Objective: To evaluate the effect of cervical muscle strength on head impact biomechanics.
Design: Prospective cohort.
Setting: Field setting.
Participants: Thirty-seven volunteer ice hockey players (age = 15.0 ± 1.0 years, height = 173.5 ± 6.2 cm, mass = 66.6 ± 9.0 kg, playing experience = 2.9 ± 3.7 years).
Interventions: Participants were equipped with accelerometer-instrumented helmets to collect head impact biomechanics (linear and rotational acceleration) throughout an entire playing season. Before the season, isometric cervical muscle strength was measured for the anterior neck flexors, anterolateral neck flexors, cervical rotators, posterolateral neck extensors, and upper trapezius. Data were analyzed using random intercept general mixed linear models, with each individual player as a repeating factor/cluster.
Main Outcome Measures: Dependent variables included linear and rotational head accelerations. Cervical strength data were categorized into tertiles, creating groups with high, moderate, and low strength. Strength measures were averaged and normalized to body mass.
Results: Significant differences in cervical muscle strength existed across our strength groups (P < 0.05). No differences were observed in linear or rotational acceleration across strength groups for the anterior neck flexors (PLin = 0.399; PRot = 0.060), anterolateral neck flexors (PLin = 0.987; PRot = 0.579), cervical rotators (PLin = 0.136; PRot = 0.238), posterolateral neck extensors (PLin = 0.883; PRot = 0.101), or upper trapezius (PLin = 0.892; PRot = 0.689).
Conclusions: Our hypothesis that players with greater static neck strength would experience lower resultant head accelerations was not supported. This contradicts the notion that cervical muscle strength mitigates head impact acceleration. Because we evaluated cervical strength isometrically, future studies should consider dynamic (ie, isokinetic) methods in the context of head impact biomechanics.
From the *Matthew Gfeller Sport-Related Traumatic Brain Injury Research Center, Department of Exercise and Sport Science; †Curriculum in Human Movement Science, Department of Allied Health Sciences, School of Medicine; and ‡Department of Epidemiology, The University of North Carolina, Chapel Hill, North Carolina; §Simbex, Lebanon, New Hampshire; ¶Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire; ‖Neuromuscular Research Laboratory, Department of Exercise and Sport Science, The University of North Carolina, Chapel Hill, North Carolina; and Departments of **Neurosurgery; and ††Sport Medicine, Emerson Hospital, Concord, Massachusetts.
Submitted for publication February 2, 2011; accepted July 6, 2011.
Supported by the Ontario Neurotrauma Foundation (Toronto, Ontario, Canada), the USA Hockey Foundation (Colorado Springs, Colorado), and the National Operating Committee on Standards for Athletic Equipment (Overland Park, Kansas).
Dr Greenwald has a financial interest in the HIT System technology used to collect data for this study.
The authors report no conflicts of interest.
Corresponding Author: Jason P. Mihalik, PhD, CAT(C), ATC, The University of North Carolina at Chapel Hill, 313 Woollen Gymnasium, Campus Box 8605, Chapel Hill, NC 27599-8605 (firstname.lastname@example.org).