Head Impact Exposure Across Levels of Play in American Football: A Systematic Review of Accelerometer Data.

With growing concern about the long-term effects of head injuries in contact sports, understanding differences in head impact exposure (HIE) across age groups is critical. Youth athletes may face heightened risks due to developmental vulnerability, yet the relationship between level of play and HIE remains unclear. This systematic review compares HIE characteristics between youth (≤14 years) and collegiate football players using accelerometer-based sensors. PubMed, Embase, and Scopus were searched (2015-2025) for studies quantifying HIE with impacts defined as acceleration events exceeding a 10-15 g threshold. Variables included cohort age, study period, sensor type, impact frequency during practice and competition, and median and 90th-95th percentile linear and rotational acceleration. Twenty-nine studies met the inclusion criteria, representing 1742 youth athletes (aged 6-14) and 3850 collegiate athletes (aged 17-23). Collegiate players sustained more cumulative seasonal impacts than youth in practice (472.1 vs. 113.0) and overall (449.0 vs. 228.0). However, impacts per individual game (youth: 10.0; collegiate: 9.8), median linear accelerations (youth: 18.6 g; college: 20.7 g), and upper-tail linear accelerations (youth 95th percentile: 46.4 g; collegiate 90th-95th percentile: 47.7 g) were similar between groups. By contrast, youth athletes exhibited higher seasonal median (1144.9 vs. 964.0 rad/s2) and upper-tail rotational accelerations (youth 95th percentile: 2929.7; collegiate 90th percentile: 2072.2 rad/s2). These findings indicate that while collegiate athletes sustain greater cumulative exposure, youth may sustain impacts of comparable or greater magnitude. Accelerometer-based data provide critical insights into age-related differences in HIE, with implications for understanding concussion pathophysiology and informing safety strategies.