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Medial Elbow Joint Space Decreases with Forearm Flexor Contraction – Implications for Elbow Joint Stability & Ulnar Collateral Ligament Injury

Research Team Members: Brett Pexa (PhD Student in Human Movement Science), Dr. Eric Ryan and Dr. Joseph Myers

elbow valgusWhy did you do this study?

Ulnar collateral ligament (UCL) tears, or commonly called ‘Tommy John’ is the tearing of the ligament on the medial portion, or inside, of the elbow. This injury is becoming more common in baseball players, and happening in younger and younger athletes. The ulnar collateral ligament is commonly injured during baseball participation due to the high loads and repetitive stress it experiences during throwing. Baseball pitching exerts a tremendous amount of force on the ulnar collateral ligament and the entire medial elbow. The forces during baseball pitching are up to three times higher than what the ulnar collateral ligament can withstand before tearing. The muscles in the forearm contract to help absorb this force, and previous research in cadaveric and computer models support this hypothesis. The use of diagnostic ultrasound is a quick and reliable way to image living tissue, we are able to look at the medial elbow joint in living tissue to assess how finger and forearm flexor activity can assist in protecting the medial elbow joint.

What did you do and what did you find in this study?


Ultrasound image of medial elbow. Dotted line represents the medial elbow joint space, which was the main measure in this study. (ME = medial epicondyle; TR = trochlea; ST = sublime tubercle; UCL = ulnar collateral ligament)

We measured the medial elbow under 3 different loading conditions: unloaded, loaded, and loaded-contracted. For the unloaded condition, the elbow was at rest. For the loaded condition, we added a cuff weight to the wrist to create stress on the medial elbow joint that mimics baseball pitching. Finally, for the loaded-contracted condition, we added a cuff weight and had the participants grip against a handgrip dynamometer. Our main outcome measure was medial elbow joint space, and this variable was the distance between the humerus (upper arm bone) and the ulna (lower arm bone). The ultrasound machine was placed in a specific location over the medial elbow and 4 specific structures were identified: The medial epicondyle, the ulnar collateral ligament, the trochlea of the humerus, and the sublime tubercle of the ulna (Figure below). Once all 4 of the structures were identified, an image was captured on our ultrasound machine. During the loaded-contracted condition, we made sure all 4 structures were present and the participant was maximally contracting against the grip dynamometer in their hand. The distance from the trochlea to the sublime tubercle was then measured and assessed across conditions. We found that the medial elbow joint space during the loaded condition was larger than the unloaded condition, and the joint space was smaller in the loaded-contracted condition than the loaded condition. This confirmed our hypothesis that the medial elbow joint does assist in absorbing force from the UCL to protect it and prevent it from tearing.


Elbow joint space across 3 loading conditions. The loaded-contracted condition was significantly lower than the loaded condition, indicating that the forearm muscles decrease the medial elbow joint space and subsequently the amount of stress on the medial elbow.

How do these findings impact the public?

These findings help stress how the forearm flexor muscles helps protect the ulnar collateral ligament. With UCL injuries on the rise in professional baseball and happening to younger athletes, rehabilitation and training regimens should address strength of this muscle group. Exercises that address grip strength, wrist strength, and even elbow strength should be added in preseason programs. High function of this muscle group is imperative to health of the UCL and medial elbow joint in baseball pitchers. Future research will investigate how fatigue of this muscle group affects its protective capability of the UCL.



Neural and Muscular Contributions to the Age-Related Reductions in Rapid Strength

We begin the 2017-18 academic year’s EXSS Impact Blog post with a recent publication by Gena Gerstner, who is a PhD student working under the mentorship of Dr. Eric Ryan.  The findings from this research were recently published in the July 2017 issue of Medicine and Science in Sports and Exercise.

The research team supporting this study include multiple masters and PhD students from the Exercise and Sport Science and Human Movement Science graduate programs, respectively.

Why did you do this study?

This is all you now!It is projected that by 2030 the number of older adults aged 65 and over will represent nearly 20% of the total population.  A large percentage of older adults experience functional limitations with everyday tasks and a high incidence of injuries resulting in a significant economic burden.  For example, one out of three older adults experience a fall each year, an event that often times results in accelerated deteriorations in health.

Aging is associated with reductions in maximal and rapid strength, with rapid strength production appearing to decrease to a greater magnitude. These changes are related to mobility limitations and the increased risk of falling. Multiple studies have reported age-related reductions in maximal voluntary isometric strength for the muscles of the lower limb, specifically in the plantarflexors.  The plantarflexors are important for carrying out functional activities and contribute to mobility and overall performance in older adults. Examining skeletal muscle quality and architecture may provide additional insight into factors influencing age-related changes in strength. Although age-related reductions in muscular strength have been well documented, we are aware of no previous studies that have simultaneously examined the neural and muscle specific factors contributing to the age-related reductions in rapid strength.

The purpose of this study was to determine specific mechanisms contributing to the age-related reduction in plantarflexion rapid strength at early (0–50 ms) and late (100–200 ms) time intervals of muscle contraction.

What did you do and what did you find in this study?

Thirty-two young and 20 older recreationally active men performed rapid plantarflexion isometric muscle actions to examine absolute and normalized rapid strength and muscle activation using electromyography at early and late time intervals. Ultrasonography was used to examine medial gastrocnemius muscle size, echo intensity for muscle quality, and muscle architecture [fascicle length and pennation angle].

We found that the older men were weaker, and had lower rapid strength in the later interval of muscle contraction in both absolute and normalized (adjusted to peak strength) terms when compared to the young men.


Absolute torque at 50, 100, and 200 ms for the young and older men during rapid plantarflexion isometric contractions. *P<0.05, significant difference between the young and older men. Data are mean (SD).

The older men also had higher EI (poorer muscle quality), smaller pennation angles, and lower muscle activation in the later interval of contraction. However, we did not observe differences in rapid strength or muscle activation for the early interval of muscle contraction, or in muscle size, or fascicle length between groups. Interestingly, lower late interval rapid strength values were related to poorer muscle quality, smaller pennation angles, and lower muscle activation values; however late interval rapid strength values were no longer related to pennation angle after taking peak torque into account.

How do these findings impact the public?

side-profile-of-calfOur findings indicated that the lack of differences in the early interval of contraction may suggest that older men initially have similar muscle activation to younger men, but are unable to sustain the same rates of muscle activation during the late intervals of contraction. Furthermore, additional factors such as poor muscle quality and smaller pennation angles appear to also play a role in the age-associated changes of rapid strength. These findings add to our understanding of the importance of the various factors that influence the age-related reductions in rapid strength, which has been shown to significantly influence function and performance in older adults.

Metabolic Characterization of Overweight and Obese Adults

Research Team Members: Katie R. Hirsch, Abbie E. Smith-Ryan, Malia N.M. Blue, Meredith G. Mock, Eric T. Trexler, Kristin S. Ondrak

Why did you do this study?

Metabolic syndrome is a chronic disease characterized by the presence of multiple risk factors, including insulin resistance and poor cholesterol, which are associated with an increased risk for the development of cardiovascular disease, type-2 diabetes, and other metabolic diseases. The presence of excess body fat is highly associated with the development of metabolic syndrome, however, previous studies have identified a significant portion of overweight and obese individuals who have no risk factors and are considered metabolically healthy despite having a high percentage of body fat.


Body composition scan using dual-energy x-ray absorptiometry

Despite an apparently normal metabolic status, excess body fat and difficulty achieving a healthy body composition may indicate the presence of underlying metabolic dysfunction overlooked by standard clinical tools. Currently, body mass index (BMI), cholesterol, and blood lipid levels serve as the primary screening tools for health risk.  However, the diagnostic value of these measures is limited by the inability to evaluate body composition (the differentiation between fat mass and lean mass) and fat distribution.  Regional distribution of body fat describes where an individual tends to store body fat.  Greater fat in the abdominal region and around the organs, known as visceral fat, is highly associated with insulin resistance in both overweight and normal weight individuals.  Visceral fat is also more highly associated with metabolic dysfunction than total body fat.  Lean mass (which includes muscle and organs) also has important associations with metabolic health.  Low relative lean mass is associated with insulin resistance, decreased metabolic rate, impaired fat metabolism, and poor functionality in activities of daily living, all of which are associated with weight gain and metabolic dysfunction.  Finally, hormonal imbalances, specifically related to insulin, leptin, estradiol, and cortisol, can lead to an unfavorable distribution of fat in the abdominal region, impair fat and glucose metabolism, and may also negatively impact energy expenditure.


Although traditional metabolic risk factors are highly associated with health risk, a more comprehensive evaluation of metabolic health may be a more appropriate and sensitive approach to evaluating metabolic status, regardless of body weight.   Evaluation of non-traditional metabolic factors, such as visceral fat, lean mass, resting metabolic rate, substrate utilization, and hormonal status, could provide valuable insight into aspects of metabolic health that may otherwise be overlooked. This in turn could improve the detection, prevention, and treatment of metabolic health issues. Therefore, the purpose of this study was to characterize metabolic health in overweight and obese adults using traditional and non-traditional metabolic variables.

What did you do and what did you find in this study?


Resting metabolic rate test using a ventilated canopy and indirect calorimetry.

Body composition, visceral fat, resting metabolic rate, resting substrate utilization (use of carbs or fat for energy at rest), fasting cholesterol, blood lipids, glucose, and the hormones insulin, leptin, estradiol, and cortisol were measured in forty-nine overweight and obese men and women.  When evaluating traditional metabolic risk factors (blood glucose, triglycerides, and HDL cholesterol) 86.7% of the individuals had no more than one risk factor and 92% had no more than two risk factors, meaning this group could be considered metabolically healthy by traditional standards.  When evaluating visceral fat, in addition to traditional risk factors, the proportion of individuals considered to have metabolic dysfunction increased to 28.9%.  The occurrence rate increased to 80% when all metabolic risk factors were considered, classifying a majority of the group as metabolically dysfunctional. For men, the most common risk factors were high LDL cholesterol (82.6%), low metabolic rate (60.9%), low HDL cholesterol (47.8%), and high total cholesterol (43.5%).  For women, low HDL cholesterol (50.0%) and high LDL cholesterol (50.0%) were the most common risk factors, followed by low metabolic rate (30.8%), high visceral fat (19.2%), and greater reliance on carbohydrates for energy at rest (19.2%).

How do these findings impact the public?



Ultrasound image of visceral fat thickness. Measurement was taken from the abdominal muscles to the aorta.

Results of this study show the importance of evaluating metabolic health beyond traditional diagnostic criteria. Evaluating components of body composition and metabolic function, such as visceral fat, lean mass, resting metabolic rate, and substrate utilization, in addition to hormonal and metabolic profiles, can give significant insights into metabolic status regardless of body weight and BMI status.  Knowledge of these factors could significantly improve lifestyle treatment approaches. Further, men and women exhibited different frequencies of risk factors, likely attributable to differences in fat distribution and hormonal status, reinforcing the importance of sex-specific evaluations. A unique aspect of this study was the use of ultrasound to measure visceral fat. Portable equipment, such as ultrasound, can improve the accuracy and evaluation of abdominal obesity-related risk, which is currently not evaluated in a clinical setting.  Additionally, connecting individuals with metabolic specialists who have access to more extensive assessment tools could lead to more effective intervention approaches.




Attenuation of Resting but Not Load-Mediated Protein Synthesis in Prostate Cancer Patients on Androgen Deprivation

Research Team Members: Erik Hanson, Andre Nelson, Daniel West, John Violet, Lannie O’Keefe, Stuart Phillips, Alan Hayes

These findings were recently published in Journal of Clinical Endocrinology and Metabolism, March 2017, 102(3): 1076-1083

Why did you do this study?

Prostate cancer is the most common non-dermatological form of cancer in US men (diagnosed in 1 in 7 men) and is the second leading cause of cancer-related death. In 2017 alone, it is estimated that 161,360 new cases of prostate cancer will be diagnosed with 26,730 deaths.

Androgen deprivation therapy (ADT) is a type of prostate cancer treatment that slows tumor growth but has several side effects, including the loss of muscle mass, strength, and physical function. All of these changes have a negative impact upon health-related quality of life. Exercise interventions have become more common to help reduce treatment-related side effects. Specifically, resistance training during ADT improves muscle strength, reduces fatigue, and enhances physical function. However, it is unclear as to whether or not significant gains in muscle mass are possible during ADT.

Looking at the recent literature, some studies have reported that no muscle hypertrophy occurs with resistance training during ADT. Others have shown that muscle gains are possible but the response is attenuated. Recently, our lab has demonstrated that high intensity resistance training induces gains in lean mass that are comparable to healthy, age-matched controls.

protein-powder-nutritional-supplementProtein supplementation is often used with resistance training to enhance the response. However, very few studies have combined these two muscle building strategies and used them during ADT as a means of preserving lean muscle mass and function and no studies have looked at the muscle protein synthesis response. Determining the acute response initially will provide important information for desiging future resistance exercise and dietary interventions, as it is repeated transient increases in muscle protein synthesis that may lead to increases in lean tissue over time.

Therefore, the purpose of this study was to determine the acute muscle protein response to whey protein supplementation with and without resistance exercise in men being treated for prostate cancer with ADT and healthy controls. We hypothesized that baseline protein synthesis would be suppressed with ADT but that diet- and exercise-induced increased in protein synthesis would be normal.

What did you do and what did you find in this study?

We measured muscle protein synthesis (MPS) from biopsy samples obtained from the thigh muscles at rest and 4h after participants consumed 40g of whey protein (Fed) and 40g of whey protein plus 3 sets of knee extension resistance exercise (Ex-Fed).

Muscle protein synthesis was lower during ADT at rest and while feeding (Fed) increased the rate of synthesis, the response was attenuated. However, the change in muscle protein synthesis from rest to Ex-Fed was similar to healthy controls.


* Significantly different from CON at the specific time point, P<0.01
† Significantly different from baseline value, P<0.001
‡ Significantly different from baseline and FED condition, P<0.001

How do these findings impact the public?

Muscle protein synthesis at rest is lower with ADT, which is likely why there is the loss of muscle mass in these patients. However, muscle protein synthesis increases following large doses of whey protein, although it is not as effective during ADT. But the combination of whey protein and vigorous resistance exercise may be an effective means to offset the side effects of prostate cancer treatment.

Future studies are needed to explore why protein synthesis is activated less with feedling alone, as this ‘anabolic resistance’ may have significant consequences for men on ADT. We are currently developing projects that will help to clarify these findings in the future.

Education Through Athletics – Possibilities for Intercollegiate Athletics Reform

This week’s EXSS Impact Post is developed by Professor Erianne Weight.

In a previous EXSS Impact blog post exploring reform approaches in intercollegiate athleticsweight1, we discussed the tension between athletics and the academy.  Many university stakeholders fully support athletics within the academy and view it as an educational endeavor complimentary to the university mission with added brand-building, relationship-forging, and student-drawing benefits.  On the other end of the spectrum, stakeholders have condemned the academy for allowing athlete exploitation, excessive commercialism, and unprincipled behavior that undermines the educational mission of the university.  Regardless of perspective, athletics has traditionally been supported within the university’s organizational structure as an extra-curricular activity peripherally related to the university mission. Perhaps it is time for this to change.

weight2Why did you do this study?

Throughout our research exploring the educational impact of intercollegiate athletics on the athlete participants, several studies have highlighted the positive impact intercollegiate athletics can have on occupational,[1] psychological,[2] physiological,[3] and long-term quality of life measures.[4] These findings contribute to a growing body of literature which supports embedding the applied study of athletics within the academy similar in form to music, dance, or theatre. Prior to exploring the interest or form of what an athletics-centric curriculum may entail, we gathered baseline data to examine current practices within NCAA Division I, II, and III institutions. The full results of this research are published in the Journal of Intercollegiate Sport.[5]

weight3What did you do and what did you find in this study?

Through survey of a stratified random sample of National Collegiate Athletics Association (NCAA) Division I, II, and III athletic academic advisors (n = 240), this exploratory study examined the prevalence, design, and institutional perceptions of classes offered exclusively for varsity athletes. Results indicate 33.9% of sample schools award credit for athletic participation (e.g. physical education), and 20.1% offer academic courses specifically for athletes (e.g. first semester “onboarding” courses, leadership courses, etc.).  Academic opportunities for athletes were greater in western, public, Division I institutions, with one of the most startling differences between western schools, wherein 65.3% award credit for participation, and southeastern schools, wherein 17.3% award credit for participation.

weight4How do these findings impact the public?

This study provides some evidence of structural and philosophical academic integration of athletics within the academy. These established courses counter the historically taboo nature of the education through athletics proposal.  This study also documents tremendous inequity in inter-institutional practices of facilitating academic courses for athletes.  This variance in institutional procedure can result in significant fluctuations in athlete time, competitive advantages, and opportunities for education through athletics.  Given the extensive policies the NCAA regulates to facilitate an even playing field, this dramatic divide in inter-institutional procedure presents an interesting challenge that warrants further inquiry.

weight5As the political-educational arena grapples with unprecedented scrutiny, faculties and administrators should focus their efforts on facilitating rich holistic educational opportunities and experiences. The athlete-educational experience that has been a concern since them inception of intercollegiate athletics has led many faculties to fear athlete-centric programming for reasons including an exacerbation of social isolation and/or the perceived nonacademic collective hubris and entitlement of athletes. Although there is a degree of isolation within every academic discipline with major-only courses and experiences that do not require justification, the unique nature of the athlete experience may necessitate additional consideration due to the social, commercial, and administrative pressures that could lead to academic clustering and athlete-segregation.

For this reason, a practical approach to athlete-centric educational experiences should be conscious of these realities and address concerns judiciously through credit limitations, cross-disciplinary faculty involvement, and the inclusion of non-athlete elite performers in the programming. Three approaches Weight & Huml (2016) recommend and expand upon in the Journal of Intercollegiate Sport article include:

  1. A 3-credit “onboarding” course specific for athletes to institutionalize many of the first-semester mandatory NCAA trainings in addition to life-skills initiatives
  2. Credit for participation in intercollegiate athletics with an infusion of faculty-led education grounded in experiential learning theory practices (e.g. a faculty-led strength training course with elements of exercise physiology and nutritional principles coupled with the strength training they engage in as a team).
  3. A minor in “elite performance” which could include varsity athletes, club sport athletes, musicians, orators, dancers, thespians, etc. Courses might include performance psychology, leadership and group dynamics, performance nutrition, media training, entrepreneurship, etc. in addition to two 3-credit “field experience opportunities that allow the students to reflect upon their elite experiences, apply literature to their (on-the-court) study, meet with a faculty and field supervisor (coach) to set and track learning goals, and infuse institutionalized scholarship and growth structures into their elite pursuits of excellence.

[1] Chalfin, P., Weight, E.A., Osborne, B., Johnson, S. (2015). The value of intercollegiate athletics participation from the perspective of employers who target athletes. Journal of Issues in Intercollegiate Athletics. 8, 1-27.

[2] Weight, E.A., Navarro, K., Huffman, L., Smith-Ryan, A. (2014). Quantifying the psychological benefits of intercollegiate athletics participation: Implications for higher education policy and practice. Journal of Issues in Intercollegiate Athletics. 7, 390-409.

[3] Weight, E.A., Navarro, K., Smith-Ryan, A., Huffman, L. (2016). Holistic Education through Athletics: Health literacy of intercollegiate athletes and traditional students. The Journal of Higher Education Athletics and Innovation. 1, 38-60.

[4] Weight, E.A., Bonfiglio, A.*, DeFreese, J.D., Kerr, Z., Osborne, B. In Review. Occupational Measures of Former NCAA Athletes and Traditional Students. The Journal of Intercollegiate Sport.

[5] Weight, E.A., Huml, M.* (2016). Facilitating education through athletics: An examination of academic courses designed for NCAA athletes. Journal of Intercollegiate Sport, 9(2), 154-174.

Fat-Free Mass Index in NCAA Division I and II Collegiate American Football Players

Research Team Members: Eric Trexler, Abbie Smith-Ryan, Malia Blue, Richard Schumacher, Jerry Mayhew, J. Bryan Mann, Pat Ivey, Katie Hirsch, Meredith Mock

Links to Study:

uncfbWhy did you do this study?

It is well known that an athlete’s body composition can influence their athletic success. Previous studies have shown that fat-free mass (FFM) is related to strength, power, speed, and sport performance. However, fat-free mass may not be the most valid indicator of an athlete’s sport-related capabilities; most sports require locomotion or propulsion of the athlete’s body, which is affected by both the capacity to produce force and the overall size of the body. In addition, taller people naturally have more FFM due to their height. Fat-free mass index (FFMI) scales an individual’s FFM to their height, which removes the bias of height and may be a more valid characterization of muscularity that translates more directly to sport-related tasks.

In sports such as American football, training and nutrition practices are often geared towards increasing FFM. Researchers have previously suggested that 25 kg∙m-2 is the natural FFMI limit for resistance-trained males; this is important because identifying upper limits would enhance the ability to set realistic body composition goals for athletes. However, the research identifying this limit used a sample of lean individuals who were not competitive athletes. As such, it is possible that this “limit” has been underestimated. Collegiate football players are an ideal population for evaluating high FFMI values, based on the sport’s emphasis on strength, power, and body size. Furthermore, evaluating a large sample of collegiate football players allowed us to determine if FFMI differs between position groups or levels of competition. This information would be tremendously valuable to nutrition and strength & conditioning professionals who assist football players in identifying and reaching body composition goals that are suitable for their playing position.

GEHC-iDXA-for-Bone-Health_OverviewWhat did you do and what did you find in this study?

For this study, we performed dual-energy x-ray absorptiometry (DEXA) scans on three separate college football teams, including two division I teams and one division II team. We compared FFMI values between position groups and levels of play, and results indicated that FFMI was significantly higher in division I players compared to division II. Further, FFMI was drastically different between position groups, with the highest values observed in offensive and defensive linemen, and the lowest values observed in offensive and defensive backs. We provided FFMI ranges for each specific position based on the data from division I athletes, which should assist players in setting position-specific goals for body composition. Most importantly, we found that 62 athletes had FFMI values above 25 kg∙m-2 (26.4% of the sample). This percentage was even higher when specifically looking at division I athletes (31.3%). The 97.5th percentile was 28.1 kg∙m-2, and the highest observed value was 31.7 kg∙m-2.

How do these findings impact the public?

Our results indicate that drug-tested, resistance-trained males can achieve FFMI values well beyond 25 kg∙m-2. We also determined that FFMI effectively discriminates between playing levels and playing positions. Coaches and athletes can use this information to set more realistic body composition goals, and college and professional football teams may use this position-specific data to assist with their recruiting and personnel decisions.

Evaluating the “Threshold theory”: Can head impact indicators help?

Research Team Members: Jason Mihalik, PhD, ATC, Robert Lynall, PhD, ATC (HMSC PhD Student now at University of Georgia), Erin Wasserman, PhD (EXSS Gfeller Center Postdoc now at Datalys Center), Kevin Guskiewicz, PhD, ATC, Steve Marshall, PhD

Why did you do this study?

concussion-blog-featured-imageAs many as 1.6 – 3.8 million sport and recreation traumatic brain injuries (TBI) occur in the US on an annual basis. The direct and indirect costs for managing all forms of TBI exceed %56B annually. Proper detection and management of sport related concussion continues to challenge clinicians working with athletes. A number of options are available to clinicians, but mostly rely on subjective and clinical expertise. One example is the Sport Concussion Assessment Tool Version 3 (includes symptom inventories, mental status tests, and balance assessments). These acute injury screening tools are typically administered only after the clinician has sufficient evidence to suspect a concussion diagnosis. In the absence of obvious concussion signs (e.g., loss of consciousness, staggered gait, etc.), clinicians must rely solely on subjective symptoms reported by athletes. Research has documented a large portion of athletes either underreport concussion symptoms or fail to report them entirely. Thus, the medical field has looked to emerging technologies to fill this shortfall and provide heightened objectivity to the dilemma.

Technological advances have resulted in the emergence of commercially available head impact measurement devices. These devices typically serve two broad functions: 1) collect data for research-based inquiry, and 2) signal to clinical staff the occurrence of high-level impacts in near real-time during sports participation. Head impact indicators—the latter function—seek to identify athletes who have sustained pronounced head impacts so that they can be evaluated for symptomology. These products are usually worn directly on the head or affixed to a helmet, and are designed to indicate to medical personnel, players, coaches, and parents when a head impact magnitude has exceeded a pre-programmed threshold. There are no fewer than 20 different products that have permeated the marketplace in the last decade, and many use differing thresholds (some unknown to the user!).


Head impact indicators are believed to identify athletes who otherwise would elect not to report symptoms to the clinical staff. If an ‘alert’ is triggered, some of the manufacturers recommend the athlete be removed from activity and evaluated for a head injury, regardless of whether or not the athlete is exhibiting signs or reporting symptoms consistent with concussion. Our own work here at UNC suggests that a single impact injury threshold is not obvious, which question the clinical utility of these head impact indicators.

What did you do and what did you find in this study?

The purpose of this study was to investigate the clinical utility of head impact magnitude thresholds employed by various commercially available head impact indicators to positively predict concussion among American football players. We hypothesized these tools, by themselves, would be limited in helping clinicians make informed decisions regarding head injury during athletics due to the inherent variability of biomechanical values observed in concussed individual and the low incidence of concussion even at very high measured impact levels.

Over the last 10 years, we have collected hundreds of thousands of head impact biomechanics from hundreds of football players. A multidisciplinary clinical team independently made concussion diagnoses during this same time period (n=24). We dichotomized each impact using diagnosis (‘yes’ they were injured, ‘no’ they were not), and across a range of plausible impact indicator thresholds (10g increments beginning with a resultant linear head acceleration of 50g and ending with 120g). We then performed computations to determine the sensitivity, specificity, negative predictive value and positive predictive value, which are common measures used to assess the clinical utility of any diagnostic or screening assessment.


How do these findings impact the public?

In particular, any head impact indicator must demonstrate that it has predictive value; that is, it is an efficient use of time and resources and that it yields a practical frequency of identified concussions to be clinically useful. All thresholds we studied had low positive predictive value (<0.4%). Even when conservatively adjusting the frequency of diagnosed concussions by a factor of 5 to account for unreported/undiagnosed injuries, the positive predictive value of head impact indicators at any threshold was no greater than 1.94%. Simply put, fewer than 4 out of 1000 trigger alerts would result in a diagnosed concussion. Or, looking at it from the vantage of clinician time resources, 996 sideline evaluations would be done in vain and at the possible detriment of distracting the sideline medical personnel from observing and intervening in other emergencies and injuries during that time.