Running Habits and Injury Frequency Following COVID-19 Restrictions in Adolescent Long-Distance Runners.

PURPOSE: A decline in youth running was observed at the start of the COVID-19 pandemic. We investigated whether the resumption of organized running after social distancing restrictions changed running habits or injury frequency in adolescent runners. METHODS: Adolescents (age = 16.1 [2.1] y) who participated in long-distance running activities completed an online survey in the Spring and Fall of 2020. Participants self-reported average weekly running habits and whether they sustained an injury during the Fall 2020 season. Poisson regression models and 1-way analysis of variance compared running habits while Fisher exact test compared differences in frequencies of injuries during Fall 2020 among season statuses (full, delayed, and canceled). RESULTS: All runners, regardless of season status, increased weekly distance during Fall 2020. Only runners with a full Fall 2020 season ran more times per week and more high-intensity runs per week compared with their Spring 2020 running habits. There were no differences in running volume or running-related injury frequency among Fall 2020 season statuses. CONCLUSIONS: There were no significant differences in running-related injury (RRI) frequency among runners, regardless of season status, following the resumption of cross-country. Health care providers may need to prepare for runners to increase running volume and intensity following the resumption of organized team activities.

Cadence in youth long-distance runners is predicted by leg length and running speed.

BACKGROUND: Lower cadence has been previously associated with injury in long-distance runners. Variations in cadence may be related to experience, speed, and anthropometric variables. It is unknown what factors, if any, predict cadence in healthy youth long-distance runners. RESEARCH QUESTION: Are demographic, anthropometric and/or biomechanical variables able to predict cadence in healthy youth long-distance runners. METHODS: A cohort of 138 uninjured youth long-distance runners (M = 62, F = 76; Mean ± SD; age = 13.7 ± 2.7; mass = 47.9 ± 13.6 kg; height = 157.9 ± 14.5 cm; running volume = 19.2 ± 20.6 km/wk; running experience: males = 3.5 ± 2.1 yrs, females = 3.3 ± 2.0 yrs) were recruited for the study. Multiple linear regression (MLR) models were developed for total sample and for each sex independently that only included variables that were significantly correlated to self-selected cadence. A variance inflation factor (VIF) assessed multicollinearity of variables. If VIF≥ 5, variable(s) were removed and the MLR analysis was conducted again. RESULTS: For all models, VIF was > 5 between speed and normalized stride length, therefore we removed normalized stride length from all models. Only leg length and speed were significantly correlated (p < .001) with cadence in the regression models for total sample (R2 = 51.9 %) and females (R2 = 48.2 %). The regression model for all participants was Cadence = -1.251 *Leg Length + 3.665 *Speed + 254.858. The regression model for females was Cadence = -1.190 *Leg Length + 3.705 *Speed + 249.688. For males, leg length, cadence, and running experience were significantly predictive (p < .001) of cadence in the model (R2 = 54.7 %). The regression model for males was Cadence = -1.268 *Leg Length + 3.471 *Speed - 1.087 *Running Experience + 261.378. SIGNIFICANCE: Approximately 50 % of the variance in cadence was explained by the individual's leg length and running speed. Shorter leg lengths and faster running speeds were associated with higher cadence. For males, fewer years of running experience was associated with a higher cadence.

Brachial plexus birth injury and cerebral palsy lead to a common contracture phenotype characterized by reduced functional muscle length and strength.

Introduction: Brachial plexus birth injury (BPBI) and cerebral palsy (CP) both cause disabling contractures for which no curative treatments exist, largely because contracture pathophysiology is incompletely understood. The distinct neurologic nature of BPBI and CP suggest different potential contracture etiologies, although imbalanced muscle strength and insufficient muscle length have been variably implicated. The current study directly compares the muscle phenotype of elbow flexion contractures in human subjects with BPBI and CP to test the hypothesis that both conditions cause contractures characterized by a deficit in muscle length rather than an excess in muscle strength. Methods: Subjects over 6 years of age with unilateral BPBI or hemiplegic CP, and with elbow flexion contractures greater than 10 degrees on the affected side, underwent bilateral elbow flexion isokinetic strength testing to identify peak torque and impulse, or area under the torque-angle curve. Subjects then underwent needle microendoscopic sarcomere length measurement of bilateral biceps brachii muscles at symmetric joint angles. Results: In five subjects with unilateral BPBI and five with hemiplegic CP, peak torque and impulse were significantly lower on the affected versus unaffected sides, with no differences between BPBI and CP subjects in the percent reduction of either strength measurement. In both BPBI and CP, the percent reduction of impulse was significantly greater than that of peak torque, consistent with functionally shorter muscles. Similarly, in both conditions, affected muscles had significantly longer sarcomeres than unaffected muscles at symmetric joint angles, indicating fewer sarcomeres in series, with no differences between BPBI and CP subjects in relative sarcomere overstretch. Discussion: The current study reveals a common phenotype of muscle contracture in BPBI and CP, with contractures in both conditions characterized by a similar deficit in muscle length rather than an excess in muscle strength. These findings support contracture treatments that lengthen rather than weaken affected muscles. Moreover, the discovery of a common contracture phenotype between CP and BPBI challenges the presumed dichotomy between upper and lower motor neuron lesions in contracture pathogenesis, instead revealing the broader concept of "myobrevopathy", or disorder of short muscle, warranting increased investigation into the poorly understood mechanisms regulating muscle length.

Interleukin-6 signaling mediates cartilage degradation and pain in posttraumatic osteoarthritis in a sex-specific manner.

Osteoarthritis (OA) and posttraumatic OA (PTOA) are caused by an imbalance in catabolic and anabolic processes in articular cartilage and proinflammatory changes throughout the joint, leading to joint degeneration and pain. We examined whether interleukin-6 (IL-6) signaling contributed to cartilage degradation and pain in PTOA. Genetic ablation of Il6 in male mice decreased PTOA-associated cartilage catabolism, innervation of the knee joint, and nociceptive signaling without improving PTOA-associated subchondral bone sclerosis or chondrocyte apoptosis. These effects were not observed in female Il6-/- mice. Compared with wild-type mice, the activation of the IL-6 downstream mediators STAT3 and ERK was reduced in the knees and dorsal root ganglia (DRG) of male Il6-/- mice after knee injury. Janus kinases (JAKs) were critical for STAT and ERK signaling in cartilage catabolism and DRG pain signaling in tissue explants. Whereas STAT3 signaling was important for cartilage catabolism, ERK signaling mediated neurite outgrowth and the activation of nociceptive neurons. These data demonstrate that IL-6 mediates both cartilage degradation and pain associated with PTOA in a sex-specific manner and identify tissue-specific contributions of downstream effectors of IL-6 signaling, which are potential therapeutic targets for disease-modifying OA drugs.

Identification of distinct non-myogenic skeletal-muscle-resident mesenchymal cell populations.

Mesenchymal progenitors of the lateral plate mesoderm give rise to various cell fates within limbs, including a heterogeneous group of muscle-resident mesenchymal cells. Often described as fibro-adipogenic progenitors, these cells are key players in muscle development, disease, and regeneration. To further define this cell population(s), we perform lineage/reporter analysis, flow cytometry, single-cell RNA sequencing, immunofluorescent staining, and differentiation assays on normal and injured murine muscles. Here we identify six distinct Pdgfra+ non-myogenic muscle-resident mesenchymal cell populations that fit within a bipartite differentiation trajectory from a common progenitor. One branch of the trajectory gives rise to two populations of immune-responsive mesenchymal cells with strong adipogenic potential and the capability to respond to acute and chronic muscle injury, whereas the alternative branch contains two cell populations with limited adipogenic capacity and inherent mineralizing capabilities; one of the populations displays a unique neuromuscular junction association and an ability to respond to nerve injury.

Hypertrophic chondrocytes serve as a reservoir for marrow-associated skeletal stem and progenitor cells, osteoblasts, and adipocytes during skeletal development.

Hypertrophic chondrocytes give rise to osteoblasts during skeletal development; however, the process by which these non-mitotic cells make this transition is not well understood. Prior studies have also suggested that skeletal stem and progenitor cells (SSPCs) localize to the surrounding periosteum and serve as a major source of marrow-associated SSPCs, osteoblasts, osteocytes, and adipocytes during skeletal development. To further understand the cell transition process by which hypertrophic chondrocytes contribute to osteoblasts or other marrow associated cells, we utilized inducible and constitutive hypertrophic chondrocyte lineage tracing and reporter mouse models (Col10a1CreERT2; Rosa26fs-tdTomato and Col10a1Cre; Rosa26fs-tdTomato) in combination with a PDGFRaH2B-GFP transgenic line, single-cell RNA-sequencing, bulk RNA-sequencing, immunofluorescence staining, and cell transplantation assays. Our data demonstrate that hypertrophic chondrocytes undergo a process of dedifferentiation to generate marrow-associated SSPCs that serve as a primary source of osteoblasts during skeletal development. These hypertrophic chondrocyte-derived SSPCs commit to a CXCL12-abundant reticular (CAR) cell phenotype during skeletal development and demonstrate unique abilities to recruit vasculature and promote bone marrow establishment, while also contributing to the adipogenic lineage.

Influence of hamstring flexibility on running kinematics in adolescent long-distance runners.

BACKGROUND: Studies have found no or minimal differences in running kinematics between flexible and inflexible adult runners. The interaction between hamstring flexibility and running kinematics has not been reported in adolescent long-distance runners. RESEARCH QUESTION: Does hamstring flexibility influence running kinematics in adolescent long-distance runners? METHODS: Adolescent long-distance runners (n = 140, ages 9-19) were enrolled in our cross-sectional study. Hamstring flexibility was assessed with the forward bending Beighton task. Runners were categorized if they tested positive or negative on the forward bending task. Participants ran at a comfortable self-selected speed on a treadmill. Runners who tested positive on the forward bending task (n = 17) were matched with runners who tested negative on the task (n = 17) according to sex, physical maturation, and running speed. Statistical parametric mapping compared trunk, pelvis, hip, and knee kinematic waveforms throughout the gait cycle and independent sample t tests compared temporal-spatial parameters between the groups. RESULTS: Runners who tested positive on the forward bending task demonstrated significantly greater anterior pelvic tilt during stance (average difference = 4.8° ± 0.4°, p < .001) and swing (average difference = 4.3° ± 0.2°, p < .01) compared to runners who tested negative on the forward bending task. No significant differences were found between groups for the remaining kinematic waveforms or for any temporal-spatial parameters (p > .05). SIGNIFICANCE: This is the first study to report the interaction between hamstring flexibility and running kinematics in adolescent long-distance runners. The greater anterior pelvic tilt demonstrated by runners with greater hamstring flexibility may place more eccentric demands on the hamstring musculature. However, as there were no other differences in joint kinematics or temporal-spatial parameters between groups, greater hamstring flexibility does not appear to have a significant interaction with running kinematics when running at sub-maximal speeds. Our results suggest hamstring flexibility does not predispose adolescent long-distance runners to sub-optimal segment positions associated with running-related injuries.

Multi-segment foot kinematics during gait following ankle arthroplasty.

Ankle arthritis is a debilitating disease marked by pain and limited function. Total ankle arthroplasty improves pain while preserving motion and offers an alternative to the traditional treatment of ankle fusion. Gait analysis and functional outcomes tools can provide an objective balanced analysis of ankle replacement for the treatment of ankle arthritis. Twenty-nine patients with end-stage ankle arthritis were evaluated before and after ankle arthroplasty. Multi-segment foot and ankle kinematics were assessed annually following surgery (average 3.5 years, range 1-6 years) using the Milwaukee Foot Model and a Vicon video motion analysis system. Functional outcomes (American Orthopedic Foot and Ankle Society [AOFAS] ankle/hindfoot scale, short form 36 [SF-36] questionnaire) and temporal-spatial parameters were also assessed. Kinematic results were compared to findings from a previously collected group of healthy ambulators. AOFAS and SF-36 mean scores improved postoperatively. Walking speed and stride length increased after surgery. There were significant improvements in tibial sagittal range of motion in terminal stance and hindfoot sagittal range of motion in preswing. Decreased external rotation of the tibia and increased external rotation of the hindfoot were noted throughout the gait cycle. Pain and function improved after ankle replacement as supported by better outcomes scores, increased temporal-spatial parameters, and significant improvement in tibial sagittal range of motion during terminal stance and hindfoot sagittal range of motion during preswing. While multi-segment foot kinematics were improved, they were not restored to control values. Statement of clinical significance: Total ankle arthroplasty does not fully normalize mutli-segment gait kinematics despite improved patient-reported outcomes and gait mechanics.

The influence of maturation and sex on pelvis and hip kinematics in youth distance runners.

OBJECTIVES: This study aimed to investigate differences in stance phase pelvic and hip running kinematics based on maturation and sex among healthy youth distance runners. DESIGN: Cross-Sectional. METHODS: 133 uninjured youth distance runners (M = 60, F = 73; age = 13.5 ±â€¯2.7 years) underwent a three-dimensional running analysis on a treadmill at a self-selected speed (2.8 ±â€¯0.6 m·s-1). Participants were stratified as pre-pubertal, mid-pubertal, or post-pubertal according to the modified Pubertal Maturational Observation Scale. Stance phase pelvis and hip range of motion (RoM) and peak joint positions were extracted. Two-way ANCOVAs (sex, maturation; covariate of running velocity) were used with Bonferroni-Holm method to control for multiple comparisons with a target alpha level of 0.05. RESULTS: A two-way interaction between sex and maturation was detected (p = 0.009) for frontal plane pelvic obliquity RoM. Post-hoc analysis identified a maturation main effect only among females (p˂0.008). Pelvic obliquity RoM was significantly greater among post-pubertal (p = 0.001) compared to pre-pubertal females. Significant main effects of sex (p = 0.02), and maturation (p = 0.01) were found for hip adduction RoM. Post-hoc analysis indicated a significant increase in hip adduction RoM from pre-pubertal to post-pubertal female runners (p = 0.001). A significant main effect of sex was found for peak hip adduction angle (p = 0.001) with female runners exhibiting greater maximum peak hip adduction compared to males. CONCLUSIONS: Maturation influences pelvic and hip kinematics greater in female than male runners. Sex differences became more pronounced during later stages of puberty. These differences may correspond to an increased risk for running-related injuries in female runners compared to male runners.

HES1 is a novel downstream modifier of the SHH-GLI3 Axis in the development of preaxial polydactyly.

Sonic Hedgehog/GLI3 signaling is critical in regulating digit number, such that Gli3-deficiency results in polydactyly and Shh-deficiency leads to digit number reductions. SHH/GLI3 signaling regulates cell cycle factors controlling mesenchymal cell proliferation, while simultaneously regulating Grem1 to coordinate BMP-induced chondrogenesis. SHH/GLI3 signaling also coordinates the expression of additional genes, however their importance in digit formation remain unknown. Utilizing genetic and molecular approaches, we identified HES1 as a downstream modifier of the SHH/GLI signaling axis capable of inducing preaxial polydactyly (PPD), required for Gli3-deficient PPD, and capable of overcoming digit number constraints of Shh-deficiency. Our data indicate that HES1, a direct SHH/GLI signaling target, induces mesenchymal cell proliferation via suppression of Cdkn1b, while inhibiting chondrogenic genes and the anterior autopod boundary regulator, Pax9. These findings establish HES1 as a critical downstream effector of SHH/GLI3 signaling in the development of PPD.

Changes in Motivation, Socialization, Wellness and Mental Health in Youth Long-Distance Runners During COVID-19 Social Distancing Restrictions.

Purpose: The COVID-19 pandemic impacted the sporting and exercise activities of millions of youth. Running is an activity that could be maintained while social distancing restrictions were implemented during the pandemic. However, a recent study has indicated that youth runners reported lower running distance, frequency, and intensity during COVID-19. The reason for this reduction and the impact on overall well-being is unknown. Therefore, the purpose of this study was to determine if the social distancing restrictions during the 2020 COVID-19 pandemic influenced running motives, socialization, wellness and mental health in youth long-distance runners. Methods: A customized, open online questionnaire was provided to runners 9-19 years of age who participated in long-distance running activities including team/club cross-country, track and field (distances ≥800 m), road races, or recreational running. Participants responded to questions about demographics, motive for running, and wellness (sleep quality, anxiety, running enjoyment, food consumption quality) 6-months before as well as during social distancing restrictions due to COVID-19. Wilcoxon signed rank tests compared differences for ratio data and Chi-square tests were used to compare proportions before and during COVID-19 social distancing restrictions. Statistical significance was set at p ≤ 0.05. Results: A total of 287 youth long-distance runners (male = 124, female = 162, unspecified = 1; age = 15.3 ± 1.7 years; running experience = 5.0 ± 2.3 years) participated. Compared to their pre-COVID-19 responses, youth long-distance runners reported lower overall motivation to run (p < 0.001) and changes to most motive rankings (p < 0.001 to p = 0.71). The proportion of youth running alone increased during COVID-19 (65.8%) compared to pre-COVID-19 (13.8%, p < 0.001). Youth long-distance runners also reported less running enjoyment (p = 0.001), longer sleep duration (p < 0.001), lower sleep quality (p = 0.05), more anxiety (p = 0.043), and lower food quality consumed (p < 0.001) during COVID-19 social distance restrictions. Conclusion: The COVID-19 social distancing restrictions resulted in significant decreases in motivation and enjoyment of running. The removal of competition and team-based interactions likely had a role in these decreases for this population. Continuing team-based activities (e.g., virtual) during social distancing may help with maintaining motivation of youth long-distance runners. Reduced running occurred concurrently with reduced overall well-being of youth long-distance runners during the COVID-19 pandemic.

Isolation and Culture of Murine Primary Chondrocytes: Costal and Growth Plate Cartilage.

Primary chondrocyte isolation and culture is a useful tool to characterize how cellular perturbations impact chondrocyte behavior and mineralization in vitro. This protocol conveys methods for isolating and culturing primary chondrocytes from costal and growth plate cartilage. Following gross dissection of the neonatal murine anterior rib cage or long bone growth plate cartilage, chondrocytes are isolated via enzymatic digestion and plated at high density. Genetic perturbation of plated primary murine chondrocytes using viral infection of Cre recombinase to excise floxed alleles and/or overexpress genes of interest are also described.

Impact of COVID-19 Social Distancing Restrictions on Training Habits, Injury, and Care Seeking Behavior in Youth Long-Distance Runners.

Purpose: The COVID-19 pandemic impacted the sporting and exercise activities of millions of youth. Running is an activity that could be maintained while social distancing restrictions were implemented during the pandemic. If running-related injuries do occur, these restrictions may also influence the access to care or care seeking behavior of this population. Therefore, the purpose of this study was to determine if the social distancing restrictions during the 2020 COVID-19 pandemic influenced training habits, injury, and care seeking behavior in youth long-distance runners. Methods: A customized, open online questionnaire was provided to runners 9-19 years of age who participated in long-distance running activities including team/club cross-country, track and field (distances ≥800 m), road races, or recreational running. Participants responded to questions about demographics, running habits, RRIs, and health care provider visits 6-months before as well as during social distancing restrictions due to COVID-19. Wilcoxon signed rank tests compared differences for ratio data and Chi-square tests were used to compare proportions before and during COVID-19 social distancing restrictions. Statistical significance was set at p ≤ 0.05. Results: A total of 287 youth long-distance runners (male = 124, female = 162, unspecified = 1; age = 15.3 ± 1.7 years; running experience = 5.0 ± 2.3 years) participated. Compared to their pre-COVID-19 responses, youth long-distance runners reported lower distances run per week (p < 0.001), fewer runs per week (p < 0.001), fewer hard runs per week (p < 0.001), fewer number of injuries (p < 0.001), and fewer injuries per 1,000 km (p = 0.002) during the COVID-19 social distancing restrictions. A lower proportion of participants reported in-person health care provider visits (p < 0.001) and a lower proportion of visits were made to an athletic trainer during COVID-19 social distancing restrictions compared to prior to COVID-19 (p < 0.001). Conclusion: The COVID-19 pandemic resulted in significant decreases in both training and injuries which were different compared to previous reports in an adult population. Many of the runners who sustained an injury during COVID-19 social distancing restrictions did not seek care, with the most prominent reduction in visits to an athletic trainer. This could impact future injury and chronic pain.

Screw Anterior Distal Femoral Hemiepiphysiodesis in Children With Cerebral Palsy and Knee Flexion Contractures: A Retrospective Case-control Study.

BACKGROUND: In children with cerebral palsy who demonstrate hamstring tightness, increasing attention is being paid to less invasive methods of correcting knee flexion contractures. Guided growth principles represent one such approach, and in tandem with a serial extension casting protocol, may provide a less invasive method of addressing these contractures. To date, no evidence is available on this combination of procedures. The purpose of this study was to investigate the effectiveness of a combined lengthening/guided growth procedure (hamstring lengthening, percutaneous anterior screw hemiepiphysiodesis, and serial extension casting) in addressing knee flexion contracture, and to compare this approach to hamstring lengthening and serial extension casting alone. METHODS: Measures from preoperative and postoperative gait analyses were reviewed retrospectively for 10 patients with cerebral palsy who underwent anterior screw hemiepiphysiodesis and hamstring lengthening followed by serial extension casting [anterior epiphysiodesis (AE) group]. These findings were compared with measures from 19 patients with cerebral palsy who underwent hamstring lengthening followed by serial extension casting [no anterior epiphysiodesis (NAE) group]. Postoperative changes in clinical, functional, and kinematic parameters were assessed. Radiographic parameters were also assessed for the AE group. RESULTS: In the AE group, improvements were measured in knee contracture, popliteal angle, peak stance phase knee extension, knee range of motion, and Gait Deviation Index. Similar results were observed in the NAE group. In the AE group, the lateral distal femoral angle increased into extension by 20.9 degrees at an average of 26-month follow-up. Both groups showed an increase in pelvic tilt postoperatively. There were no surgical complications associated with the screw anterior hemiepiphysiodesis. Four patients did have complaints of knee pain, but the pain was attributable to the implants in only one patient. DISCUSSION: The AE group demonstrated statistically greater postoperative improvement in popliteal angle, knee flexion contracture, and peak knee extension during stance than the NAE group. Both procedures led to improvements in clinical and functional measures, indicating the validity of this approach as a means of correcting flexion contracture that is less invasive and allows immediate weight bearing. LEVEL OF EVIDENCE: Level III-therapeutic study.

Improved Clinical and Functional Outcomes in Crouch Gait Following Minimally Invasive Hamstring Lengthening and Serial Casting in Children With Cerebral Palsy.

BACKGROUND: Serial extension casting represents a novel solution for addressing residual knee flexion contractures following hamstring lengthening in children with cerebral palsy. The purpose of this study was to investigate postoperative changes in patients following hamstring lengthening with a serial casting protocol. METHODS: Measures from preoperative and postoperative gait analyses were reviewed retrospectively for 19 patients with cerebral palsy who underwent hamstring lengthening followed by serial extension casting. Postoperative changes in clinical, functional, and kinematic parameters were assessed using paired parametric methods. RESULTS: Improvements were measured in popliteal angle, knee contracture, peak stance phase knee extension, sagittal plane range of motion of the knee during walking, Gait Deviation Index, and pediatric outcomes data collection instrument Global score. Nearly 80% of the cohort (15/19 patients) demonstrated a significant or moderate response to the intervention, whereas 20% demonstrated no improvement. Of note, significantly increased anterior pelvic tilt was also observed. CONCLUSIONS: Hamstring lengthening combined with a serial casting protocol was associated with significant postoperative improvements in a range of clinical (eg, knee contracture), functional (eg, pediatric outcomes data collection instrument Global), and kinematic (eg, knee extension in stance) parameters. Improvements following this minimally invasive surgery were comparable to outcomes from procedures with higher complication rates. LEVEL OF EVIDENCE: This is a Level III Therapeutic Study (retrospective study investigating the results of a treatment).

Assessment of waveform similarity in youth long-distance runners.

BACKGROUND: Although unimpaired gait is typically assumed to be symmetrical, side-to-side differences in discrete instances of time have been reported in adult and youth runners. These previous results fail to account for the entirety of the motion. RESEARCH QUESTION: Are waveform pattern similarities strong in youth long-distance runners and are the waveform pattern similarities influenced by sex and maturation? METHODS: A cohort of injury-free children and adolescents (n = 103) who participated in long-distance running activities were recruited for the study. Three-dimensional kinematics were collected as participants ran on a treadmill at a self-selected speed. Lower extremity side-to-side waveform symmetries were assessed using the Linear Fit Model. Unpaired t-tests and one-way ANOVA with post-hoc analysis were calculated to determine if sex and/or maturation influenced waveform symmetries. RESULTS: As a whole, waveform similarities were found to be strongest in the sagittal plane and weaker, but still of appropriate strength, in the coronal and transverse planes. Hip rotation and knee varus/valgus measures were found to have the weakest waveform similarities. High waveform similarity variability was measured within the cohort, particularly in the coronal and transverse planes. Waveform similarities were not found to be influenced by either sex or maturation. SIGNIFICANCE: While the group as a whole demonstrated strong waveform similarities, some level of asymmetry in a population of uninjured, long-distance youth runners is normal as none of the measures demonstrated perfect symmetry. Prospective study is warranted to identify thresholds of waveform similarity and to determine if these findings can be used to predict running performance and injury risk.

Therapy Workloads in Pediatric Health: Preliminary Findings and Relevance for Defining Practice.

PURPOSE: To measure time spent by pediatric physical and occupational therapists in performing daily work activities. METHODS: Physical and occupational therapists at an urban pediatric academic hospital were observed during a standard workday. Time studies recorded total time spent performing patient care and other workplace-specific tasks. Data were analyzed to identify trends. RESULTS: Broad similarities existed in average amounts of time spent in direct patient care, indirect patient care, and nonpatient care tasks. Indirect patient care tasks demonstrated the lowest variability in time spent. CONCLUSIONS: This is the first report of pediatric physical and occupational therapists' time in performing daily tasks. The metric and tools derived from these findings support managerial decision-making, provide a comparison of actual versus targeted workload, assist with determining appropriate and safe staffing caseloads, and contribute to measurements of a patient's therapy acuity level.Video Abstract: For more insights from the authors, access Supplemental Digital Content 1, available at: http://links.lww.com/PPT/A280.

Variation inflation factor-based regression modeling of anthropometric measures and temporal-spatial performance: Modeling approach and implications for clinical utility.

BACKGROUND: Understanding the relationship of underlying anthropometry to temporal-spatial performance is critical to appropriate assessment of patients with ambulatory dysfunction. The current body of literature has established the importance of limb length in this relationship. This study sought to re-examine these relationships in light of recent trends in body habitus and obesity, using Variation Inflation Factor analysis to optimize the model. METHODS: Elementary school children (n=452; ages 5-13) were tested during walking at a self-selected speed across an instrumented walkway. Temporal-spatial and anthropometric measures were compiled for all children. The relationship between temporal-spatial and anthropometric measures was assessed using regression modeling with Variation Inflation Factor optimization. FINDINGS: Body weight was identified as a significant predictor of cycle duration, stride length, stance duration, and step width during initial modeling. However, it did not meet the constraints imposed during Variation Inflation Factor optimization and was removed from the final models. The final optimized models identified significant relationships between both temporal-spatial parameters of interest and other temporal-spatial measures, with the best fit identified for walking speed (R2=0.6148). INTERPRETATION: The use of the Variation Inflation Factor constraint during the regression modeling process ensured final models composed of truly independent predictor variables. The resulting models are highly robust and highlight the complex relationships between body structure, functional conditions, and walking performance. These models have value for routine clinical assessment of ambulatory dysfunction, and may provide a foundation for classifying temporal-spatial performance in the context of multiple contributing parameters.

Sagittal Fluoroscopy for the Assessment of Hindfoot Kinematics.

Current methods of quantifying foot kinematics during gait typically use markers placed externally on bony anatomic locations. These models are unable to analyze talocrural or subtalar motion because the talus lacks palpable landmarks to place external markers. Alternative methods of measuring these clinically relevant joint motions are invasive and have been limited to research purposes only. This study explores the use of fluoroscopy to noninvasively quantify talocrural and subtalar sagittal plane kinematics. A fluoroscopy system (FS) was designed and built to synchronize with an existing motion analysis system (MAS). Simultaneous fluoroscopic, marker motion, and ground reaction force (GRF) data were collected for five subjects to demonstrate system application. A hindfoot sagittal plane model was developed to evaluate talocrural and subtalar joint motion. Maximum talocrural plantar and dorsiflexion angles averaged among all the subjects occur at 12% and 83% of stance, respectively, with a range of motion of 20.1 deg. Maximum talocrural plantar and dorsiflexion angles averaged among all the subjects occur at toe-off and 67% of stance, respectively, with a range of motion of 8.7 deg. Based on the favorable comparison between the current fluoroscopically measured kinematics and previously reported results from alternative methods, it is concluded that fluoroscopic technology is well suited for measuring the sagittal plane hindfoot motion.

Jun N-terminal kinase activity is required for invagination but not differentiation of the sea urchin archenteron.

Although sea urchin gastrulation is well described at the cellular level, our understanding of the molecular changes that trigger the coordinated cell movements involved is not complete. Jun N-terminal kinase (JNK) is a component of the planar cell polarity pathway and is required for cell movements during embryonic development in several animal species. To study the role of JNK in sea urchin gastrulation, embryos were treated with JNK inhibitor SP600125 just prior to gastrulation. The inhibitor had a limited and specific effect, blocking invagination of the archenteron. Embryos treated with 2 µM SP600125 formed normal vegetal plates, but did not undergo invagination to form an archenteron. Other types of cell movements, specifically ingression of the skeletogenic mesenchyme, were not affected, although the development and pattern of the skeleton was abnormal in treated embryos. Pigment cells, derived from nonskeletogenic mesenchyme, were also present in SP600125-treated embryos. Despite the lack of a visible archenteron in treated embryos, cells at the original vegetal plate expressed several molecular markers for endoderm differentiation. These results demonstrate that JNK activity is required for invagination of the archenteron but not its differentiation, indicating that in this case, morphogenesis and differentiation are under separate regulation.