Positional Differences in American Football Players Internal Load and Recovery Over a 10-Week In-Season

Abstract

Internal load metrics may better reflect the increased metabolic demands of American football linemen, not fully appreciated using external load metrics alone. This pilot study served to investigate both (1) internal workload and (2) autonomic nervous system (ANS) recovery using heart rate (HR) metrics in 28 collegiate football players, subdivided into three player position groups: BIG (linemen; n=20), COMBO (quarterbacks, linebackers, and tight ends; n=3), and SKILL (receivers and running backs; n=5) players. HR data were collected using chest-strap monitors (Firstbeat™) worn during the first two practices of each week, over a 10-week season. Internal load was assessed using training impulse (TRIMP) while ANS recovery was measured, pre-practice, using heart rate variability (HRV). Kruskal-Wallis non-parametric tests were used to compare the overall differences between the three player position groups. For internal load, TRIMP was statistically different between groups, H(2)=23.25, p=0.001. TRIMP values for BIG, COMBO, and SKILL were: 135.0±61.0AU, 123.0±50.8AU, and 101.0±53.1AU. Post-hoc pairwise comparisons revealed the only significant TRIMP difference was between the BIG group and the SKILL group (p=0.001). For ANS recovery metrics, HRV pairwise comparisons showed significant differences between BIG (53.4±25.2ms) and SKILL (72.6±30.5ms) position groups (p=0.001). These data suggest that BIG position group players may experience significantly greater internal loads and demonstrate the least ANS recovery, compared with SKILL players, across midweek practice sessions. These high metabolic loads may help explain why linemen are at greatest risk for heatstroke during practice.