Context: Guardian Caps (GCs) are currently the most popular external helmet add-on designed to reduce the magnitude of head impacts experienced by American football players. Guardian Caps have been endorsed by influential professional organizations; however, few studies evaluating their efficiency are publicly available. Objective: To present preliminary on-field head kinematics data for National Collegiate Athletic Association (NCAA) Division I American football players using instrumented mouthguards through closely matched preseason workouts with and without GCs. Design: Case series. Setting: The 2022 American football preseason. Patients or Other Participants: Twenty-five male NCAA Division I student-athletes participating in American football completed some portion of the 6 workouts included in this study. Of the 25 participants, 7 completed all 6 workouts using their instrumented mouthguards. Main Outcome Measure(s): Peak linear acceleration (PLA), peak angular acceleration (PAA), and total impacts were collected via instrumented mouthguards during 3 preseason workouts using traditional helmets (TRAD condition) and 3 using a TRAD and GCs (GC condition). The TRAD and GC values for PLA, PAA, and total impacts were evaluated using analyses of variance. Results: No difference was present between the collapsed mean values for the entire sample between the TRAD and GC conditions for PLA (TRAD = 16.3g +/- 2.0g, GC = 17.2g +/- 3.3g, P = .20), PAA (TRAD = 992.1 +/- 209.2 rad/s2, 2 , GC = 1029.4 +/- 261.1 rad/s2, 2 , P = .51), or the total number of impacts (TRAD = 9.3 +/- 4.7, GC = 9.7 +/- 5.7, P = .72). Similarly, no difference was observed between the TRAD and GC conditions for PLA (TRAD = 16.1 g +/- 1.2g, GC = 17.2g +/- 2.79g, P = .32), PAA (TRAD = 951.2 +/- 95.4 rad/s2, 2 , GC = 1038.0 +/- 166.8 rad/s2, 2 , P = .29), or total impacts (TRAD = 9.6 +/- 4.2, GC = 9.7 +/- 5.04, P = .32) between sessions for the 7 players who completed all 6 workouts. Conclusions: These data suggested no difference in head kinematics data (PLA, PAA, and total impacts) when GCs were worn. Therefore, GCs may not be effective in reducing the magnitude of head impacts experienced by NCAA Division I American football players.
