Background: Sport-related concussion (SRC) is estimated to affect ~10,000 National Collegiate Athletic Association athletes each year (Kerr et al., 2015), with female collegiate athletes showing higher rates of SRC in sex-comparable sports (Covassin et al., 2016). Sex differences in neck strength is one potential mechanism underlying differences in SRC risk. SRC has been directly linked to lower neck strength in high school students (Collins et al., 2014) and lower neck strength has been associated with greater linear and rotational accelerations upon impact (Caccese et al, 2017). Relative to male athletes, female athletes show lower neck strength and more linear and rotational head acceleration upon impact (Tierney et al., 2005).

Objective: The aim of our study was to develop a comprehensive assessment of neck strength, and examine whether neck strength differs dependent on sex, sport risk (contact and non-contact sport athletes), and SRC history.

Method: High sport risk (n=29 contact sport; 52% female) and low sport risk athletes (n=56 limited/non-contact sports; 64% female) were assessed at the start of their athletic season. Isometric neck strength in six motions was collected using handheld dynamometry. Peak force values were averaged across three trials and used as measures of neck strength. Neck strength symmetry was evaluated using paired t-tests. An equal number of athletes in contact (n=8) and limited/non-contact (n=8) sports reported a history of SRC; thus, differences in neck strength in athletes with a history of SRC dependent on sport risk was examined.

Results: Relative to female athletes, male athletes demonstrated more strength across all motions assessed (p < 0.005). Males demonstrated greater flexion relative to extension strength (p=0.015) while females showed greater extension relative to flexion strength (p=0.001). Males also showed greater left relative to right SCM strength (p=0.003) and females showed greater right relative to left rotation strength (p=0.044). No significant differences in strength dependent on SRC history or sport risk were noted. In athletes with a history of SRC, however, contact sport athletes showed significant asymmetry in SCM strength (p<0.05) that was not observed in athletes participating in limited/non-contact sports.

Conclusion: Consistent with past work, sex differences in neck strength were noted across all measures. In addition, we noted sex differences in neck muscle symmetry. Although no symmetry differences were observed dependent on sport risk or SRC history, significant asymmetries in SCM strength were shown in athletes with a SRC history participating in contact sports. These results suggest that neck strength may be a critical factor in SRC, specifically for contact sport athletes. Future research should consider SCM asymmetries because they may strongly contribute to SRC risk and could be a focus for SRC prevention protocols.

Differences in Neck Strength and Symmetry Dependent on Sex, Sport Risk, and Sport-Related Concussion History