40-Yard Dash Training: Korfist and Fichter on the Real Numbers

Based on Episode 5 of The Fast Lane, a conversation between host Chris Kerr and coaches Chris Korfist and Dan Fichter.

Most 40 yard dash training advice starts with the stopwatch. Chris Korfist and Dan Fichter start somewhere less comfortable: with the arithmetic that says most of the 4.4s coaches report cannot be real, and with the question of what an athlete’s body has to produce, per kilogram, before a fast time is even available to them. What follows is less about drills and more about the numbers that decide whether the drills matter.

Key Takeaways

• The 4.4 is mostly arithmetic. Certain vertical jump and sprint numbers make a genuine 4.4 mathematically unavailable.
• Force per bodyweight is the gate. Roughly 8 newtons per kilogram out of the stance, with a real ceiling above it.
• There is a narrow window. Push too long and you are late; push too little and your foot lands out in front.
• Combine separation is not max velocity. Elite athletes accelerate alike; lighter athletes simply keep turning over.
• Acceleration starts with permission to fall. Fichter treats falling as a trainable skill, not a byproduct.

Why most 4.4s are not real

Korfist has made this argument in print before, and Kerr reads it back to him on air from his SimpliFaster article on the 4.4. The claim is not that athletes are lying, but that the supporting numbers do not permit the time.

The athlete with a 24-inch vertical jump does not run a 4.4. A 55-meter sprinter who runs a 6.9 FAT doesn’t run a 4.4. An 11.5 100-meter dash kid does not run a 4.4. It is mathematically impossible for an athlete to run that time and still get a 4.4.

His reasoning is that the 40 imposes requirements at every phase, and the opening is the least forgiving of them. A 24-inch vertical, in his framing, indicates an athlete who cannot project their body out hard enough for the time to be on the table.

He also separates the timing methods rather than treating a number as a number, and he is careful not to exempt the Combine.

Most people get the coaches’ 4.4, which is great. But when you see a real 4.4, and not a combine one, because remember the combine timing isn’t perfect either. When you see someone legitimately that fast, you’re like, yeah, that’s just different.

Force per kilogram is the gate

The most portable idea in the episode is that acceleration has an entry requirement expressed relative to bodyweight. Korfist puts a number on it.

Your force out of the block per body weight would probably be eight, eight newtons per kilogram.

He is equally clear that more is not simply better, because ground contact time constrains how much force can be applied at all.

There’s a threshold. You can only press so much because you only have so much time on the ground. The most on my metrics is like 8.4 or 8.5 newtons per kilogram. If you push longer than that, you’re on the ground too long, and then you’re late, so now you’re gonna fall.

And below the window, the failure shows up as a braking step rather than as weakness.

If you’re below 7.9, now you’re behind. You haven’t pushed hard enough to let your mass clear that leg that’s on the ground, and so that foot’s gonna strike out in front. So there’s this very narrow area that you’ve gotta press in.

For power he uses watts per kilogram, which he describes simply as how much power an athlete puts into the ground per unit of body mass.

For me to run a 4.4, those numbers are gonna range between 21 and 23 watts per kilogram. That’s on my timing, on my track. I’ve probably seen more data than anyone else, and the highest is 24.

What the Combine data actually shows

Korfist spends time on Dr. Ken Clark’s research on Combine 40s, and his reading of it corrects a common misinterpretation. When every athlete at the Combine is elite, the acceleration curves look alike.

Everyone that shows up at the combine is an elite athlete. When Ken flattens out all the steps and makes that graph, everyone accelerates at that same rate. The 310-pound guy has a great first step. It’s just his mass is so much that he can’t get that mass to move far enough or his legs to spin fast enough.

That leads to the conclusion coaches most often get backwards about the back half of the run.

When you see the two lines separate after the acceleration, that’s really just because they weigh less, and because they weigh less, they can make their legs turn over faster. So it’s deceiving. It’s not truly max velocity, because you’ve developed all of that potential in your acceleration.

He adds a practical observation from 1080 Sprint data that runs against the stereotype about big athletes.

You’d be amazed at how great the first step is for some of these really big guys. Some of the defensive ends that are making a lot of money, their first step might be even a little bit better than some of the wide receivers.

Fichter: acceleration begins when the brain lets you fall

Fichter approaches the same problem from the nervous system rather than the force plate. In his model an athlete cannot accelerate until the brain permits a controlled loss of balance.

Your brain has to permit a forward loss of balance in order for you to even start to accelerate. So if it’s not comfortable in those positions, you’re gonna hesitate, you’re gonna stumble.

That leads him somewhere most speed programs do not go: treating falling itself as something to train.

Your acceleration for me begins when the brain allows you to fall, and I believe falling is a training entity. Like, you need to train it.

He also offers a long-held hypothesis about where that comfort comes from, which he is careful to present as his own theory rather than a finding.

I had a theory, and I talk about this for the last 20 years, that I think really fast people when they were kids, if you ever tracked them, fell a lot. As you develop your vestibular system as a kid, if your head is constantly out in front of your center of mass, you have to adapt your stumble reflexes, and all these things make you a better positional accelerator.

Practically, that shows up as curved runs on field lines, which he uses to challenge the vestibular system and build tolerance for the positions acceleration demands.

Data Points and Metrics

Frequently Asked Questions

What force does an athlete need for a fast 40 yard dash?
Korfist works from roughly 8 newtons per kilogram of bodyweight out of the stance. He describes a practical ceiling around 8.4 to 8.5 N/kg, because ground contact time limits how much force can actually be applied, and says an athlete below about 7.9 N/kg is already behind.

Why do coaches report 4.4s that are not real?
Because timing method and supporting numbers get separated from the claim. Korfist distinguishes coach-timed, Combine-timed, and true electronic times, and argues that certain markers, such as a 24-inch vertical jump, a 6.9 FAT 55 meter, or an 11.5 100 meter, make a genuine 4.4 mathematically unavailable.

Is the NFL Combine 40 accurately timed?
Not perfectly, in Korfist’s view. He explicitly declines to treat Combine times as a clean standard, noting the Combine timing “isn’t perfect either” when distinguishing a real 4.4 from a reported one.

What does watts per kilogram mean for sprinting?
It is power relative to body mass, or how much power an athlete generates into the ground per unit of bodyweight. Korfist puts a 4.4 in the range of 21 to 23 watts per kilogram on his own timing setup, with 24 the highest he has recorded.

How do you train acceleration according to Dan Fichter?
By training the athlete’s willingness to fall. Fichter argues the brain must permit a forward loss of balance before acceleration can begin, treats falling as a trainable quality rather than a byproduct, and uses tools such as curved runs to challenge the vestibular system and build comfort in those positions.

Related on SimpliFaster

• The 4.4 40
• Speed Goals: Decoding the 40-Yard Dash
• Korfist and Fichter on Foot Strength and Wave Sprints
• Acceleration Exercises for Athletes, With Cameron Josse

About the Speakers

Chris Korfist is a longtime high school track and football coach, the founder of Slow Guy Speed School, and a co-founder of the Track Football Consortium. He is known for applied speed training and for hands-on use of timing and resistance technology including the 1080 Sprint.

Dan Fichter is the owner of Wannagetfast Power/Sport Training near Rochester, New York. He works across sports with a strong emphasis on the nervous system, reflexive performance, and the positional and vestibular demands of acceleration.

Chris Kerr hosts The Fast Lane for SimpliFaster, where he brings coaching questions from the field directly to practitioners.