Position-specific allometric adjustment of NFL Combine tests: evaluation across year cohorts
This study evaluates position-specific allometric body-mass adjustments for NFL Combine tests across multiple years, finding that while such adjustments significantly improve prediction accuracy for body-transport tasks like sprinting and jumping—particularly for defensive linemen—their benefits are inconsistent across other tests and require careful calibration to account for cohort-specific score offsets.
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Every year, thousands of young athletes gather for the National Football League Combine, a massive testing event where they prove their physical worth before the draft. Scouts and coaches watch them sprint, jump, lift heavy weights, and change direction with explosive speed. The goal is to find the next great player, but comparing these athletes is notoriously difficult because they are built so differently. A defensive lineman might weigh over 300 pounds, while a wide receiver might weigh less than 200. If you simply look at the raw numbers, the heavier athletes often look slower or less agile, while the lighter ones might struggle to move the massive weight required for strength tests. This creates a puzzle: how do you fairly judge a giant's speed against a smaller athlete's speed, or a lightweight's jumping ability against a heavyweight's?
For decades, sports scientists have tried to solve this by adjusting scores based on body weight. The idea is to ask a different question: "How well did this athlete perform for their specific size?" This approach, known as allometric scaling, attempts to strip away the advantage or disadvantage of sheer mass to reveal the athlete's true engine. However, the math behind these adjustments is tricky. A simple rule that works for one type of movement might fail for another, and a formula that fits one group of players might be completely wrong for a different position. If the adjustment is done poorly, it can hide the very differences that matter, or worse, create a false sense of fairness where none exists.
In a new study, researcher Thomas Davin Fahey set out to test whether these size-adjusted scores actually work when applied to real NFL draft prospects across different years. He did not just look at the numbers from a single year; he gathered records from 2,333 athletes tested between 2020 and 2026. He looked at six specific tests: the 40-yard dash, vertical jump, broad jump, bench press repetitions, the shuttle run, and the three-cone drill. Instead of treating all players as one big group, he broke them down by their playing positions, such as defensive linemen, linebackers, quarterbacks, and receivers. For each position and each test, he built a model to predict what a player of a certain weight should achieve, then compared the actual results against that prediction.
The results revealed a story of sharp contrasts rather than a single universal rule. The size adjustments worked remarkably well for defensive linemen. For these massive players, the adjusted scores significantly improved the ability to predict performance in sprinting, jumping, and agility drills. In fact, for defensive linemen, the adjusted scores were far better at explaining their results than just looking at their raw times or distances. It turned out that for these players, knowing their weight helped explain why they ran the way they did. However, this benefit did not spread to everyone else. For many other positions, such as linebackers or offensive linemen, the size adjustments offered little to no improvement. In some cases, the adjustments actually made the predictions worse, adding noise rather than clarity.
The study also uncovered that the type of test mattered just as much as the player's position. For tests that require moving one's own body through space, like sprinting or jumping, the relationship between weight and performance was complex and varied by position. But for the bench press, where athletes push a fixed weight, the relationship was different. The researchers found that a simple, fixed mathematical rule often worked just as well as, or even better than, a complex, custom-tuned model for the bench press. This suggests that there is no single "magic formula" that fits every athlete and every task.
Perhaps the most important finding came from looking at how these models held up over time. The researchers tested their equations on data from later years to see if they would still work. While the adjustments helped in many areas, they failed to predict the performance of broad jumpers and bench pressers in the most recent cohort of data. This indicates that the relationship between body weight and performance can shift from year to year, possibly due to changes in training, rules, or the types of players entering the league. The study concludes that while adjusting for body weight can be a powerful tool for specific groups like defensive linemen, it is not a one-size-fits-all solution. Coaches and scouts should not rely on these adjusted scores as a standalone measure of talent. Instead, they must use them carefully, understanding that a score adjusted for size tells a different story than a raw time or distance, and that story is only accurate when the right model is applied to the right player.
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