Physical Performance Measures Correlate with Head Impact Exposure in Youth Football.

Head impact exposure (HIE) (i.e., magnitude and frequency of impacts) can vary considerably among individuals within a single football team. To better understand individual-specific factors that may explain variation in head impact biomechanics, this study aimed to evaluate the relationship between physical performance measures and HIE metrics in youth football players.Head impact data were collected from youth football players using the Head Impact Telemetry (HIT) System. HIE was quantified in terms of impact frequency, linear and rotational head acceleration, and risk-weighted cumulative exposure metrics (RWELinear, RWERotational, and RWECP). Study participants completed 4 physical performance tests: vertical jump, shuttle run, 3-cone, and 40 yard sprint. The relationships between performance measures and HIE metrics were evaluated using linear regression analyses.A total of 51 youth football athletes (ages: 9-13 years old) completed performance testing and received a combined 13,770 head impacts measured with the HIT System for a full season. All performance measures were significantly correlated with total number of impacts in a season, RWELinear-Season, and all RWE-Game metrics. The strongest relationships were between 40 yard sprint speed and all RWE-Game metrics (all p≤0.0001 and partial R>0.3). The only significant relationships among HIE metrics in practice were between shuttle run speed and total practice impacts and RWELinear-Practices, 40 yard sprint speed and total number of practice impacts, and 3-cone speed and 95th percentile number of impacts/practice.Generally, higher vertical jump height and faster times in speed and agility drills were associated with higher HIE, especially in games. Physical performance explained less variation in HIE in practices, where drills and other factors, such as coaching style, may have a larger influence on HIE.