, so you’re only sharing 30% of the variance.

A cycle sprint is concentric-only muscle power, and it barely explains sprint performance. His takeaway is specificity: the qualities that transfer to running are the ones trained in positions and time frames that look like running, which is why he keeps steering strong athletes back toward event-specific work rather than more general power.

Foot strength and the little things

Ross adds foot strength to nearly every warm-up, treating it as a cheap add-on that protects the force an athlete has already built.

When you’re running, it’s all very well developing this enormous power production capacity through your glutes and hamstrings and the muscles in the hip region. If you damp through your feet so much that you can’t express it, you can’t use it.

Barefoot skipping, toe raises, and sand work sit inside a warm-up he was going to do anyway, so the cost is low and the payoff, a stiffer foot that transmits force instead of absorbing it, is directly relevant to sprinting. It is the same logic as the leg spring, applied one joint lower.

Frequently asked questions

Can you change fast twitch muscle fibers with training?
Ross says most athletes can shift fiber composition with the right stimulus, and that the stimulus he trusts most for moving it toward fast twitch is heavy eccentric training. Ordinary heavy lifting tends to move fibers the other way, toward fatigue-resistant types.

Does eccentric training build fast twitch fibers?
In his reading of two decades of research, eccentric training is the one modality that can raise fast-twitch cross-sectional area and fiber type at the same time. That is his main argument for programming it when speed is the goal.

What is the best way to train fast twitch muscle fibers?
Ross programs eccentric overload in the preparatory period, expects a short-term performance dip, then tapers so the adaptation surfaces. Overload can be as simple as a partner adding force on the lowering phase of a kettlebell swing or a weight-stack exercise.

How much strength does a sprinter need?
Enough to build a useful strength reserve, and then technical and specific work take over. Past that point Ross believes extra traditional strength training can make an athlete slower and “married to the weight room.”

Does weightlifting make you slower?
It can, if it is the wrong kind or too much of it. Ross notes that typical resistance training shifts muscle toward more fatigue-resistant, slightly slower fibers, which is why he emphasizes eccentric work and specificity over piling on general strength.

About the authors

Dr. Angus Ross is a physiologist and strength expert with High Performance Sport New Zealand, with a background as a track and bobsled athlete and a research interest in eccentric training, muscle fiber type, and the physical qualities behind speed and power.

Joel Smith is the host of the Just Fly Performance Podcast and the founder of Just Fly Sports, a former collegiate strength and track and field coach focused on speed, power, and athletic development. Listen to the full episode with Dr. Angus Ross on Just Fly Sports.