When Buffalo Bills star Josh Allen comes across YouTube clips of himself throwing passes for the University of Wyoming, he swears he doesn’t recognize that guy.

“It’s night and day in terms of the type of thrower I am,” Allen said this summer. “Where I held the ball, where I released the ball — it looks like a different guy. It’s kind of gross to look at sometimes. But I don’t think it’s as gross anymore.”

Allen, like many other NFL quarterbacks, spends time each offseason tweaking details of his throwing motion, “just trying to be as efficient as possible,” he said. And efficiency is the specialty of biomechanics experts such as Chris Hess, the founder of the 3D motion analysis company Biometrek.

A quarterback is a “rotational athlete,” one who rotates the body in order to throw, swing or hit. Hess and other specialists in the private sector specifically focus on the kinetic sequence, the transfer of energy during that rotation from the base of the body up through the arm.

An efficient thrower’s accuracy increases, biomechanists say, because his energy travels in the correct sequence: from legs to pelvis to torso to arm, with each reaching peak rotational velocity as the next begins. More efficient throwers also put less stress on their arms over time because the body properly produces and transfers the energy required to throw.

“Accuracy isn’t voodoo,” Hess likes to say, “it’s biomechanical science.”

Allen has worked with Hess and his motion-capture software since 2020 and believes this has helped make him a more accurate, controlled thrower. There is some evidence to support this. Allen’s completion percentage jumped from 52.8 and 58.8 in 2018 and 2019 to 69.2 percent in 2020 and has not dipped below 63 percent since (even while playing through a partially torn ulnar collateral ligament in his right elbow in 2022).

A rising number of NFL quarterbacks rely on independent professionals like Hess to incorporate biomechanics and its corresponding technology into their offseason training. Young stars like Allen, C.J. Stroud, Caleb Williams, Anthony Richardson and Brock Purdy have consulted with Hess to gather vast pools of data that tell them everything about how efficiently or inefficiently they throw using motion-capture technology.

After collecting and interpreting the data, Hess collaborates with physical therapists such as Dr. Tom Gormley to help them make body adjustments while private quarterbacks coaches such as Will Hewlett, Jordan Palmer and Adam Dedeaux fine-tune mechanics and technique. They develop injury prevention and recovery plans, pre-throw and post-throw routines and more — all with the hope of maximizing a quarterback’s arm, the tool that can make or break his career.

“It’s the most important position in all of sports, so you’re constantly evolving, trying to find ways to get mental reps, physical reps, without overdoing it,” said Bills GM Brandon Beane. “There is so much invested in that position that you are always looking for any area to improve to give your guys even the slightest advantage.”

Each spring, Hess travels the country to put quarterbacks through his motion capture programming at the request of their private coaches and occasionally NFL teams. His pack-and-go equipment, which uses high-resolution cameras to track movement rather than attaching sensors to the player, builds a perimeter of the cameras on a field like a super-sized imitation of a quarterback’s pocket.

The quarterback executes a range of spot throws from inside that pocket to establish a baseline. Once the system is calibrated, Hess has quarterbacks throw to receivers running a variety of routes. The quarterback can bootleg in and out of the perimeter of cameras, as the testing aims to simulate as many football movements as possible.

Streams of data emerge as the quarterback’s movement is translated by a computer into speed and energy outputs from every part of his body at each millisecond of every throw. Hess organizes the data into digestible pieces, including graphs and a visual display of the quarterback’s body as he throws — a skeleton frame with flashing colors that represent his energy transfer.

Hess and the physical therapists and private quarterbacks coaches he works with aren’t looking for massive issues. They emphasize the tiniest of adjustments that, over time, build the most efficient throwing motions possible.

“If you’re calling me, you’re ready for some granular information,” Hess said.

(Chris Hess / Biometrek)

For example, if a right-handed quarterback’s right leg extends even by a small degree before the pelvis starts to rotate — an issue common among throwers — that creates more forward momentum, not rotational momentum. Over time, such a movement puts more stress on the arm because the quarterback makes up for a lack of rotational energy by producing more effort with his shoulder/arm and tends to have less “feel” in his throw, which can turn into inaccuracy.

Once identified by Hess, the team of private specialists can introduce small, repetitive drills and exercises to correct the issue over weeks and months of offseason training.

“In 2020, when we first started working together, (Allen) felt like he had to rip every ball as hard as possible to get it to go where it was,” said Hess. “Whenever he had to throw something intermediate or short … he was kind of trying to de-accelerate his arm to slow the ball down to get touch. And it just made it so inconsistent.

“We gave him the information and helped him understand how to become rotational. Once he knew that, now Josh can speed up and slow down the ball with his body — the hand is just out there guiding the ball.”

Much of the science informing Hess and others comes from over a decade of research and application of biomechanics in baseball and golf.

“Baseball is pretty much light years ahead of the NFL as far as the ability to integrate sports science and also be data-driven,” said Dr. Emily Ferree, a physical therapist, biomechanist and movement specialist who consults for Major League Baseball teams, private quarterback coaches and NFL and college football players.

Baseball was an early investor in biomechanical application. There are dozens of “arms” in a given MLB team’s farm system, so huge amounts of data can be collected and studied each year, and technology and methods advance quickly as a result. The sport is even built to help keep that data clean. Pitchers may use different types of throws, but the ball is always thrown a specific distance from a specific spot on the field.

“There is a very repeatable, very controllable movement that you can test and measure (in a lab) that is almost identical to the performance environment,” Ferree said.

A quarterback can go into a play with a specific plan for his throw, but anything can happen after the snap to change that plan. What are his body and arm doing when he is scrambling away from pressure or suddenly opting to throw a sidearm pass while on the move in order to thread the ball between two defenders?

“There are so many things that happen in an NFL game that change the way the quarterback moves that it’s hard to do a singular throwing evaluation,” said Ferree. “That doesn’t mean that I don’t think it’s worth it. It gives us their baseline movement pattern — this is how your arm works, this is how it connects to your torso, this is how you generally transfer energy from your lower extremities to your upper extremities, this is how efficient you are, this is how (in)-efficient you are.”

Biomechanics-specific motion capture technology has proven useful in injury prevention and recovery. Ferree often sees quarterbacks try to “protect their elbow” as they return to throwing after a significant arm surgery (such as the UCL repair Purdy underwent in 2023, when he worked with Gormley and Hewlett throughout the recovery process). Their rotation changes — which has a ripple effect on the rest of their body.

“They just really aren’t efficient in their throwing motion,” Ferree said, “Motion capture in the rehab process can be huge because it allows you to track their arm path and basically tailor their throwing program to make sure they’re coming back as efficiently and as well as possible.”

The technology can also help quantify fatigue. Biomechanics experts can now see exactly when a thrower begins to wear down because they can measure micro changes in their transfer of energy. From there, experts can plan the quarterback’s ideal workload through the course of a practice week.

(Chris Hess / Biometrek)

Many NFL strength and conditioning and medical staffs collaborate with quarterbacks using data gathered from private offseason specialists to formulate an overall plan for injury recovery, arm maintenance and workload management. But the investment in sports science, medical and conditioning staffs and technology varies among the 32 organizations.

Some owners are simply willing to spend more money in that area than others. Plus, the NFL can be a hard environment for experimenting with new data and technology — some teams feel there is not enough time or comfort to try new things while maintaining care for a 90-man offseason roster and 53-man in-season roster.

Some quarterbacks want more than teams can offer — or simply feel more comfortable working with specialists where they can receive niche programming. At times, there have been highly publicized rifts between a quarterback and his independent coaches on one side and the organization on the other (think Tom Brady and Alex Guerrero chafing against Bill Belichick in the mid-2010s) that have given owners pause when working with the private sector.

Bridging the gap between those specialists and an NFL team requires balance. NFL teams have to look at the entire roster when choosing which technologies they champion and which experts they employ. Certain quarterback-specific practices, for example, are of no use to the rest of the players on the roster. A sports performance director, and ultimately a team’s owner, decides whether an investment is worth it or not.

A team could hire a quarterback-focused biomechanist and invest in its own motion capture technology, similar to the model of many MLB teams, but what other role would that person hold in an NFL building? The work done by private specialists includes making tiny adjustments to how a player throws and his workload to maximize arm strength and preserve its health. Would that bump up against the work of NFL team’s quarterbacks coach? It might not matter — quarterbacks coaches in some buildings are more focused on game planning and play installation during the season and less on actual player development.

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Turnover also works against the full implementation of biomechanical data and training methods. Gathering enough data to turn into useful applications can take years. A lack of continuity at head coach and in the front office can sometimes mean the same in a team’s athletic training and sports medicine departments.

Some teams outsource biomechanical work, especially for quarterbacks. In that case communication with the quarterback about the data gathered from his offseason training — and an understanding of how to apply it from late July to February, when the player is with the team — is crucial.

“We are in an unprecedented time with this steep curve of technology coming out so fast — more than we probably can ingest it, to be honest,” said Tyler Williams, the Minnesota Vikings’ VP of player health and performance. “That gets a little dangerous. You’re trying to figure out, ‘How do we filter out the noise’?”

Under Williams, the Vikings test certain technologies throughout the year, accumulating data in as real a football environment as possible and studying the results over a long time. The team puts accelerometers in its practice footballs to measure changes in velocity, rotation and distance. They match those changes with movement trackers that assess energy output and stress on the body and parse this in combination with motion capture software and practice film.

The idea is to see what patterns might emerge regarding how players expend energy, the effect of certain movements and drills on the body and more.

“You’re pairing biomechanical (study), motion capture, different variables. It gives you a way further granular picture of how the quarterback moves (and) what makes them successful,” Williams said.

“You’re building a picture with puzzle pieces. In 1985, we were using the little kid puzzles that had eight pieces. … Eventually, with mobile motion capture, accelerometers, on-field player tracking from RFID technologies, force plate technologies — all of these different types of entities — we can measure the athlete (with), now we’re probably playing with a picture that is like, a 500-piece puzzle.”

Rams QB Matthew Stafford flips a sidearm pass during the playoffs last season in Detroit. (David Reginek / USA Today)

Like the Vikings, the Rams’ sports science department — once led by Williams and now by Trent Frey, who spent the last six years in a similar role with the NHL’s Los Angeles Kings — places sensors in the practice footballs. The Rams also collect movement tracking data for the entire roster and can quantify energy output per movement, which helps when building workload management plans for players.

Frey and the Rams’ medical and strength and conditioning staff then work with coaches to script out practices and weight room periods. The idea is to get every player as individualized a plan as possible while keeping a team atmosphere intact. The quarterback will not have the same weight training and injury prevention programming as a receiver, who will not have the same programming as a defensive end and so on.

It wasn’t so long ago, said Rams director of strength and conditioning Justin Lovett, that NFL quarterbacks protested getting pulled off of “the main lift” (the group weight training session) in the interest of more specialized training.

“There was a little bit of a culture shock,” Lovett said. “The coaches and the quarterbacks would say, ‘I need my guys to see us work.’ … Sometimes that would cut at the grit or the culture that your head coach is trying to establish.”

Lovett wants to blend the months of independent offseason training and biomechanics work into a much tighter NFL ramp-up period in the spring. “It’s really accessing that network and then carrying where they left off,” he said.

When Hess works with quarterbacks, he runs them through a final motion capture session right before OTAs, and the player’s team receives the results. From there, Gormley or another specialist can explain what adjustments he and the player’s private coach made, what warmup and recovery exercises they implemented — and show exactly why using Hess’ data.

With the Rams, Gormley went a step further. Lovett hosted him for two days this spring at their practice facility in Thousand Oaks, Calif., to talk to the strength and conditioning and sports performance staff about biomechanics and the physical application of available technology.

Lovett believes the private sector has gotten so advanced that it can give an open-minded team an edge in building out its quarterback’s in-season training plan. External specialists and the quarterbacks they work with in the offseason have more information about a thrower’s arm than ever before.

As investments into the position increase by millions each year, figuring out how to best tap into that information year-round might be NFL teams’ next advantage.

(Illustration: Dan Goldfarb / The Athletic; photos: Robin Alam / ISI Photos, Brian Rothmuller / Icon Sportswire via Getty Images)