Tackling training adherence and its effect on head impact biomechanics in high school football

Abstract

CHAPTER 1: DIFFERING ADHERENCE RATES TO HuTT® AND ITS EFFECTS ON HEAD IMPACTS IN HIGH SCHOOL FOOTBALL Despite advancements in head safety measures in American football, head injuries remain prominent in the sport. While resources promoting safer tackling and blocking techniques exist (HUF, Shoulder Tackling system, etc.), the effectiveness of improving players’ head safety by utilizing these resources is determined by consistent adherence and proper compliance by the coaches and athletes. There are currently no standardized regulations for a tackling training program, and research regarding adherence rates to a behavioral intervention is limited. This study aimed to determine the minimal rate of adherence for effectiveness of the HuTT® intervention in high school football. Five teams (n = 181) were prescribed a helmetless tackling training program (HuTT®), and each team had varying adherence and compliance rates throughout one season. Head impact data were collected through the Riddell InSite Impact Response systems, a sensor inside each helmet. The reported head impact data was used to calculate the rate of impacts per athlete exposure (Imp/AE). Linear regressions and independent sample T-tests were run to analyze the relationship between Imp/AE and tackling training adherence rates with an alpha level of p < 0.05. Participants who completed ≥60% of the HuTT® intervention were considered adherent and were found to have significantly lower Imp/AE (p <0.001; n = 129, 2.06 ± 2.28) when compared to the non-adherent group that completed <60% of the intervention (n = 52, 4.06 ± 3.45). Exploratory analysis with non-adherent groups set at <50% and <30% also found significantly higher Imp/AE compared to those who were ≥50% (p =0.004; n = 147, 2.20 ± 2.44) and ≥40% (p =0.014; n = 148, 2.20 ± 2.43) adherent, respectively. This study suggests an adherence rate of ≥60% to the HuTT® intervention significantly reduces head impact frequency in high school football. An adherence rate of ≥60% aligns with findings from Swartz et al.6 and provides additional guidance for behavioral intervention adherence. CHAPTER 2: VARYING ADHERENCE TO A TACKLING TRAINING PROGRAM AND ITS EFFECTS ON HEAD IMPACT CHARACTERISTICS While full adherence to research interventions is often assumed, variations in adherence and compliance occur and can affect outcomes. In football, helmetless tackling training (HuTT®) aims to correct head-leading behavior but the effects of varying adherence and compliance rates over time remain unexplored. This study investigates the sustained effectiveness of HuTT® across teams with consistent adherence in Year 1 but differing adherence/compliance in Year 2. Repeated participants from three high school football programs (n = 33) were tracked over two consecutive seasons. Teams were adherent to a prescribed HuTT® intervention in Year 1. In Year 2, one team maintained adherence with modified compliance (Team A), one ceased participation (Team B), and one had reduced adherence and compliance rates (Team C). Head impact data (frequency, magnitude) were collected using Riddell InSite Impact Response systems, a sensor inside each helmet. Individual intervention completion rates, head impact magnitude cumulation, and Imp/AE for practice, game, and overall exposure were calculated. Paired sample T-tests compared Year 1 to Year 2 changes in Imp/AE and total magnitude burden for an adherent-adherent group (Team A) and an adherent-nonadherent group (Teams B+C combined). The adherent-adherent group (n=12) showed a significant decrease in overall Imp/AE (p =0.014), practice Imp/AE (p =0.011), game Imp/AE (p =0.018), and total burden (p =0.012) between Year 1 and Year 2. The adherent-nonadherent group revealed a significant increase in game Imp/AE (p =0.004) and total burden (p =0.032) between Year 1 and Year 2. The reduction of all head-safety characteristics in the adherent-adherent group suggests that consistent engagement in tackling training is beneficial in reducing head-safety characteristics and potentially refine tackling skills over time. In the adherent-nonadherent group, an increase in game Imp/AE and total burden highlights that ceasing or significantly reducing tackling training can negatively impact players' head impact behavior, particularly in competitive settings. CHAPTER 3: WEEKLY CHANGES IN HEAD IMPACT LOCATION AND MAGNITUDE BURDEN TO A TACKLING TRAINING INTERVENTION Head impact telemetry (HIT) systems assist in measuring impact frequency, magnitude, and location to better understand head impact safety and concussions. Current research has shown that concussions were sustained from impacts averaging around 90g of linear force in high school-aged football players. Lab-recorded head impact locations have been shown to affect brain tissue strain most on the sides of the head, while on-field data has shown impacts to the front resulted in most reported concussions in high school football. Tackling training aims to reduce head-leading behavior, potentially lowering impact magnitude and altering locations. This study investigates weekly changes in head impact location and magnitude burden over two seasons in repeated participants in one high school football team. Repeated participants (n = 16) in one football team were observed over two seasons. In Year 1, the team completed 100% of a prescribed tackling training program (HuTT®) and discontinued the prescription in Year 2. Timestamped head impact data (frequency, magnitude, location – front, top, side, back) were collected weekly using helmets with Riddell InSite Impact Response systems. The weekly cumulative impact frequency and magnitude burden for each location were calculated. Fixed-effect longitudinal models compared individual week-to-week changes in impact frequency and burden by location in each year. Total impact frequency and burden were also compared from Year 1 to Year 2. A significant weekly decrease was found in impact frequency (p =0.036) and burden (p = 0.038) to the top location in Year 1, with no significant weekly changes in Year 2. When comparing Year 1 to Year 2, Year 2 had a significantly higher impact frequency (p < 0.001) and burden (p < 0.001) to the front location. Significantly higher overall impact frequency (p < 0.001) and burden (p < 0.001) were also found in Year 2. Year 1 findings suggest that the HuTT® program reduces top-of-head impact frequency and burden over a football season, potentially mitigating 'head-down’ behavior. The significant increase of impacts and burden to the front and overall impacts and burden in Year 2, compared to Year 1, reiterates the potential benefits of consistent tackling training in reducing these metrics.