The Iron Mile is a 20-minute field test that combines a heavy deadlift with a mile run for time.
The resulting data is used to calculate your Hybrid Strength Index (HSI) — a single number that reveals how well your strength holds up under real fatigue.
The deadlift measures raw force production across the entire kinetic chain. The mile run tests your ability to perform both anaerobically and aerobically.
In a truly effective hybrid program, both numbers should improve together. As soon as one begins to outpace the other, you’ve shifted from hybrid development into specialization. Specialization has its place — but for the Hybrid athlete, Hyrox competitor, CrossFit athlete, or tactical professional, too much of it usually comes at the cost of overall performance.
Field HSI: 1RM deadlift (lb) / mile time (minutes)
Scores from this 20-minute window run lower than fresh, rested testing. Compare only against your own Iron Mile results.