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Velocity and Acceleration of the Head during Emergency Shoulder Pad Removal

Hall BT*, Swartz EE*, Al-Darraji SJ†, Bric JD†, Decoster LC†, Mihalik JP‡: *University of New Hampshire, Durham, NC, †New Hampshire Musculoskeletal Institute, Manchester, NH, ‡University of North Carolina, Chapel Hill, NC

Context: As American football equipment designs introduce new technology to improve safety, evidence-based techniques for their emergent removal must coincide.  Previous research in emergency removal of shoulder pads has investigated the time for removal and the induced motion within the cervical spine. Velocities and accelerations of the head and cervical spine during these interventions are important considerations that have not been extensively studied.

Objective: To examine head velocity and acceleration when removing two styles of football shoulder pads. We hypothesized that a new quick release style of shoulder pads would result in less acceleration and velocity at the head during shoulder pad removal.

Design: Quasi-experimental.

Setting: Research laboratory.

Patients or Other Participants: Forty certified athletic trainers (ATs) free of physical pathology preventing them from completing the required tasks were recruited (males=21; females=19; age=33.7±11.2 yrs; mass=80.7±17.1 kg; height=173.1±9.2 cm; AT experience=10.6±10.4 yrs).

Interventions: The independent variable was the shoulder pad design (Traditional or Riddell RipKordTM). After practicing and familiarizing themselves, paired participants conducted 8 successful, randomized trials where they removed traditional (Trad) shoulder pads (using the flat torso technique) or RipKordTM (Rip) shoulder pads from a live model (4 trials of each). An eight-camera three-dimensional motion system with two, three-point segment marker sets (head and torso) were used in capturing head and torso motion. Kintrak 6.0 and Eva-RT 5.0 (Motion Analysis, Inc.) software was used to digitize motion trials and process the outcome variables.

Main Outcome Measures: Dependent variables involved integrated velocity and integrated acceleration of the head in each of the three planes (sagittal, frontal, transverse). Trials for each pair were ensemble averaged. Due to our participant pairing, our analyses were based on a sample of n=20.  Six paired samples t-tests compared means in each plane (P=0.05).

Results: Removing traditional shoulder pads resulted in significantly less acceleration compared to removing RipKordTM shoulder pads in the sagittal [(t19 = -4.404,P<.001) Trad=1964.53 ±639.01 m/s2, Rip=2915.47±780.02 m/s2], and frontal  [(t19= -2.620, P=.017) Trad=842.32±336.22 m/s2, Rip=1255.55±566.91 m/s2] planes. Removing traditional shoulder pads also resulted in significantly less velocity in all three planes [[(t19= -4.194, P<.00) Trad=94.63±23.44 m/s, Rip=136.07±38.49 m/s; (t19= -3.822, P=.001) Trad=35.60±8.22 m/s, Rip=49.30±15.01 m/s; (t19= -2.632, P=.016) Trad= 55.83±16.74 m/s, Rip=70.60±20.55 m/s].

Conclusions: Our hypotheses were rejected in that the data presented suggest that when using the flat torso technique, a traditional style of shoulder pads will result in lower velocity and acceleration of the head compared to the RipKord TM shoulder pads. This data does not reflect the amount of motion experienced in the cervical spine at time of removal. Future research should investigate these variables in different styles of shoulder pads using other removal techniques (i.e., full body levitation, torso lift).  This study was funded by the Eastern Athletic Trainers’ Association and the Hamel Center for Undergraduate Research.