Adam W. Kiefer

University of North Carolina at Chapel Hill | UNC · Department of Exercise and Sport Science

Athletic injuries typically occur when the stable, emergent coordination between behavioral processes breaks down due to external noise, or variability. A physiological system that operates at an optimal point on a spectrum of rigidity and flexibility may be better prepared to handle extreme external variability, and the purpose of the current expe...

Coherent collective behavior emerges from local interactions between individuals that generate group dynamics. An outstanding question is how to quantify group coordination of non-rhythmic behavior, in order to understand the nature of these dynamics at both a local and global level. We investigate this problem in the context of a small group of fo...

Lack of adequate physical activity in children is an epidemic that can result in obesity and other poor health outcomes across the lifespan. Physical activity interventions focused on motor skill competence continue to be developed, but some interventions, such as neuromuscular training (NMT), may be limited in how early they can be implemented due...

This commentary focuses on a complementary theoretical–experimental approach to the target article by Hill, Den Hartigh, Meijer, De Jonge, and Van Yperen (2018). In the target article, the authors develop an initial roadmap for identifying persistent behavioral patterns (i.e., athletic resilience) through measurements to identify specific attractor...

Biomechanical analysis has typically been confined to a laboratory setting. While attempts have been made to take laboratory testing into the field, this study was designed to assess whether augmented reality (AR) could be used to bring the field into the laboratory. This study aimed to measure knee load in volleyball players through a jump task in...

Head impacts and physical exertion are ubiquitous in American football, but the relationship between these factors is poorly understood across a competitive season or even within an individual session. Gameplay characteristics, including player position and session type, may contribute to these relationships but have not been prospectively examined...

Purpose: The present study investigated Special Operations Forces (SOF) combat Servicemember mental health at different SOF career stages in association with resilience. Methods: Fifty-eight SOF combat Service Members either entering SOF (career start; n=38) or multiple years with their SOF organization (mid-career; n=20) self-reported mild trau...

Purpose: Our aim in this study was to psychometrically test resilience assessments (Ego Resiliency Scale [ER89], Connor-Davidson Resilience Scale [CD-RISC 25], Responses to Stressful Experiences Scale [RSES short-form]) and describe resilience levels in a Special Operations Forces (SOF) combat sample. Methods: Fifty-eight SOF combat Servicemembe...

Context Neuromuscular training (NMT) facilitates the acquisition of new movement patterns that reduce ACL injury risk; however, the neural mechanisms underlying these changes are unknown. Objective Determine the relationship between brain activation and biomechanical changes following NMT with biofeedback. Study Design Controlled Laboratory Study...

Markerless motion capture systems are promising for the assessment of movement in more real world research and clinical settings. While the technology has come a long way in the last 20 years, it is important for researchers and clinicians to understand the capacities and considerations for implementing these types of systems. The current review pr...

The best predictor of future injury is previous injury and this has not changed in a quarter century despite the introduction of evidence-based medicine and associated revisions to post-injury treatment and care. Nearly nine million sports-related injuries occur annually, and the majority of these require medical intervention prior to clearance for...

Athletes commonly make decisions about the passability of closing gaps when navigating sport environments. This study examined whether increased temporal pressure to arrive at a desired location modifies these decisions. Thirty participants navigated toward a waypoint in a virtual, sport-inspired environment. To do so, they had to decide whether th...

PURPOSE: New methods are needed to identify those at risk of developing posttraumatic osteoarthritis (PTOA). We employed a novel e X plainable machine learning (X-ML) approach to predict PTOA-related symptoms and identify differentiating markers post-anterior cruciate ligament reconstruction (ACLR) via serum biomarkers and patient demographics. MET...

Background Anterior cruciate ligament (ACL) injury is secondary to a multifactorial etiology encompassing anatomical, biological, mechanical, and neurological factors. The nature of the injury being primarily due to non-contact mechanics further implicates neural control as a key injury-risk factor, though it has received considerably less study....

(1) Background: Biomechanics during landing tasks, such as the kinematics and kinetics of the knee, are altered following anterior cruciate ligament (ACL) injury and reconstruction. These variables are recommended to assess prior to clearance for return to sport, but clinicians lack access to the current gold-standard laboratory-based assessment. I...

s Biofeedback has been effectively implemented to improve the mediation and distribution of joint loads during gait, however, the inability to effectively coordinate lower limb movement by altering loading patterns may increase pathological stress and risk of injury and deleterious joint changes. This study examined the influence cueing an increase...

Background: Carotid to femoral pulse wave velocity (cfPWV), the gold-standard measure of aortic stiffness, is associated with the incidence of cardiovascular disease (CVD) events. Most cfPWV measurements depend on technical proficiency, which limit broader implementation in clinical settings. Recently, an estimated pulse wave velocity (ePWV) measur...

presents a novel technology platform for assessing quiet eye performance during esports.

Background The development of stable postural control is characterized by changes in sway variability and periods of rapid reorganization of motor system components. Research question The current study examined whether changing biomechanical and perceptual demands influences the postural control behavior during development. Method The center of p...

Military resilience research is increasing due to the growing literature associating resilience with stress adaptation. The present study aimed to investigate which physiological stress adaptation components were associated with resilience in Special Operation Forces combat service members. Special Operations Forces combat service members (n=117) s...

Heart rate variability (HRV) provides insight into the dynamic ways in which individuals adapt to changing environments, reflecting the interaction between parasympathetic and sympathetic systems. For trauma survivors, studies have suggested that survivors may experience inflexible physiological adaptation (e.g., low HRV) or over-responding (e.g.,...

In the past decades, much research has examined the negative effects of stressors on the performance of athletes. However, according to evolutionary biology, organisms may exhibit growth under stress, a phenomenon called antifragility. For both coaches and their athletes, a key question is how to design training conditions to help athletes develop...

This technical report describes the design and implementation of a novel biofeedback system to reduce biomechanical risk factors associated with anterior cruciate ligament (ACL) injuries. The system provided objective real-time biofeedback driven by biomechanical variables associated with increased ACL injury risk without the need of a present expe...

Background: Improving the assessment and training of tracheal intubation is hindered by the lack of a sufficiently validated profile of expertise. Although several studies have examined biomechanics of tracheal intubation, there are significant gaps in the literature. We used 3-dimensional motion capture to study pediatric providers performing sim...

Prospective evidence indicates that functional biomechanics and brain connectivity may predispose an athlete to an anterior cruciate ligament injury, revealing novel neural linkages for targeted neuromuscular training interventions. The purpose of this study was to determine the efficacy of a real-time biofeedback system for altering knee biomechan...

Anterior cruciate ligament (ACL) injuries are physically and emotionally debilitating for athletes, while motor and biomechanical deficits that contribute to ACL injury have been identified, limited knowledge about the relationship between the central nervous system (CNS) and biomechanical patterns of motion has impeded approaches to optimize ACL i...

Mistaken beliefs pose a barrier to science learning. For this reason, it is important to understand the circumstances in which they emerge and change. In the current paper, we apply complexity theory to shed light on the nature of mistaken beliefs. The strength of this approach lies in conceptualizing beliefs as dynamic stabilities, a well-defined...

Biomechanical analysis can effectively identify factors associated with task performance and injury risk, but often does not account for the interaction among the components that underlie task execution. Uncontrolled manifold (UCM) analyses were applied to data from 38 female, adolescent athletes performing single-leg drop landings and were used to...

Intercepting and impeding an opponent is a fairly common behavior in contact and collision sports such as soccer, football, lacrosse or basketball. In soccer, for example, the main objective of a defender is to intercept and impede an attacking opponent as he or she navigates toward the goal. These athlete vs. athlete interactions often lead to col...

Anterior cruciate ligament (ACL) injury is associated with alterations in the central nervous system and resultant sensorimotor control (Courtney et al., 2005; Grooms et al., 2017). Our prospective data indicates that altered knee-motor functional brain connectivity is associated with increased risk for ACL injury (Diekfuss et al., revisions invite...

Context: Existing anterior cruciate ligament (ACL) injury prevention programs have failed to reverse the high rate of ACL injuries in adolescent female athletes. Objective: This investigation attempts to overcome factors that limit efficacy with existing injury prevention programs through the use of a novel, objective, and real-time interactive...

Context: Laboratory-based biomechanical analyses of sport-relevant movements such as landing and cutting have classically been used to quantify kinematic and kinetic factors in the context of injury risk, which are then used to inform targeted interventions designed to improve risky movement patterns during sport. However, the noncontextual nature...

Human motion is highly variable due to the effects of interaction with the environment and the intentionality of movement. Current assistive device control systems struggle to support this variable human motion as they restrict typically uncontrolled degrees of freedom resulting in unnatural, mechanistic and highly repetitive (i.e., artificially in...

Exposure to explosive blasts places one at risk for traumatic brain injury, especially for special weapons and tactics (SWAT) and military personnel, who may be repeatedly exposed to blasts. In the current study, the effectiveness of a jugular vein compression collar to prevent alterations in resting-state electrocortical activity following a singl...

Background: Female athletes are at an increased risk of developing patellofemoral pain (PFP) relative to male athletes. The unique effects of maturation may compound that risk. Hypothesis/Purpose: The purpose was to evaluate the neuromuscular control mechanisms that are adaptive to pubertal maturation and determine their relative contribution to P...

Dyslexia, or reading difficulty (RD), is characterized by slow, inaccurate reading and accompanied by deficit in executive functions (EF) and altered functional connectivity (FC) in the related networks (i.e., cingulo‐opercular). Individuals with RD also present with altered oculomotor gaze patterns that include longer fixation times. The researche...

Objective To estimate the incidence proportion (IP) and incidence rate (IR) of ACL injury in football players. Design Systematic review with meta-analysis. Data sources PubMed, CINAHL and SPORTDiscus electronic databases were searched from inception to 20 January 2017. Eligibility criteria for selecting study Studies that reported the total numb...

Context: A limiting factor for reducing anterior cruciate ligament (ACL) injury risk is ensuring that the movement adaptions made during the prevention program transfer to sport-specific activity. Virtual reality provides a mechanism to assess transferability and neuroimaging provides a means to assay the neural processes allowing for such skill t...

The recent debunking by Brown, Sokal, and Friedman of some high-profile results applying chaos theory to positive psychology creates the opportunity to shed light on the quality work that has been done by others in this area. Too many humanists may be unaware of the large volume of legitimate work that exists in the literature apart from Fredrickso...

Approximately 1.5 million senior citizens live under nursing supervision, and most require assistance with at least one or more Activities of Daily Living (ADL). These include transferring in and out of chairs, beds and toilets, which necessitates the ability to perform sit-to-stand transitions. The sit-to-stand transition is a complex full-body ac...

Two conference abstracts from our symposium titled, "Developing Resilience in Athletes and Teams".

Objectives: To evaluate associations between pre-season oculomotor performance on visual tracking tasks and in-season head impact incidence during high school boys ice hockey. Design: Prospective observational study design. Methods: Fifteen healthy high school aged male hockey athletes (M=16.50±1.17years) performed two 30s blocks each of a pro...

Successfully meeting a shared goal usually requires co-actors to adopt complementary roles. However, in many cases, who adopts what role is not explicitly predetermined, but instead emerges as a consequence of the differences in the individual abilities and constraints imposed upon each actor. Perhaps the most basic of roles are leader and follower...

Emerging evidence indicates that repetitive head impacts, even at a sub-concussive level, may result in exacerbated or prolonged neurologic deficits in athletes. This study aimed to: 1) quantify the effect of repetitive head impacts on the alteration of neuronal activity based on fMRI of working memory after a high school football season; and 2) de...

Resistance training often is not an inherent component of current dance training for pediatric female dancers. Reasons for this include concerns surrounding injury to the immature skeleton and diminishing dancer aesthetic appearance, as well as questions related to the effectiveness of such training for increasing dancer strength and muscle enduran...

Background Historical approaches to protect the brain from outside the skull (eg, helmets and mouthpieces) have been ineffective in reducing internal injury to the brain that arises from energy absorption during sports-related collisions. We aimed to evaluate the effects of a neck collar, which applies gentle bilateral jugular vein compression, res...

Objectives: Utilize a prospective in vivo clinical trial to evaluate the potential for mild neck compression applied during head impact exposure to reduce anatomical and physiological biomarkers of brain injury. Methods: This project utilized a prospective randomized controlled trial to evaluate effects of mild jugular vein (neck) compression (c...

PART I OF THIS REVIEW DESCRIBES THE MOST IMPORTANT NEUROMUSCULAR SPORTS INJURY RISK FACTORS IN YOUTH ATHLETES: MUSCLE FATIGUE, ALTERED TIMING AND MAGNITUDE OF MUSCLE ACTIVATION, STRENGTH DEFICITS, PREDOMINANCE OF FRONTAL PLANE CONTROL STRATEGIES, NEUROMUSCULAR IMBALANCES BETWEEN LIMBS, INADEQUATE MUSCLE STIFFNESS, DEFICITS IN POSTURAL STABILITY, AL...

Background: Anterior cruciate ligament (ACL) injuries are physically and financially devastating but affect a relatively small percentage of the population. Prospective identification of risk factors for ACL injury necessitates a large sample size; therefore, study of this injury would benefit from a multicenter approach. Purpose: To determine t...

Assessment of deficits in oculomotor function may be useful to detect visuomotor impairments due to a closed head injury. Systematic analysis schemes are needed to reliably quantify oculomotor deficits associated with oculomotor impairment via brain trauma. We propose a systematic, automated analysis scheme using various eye-tracking tasks to asses...

Human performance is often characterized in terms of information processing demands via summary measures such as errors and reaction times. There is a class of tasks, however, that is more readily characterized in terms of dynamical systems theory via temporally-sensitive measures (i.e., in terms of task dynamics). These differing theoretical chara...