Papers by Adam W . Kiefer
— Dyslexia, or reading difficulty (RD), is characterized by slow, inaccurate reading and accompan... more — 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 researchers examined the relationship between fixation times and FC of neural circuits related to EF during rest in children with RD and typical readers. Nineteen children participated in a 10-min resting-state scan. FC analysis was performed with the anterior cingulate cortex (ACC), related to cognitive control, chosen as a seed. Fixation time during word reading was used as a covariate of interest. Results demonstrated that FC between the ACC and the left inferior frontal cortex pars triangularis and left inferior
Journal of Sport Rehabilitation, 2018
Exposure to explosive blasts places one at risk for traumatic brain injury, especially for specia... more 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 single-SWAT breacher training session was investigated. SWAT team personnel were randomly assigned to wear a compression collar during breacher training and resting state electroencephalography (EEG) was measured within 2 days prior to and two after breacher training. It was hypothesized that significant changes in brain dynamics—indicative of possible underlying neurodegenerative pro-cesses—would follow blast exposure for those who did not wear the collar, with ameliorated changes for the collar-wearing group. Using recurrence quantification analysis (RQA) it was found that participants who did not wear the collar displayed longer periods of laminar electrocortical behavior (as indexed by RQA's vertical max line measure) after breacher training. It is proposed that the blast wave exposure for the no-collar group may have reduced the number of pathways, via axonal disruption—for electrical transmission—resulting in the EEG signals becoming trapped in laminar states for longer periods of time. Longer laminar states have been associated with other electrocortical pathologies, such as seizure, and may be important for understanding head trauma and recovery. Keywords Recurrence quantification analysis (RQA) · Mild traumatic brain injury (mTBI) · Special weapons and tactics (SWAT) team · Electroencephalography (EEG) · Spontaneous activity
Background: Female athletes are at an increased risk of developing patellofemoral pain (PFP) rela... more 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.
Successfully meeting a shared goal usually requires co-actors to adopt complementary roles. Howev... more 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. Here, we investigated the emergence of " leader-follower " dynamics in inter-personal coordination using a joint supra-postural task paradigm (Ramenzoni et al., 2011; Athreya et al., 2014). Pairs of actors were tasked with holding two objects in alignment (each actor manually controlled one of the objects) as they faced different demands for stance (stable vs. difficult) and control (which actor controlled the larger or smaller object). Our results indicate that when actors were in identical stances, neither led the inter-personal (between actors) coordination by any systematic fashion. Alternatively, when asymmetries in postural demands were introduced, the actor with the more difficult stance led the coordination (as determined using cross-recurrence quantification analysis). Moreover, changes in individual stance difficulty resulted in similar changes in the structure of both intra-personal (individual) and inter-personal (dyadic) coordination, suggesting a scale invariance of the task dynamics. Implications for the study of interpersonal coordination are discussed.
This commentary focuses on a complementary theoretical– experimental approach to the target artic... more 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 states and/or the attractor landscape. The goal of this approach is to promote a more complete understanding of the underlying attractor dynamics that give rise to resilient behavior. We extend the thesis of the target article via the concept of metastability. Metastable dynamics are the result of the system remaining poised on the edge of criticality. We argue that metastability is key for positively adapted behavior and, ultimately, successful athletic performance. When considered in this light, positive adaptations to adversity (i.e., resilience) are the minimum outcome, with performance enhancement in the face of adversity as the true performance goal. Such growth from adversity is termed antifragility. We next couch this concept in the context of evolutionary biology to leverage biological hormesis as a stress-response model for athletic performance. This allows for biology-inspired fitness profiles that provide a quantifiable measure of stress response relative to environmental change. From there, phenotypic plasticity can be calculated to further elucidate the relation between adversity and performance responses as a quantifiable index of antifragility. Finally, this approach is discussed in the context of personalized training interventions that facilitate the emergence of metastable dynamics that underlie phenotypic plasticity, with critical training windows introduced as opportunities to increase athletic antifragility.
Coherent collective behavior emerges from local interactions between individuals that generate gr... more 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 four pedestrians walking to a goal, treating their speed, and heading as behavioral variables. To measure the local coordination between pairs of pedestrians, we employ cross-correlation to estimate coupling strength and cross-recurrence quantification (CRQ) analysis to estimate dynamic stability. When compared to reshuffled virtual control groups, the results indicate lower-dimensional behavior and a stronger, more stable coupling of walking speed in real groups. There were no differences in heading alignment observed between the real and virtual groups, due to the common goal. By modeling the local speed coupling, we can simulate coordination at the dyad and group levels. The findings demonstrate spontaneous coordination in pedestrian groups that gives rise to coherent global behavior. They also offer a methodological approach for investigating group dynamics in more complex settings.
Nonlinear dynamics, psychology, and life sciences, 2015
Athletic injuries typically occur when the stable, emergent coordination between behavioral proce... more 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 experiment was to examine whether targeted neuromuscular training resulted in changes to the rigidity and flexibility of the gluteal muscle tonus signal as measured with electromyography prior to the landing phase of a drop vertical jump task. 10 adolescent female athletes who participated in a targeted 10-week neuromuscular training program and 6 controls participated, and their tonus dynamics were examined with recurrence quantification analysis prior to training and after the 10-week program. The dependent measures, percent laminarity (%LAM) and percent determinism (%DET) were hypothesized to decrease following training, and were submitted ...
Sports health, Jan 30, 2015
Many coaches, parents, and children believe that the best way to develop elite athletes is for th... more Many coaches, parents, and children believe that the best way to develop elite athletes is for them to participate in only 1 sport from an early age and to play it year-round. However, emerging evidence to the contrary indicates that efforts to specialize in 1 sport may reduce opportunities for all children to participate in a diverse year-round sports season and can lead to lost development of lifetime sports skills. Early sports specialization may also reduce motor skill development and ongoing participation in games and sports as a lifestyle choice. The purpose of this review is to employ the current literature to provide evidence-based alternative strategies that may help to optimize opportunities for all aspiring young athletes to maximize their health, fitness, and sports performance. Nonsystematic review with critical appraisal of existing literature. Clinical review. Level 4. Based on the current evidence, parents and educators should help provide opportunities for free unst...
Clinical Biomechanics, 2015
Athletes who return to sport after anterior cruciate ligament reconstruction are at increased ris... more Athletes who return to sport after anterior cruciate ligament reconstruction are at increased risk of future ACL injury. Altered coordination of lower extremity motion may increase this risk. The purpose of this study was to prospectively determine if altered lower extremity coordination patterns exist in athletes who go on to sustain a 2nd anterior cruciate ligament injury. Sixty-one female athletes who were cleared to return to sport after anterior cruciate ligament reconstruction were included. Hip-ankle coordination was assessed prior to return to sport with a dynamic postural coordination task. Within 12months, 14 patients sustained a 2nd ACL injury. Fourteen matched subjects were selected for comparative analysis. Cross-recurrence quantification analysis characterized hip-ankle coordination patterns. A group×target speed (slow vs. fast)×leg (involved vs. uninvolved) analysis of variance was used to identify differences. A main effect of group (P=0.02) indicated that the single injury group exhibited more stable hip-ankle coordination [166.2 (18.9)] compared to the 2nd injury group [108.4 (10.1)]. A leg×group interaction was also observed (P=.04). The affected leg of the single injury group exhibited more stable coordination [M=187.1 (23.3)] compared to the affected leg of the 2nd injury group [M=110.13 (9.8)], P=0.03. Hip-ankle coordination was altered in female athletes who sustained a 2nd anterior cruciate ligament injury after return to sport. Failure to coordinate lower extremity movement in the absence of normal knee proprioception may place the knee at risk.
Physical Therapy in Sport
Objectives Compare the ability of commonly used comparison models to detect neuromuscular asymmet... more Objectives Compare the ability of commonly used comparison models to detect neuromuscular asymmetries. A secondary purpose was to determine which neuromuscular task(s) has the greatest sensitivity to identify asymmetries based on the ASI (asymmetry index) calculation. Methods Elite female youth basketball players (N = 29, age = 15.7 ± 1.34 y) performed the single leg countermovement jump in vertical, horizontal, and lateral directions, the star excursion balance test in the anterior, posteromedial, and posterolateral directions, and the sprint test with change of direction. Paired t-tests compared right and left limbs, the dominant (DL) and non-dominant (NDL) limbs, and the more/less skillful limbs. Results The coincident identification between the more skillful leg and the leg subjectively described as the DL was low for all of the tasks performed (35% - 52%). There were significant differences between the more and less skillful legs for all tasks, while performances between the ri...
Medicine & Science in Sports & Exercise, 2015
Knee abduction moment (KAM) is an injury risk factor for ACL injury that shows divergent incidenc... more Knee abduction moment (KAM) is an injury risk factor for ACL injury that shows divergent incidence between males and females during adolescence. Objectives of this study were to determine the relationship between skeletal growth and increased KAM. The hypotheses tested were that females would demonstrate peak KAM during landing at peak height velocity (PHV) and they would diverge from males at PHV. The subject pool consisted of 674 females and 218 males (1387 female; 376 male assessments) who participated in a pre-season testing session prior to their basketball or soccer seasons. They were tested longitudinally for multiple years (2±1) to capture maturation via estimates of percent (%) adult stature and biomechanical analysis during a drop vertical jump maneuver. Data were analyzed using 3D motion analysis that employed a 37 retro-reflective marker body model and inverse dynamics to calculate segment joint centers and peak KAM. Mature females, as defined as 92% adult stature or greater, displayed increased peak KAM and knee abduction angles (KAA) relative to growing (≤91% adult stature) adolescent females (p < 0.001). A significant sex by maturation (% adult stature) interaction (p < 0.001) in peak KAM was observed. Post-hoc analyses showed consistent sex differences in groups greater than or equal to, but not less than, 92% adult stature, which is approximately at peak height velocity. Hence, sex differences in peak KAM and PHV coincide. Increases in peak KAM during and following PHV appear to coincide with increased risk of ACL injury in females. KAM peaked in females at PHV. Tracking longitudinal increases in peak KAM may be useful for the identification of females at increased risk of ACL injury.This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License, where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially.
Human Walking in Virtual Environments, 2013
2013 International Conference on Virtual Rehabilitation (ICVR), 2013
ABSTRACT Fractal patterns in gait are a hallmark of a healthy and adaptive locomotor system. Thes... more ABSTRACT Fractal patterns in gait are a hallmark of a healthy and adaptive locomotor system. These fractal patterns degrade with natural aging or pathology, potentially reflecting a decline in gait functionality. This experiment replicated our previous work that indicated fractal patterns in gait could be manipulated by synchronizing to fractal visual stimuli presented in virtual reality and examined factors that may influence retention. Visual stimuli that were presented at discrete time intervals led to retained fractal patterns in gait, whereas continuously presented visual stimuli did not lead to retention.
Physical Therapy in Sport, 2015
Compare the ability of commonly used comparison models to detect neuromuscular asymmetries. A sec... more Compare the ability of commonly used comparison models to detect neuromuscular asymmetries. A secondary purpose was to determine which neuromuscular task(s) has the greatest sensitivity to identify asymmetries based on the ASI (asymmetry index) calculation. Elite female youth basketball players (N = 29, age = 15.7 ± 1.34 y) performed the single leg countermovement jump in vertical, horizontal, and lateral directions, the star excursion balance test in the anterior, posteromedial, and posterolateral directions, and the sprint test with change of direction. Paired t-tests compared right and left limbs, the dominant (DL) and non-dominant (NDL) limbs, and the more/less skillful limbs. The coincident identification between the more skillful leg and the leg subjectively described as the DL was low for all of the tasks performed (35%-52%). There were significant differences between the more and less skillful legs for all tasks, while performances between the right and left limbs and DL and NDL differed significantly for only one task each. The largest ASI detected in this study was found in the vertical single leg countermovement jump (14.11%). The skillful limb model of comparison may be more useful than other models to detect neuromuscular asymmetries.
Journal of sports science & medicine, 2015
Anterior cruciate ligament injury and the associated long-term sequelae, such as immediate reduct... more Anterior cruciate ligament injury and the associated long-term sequelae, such as immediate reductions in physical inactivity, increased adiposity and increased risk of osteoarthritis throughout adulthood, are a major health concern for adolescent athletes. Current interventions for injury prevention may have limited effectiveness, are susceptible to issues of compliance and have not achieved the widespread acceptance necessary to promote full adoption. Neuromuscular training (NMT) is a well-established training intervention introduced to affect change in modifiable biomechanical risk factors to reduce the risk of injury in these athletes. Despite moderate success, neuromuscular training is still limited by its reliance on subjective feedback and after the fact (i.e., offline) objective feedback techniques. The purpose of this commentary is to discuss technological tools that could be used to enhance and objectify targeted biofeedback interventions to complement NMT. Electromyography...
Journal of Orthopaedic and Sports Physical Therapy
Medical Engineering & Physics, 2014
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Papers by Adam W . Kiefer
Acknowledgements: This research is funded by NIH 5R01 EY010923-25. The authors would also like to thank Christina Gambacorta, Dylan Rose, Henry Harrison and Michael Fitzgerald for their help with subject recruitment and data collection.