Effect of neck muscle strength and anticipatory cervical muscle activation on the kinematic response of the head to impulsive loads.
BACKGROUND
Greater neck strength and activating the neck muscles to brace for impact are both thought to reduce an athlete's risk of concussion during a collision by attenuating the head's kinematic response after impact. However, the literature reporting the neck's role in controlling postimpact head kinematics is mixed. Furthermore, these relationships have not been examined in the coronal or transverse planes or in pediatric athletes.


OBJECTIVE
In each anatomic plane, peak linear velocity (ΔV) and peak angular velocity (Δω) of the head are inversely related to maximal isometric cervical muscle strength in the opposing direction (H1). Under impulsive loading, ΔV and Δω will be decreased during anticipatory cervical muscle activation compared with the baseline state (H2).


METHODS
Descriptive laboratory study.


METHODS
Maximum isometric neck strength was measured in each anatomic plane in 46 male and female contact sport athletes aged 8 to 30 years. A loading apparatus applied impulsive test forces to athletes' heads in flexion, extension, lateral flexion, and axial rotation during baseline and anticipatory cervical muscle activation conditions. Multivariate linear mixed models were used to determine the effects of neck strength and cervical muscle activation on head ΔV and Δω.


RESULTS
Greater isometric neck strength and anticipatory activation were independently associated with decreased head ΔV and Δω after impulsive loading across all planes of motion (all P < .001). Inverse relationships between neck strength and head ΔV and Δω presented moderately strong effect sizes (r = 0.417 to r = 0.657), varying by direction of motion and cervical muscle activation.


CONCLUSIONS
In male and female athletes across the age spectrum, greater neck strength and anticipatory cervical muscle activation ("bracing for impact") can reduce the magnitude of the head's kinematic response. Future studies should determine whether neck strength contributes to the observed sex and age group differences in concussion incidence.


CONCLUSIONS
Neck strength and impact anticipation are 2 potentially modifiable risk factors for concussion. Interventions aimed at increasing athletes' neck strength and reducing unanticipated impacts may decrease the risk of concussion associated with sport participation.
James T. Eckner, University of Michigan, Department of Physical Medicine & Rehabilitation, 325 E Eisenhower Pkwy, Ann Arbor, MI, 48108, USA. jeckner@med.umich.edu.
James T
JT
Eckner
Youkeun K
YK
Oh
Monica S
MS
Joshi
James K
JK
Richardson
James A
JA
Ashton-Miller
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001696:Biomechanical Phenomena / Q000502:physiology; D001924:Brain Concussion / Q000503:physiopathology / Q000517:prevention & control*; D002648:Child; D006259:Craniocerebral Trauma / Q000503:physiopathology*; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D015999:Multivariate Analysis; D053580:Muscle Strength / Q000502:physiology*; D009334:Neck Muscles / Q000502:physiology*; D012307:Risk Factors; D012399:Rotation; D014159:Transducers
head injuries/concussion; head kinematics; injury biomechanics; neck muscle activation; neck strength