Postural Control Deficits After Repetitive Soccer Heading.

OBJECTIVE: To determine the acute effects of repetitive soccer heading on postural control. DESIGN: Prospective study; participants were divided into 2 groups: a soccer heading group and a control group. SETTING: Biomechanics laboratory. PARTICIPANTS: One hundred sixty participants, including youth (age = 13.0 ± 0.8 years), high school (age = 17.2 ± 1.0 years), and collegiate (age = 20.2 ± 1.3 years) male and female soccer players, participated in this study. INTERVENTIONS: Participants in the soccer heading group performed 12 soccer headers (initial velocity = 11.2 m/s). Postural control testing was performed both before (PRE) and immediately after (POST) the purposeful soccer headers. Control participants performed postural control testing PRE and POST a 15-minute wait period. During postural control testing, participants were asked to stand on the MobileMat (Tekscan Inc, Boston, Massachusetts) for two 2-minute intervals with their hands on their hips and their feet together with one eyes-open and one eyes-closed trial. MAIN OUTCOME MEASURES: Using the center-of-pressure data, 95% area, sway velocity, and ApEn were calculated. Multilevel linear models were used to analyze the effects of age, sex, group, condition, and concussion history simultaneously. RESULTS: Participants in the soccer heading group had significantly higher sway velocity POST than participants in the control group after controlling for age, sex, concussion history, condition, and PRE (t = -3.002; P = 0.003; 95% confidence interval, -0.482 to -0.100). There were no significant differences from PRE to POST for 95% area, M/L ApEn, and A/P ApEn. CONCLUSIONS: Repetitive soccer heading does not affect most postural control measures, even among youth athletes. However, sway velocity increased after heading relative to control participants independent of age, sex, and concussion history.

The effect of an interval fatigue protocol on Vestibular/Ocular Motor Screening (VOMS) performance.

Objective: The purpose of this study was to examine the effect of a fatigue protocol on Vestibular/Ocular Motor Screening (VOMS) performance.Design: Within subjects, repeated measures, crossover.Methods: Fifteen healthy, physically-active participants (22.20 ± 1.424 years) completed 2 sessions under 2 conditions. A pretest VOMS, condition protocol, and a posttest VOMSwere performed. The control condition consisted of rest, while the experimental consisted of a fatigue protocol.Results: The primary outcome measures were VOMS performance scores and Near Point of Convergence (NPC) measurements. Statistically significant interaction effects for NPC, F(1,14) = 9.38, p = .008, and total VOMS score, F(1,14) = 10.96, p = .005 were observed. For NPC, posttest (9.12 ± 4.99 cm) was significantly different, t(14) = -2.60, p = .021, than pretest scores (7.12 ± 3.19 cm). For total VOMS score, posttest experimental scores (4.93 ± 5.12) were significantly different, t(14) = -3.06, p = .009, than pretest severity scores (1.73 ± 3.67).Conclusions: Significant increases were found in total VOMS and NPC scores following exertional fatigue. Exertional fatigue affects symptoms associated with vestibular, and/or ocular motor system assessments. Clinicians should use the VOMS with caution immediately following activity and allow time for recovery from acute fatigue.

Sex and age differences in head acceleration during purposeful soccer heading.

Differences in head-neck segment mass, purposeful heading technique, and cervical strength and stiffness may contribute to differences in head accelerations across sex and age. The purpose of this study was to compare head acceleration across sex and age (youth [12-14 years old], high school and collegiate) during purposeful soccer heading. One-hundred soccer players (42 male, 58 female, 17.1 ± 3.5 years, 168.5 ± 20.3 cm, 61.5 ± 13.7 kg) completed 12 controlled soccer headers at an initial ball velocity of 11.2 m/s. Linear and rotational accelerations were measured using a triaxial accelerometer and gyroscope and were transformed to the head centre-of-mass. A MANOVA revealed a significant multivariate main effect for sex (Pillai's Trace = .165, F(2,91) = 11.868, p < .001), but not for age (Pillai's Trace = .033, F(4,182) = 0.646, p = .630). Peak linear and rotational accelerations were higher in females (40.9 ± 13.3 g; 3279 ± 1065 rad/s2) than males (27.6 ± 8.5 g, 2219 ± 823 rad/s2). These data suggest that under controlled soccer heading conditions, females may be exposed to higher head accelerations than males.

Head and neck size and neck strength predict linear and rotational acceleration during purposeful soccer heading.

There is increasing societal concern about the long-term effects of repeated impacts from soccer heading, but there is little information about ways to reduce head impact severity. The purpose of this study was to identify factors that contribute to head acceleration during soccer heading. One-hundred soccer players completed 12 controlled soccer headers. Peak linear (PLA) and rotational (PRA) accelerations were measured using a triaxial accelerometer and gyroscope. Head acceleration contributing factors were grouped into 3 categories: size (head mass, neck girth), strength (sternocleidomastoid, upper trapezius) and technique [kinematics (trunk, head-to-trunk range-of-motion), sternocleidomastoid and upper trapezius activity]. Multiple regression analyses indicated size variables explained 22.1% of the variance in PLA and 23.3% of the variance in PRA; strength variables explained 13.3% of the variance in PLA and 17.2% of the variance in PRA; technique variables did not significantly predict PLA or PRA. These findings suggest that head and neck size and neck strength predict PLA and PRA. Anthropometric and neck strength measurements should be considered when determining an athlete's readiness to begin soccer heading.

Sex Differences in Anthropometrics and Heading Kinematics Among Division I Soccer Athletes.

BACKGROUND: Soccer players head the ball repetitively throughout their careers; this is also a potential mechanism for a concussion. Although not all soccer headers result in a concussion, these subconcussive impacts may impart acceleration, deceleration, and rotational forces on the brain, leaving structural and functional deficits. Stronger neck musculature may reduce head-neck segment kinematics. HYPOTHESIS: The relationship between anthropometrics and soccer heading kinematics will not differ between sexes. The relationship between anthropometrics and soccer heading kinematics will not differ between ball speeds. STUDY DESIGN: Pilot, cross-sectional design. LEVEL OF EVIDENCE: Level 3. METHODS: Division I soccer athletes (5 male, 8 female) were assessed for head-neck anthropometric and neck strength measurements in 6 directions (ie, flexion, extension, right and left lateral flexions and rotations). Participants headed the ball 10 times (25 or 40 mph) while wearing an accelerometer secured to their head. Kinematic measurements (ie, linear acceleration and rotational velocity) were recorded at 2 ball speeds. RESULTS: Sex differences were observed in neck girth ( t = 5.09, P < 0.001), flexor and left lateral flexor strength ( t = 3.006, P = 0.012 and t = 4.182, P = 0.002, respectively), and rotational velocity at both speeds ( t = -2.628, P = 0.024 and t = -2.227, P = 0.048). Neck girth had negative correlations with both linear acceleration ( r = -0.599, P = 0.031) and rotational velocity at both speeds ( r = -0.551, P = 0.012 and r = -0.652, P = 0.016). Also, stronger muscle groups had lower linear accelerations at both speeds ( P < 0.05). CONCLUSION: There was a significant relationship between anthropometrics and soccer heading kinematics for sex and ball speeds. CLINICAL RELEVANCE: Neck girth and neck strength are factors that may limit head impact kinematics.

Biochemical Response to a Moderate Running Bout in Participants With or Without a History of Acute Knee Injury.

CONTEXT: Individuals with an acute knee-injury history are 4 times more likely to develop knee osteoarthritis than those without a prior knee injury, and it is unknown why. Individuals with an injury history may exhibit aberrant changes in tissue turnover after physical activity (eg, running), which could lead to osteoarthritis, but this has yet to be determined among young, physically active individuals. OBJECTIVE: To determine collagen degradation and synthesis and inflammatory biomarker concentration levels before exercise and changes in response to an acute running bout in injured participants compared with healthy control participants. DESIGN: Cohort study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 22 physically active individuals between 18 and 25 years of age were recruited for the study: 11 injured participants (knee injury within 4 years of the study) who were medically cleared for physical activity and 11 matched healthy control participants. MAIN OUTCOME MEASURE(S): The independent variable was group (injured or control). Dependent variables were serum biomarker concentrations for cartilage oligomeric matrix protein, matrix metalloproteinase-13, proinflammatory marker interleukin-1ß, c-terminal cross-linking telopeptide of type II collagen, and type II collagen synthesis marker. Each participant provided prerun and postrun blood samples for biomarker-concentration analysis. RESULTS: No group differences existed in serum biomarker concentrations before exercise or in serum biomarker changes from pre-exercise to postexercise. CONCLUSIONS: After an acute bout of moderate-intensity running, young, active individuals in a high-risk postinjury population had similar biochemical responses as matched healthy controls. However, the external generalizability of these findings to other exercises and populations has yet to be determined.

Blood biomarkers for brain injury: What are we measuring?

Accurate diagnosis for mild traumatic brain injury (mTBI) remains challenging, as prognosis and return-to-play/work decisions are based largely on patient reports. Numerous investigations have identified and characterized cellular factors in the blood as potential biomarkers for TBI, in the hope that these factors may be used to gauge the severity of brain injury. None of these potential biomarkers have advanced to use in the clinical setting. Some of the most extensively studied blood biomarkers for TBI include S100ß, neuron-specific enolase, glial fibrillary acidic protein, and Tau. Understanding the biological function of each of these factors may be imperative to achieve progress in the field. We address the basic question: what are we measuring? This review will discuss blood biomarkers in terms of cellular origin, normal and pathological function, and possible reasons for increased blood levels. Considerations in the selection, evaluation, and validation of potential biomarkers will also be addressed, along with mechanisms that allow brain-derived proteins to enter the bloodstream after TBI. Lastly, we will highlight perspectives and implications for repetitive neurotrauma in the field of blood biomarkers for brain injury.

Genetic variation in SLC17A7 promoter associated with response to sport-related concussions.

OBJECTIVE: To determine the association of the single nucleotide polymorphism (SNP) rs74174284 within SLC17A7 promoter with concussion severity or duration. DESIGN: A between-subjects design was utilized. METHODS: Saliva samples and concussion severity and duration data were collected from 40 athletes diagnosed with a sport-related concussion by a physician, utilizing a standardized concussion assessment protocol. DNA was extracted, estimated and genotyped. RESULTS: An association was found between the dominant genetic model (CC vs GG + GC; p = 0.0179) and recovery, where those carrying the minor allele were 6.33-times more likely to experience prolonged recovery rates. Within the ImPACT assessment, those carrying the CC genotype (33.38 ± 10.15, p = 0.01) had worse motor speed scores upon initial assessment compared to both heterozygous (CG) and homozygous (GG) genotypes (41.59 ± 7.39). CONCLUSIONS: This study was the first to demonstrate an association between genetic polymorphism at rs7417284 SNP in the promoter region of the SLC17A7 gene and concussion severity and duration. Based upon these findings, rs74174284 is a potential predictive genetic marker for identifying athletes who are more susceptible for altered recovery times and worse motor speed ImPACT scores after sport-related concussion.

Effect of soccer heading ball speed on S100B, sideline concussion assessments and head impact kinematics.

OBJECTIVE: To examine the effect of soccer heading ball speed on S-100B serum concentration, concussion sideline assessments and linear head impact acceleration. METHODS: Sixteen division I soccer players participated in this pre-test post-test design study. Athletes performed five standing headers over a 10 minute period at 30 (n = 5), 40 (n = 5) or 50 (n = 6) miles per hour (mph) (randomized). S-100B serum concentration (ng mL-1) and sideline concussion assessments were measured prior to and post-heading. Peak resultant linear head acceleration (gravitational units; g) was measured during soccer heading. RESULTS: No statistically significant interaction effects were identified between ball velocity groups over time on S100B (effect sizes ranged from 0.03-0.23) or concussion assessments tests. There was a non-significant increase (p = 0.06) in head impact acceleration from the 30 (30.6; SD = 6.2 g) to 50 mph (50.7; SD = 7.7 g) ball speed. CONCLUSIONS: In this controlled setting, an acute bout of soccer heading across various ball velocities did not affect S100B or concussion assessment test scores. These findings are preliminary, as the small sample size in each group may have played a role in the lack of significant findings.

Consequences of pediatric obesity on the foot and ankle complex.

BACKGROUND: Anthropometric status can influence gait biomechanics, but there is relatively little published research regarding foot and ankle characteristics in the obese pediatric population. We sought to compare the structural and functional characteristics of the foot and ankle complex in obese and non-obese children. METHODS: Twenty healthy children (ten obese and ten normal weight) were recruited for a cross-sectional research study. Anthropometric parameters were measured to evaluate active ankle dorsiflexion, arch height (arch height index, arch rigidity index ratio, and arch drop), foot alignment (resting calcaneal stance position and forefoot-rearfoot alignment in unloaded and loaded positions), and foot type (malleolar valgus index). Independent t tests determined significant differences between groups for all assessed parameters. Statistical significance was set at P < .0125. RESULTS: Compared with non-obese participants, obese participants had significantly greater arch drop (mean ± SD: 5.10 ± 2.13 mm versus 2.90 ± 1.20 mm; P =.011) and a trend toward lower arch rigidity index ratios (mean ± SD: 0.92 ± 0.03 versus 0.95 ± 0.02; P = .013). In addition, obese participants had significantly less active ankle dorsiflexion at 90° of knee flexion versus non-obese participants (mean ± SD: 19.57 ± 5.17 versus 29.07 ± 3.06; P < .001). No significant differences existed between groups for any other anthropometric measurements. CONCLUSIONS: The decreased active ankle dorsiflexion in the obese group can increase foot contact for a longer period of the stance phase of gait. Obese participants also presented with a more flexible foot when bearing weight.

Neuronal structural protein polymorphism and concussion in college athletes.

OBJECTIVE: To examine the association between a neuronal structural protein polymorphism and the frequency and severity of concussions in college athletes. METHODS: Forty-eight athletes with previous self-reported history of a concussion were matched with 48 controls that did not report a history of concussion. Each group was genotyped for neurofilament heavy (NEFH) polymorphism rs#165602 in this retrospective case-control study. RESULTS: There was no significant association (χ(2 )= 0.487, p = 0.485) between carrying the NEFH rare allele and a history of one or more concussions due to small effect sizes. A Fisher's exact test revealed no significant association (p = 1.00, ϕ = -0.03) between the presence of NEFH rare allele and a history of multiple concussions. The independent t-tests revealed no significant differences in duration of signs and symptoms (t = 1.41, p = 0.17, d = 0.48) or return to play (t = 0.23, p = 0.82, d = 0.08) between NEFH rare allele carrier and non-carriers. CONCLUSIONS: Among college athletes, carrying the rare allele assessed may not influence an athlete's susceptibility to sustaining a concussion or return to play duration following a concussion.

Apolipoprotein E genotype and concussion in college athletes.

OBJECTIVE: To evaluate the association between apolipoprotein E (APOE) polymorphisms (E2, C/T Arg158Cys; E4, T/C Cys112Arg; and promoter, g-219t) and the history of concussion in college athletes. We hypothesized that carrying 1 or more APOE rare (or minor) allele assessed in this study would be associated with having a history of 1 or more concussions. DESIGN: Multicenter cross-sectional study. SETTING: University athletic facilities. PARTICIPANTS: One hundred ninety-six male football (n = 163) and female soccer (n = 33) college athletes volunteered. INTERVENTIONS: Written concussion history questionnaire and saliva samples for genotyping. MAIN OUTCOME MEASURES: Self-reported history of a documented concussion and rare APOE genotype (E2, E4, promoter). RESULTS: There was a significant association (Wald χ² = 3.82; P = 0.05; odds ratio = 9.8) between carrying all APOE rare alleles and the history of a previous concussion. There was also a significant association (Wald χ² = 3.96, P = 0.04, odds ratio = 8.4) between carrying the APOE promoter minor allele and experiencing 2 or more concussions. CONCLUSIONS: Carriers of all 3 APOE rare (or minor) alleles assessed in this study were nearly 10 times more likely to report a previous concussion and may be at a greater risk of concussion versus noncarriers. Promoter minor allele carriers were 8.4 times more likely to report multiple concussions and may be at a greater risk of multiple concussions versus noncarriers. Research involving larger samples of individuals with multiple concussions and carriers of multiple APOE rare alleles is warranted.

Concussive signs and symptoms following head impacts in collegiate athletes.

OBJECTIVE: To evaluate the association between having a previously documented concussion and experiencing concussive signs and symptoms (S&S) following head impacts in collegiate athletes. METHODS: Two hundred and one college male football (n = 168) and female women's soccer (n = 33) athletes participated in this retrospective case-control study. Athletes completed a questionnaire and reported if they had been diagnosed with concussion and if they experienced concussive S&S following a head impact during a game or practice in the previous year. RESULTS: Almost 60% (89 of 152) of non-concussed athletes reported experiencing S&S following head impacts in the previous year compared to 80% (39 of 49) of concussed athletes. The Phi coefficient (r = 0.196, p = 0.005) results indicated a significant association between previous history of concussion and the occurrence of S&S following a head impact. CONCLUSIONS: A large percentage of non-concussed athletes are experiencing concussive S&S following head impacts during games and practices. Previously concussed athletes, however, report experiencing S&S more frequently following head impacts than their non-concussed counterparts. Although this study is subject to the limitations of a retrospective research design, these findings highlight the need for more diligent surveillance from clinicians, as many concussions are being missed.

Lacrosse equipment and cervical spinal cord space during immobilization: preliminary analysis.

CONTEXT: Removal of the lacrosse helmet to achieve airway access has been discouraged based only on research in which cervical alignment was examined. No researchers have examined the effect of lacrosse equipment on the cervical space available for the spinal cord (SAC). OBJECTIVE: To determine the effect of lacrosse equipment on the cervical SAC and cervical-thoracic angle (CTA) in the immobilized athlete. DESIGN: Observational study. SETTING: Outpatient imaging center. PATIENTS OR OTHER PARTICIPANTS: Ten volunteer lacrosse athletes (age = 20.7 +/- 1.87 years, height = 180.3 +/- 8.3 cm, mass = 91 +/- 12.8 kg) with no history of cervical spine injury or disease and no contraindications to magnetic resonance imaging (MRI). INTERVENTION(S): The lacrosse players were positioned supine on a spine board for all test conditions. An MRI scan was completed for each condition. MAIN OUTCOME MEASURE(S): The independent variables were condition (no equipment, shoulder pads only [SP], and full gear that included helmet and shoulder pads [FG]), and cervical spine level (C3-C7). The dependent variables were the SAC and CTA. The MRI scans were evaluated midsagittally. The average of 3 measures was used as the criterion variable. The SAC data were analyzed using a 3 x 5 analysis of variance (ANOVA) with repeated measures. The CTA data were analyzed with a 1-way repeated-measures ANOVA. RESULTS: We found no equipment x level interaction effect (F(3.7,72) = 1.34, P = .279) or equipment main effect (F(2,18) = 1.20, P = .325) for the SAC (no equipment = 5.04 +/- 1.44 mm, SP = 4.69 +/- 1.36 mm, FG = 4.62 +/- 1.38 mm). The CTA was greater (ie, more extension; critical P = .0167) during the SP (32.64 degrees +/- 3.9 degrees) condition than during the no-equipment (25.34 degrees +/- 2.3 degrees ; t(9) = 7.67, P = .001) or FG (26.81 degrees +/- 5.1 degrees; t(9) = 4.80, P = .001) condition. CONCLUSIONS: Immobilizing healthy lacrosse athletes with shoulder pads and no helmets affected cervical spine alignment but did not affect SAC. Further research is needed to determine and identify appropriate care of the lacrosse athlete with a spine injury.

Effects of pediatric obesity on joint kinematics and kinetics during 2 walking cadences.

UNLABELLED: Shultz SP, Sitler MR, Tierney RT, Hillstrom HJ, Song J. Effects of pediatric obesity on joint kinematics and kinetics during 2 walking cadences. OBJECTIVE: To determine whether differences existed in lower-extremity joint biomechanics during self-selected walking cadence (SW) and fast walking cadence (FW) in overweight- and normal-weight children. DESIGN: Survey. SETTING: Institutional gait study center. PARTICIPANTS: Participants (N=20; mean age +/- SD, 10.4+/-1.6y) from referred and volunteer samples were classified based on body mass index percentiles and stratified by age and sex. Exclusion criteria were a history of diabetes, neuromuscular disorder, or recent lower-extremity injury. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Sagittal, frontal, and transverse plane angular displacements (degrees) and peak moments (newton meters) at the hip, knee, and ankle joints. RESULTS: The level of significance was set at P less than .008. Compared with normal-weight children, overweight children had greater absolute peak joint moments at the hip (flexor, extensor, abductor, external rotator), the knee (flexor, extensor, abductor, adductor, internal rotator), and the ankle (plantarflexor, inverter, external/internal rotators). After including body weight as a covariate, overweight children had greater peak ankle dorsiflexor moments than normal-weight children. No kinematic differences existed between groups. Greater peak hip extensor moments and less peak ankle inverter moments occurred during FW than SW. There was greater angular displacement during hip flexion as well as less angular displacement at the hip (extension, abduction), knee (flexion, extension), and ankle (plantarflexion, inversion) during FW than SW. CONCLUSIONS: Overweight children experienced increased joint moments, which can have long-term orthopedic implications and suggest a need for more nonweight-bearing activities within exercise prescription. The percent of increase in joint moments from SW to FW was not different for overweight and normal-weight children. These findings can be used in developing an exercise prescription that must involve weight-bearing activity.

Sex differences in head acceleration during heading while wearing soccer headgear.

CONTEXT: Researchers have indicated that female soccer players may be at greater risk of concussion compared with their male counterparts. Soccer headgear is marketed for reducing head acceleration and risk of concussion. OBJECTIVE: To determine the effect of sex and soccer headgear on head impact kinematics and dynamic stabilization during soccer heading. DESIGN: Cross-sectional design. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Forty-four college-aged soccer players (29 women, 15 men). INTERVENTION(S): Using a head impact model, participants performed 4 soccer headers under 3 headgear conditions (control, Head Blast Soccer Band, and Full90 Select Performance Headguard). MAIN OUTCOME MEASURE(S): Dependent variables assessed before soccer heading were head-neck anthropometrics and isometric neck muscle strength, and those assessed during soccer headers were resultant linear head acceleration, Head Injury Criteria (HIC(36)), and superficial neck muscle electromyography. Statistical analyses included multivariate and univariate analyses of variance with repeated measures, independent-samples t tests, appropriate follow-up analyses of variance and post hoc t tests, and Pearson product moment correlations (alpha = .05). RESULTS: Head acceleration in women was 32% and 44% greater than in men when wearing the Head Blast (21.5 g versus 16.3 g) and Full90 Select (21.8 g versus 15.2 g), respectively (P < .05). Compared with men, women exhibited 10% greater head accelerations (20.2 g versus 18.2 g) during the control condition (P = .164). CONCLUSIONS: Female soccer players exhibited greater head accelerations than their male counterparts when wearing headgear. Our results are important clinically because they indicate that soccer headgear may not be an appropriate head injury prevention tool for all athletes.

Effects of sport massage on limb girth and discomfort associated with eccentric exercise.

CONTEXT: Sport massage is often used to help prepare for exercise, expedite recovery from muscle soreness, and enhance athletic performance. However, the effect of sport massage on recovery from delayed-onset muscle soreness is unknown. OBJECTIVE: To determine the effect of a short sport massage treatment on intramuscular swelling and pain in response to eccentric exercise. DESIGN: We used a 2 x 8 (treatment x time) repeated-measures design to compare triceps surae muscle girth and pain ratings over the 72 hours after eccentric exercise. SETTING: University research laboratory. PATIENTS OR OTHER PARTICIPANTS: Nineteen healthy, college-aged subjects. INTERVENTION(S): Delayed-onset muscle soreness was induced with several sets of eccentric triceps surae contractions at 90% of the estimated concentric, 1-repetition maximum weight. Subjects returned on 3 consecutive days after eccentric exercise with a cycle ergometer for active rest treatments. In addition, 1 leg received the sport massage. MAIN OUTCOME MEASURE(S): Girth measurements were taken at 5.08 cm (2 in), 10.16 cm (4 in), 15.24 cm (6 in), and 20.32 cm (8 in) below the knee joint line, and pain was assessed with a visual analog scale before and after all 4 sessions. RESULTS: No interaction was noted between treatment and time for any girth or pain measurements, and no main effect was seen for treatment. CONCLUSIONS: Sport massage did not reduce girth or pain in the lower leg after eccentric exercise within 72 hours.

Gender differences in head-neck segment dynamic stabilization during head acceleration.

PURPOSE: Recent epidemiological research has revealed that gender differences exist in concussion incidence but no study has investigated why females may be at greater risk of concussion. Our purpose was to determine whether gender differences existed in head-neck segment kinematic and neuromuscular control variables responses to an external force application with and without neck muscle preactivation. METHODS: Forty (20 females and 20 males) physically active volunteers participated in the study. The independent variables were gender, force application (known vs unknown), and force direction (forced flexion vs forced extension). The dependent variables were kinematic and EMG variables, head-neck segment stiffness, and head-neck segment flexor and extensor isometric strength. Statistical analyses consisted of multiple multivariate and univariate analyses of variance, follow-up univariate analyses of variance, and t-tests (P < or = 0.05). RESULTS: Gender differences existed in head-neck segment dynamic stabilization during head angular acceleration. Females exhibited significantly greater head-neck segment peak angular acceleration (50%) and displacement (39%) than males despite initiating muscle activity significantly earlier (SCM only) and using a greater percentage of their maximum head-neck segment muscle activity (79% peak activity and 117% muscle activity area). The head-neck segment angular acceleration differences may be because females exhibited significantly less isometric strength (49%), neck girth (30%), and head mass (43%), resulting in lower levels of head-neck segment stiffness (29%). CONCLUSION: For our subject demographic, the results revealed gender differences in head-neck segment dynamic stabilization during head acceleration in response to an external force application. Females exhibited significantly greater head-neck segment peak angular acceleration and displacement than males despite initiating muscle activity earlier (SCM only) and using a greater percentage of their maximum head-neck segment muscle activity.

Resistance training and head-neck segment dynamic stabilization in male and female collegiate soccer players.

CONTEXT: Cervical resistance training has been purported to aid in reducing the severity of brain injuries in athletes. OBJECTIVE: To determine the effect of an 8-week resistance-training program on head-neck segment dynamic stabilization in male and female collegiate soccer players. DESIGN: Pretest and posttest control group design. SETTING: University research laboratory and fitness center. PATIENTS OR OTHER PARTICIPANTS: Thirty-six National Collegiate Athletic Association Division I collegiate soccer players (17 men, 19 women). INTERVENTION(S): The resistance training group underwent an 8-week cervical resistance training program that consisted of 3 sets of 10 repetitions of neck flexion and extension at 55% to 70% of their 10-repetition maximum 2 times a week. Participants in the control group performed no cervical resistance exercises. MAIN OUTCOME MEASURE(S): Head-neck segment kinematics and stiffness, electromyographic activity of the upper trapezius and sternocleidomastoid muscles during force application to the head, and neck flexor and extensor isometric strength. RESULTS: No kinematic, electromyographic, or stiffness training effects were seen. The posttest resistance training group isometric neck flexor strength was 15% greater than the pretest measurement. Isometric neck extensor strength in the female resistance training group was 22.5% greater at the posttest than at the pretest. Women's neck girth increased 3.4% over time regardless of training group level. Women exhibited 7% less head-neck segment length and 26% less head-neck segment mass than men. CONCLUSIONS: Despite increases in isometric strength and girth, the 8-week isotonic cervical resistance training did not enhance head-neck segment dynamic stabilization during force application in collegiate soccer players. Future researchers should examine the effect of head-neck segment training protocols that include traditional and neuromuscular activities (eg, plyometrics) with the focus of reducing head acceleration on force application.