The Minimum Effective Dose, With Chris Korfist

Based on Episode 5 of the Just Fly Performance Podcast, a conversation between host Joel Smith and sprint coach Chris Korfist.

The minimum effective dose is the idea that a small, precise amount of the right training produces the change you want, and that anything past it is waste at best and harm at worst. Chris Korfist, a longtime sprint coach and one of the earliest adopters of training technology like the 1080 Sprint and K-Box, arrived at it by watching numbers. Once he could measure bar speed, power output, and sprint velocity in real time, he kept seeing the same thing: athletes hit their best rep early, then fell off a cliff. This early conversation is a tour of what that realization changed, from how much he has athletes do, to how he runs an off-season, to why he stopped trusting agility ladders and the squat rack as ends in themselves.

Key Takeaways

• Two or three good reps is often the whole dose. With live feedback, Korfist sees numbers drop fast, so he stops before quality does.
• The goal is a neural change, not fatigue. You are trying to make the body come back and do it a little better, not to grind it down.
• There is no magic bullet. After 25 years of looking, Korfist’s edge is measurement and the willingness to drop what the data says isn’t working.
• Over-speed lives in a narrow band. Three to five percent over max velocity works; past it, athletes brake and their heels start hitting.
• Agility is recognition, not footwork. Ladder drills keep both feet near the ground and the eyes down, which is the opposite of sport.

The minimum effective dose

Korfist’s central lesson came straight off the readouts of his equipment. Whether he is watching a GymAware on the bar, a K-Box meter, or power on the 1080, the story repeats.

You don’t need to do much to make a change. Kids get tired pretty quick. Two to three reps and usually they’re done, and then you see big drops in numbers, because you’re starting to recruit other muscles, you’re fatigued. So I’ve learned to really cut back on what we do. Sometimes less is better.

The point of stopping early is not caution for its own sake; it is that the adaptation he wants is a nervous-system change, and a fatigued rep trains the wrong thing.

You’re just trying to make a neural change so the body responds and comes back and does it a little bit better the next time.

He is blunt that the search for a shortcut is a dead end, and that the real skill is honesty with your own data.

Everyone’s looking for the magic bullet. I’ve been looking for one for 25 years, and they don’t exist.

“Our sport is sprinting”

The same logic shapes how Korfist runs an off-season. Asked how he handles strength training for track athletes through the summer, his answer is a punchline that is also a philosophy.

We do speed. Sprinting is four or five times your body weight. If I have two days, one day we’ll do a fly of some sort, and the other an acceleration day, and we’ll keep doing that until the weather turns crappy.

He extends the minimum-effective-dose idea to conditioning, and he is pointed about coaches who bury athletes in volume to feel prepared. He watched an NFL team cut its running load after GPS data showed they were the cause of their own injuries.

When you do ten sets of 100, you’re training kids to be slow, training them to run inefficiently. Coaches say we need to get in better shape, but they’re already in shape. Basketball is an anaerobic sport. Why do you have to run a gazillion gassers?

The over-speed window on the 1080

Korfist’s favorite illustration of precision is towed over-speed running, where the 1080 lets him set an exact target speed rather than guess with a bungee. The band that works is narrow.

Over-speed is supposed to be three to five percent over your maximum velocity. If I know your fly-ten time, I can walk you off 100 meters and drag you at exactly that speed. If you go too fast, kids come back and say, coach, I felt my heels hitting, it’s too fast.

The most memorable proof was the day everything lined up, the right athletes, the right speed, and ninety-degree heat, and the dose was potent enough to shock the system.

I got the speed right and they got sick. One kid threw up, the other two didn’t feel great, and they told me, coach, we’re in great shape. But when they came back three days later, they ran and jumped better than they ever had. That’s when I had the right exercise at the right time.

Agility is recognition, not footwork

If there is a drill Korfist has fully abandoned, it is the agility ladder, and his reasoning is mechanical.

Both feet are almost on the ground at the same time the whole time you’re doing that drill. In sport, if both feet are on the ground, you’re really not going anywhere. You’re not putting force into the ground, there’s no hip movement. It’s almost a dance move.

Worse, in his view, the ladder trains the athlete to look down, which removes the very thing agility depends on.

You’ve taken away people’s vision, because you’re looking down, and that’s part of agility: recognizing what’s going on and getting there, by reaction time from your visual field to your brain to your feet.

His replacement is any drill with a read built in, colored cones he calls out, reaction lights, or simply starting an athlete off balance and facing the wrong way, so they have to find balance and then accelerate rather than rehearse a pre-planned pattern.

The first step, and getting the hip up

When the conversation turns to acceleration, Korfist points to the hip on that first step, an idea he credits to Frans Bosch. Getting one leg high creates time for the foot to land under the center of mass instead of out in front of it.

Bosch calls it the locked position of the hip in swing-leg retraction. You ratchet that hip up and forward, and it creates more time for your foot to come underneath your center of mass instead of out in front, and you get much better extension.

The cue he found most useful for it came from Jimmy Radcliffe: how much separation can you create between your knees? Korfist likes that the same drill serves cutting, accelerating, and agility at once, which matters when a summer session is only twenty or thirty minutes. It also connects to what he and Joel call exit velocity, how fast an athlete is already moving before the first step lands.

Don’t marry an exercise

Underneath all of it is a discipline Korfist learned the slow way, having started, like many coaches of his era, convinced the squat was the answer. Years and a lot of equipment later, the rule is to follow the data even when it stings.

You have to be brave enough to get rid of what doesn’t work and look at your data in a hardcore fashion, not married to any movement. I went through it this year on the 1080. We measure every three or four weeks, and we hit a stretch where we got worse. I wanted to say, how could it be me, this has worked forever. But here’s the data. It’s not working. I need to change what I’m doing.

That willingness to drop a favorite tool is, in his telling, the same instinct as the minimum effective dose: keep what earns its place, and cut everything that doesn’t.

Frequently asked questions

What is the minimum effective dose in speed training?
It is the smallest amount of high-quality work that produces the adaptation you want. Korfist finds that with real-time feedback from tools like the 1080, K-Box, and GymAware, athletes hit their best rep within two to four reps and then decline, so he stops there. The aim is a neural change, and pushing past the drop-off just adds fatigue and trains inefficiency.

How do you set the speed for over-speed running?
Korfist targets three to five percent over an athlete’s maximum velocity. Knowing a fly-ten time, he can set a motorized unit to tow at exactly that speed. Going faster makes athletes brake, and they report feeling their heels hit the ground, which defeats the purpose.

Are agility ladders useful?
Korfist doesn’t use them. He argues both feet stay near the ground throughout, so little force goes into the ground and there’s no real hip action, and the drill trains athletes to look down, removing the recognition and reaction that agility actually requires. He prefers reaction-based drills with colored cones, lights, or off-balance starts.

How should you train the first step for acceleration?
Korfist focuses on getting the hip up and forward on that first step, what Frans Bosch calls the locked position of the hip in swing-leg retraction, so the foot lands under the center of mass. He uses Jimmy Radcliffe’s cue of creating separation between the knees, which trains cutting, acceleration, and agility together.

How much should you cut back on training volume?
More than most coaches expect. Korfist’s experience, backed by his data and by GPS monitoring he saw with an NFL team, is that high volume trains athletes to be slow and drives injuries. He keeps quality work to a few reps and treats extra conditioning skeptically, especially for anaerobic sports.

About the authors

Chris Korfist is a longtime sprint and speed coach and one of the most prolific contributors to SimpliFaster. At the time of this episode he coached sprints at Montini Catholic High School in Lombard, Illinois, and ran Slow Guy Speed School, developing numerous all-state athletes and state champions while consulting with professional athletes. He is known as an early adopter of training technology, including the 1080 Sprint, K-Box, and GymAware.

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 Chris Korfist on Just Fly Sports.