Comparative analysis between operative and non-operative acetabular labral tear injuries in division 1 collegiate athletes.

Acetabular labral tears have shown to be difficult to diagnose and manage in an active and competitive athletic population. The goal of this study was to compare NCAA Division 1 collegiate athletes undergoing operative and non-operative management of their labral injuries by assessing ability to return to competition and secondarily evaluate days lost from sport. A retrospective cohort analysis was conducted on Division 1 collegiate athletes from 2005 to 2020, incorporating all varsity university sports. Records showing MRI confirmed diagnosis were included in the cohort, as well as all pertinent clinical data. Data revealed 10/18 (55%) of individuals managed conservatively versus 23/29 (79%) surgically (p-value = 0.0834) were able to return to sport following treatment. Of those athletes, 22 surgical patients experienced a mean of 324 days ± 223 days lost from sport and nine conservatively managed patients experienced a mean of 27 days ± 70 lost days (p-value < 0.001) Seven of nine conservatively managed patients were able to continue competition while undergoing treatment. Findings suggest no statistical significance regarding operative vs non-operative management of acetabular labral tears. The majority of athletes returning to sport and treated conservatively were able to resume competition during treatment. Therefore, treatment of these injuries should be individualized based on athlete's symptoms.

A novel murine muscle loading model to investigate Achilles musculotendinous adaptation.

Achilles tendinopathy is a debilitating condition affecting the entire spectrum of society and a condition that increases the risk of tendon rupture. Effective therapies remain elusive, as anti-inflammatory drugs and surgical interventions show poor long-term outcomes. Eccentric loading of the Achilles muscle-tendon unit is an effective physical therapy for treatment of symptomatic human tendinopathy. Here, we introduce a novel mouse model of hindlimb muscle loading designed to achieve a tissue-targeted therapeutic exercise. This model includes the application of tissue (muscle and tendon)-loading "doses," coupled with ankle dorsiflexion and plantarflexion, inspired by human clinical protocols. Under computer control, the foot was rotated through the entire ankle joint range of motion while the plantar flexors simultaneously contracted to simulate body mass loading, consistent with human therapeutic exercises. This approach achieved two key components of the heel drop and raise movement: ankle range of motion coupled with body mass loading. Model development entailed the tuning of parameters such as footplate speed, number of repetitions, number of sets of repetitions, treatment frequency, treatment duration, and treatment timing. Initial model development was carried out on uninjured mice to define a protocol that was well tolerated and nondeleterious to tendon biomechanical function. When applied to a murine Achilles tendinopathy model, muscle loading led to a significant improvement in biomechanical outcome measures, with a decrease in cross-sectional area and an increase in material properties, compared with untreated animals. Our model facilitates the future investigation of mechanisms whereby rehabilitative muscle loading promotes healing of Achilles tendon injuries.NEW & NOTEWORTHY We introduce a novel mouse model of hindlimb muscle loading designed to achieve a tissue-targeted therapeutic exercise. This innovative model allows for application of muscle loading "doses," coupled with ankle dorsiflexion and plantarflexion, inspired by human loading clinical treatment. Our model facilitates future investigation of mechanisms whereby rehabilitative muscle loading promotes healing of Achilles tendon injuries.

Psychometric properties of the standardized assessment of concussion in youth football: Validity, reliability, and demographic factors.

The objective of this study was to determine the psychometrics (reliability, validity) of the original Standardized Assessment of Concussion (SAC) in a youth sample (ages 11 to 13). Demographic factors of race, level of vocabulary knowledge, mother's level of education were also considered. Over 150 youth football athletes completed the SAC and a brief battery of NIH Toolbox cognitive tests as part of a larger study on biomechanical factors in youth sport concussion. This was a within-subjects design (pre-season, post-season assessments), and correlational analysis of convergent and discriminant validity. Between groups analysis based on demographic differences was also employed. The pre-season SAC scores were not different by age; however, SAC scores were statistically different by race: t(155) = 3.162, p = .002, d = .519. Maternal level of education and participant vocabulary scores were related to racial group membership. Convergent and discriminant validity were established compared to NIH Toolbox tests of memory and speed. Pre-post-season tests for 108 participants established marginally acceptable test-retest reliability (ICC = .692). These data support the use of the original SAC in youth football although clinicians must be aware of racial differences in scores.

Neuropsychological Change After a Single Season of Head Impact Exposure in Youth Football.

OBJECTIVES: Head impact exposure (HIE) in youth football is a public health concern. The objective of this study was to determine if one season of HIE in youth football was related to cognitive changes. METHOD: Over 200 participants (ages 9-13) wore instrumented helmets for practices and games to measure the amount of HIE sustained over one season. Pre- and post-season neuropsychological tests were completed. Test score changes were calculated adjusting for practice effects and regression to the mean and used as the dependent variables. Regression models were calculated with HIE variables predicting neuropsychological test score changes. RESULTS: For the full sample, a small effect was found with season average rotational values predicting changes in list-learning such that HIE was related to negative score change: standardized beta (ß) = -.147, t(205) = -2.12, and p = .035. When analyzed by age clusters (9-10, 11-13) and adding participant weight to models, the R2 values increased. Splitting groups by weight (median split), found heavier members of the 9-10 cohort with significantly greater change than lighter members. Additionaly, significantly more participants had clinically meaningful negative changes: X2 = 10.343, p = .001. CONCLUSION: These findings suggest that in the 9-10 age cluster, the average seasonal level of HIE had inverse, negative relationships with cognitive change over one season that was not found in the older group. The mediation effects of age and weight have not been explored previously and appear to contribute to the effects of HIE on cognition in youth football players.

Perturbation-based balance training targeting both slip- and trip-induced falls among older adults: a randomized controlled trial.

BACKGROUND: Falls are the leading cause of injuries among older adults. Perturbation-based balance training (PBT) is an innovative approach to fall prevention that aims to improve the reactive balance response following perturbations such as slipping and tripping. Many of these PBT studies have targeted reactive balance after slipping or tripping, despite both contributing to a large proportion of older adult falls. The goal of this randomized controlled trial was to evaluate the effects of PBT targeting slipping and tripping on laboratory-induced slips and trips. To build upon prior work, the present study included: 1) a control group; 2) separate training and assessment sessions; 3) PBT methods potentially more amenable for use outside the lab compared to methods employed elsewhere, and 4) individualized training for older adult participants. METHODS: Thirty-four community-dwelling, healthy older adults (61-75 years) were assigned to PBT or a control intervention using minimization. Using a parallel design, reactive balance (primary outcome) and fall incidence were assessed before and after four sessions of BRT or a control intervention involving general balance exercises. Assessments involved exposing participants to an unexpected laboratory-induced slip or trip. Reactive balance and fall incidence were compared between three mutually-exclusive groups: 1) baseline participants who experienced a slip (or trip) before either intervention, 2) post-control participants who experienced a slip (or trip) after the control intervention, and 3) post-PBT participants who experienced a slip (or trip) after PBT. Neither the participants nor investigators were blinded to group assignment. RESULTS: All 34 participants completed all four sessions of their assigned intervention, and all 34 participants were analyzed. Regarding slips, several measures of reactive balance were improved among post-PBT participants when compared to baseline participants or post-control participants, and fall incidence among post-PBT participants (18%) was lower than among baseline participants (80%). Regarding trips, neither reactive balance nor fall incidence differed between groups. CONCLUSIONS: PBT targeting slipping and tripping improved reactive balance and fall incidence after laboratory-induced slips. Improvements were not observed after laboratory-induced trips. The disparity in efficacy between slips and trip may have resulted from differences in dosage and specificity between slip and trip training. TRIAL REGISTRATION: Name of Clinical Trial Registry: clinicaltrials.gov Trial Registration number: NCT04308239. Date of Registration: March 13, 2020 (retrospectively registered).

Prolotherapy Induces an Inflammatory Response in Human Tenocytes In Vitro.

BACKGROUND: Proliferative therapy, or prolotherapy, is a controversial treatment method for many connective tissue injuries and disorders. It involves the injection of a proliferant, or irritant solution, into the site of injury, which causes small-scale cell death. This therapeutic trauma is theorized to initiate the body's wound-healing cascade, perhaps leading to tissue repair. The immediate effects of many of these proliferants are poorly characterized, as are the cellular responses to them; here, we sought to evaluate the immediate effects of two common proliferants (dextrose and P2G, a combination of phenol, glucose, and glycerin) on the cellular response of human tenocytes, and begin to explicate the mechanisms with which each proliferant functions. QUESTIONS/PURPOSES: We asked: What are the effects of treating cultured tenocytes with proliferative treatment agents on their (1) cellular metabolic activity, (2) RNA expression, (3) protein secretion, and (4) cell migration? METHODS: Using human hamstring and Achilles tendon cells, we attempted to answer our research questions. We used a colorimetric metabolic assay to assess the effect of dextrose and P2G proliferant treatment on cell mitochondrial activity compared with nontreated tenocytes. Next, using quantitative PCR, ELISA, and a reporter cell line, we assessed the expression of several key markers involved in tendon development and inflammation. In addition, we used a scratch wound-healing assay to evaluate the effect of proliferant treatment on tenocyte migration. RESULTS: Results showed that exposure to both solutions led to decreased metabolic activity of tenocytes, with P2G having the more pronounced effect (75% ± 7% versus 95% ± 7% of untreated control cell metabolic levels) (ANOVA; p < 0.01; mean difference, 0.202; 95% CI, 0.052-0.35). Next, gene expression analysis confirmed that treatment led to the upregulation of key proinflammatory markers including interleukin-8 and cyclooxygenase-2 and downregulation of the matrix marker collagen type I. Furthermore, using a reporter cell line for transforming growth factor-ß (TGF-ß), a prominent antiinflammatory marker, we showed that treatments led to decreased TGF-ß bioactivity. Analysis of soluble proteins using ELISA revealed elevated levels of soluble prostaglandin E2 (PGE2), a prominent inducer of inflammation. Finally, both solutions led to decreased cellular migration in the tenocytes. CONCLUSIONS: Taken together, these results suggest that prolotherapy, more so with P2G, may work by decreasing cellular function and eliciting an inflammatory response in tenocytes. Additional studies are needed to confirm the cellular signaling mechanisms involved and the resulting immediate response in vivo. CLINICAL RELEVANCE: If these preliminary in vitro findings can be confirmed in an in vivo model, they may provide clues for a possible cellular mechanism of a common alternative treatment method currently used for certain soft tissue injuries.

Prevalence and characterization of methicillin-resistant Staphylococcus aureus isolates from healthy university student athletes.

BACKGROUND: The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) has been increasing in the general population, and there is concern that close or physical contact, such as in professional and collegiate sports, may increase spread of MRSA. We sought to determine the prevalence of MRSA colonization of male and female athletes from 9 different sports at a major, Division I University during a 12-week period, and determine the USA and SCCmec type from select isolates. METHODS: Swabs for culture of MRSA were obtained from nasal, axillary, and inguinal sites from healthy, asymptomatic student athletes and support staff each week for 12 weeks. Select MRSA isolates were typed by pulsed field gel electrophoresis (PFGE), and the genes encoding for MecA, cassette chromosome recombinase (Ccr), and several toxins were determined by multiplex polymerase chain reaction (PCR). Discrepant results were clarified by multi-locus sequence typing (MLST) and spa typing. RESULTS: Thirty-five percent (78/223) of test subjects were positive for MRSA during the study period, resulting in isolation of 139 MRSA isolates. However, 47% (37/78) of MRSA-positive participants carried MRSA in axillary or inguinal sites, but not in the anterior nares. There was significant correlation between MRSA carriage and participation in wrestling (76%, 19/25; adjusted odds ratio 29.7, 95% CI 5.8-151.5) and baseball (44%, 17/39; adjusted odds ratio 4.4, 95% CI 1.1- 17.4), compared with a staff prevalence of 18.1% (4/22), but other factors were not examined. Multiplex PCR analysis indicated that of the 32 isolates examined 26 could be typed, and all of these carried the SCCmec type IV cassette. PFGE typing identified USA types 300, 400, 500, 700, and 800. However, one isolate was not a known USA type, but was identified as a novel ST951 by MLST, and as spa type t216. Of the strains typed from the same individual, there was consistency, but also variation and alternation of the SCCmec and spa types isolated from individual subjects. Various staphylococcal toxin genes were identified in 31 of the 32 isolates analyzed. CONCLUSIONS: Colonization by MRSA was greater in some student athletes than the average carriage rate for the general population, and only 53% of MRSA carriers were identified by nasal cultures. Carriage of MRSA clones on the same individual and transmission to contacts could vary over time, indicating colonization can be a dynamic process that may be difficult to control.

Can helmet design reduce the risk of concussion in football?

Of all sports, football accounts for the highest incidence of concussion in the US due to the large number of athletes participating and the nature of the sport. While there is general agreement that concussion incidence can be reduced through rule changes and teaching proper tackling technique, there remains debate as to whether helmet design may also reduce the incidence of concussion. A retrospective analysis was performed of head impact data collected from 1833 collegiate football players who were instrumented with helmet-mounted accelerometer arrays for games and practices. Data were collected between 2005 and 2010 from 8 collegiate football teams: Virginia Tech, University of North Carolina, University of Oklahoma, Dartmouth College, Brown University, University of Minnesota, Indiana University, and University of Illinois. Concussion rates were compared between players wearing Riddell VSR4 and Riddell Revolution helmets while controlling for the head impact exposure of each player. A total of 1,281,444 head impacts were recorded, from which 64 concussions were diagnosed. The relative risk of sustaining a concussion in a Revolution helmet compared with a VSR4 helmet was 46.1% (95% CI 28.1%-75.8%). When controlling for each player's exposure to head impact, a significant difference was found between concussion rates for players in VSR4 and Revolution helmets (χ(2) = 4.68, p = 0.0305). This study illustrates that differences in the ability to reduce concussion risk exist between helmet models in football. Although helmet design may never prevent all concussions from occurring in football, evidence illustrates that it can reduce the incidence of this injury.

Management of sport-related concussion: a review.

OBJECTIVE: To systematically review the evidence for rest, treatment, and rehabilitation after sport-related concussion. DATA SOURCES: Nine databases including PubMed, Cochrane Central Register of Controlled Trials, Sport Discus, and Web of Science were searched for studies that evaluated the effect of rest separately from the effects of treatment and/or rehabilitation, using words related to concussion, mild traumatic brain injury, rest, treatment outcome, and therapy. STUDY SELECTION: Inclusion criteria were published reports (either articles or abstracts) of original peer-reviewed research that investigated sport-related concussions and evaluated the effects of rest or treatment on the symptoms. One investigator performed the searches. From 749 articles evaluating rest and 1175 evaluating treatment, 2 studies met criteria for the effect of rest and 10 abstracts met criteria for treatment. Three further treatment articles were identified by the authors. DATA EXTRACTION: Details of study design, samples, type and duration of treatment, outcome measures, and main results, with effect sizes, were extracted. Confidence intervals (CI) were extracted or calculated where possible. Level of evidence was graded (1-5; best to poorest) using Downs and Black criteria to assess study quality. MAIN RESULTS: The 3 studies that investigated rest after concussion were all retrospective case series. The studies were too heterogeneous for a clear assessment of the benefits of rest. Other treatments (evaluated by case studies, retrospective case series, or other level 4 or 5 studies) were subcutaneous sumatriptan, hyperbaric oxygen therapy, amantadine, ibuprofen, and various hormonal treatments. Light exercise, or daily exercise after a 2-week baseline period, appeared to encourage return to physical activity in children and adults. The only randomized controlled trial (with blinded assessment) investigated individualized treatment of 31 participants with symptoms from sport-related concussion that persisted for 12 to 30 months. Interventions included manual spinal therapy, physiotherapy, and neuromotor and sensorimotor retraining compared with rest and graduated exercise, for up to 8 weeks. More participants in the intervention group were medically cleared to return to sport within 8 weeks of initiating treatment (risk ratio 10.3; 95% CI, 1.51-69.6). CONCLUSIONS: Studies of management of concussion were so poor that conclusions that rest was not helpful or that exercise might be beneficial are premature. Better evidence showed that individualized treatment of long-standing symptoms may allow earlier return to sport than rest and exercise alone.

Head impact exposure sustained by football players on days of diagnosed concussion.

PURPOSE: This study compares the frequency and severity of head impacts sustained by football players on days with and without diagnosed concussion and to identify the sensitivity and specificity of single-impact severity measures to diagnosed injury. METHODS: One thousand two hundred eight players from eight collegiate football teams and six high school football teams wore instrumented helmets to measure head impacts during all team sessions, of which 95 players were diagnosed with concussion. Eight players sustained two injuries and one sustained three, providing 105 injury cases. Measures of head kinematics (peak linear and rotational acceleration, Gadd severity index, head injury criteria (HIC15), and change in head velocity (Δv)) and the number of head impacts sustained by individual players were compared between days with and without diagnosed concussion. Receiver operating characteristic curves were generated to evaluate the sensitivity and specificity of each kinematic measure to diagnosed concussion using only those impacts that directly preceded diagnosis. RESULTS: Players sustained a higher frequency of impacts and impacts with more severe kinematic properties on days of diagnosed concussion than on days without diagnosed concussion. Forty-five injury cases were immediately diagnosed after head impact. For these cases, peak linear acceleration and HIC15 were most sensitive to immediately diagnosed concussion (area under the curve = 0.983). Peak rotational acceleration was less sensitive to diagnosed injury than all other kinematic measures (P = 0.01), which are derived from linear acceleration (peak linear, HIC15, Gadd severity index, and Δv). CONCLUSIONS: Players sustained more impacts and impacts of higher severity on days of diagnosed concussion than on days without diagnosed concussion. In addition, of historical measures of impact severity, those associated with peak linear acceleration are the best predictors of immediately diagnosed concussion.

Timing of concussion diagnosis is related to head impact exposure prior to injury.

PURPOSE: Concussions are commonly undiagnosed in an athletic environment because the postinjury signs and symptoms may be mild, masked by the subject, or unrecognized. This study compares measures of head impact frequency, location, and kinematic response before cases of immediate and delayed concussion diagnosis. METHODS: Football players from eight collegiate and six high school teams wore instrumented helmets during play (n = 1208), of which 95 were diagnosed with concussion (105 total cases). Acceleration data recorded by the instrumented helmets were reduced to five kinematic metrics: peak linear and rotational acceleration, Gadd severity index, head injury criterion, and change in head velocity (Δv). In addition, each impact was assigned to one of four general location regions (front, back, side, and top), and the number of impacts sustained before injury was calculated over two periods (1 and 7 days). RESULTS: All head kinematic measures associated with injury, except peak rotational acceleration (P = 0.284), were significantly higher for cases of immediate diagnosis than delayed diagnosis (P < 0.05). Players with delayed diagnosis sustained a significantly higher number of head impacts on the day of injury (32.9 ± 24.9, P < 0.001) and within 7 d of injury (69.7 ± 43.3, P = 0.006) than players with immediate diagnosis (16.5 ± 15.1 and 50.2 ± 43.6). Impacts associated with concussion occurred most frequently to the front of the head (46%) followed by the top (25%), side (16%), and back (13%) with the number of impacts by location independent of temporal diagnosis (χ(3) = 4.72, P = 0.19). CONCLUSIONS: Concussions diagnosed immediately after an impact event are associated with the highest kinematic measures, whereas those characterized by delayed diagnosis are preceded by a higher number of impacts.

Spectrum of acute clinical characteristics of diagnosed concussions in college athletes wearing instrumented helmets: clinical article.

OBJECT: Concussive head injuries have received much attention in the medical and public arenas, as concerns have been raised about the potential short- and long-term consequences of injuries sustained in sports and other activities. While many student athletes have required evaluation after concussion, the exact definition of concussion has varied among disciplines and over time. The authors used data gathered as part of a multiinstitutional longitudinal study of the biomechanics of head impacts in helmeted collegiate athletes to characterize what signs, symptoms, and clinical histories were used to designate players as having sustained concussions. METHODS: Players on 3 college football teams and 4 ice hockey teams (male and female) wore helmets instrumented with Head Impact Telemetry (HIT) technology during practices and games over 2-4 seasons of play. Preseason clinical screening batteries assessed baseline cognition and reported symptoms. If a concussion was diagnosed by the team medical staff, basic descriptive information was collected at presentation, and concussed players were reevaluated serially. The specific symptoms or findings associated with the diagnosis of acute concussion, relation to specific impact events, timing of symptom onset and diagnosis, and recorded biomechanical parameters were analyzed. RESULTS: Data were collected from 450 athletes with 486,594 recorded head impacts. Forty-eight separate concussions were diagnosed in 44 individual players. Mental clouding, headache, and dizziness were the most common presenting symptoms. Thirty-one diagnosed cases were associated with an identified impact event; in 17 cases no specific impact event was identified. Onset of symptoms was immediate in 24 players, delayed in 11, and unspecified in 13. In 8 cases the diagnosis was made immediately after a head impact, but in most cases the diagnosis was delayed (median 17 hours). One diagnosed concussion involved a 30-second loss of consciousness; all other players retained alertness. Most diagnoses were based on self-reported symptoms. The mean peak angular and rotational acceleration values for those cases associated with a specific identified impact were 86.1 ± 42.6g (range 16.5-177.9 g) and 3620 ± 2166 rad/sec( 2 ) (range 183-7589 rad/sec( 2 )), respectively. CONCLUSIONS: Approximately two-thirds of diagnosed concussions were associated with a specific contact event. Half of all players diagnosed with concussions had delayed or unclear timing of onset of symptoms. Most had no externally observed findings. Diagnosis was usually based on a range of self-reported symptoms after a variable delay. Accelerations clustered in the higher percentiles for all impact events, but encompassed a wide range. These data highlight the heterogeneity of criteria for concussion diagnosis, and in this sports context, its heavy reliance on self-reported symptoms. More specific and standardized definitions of clinical and objective correlates of a "concussion spectrum" may be needed in future research efforts, as well as in the clinical diagnostic arena.

Rotational head kinematics in football impacts: an injury risk function for concussion.

Recent research has suggested a possible link between sports-related concussions and neurodegenerative processes, highlighting the importance of developing methods to accurately quantify head impact tolerance. The use of kinematic parameters of the head to predict brain injury has been suggested because they are indicative of the inertial response of the brain. The objective of this study is to characterize the rotational kinematics of the head associated with concussive impacts using a large head acceleration dataset collected from human subjects. The helmets of 335 football players were instrumented with accelerometer arrays that measured head acceleration following head impacts sustained during play, resulting in data for 300,977 sub-concussive and 57 concussive head impacts. The average sub-concussive impact had a rotational acceleration of 1230 rad/s(2) and a rotational velocity of 5.5 rad/s, while the average concussive impact had a rotational acceleration of 5022 rad/s(2) and a rotational velocity of 22.3 rad/s. An injury risk curve was developed and a nominal injury value of 6383 rad/s(2) associated with 28.3 rad/s represents 50% risk of concussion. These data provide an increased understanding of the biomechanics associated with concussion and they provide critical insight into injury mechanisms, human tolerance to mechanical stimuli, and injury prevention techniques.

Effect of prolotherapy on cellular proliferation and collagen deposition in MC3T3-E1 and patellar tendon fibroblast populations.

Proliferative therapy, or prolotherapy, is a treatment for damaged connective tissues involving the injection of a solution (proliferant) which causes local cell death and triggers the body's wound healing cascade. Physicians vary in their use of this technique; it is employed for ligaments but has also been investigated for tissues such as cartilage. Physicians also vary in treatment regiments using different dosses of the proliferant. This study evaluates several proliferant dosages develop an optimal dosage that maximizes cell and collagen regeneration. This study also looks at cell and collagen regeneration in response to proliferant exposure outside of the healing cascade. MC3T3-E1 cells and patellar tendon fibroblasts were exposed to various amounts of the proliferant P2G and monitored over several weeks. The results showed an inverse relationship between proliferant concentration and cell viability and collagen production in MC3T3-E1 cells. Following exposure, cell populations experienced an initial decrease in cell number followed by increased proliferation. Trichrome staining over 4 weeks showed an increase in collagen production after proliferant exposure. However the cell numbers and amounts of collagen from the treated groups never surpassed those of the untreated groups, although collagen production was comparable in fibroblasts. The results of this basic study show that there is an effective proliferant dosage and point to a local response to the proliferant that increases cell proliferation and collagen production separate from the wound healing cascade. This local response may not be adequate for complete healing and assistance from the body's healing cascade may be required.

Correlating cumulative sub-concussive head impacts in football with player performance - biomed 2009.

The objective of this study was to investigate the effect of cumulative sub-concussive head impacts on football player performance. The helmets of three Virginia Tech football players were instrumented with a six accelerometer sensor capable of measuring head acceleration. Helmets were instrumented for every game during the 2006 and 2007 football seasons. Each time the head was impacted during a game, the sensor recorded the impact and wirelessly transmitted the data to a sideline computer. Furthermore, the coaching staff at Virginia Tech reviewed post-game film and evaluated each player's performance based on strict criteria. Players were awarded positive points for good plays and negative points for bad plays. Their performance scores were then normalized to a per play basis. Correlations of player performance with cumulative peak linear acceleration and cumulative head injury criterion (HIC) were evaluated. No consistent head acceleration-based measure showed a strong correlation with significance. In addition, relationship trends varied on a position basis. There are many factors other than head impacts that can affect a player's performance and more research is needed to further quantify such effects.

Biomechanical analysis of football neck collars.

OBJECTIVE: To determine the load-limiting capabilities of protective neck collars used in football through dynamic impact testing. DESIGN: A 50th-percentile male Hybrid III dummy was used in 48 dynamic impact tests comparing The Cowboy Collar, Bullock Collar, and Kerr Collar. A control and each collar were tested at two velocities (5 m/s and 7 m/s), three impact locations (front, top, and side of the helmet), and two shoulder pad positions (normal and raised). SETTING: Research laboratory. PATIENTS: None. INTERVENTIONS: None. Independent variables were the neck collars, impact velocity, and shoulder pad position. MAIN OUTCOME MEASUREMENTS: In addition to range of motion, upper and lower neck forces and moments were measured. RESULTS: With the top impact location, it was found that the Kerr Collar and Bullock Collar reduced head accelerations and force transmission through the neck. With the front impact location, all the collars reduced lower neck moment. The Kerr Collar was also capable of reducing the lower neck force and upper neck moment. With the side impact location, the Kerr Collar substantially reduced lower neck moment. CONCLUSIONS: These reductions in loads correlate with the degree to which each collar restricted the motion of the head and neck. By restricting the range of motion of the neck and redistributing load to the shoulders, neck loads can be effectively lowered.

Exercise and the immune system.

Exercise has a variable effect on the immune system. The underlying reasons for this variability are multifactorial and include infectious, neuroedocrine, and metabolic factors, with nutritional status of the athlete and the training load playing a role. Environmental factors such as living quarters, travel requirements, and the type of sport (team versus individual) also contribute to infectious risk. Regarding the direct effect of exercise on the immune system, moderate exercise seems to exert a protective effect, whereas repeated bouts of strenuous exercise can result in immune dysfunction. Understanding the relationship between exercise and infectious disease has important potential implications for public health and for clinicians caring for athletes and athletic teams.