Should Adolescents Run Marathons?: Youth Marathon Training Injury Epidemiology and Risk Factors.

OBJECTIVE: Youth participation in distance running has increased, yet little data exist about the injury patterns and safety of such activity. This study seeks to determine the types and rates of injuries seen in an adolescent marathon training program. DESIGN: Observational prospective cohort study. SETTING: Community-based adolescent marathon training program. PARTICIPANTS: The study enrolled 1927 students from 50 high schools (HS) and 34 middle schools (MS) participating in the 2017 to 2018 Students Run Los Angeles marathon training program. ASSESSMENT OF RISK FACTORS: Weekly injury reports completed by running coaches. Data elements included participant demographics, weekly training distance, injury type, injury acuity, and missed training time. MAIN OUTCOME MEASURES: Epidemiology of self-reported injury in adolescent runners. RESULTS: A total of 583 injuries occurred in 18% of runners during the training program. High schools runners were more likely to be injured than MS runners (20.8% vs 14.2%, P < 0.001). Seventy-two percent of injuries were acute with a mean missed training time of 4.8 days (SD 4.8). The most frequent site of injury was the knee (33%). Overall, runners with injuries ran a significantly greater distance per week than uninjured runners (14.6 mi vs 12.0 mi, P < 0.001). Ninety-nine percent of marathon participants completed the race. CONCLUSIONS: During a 28-week marathon training program, 18% of adolescent participants reported an injury. More injuries occurred in HS students, were acute, and involved the knee. This study represents one of the largest descriptions of injury prevalence in adolescent distance running and highlights a lower injury rate than adults during marathon training.

Pathophysiology of Pediatric Traumatic Brain Injury.

The national incidence of traumatic brain injury (TBI) exceeds that of any other disease in the pediatric population. In the United States the Centers for Disease Control and Prevention (CDC) reports 697,347 annual TBIs in children ages 0-19 that result in emergency room visits, hospitalization or deaths. There is a bimodal distribution within the pediatric TBI population, with peaks in both toddlers and adolescents. Preclinical TBI research provides evidence for age differences in acute pathophysiology that likely contribute to long-term outcome differences between age groups. This review will examine the timecourse of acute pathophysiological processes during cerebral maturation, including calcium accumulation, glucose metabolism and cerebral blood flow. Consequences of pediatric TBI are complicated by the ongoing maturational changes allowing for substantial plasticity and windows of vulnerabilities. This review will also examine the timecourse of later outcomes after mild, repeat mild and more severe TBI to establish developmental windows of susceptibility and altered maturational trajectories. Research progress for pediatric TBI is critically important to reveal age-associated mechanisms and to determine knowledge gaps for future studies.

Sex Differences in Neurophysiological Changes Following Voluntary Exercise in Adolescent Rats.

Background: Adolescence is a period of time characterized by the onset of puberty and is marked by cognitive and social developments and gross physical changes that can play a role in athletic performance. Sex differences are present with differences in body size, height, physiology and behavior which contribute to differences in athletic performance as well. Pre-clinical studies representing this active group are lacking. Methods: Acute and chronic effects of exercise were evaluated. Male and female adolescent rats were given voluntary access to a running wheel for 10 consecutive days. Running behavior (males and females) and estrous cycling (females only) were analyzed daily. A second group was given 10 days of voluntary access to a running wheel, then rested for 10 days to determine the long-term effects of exercise on the adolescent brain. Brain and muscle tissue were harvested at 10 and 20 day time points to understand exercise-dependent changes in mitochondrial activity and neuroplasticity. Animal cohorts were carried out at two different sites: University of California Los Angeles and Pepperdine University. Results: On average, running distance, intensity of run, and length of running bout increased for both male and female rats across the 10 days measured. Females ran significantly further and for longer intervals compared to males. Cortical and muscle expression of PGC1α showed similar levels at 10 days regardless of sex and exercise. There was a significant increase in expression at 20 days in all groups correlating with body size (p's < 0.05). Cortical and hippocampal levels of BDNF were similar across all groups, however, BDNF was significantly higher in exercised females at the acute compared to long-term time point. Discussion: Adolescent rats allowed 10 days of exercise show changes in physiologic function. There are sex differences in running behavior not impacted by sex hormones. These results are important to further our understanding of how exercise impacts the adolescent brain.

Developmental exposure to 17α-hydroxyprogesterone caproate impairs adult delayed reinforcement and reversal learning in male and female rats.

Women with a history of unexplained miscarriage are frequently prescribed the synthetic progestin, 17α-hydroxyprogesterone caproate (17-OHPC) during the middle trimester of pregnancy. However, little is known about the long-term behavioural effects of 17-OHPC. Work in rodents suggests that the developing brain is sensitive to progestins. Neonatal 17-OHPC impairs adult performance in set-shifting and delay discounting. The present study tested the effects of 17-OHPC (0.5 mg kg-1 ) or vehicle administration from postnatal days 1-14 on cognitive function in adulthood in rats. Cognitive function was assessed in males and females (n = 8-10 per group) by operant responding for sugar pellets, measuring delayed reinforcement or reversal learning. For delayed reinforcement, the rat must wait 15 seconds for pellets after responding on a lever. Delay is signalled by a light or is unsignalled. For reversal learning, the rat must respond on the lever under a stimulus light, and then learn to respond on the unlit lever. For delayed reinforcement, rats earned more pellets under signalled vs unsignalled conditions. Likewise, males made more responses and earned more pellets compared to females. Under signalled conditions, 17-OHPC-treated rats earned fewer pellets than controls. For reversal learning, the results were similar. Females required more trials than males to respond correctly for the new rule, and 17-OHPC-treated rats required more trials than controls. This suggests that 17-OHPC exposure during development may impair cognitive function. Considering that questions have been raised as to the efficacy of 17-OHPC to prevent miscarriage, it may be necessary to rethink the use of progestin therapy during pregnancy.

Prospective Study of Acute Opioid Use After Adolescent Anterior Cruciate Ligament Reconstruction Shows No Effect From Patient- or Surgical-Related Factors.

INTRODUCTION: Patient-reported pain scores and opioid use have not been quantified after outpatient adolescent anterior cruciate ligament reconstruction (ACLR). METHODS: Patients aged 12 to 18 years undergoing primary isolated ACLR, with or without meniscal treatment, were prospectively recruited. Patients actively taking opioids or with previous extended use of opioids were excluded. Two orthopaedic surgeons performed ACLR and determined the use of a hamstring or bone-patellar tendon-bone autograft. For postoperative pain management, patients were prescribed 40 tablets of hydrocodone/acetaminophen 5/325 mg. Patients were instructed to document daily pill consumption and side effects through a daily log for 6 weeks. Patients completed the American Pain Society Patient Outcome Questionnaire at the end of weeks 1 and 6. RESULTS: One hundred three patients were enrolled, with age: 12.5 to 18.9 years (mean 16.2 y ± 1.3), weight: 41.3 to 113.6 kg (mean 72.4 kg ± 17.2), and body mass index: 17.8 to 40.1 (mean 25.9 ± 4.9). Sixty-nine patients received a hamstring autograft, and 34 received a bone-patellar tendon-bone autograft. Fifty-six received additional meniscal procedures. The median number of postoperative opioids taken by patients was 17 (range 0 to 40). No notable differences were found in total pill consumption with regard to age, weight, body mass index, sex, block type, autograft type, or meniscal treatment at 1 week post-op or 6 weeks post-op. No correlation was found between the self-reported "worst pain in the past 24 hours" at the end of the first postoperative week or after 6 weeks (r = 0.112, P = 0.26, and r = 0.093, P = 0.36). No correlation was found between the level of satisfaction with pain treatment and total number of pills taken during the first postoperative week or at the end of 6 weeks (r = -0.090, P = 0.37, and r = -0.172, P = 0.08). CONCLUSION: Patients take most pain medication during the first postoperative week after adolescent ACLR, although patient and surgical variables had no notable influence on pill consumption. LEVEL OF EVIDENCE: Level IV, case series.

Recovery From Repeat Mild Traumatic Brain Injury in Adolescent Rats Is Dependent on Pre-injury Activity State.

Adolescents and young adults have the highest incidence of mild traumatic brain injury (mTBI); sport-related activities are a major contributor. Roughly a third of these patients diagnosed with mTBI are estimated to have received a subsequent repeat mTBI (rTBI). Previously, animal studies have only modeled mTBI in sedentary animals. This study utilizes physical activity as a dependent variable prior to rTBI in adolescent rats by allowing voluntary exercise in males, establishing the rat athlete (rathlete). Rats were given access to locked or functional running wheels for 10 d prior to sham or rTBI injury. Following rTBI, rathletes were allowed voluntary access to running wheels beginning on different days post-injury: no run (rTBI+no run), immediate run (rTBI+Immed), or 3 day delay (rTBI+3dd). Rats were tested for motor and cognitive-behavioral (anxiety, social, memory) and mechanosensory (allodynia) dysfunction using a novel rat standardized concussion assessment tool on post-injury days 1,3,5,7, and 10. Protein expression of brain derived neurotrophic factor (BDNF) and proliferator-activated gamma coactivator 1-alpha (PGC1α) was measured in the parietal cortex, hippocampus, and gastrocnemius muscle. Sedentary shams displayed lower anxiety-like behaviors compared to rathlete shams on all testing days. BDNF and PGC1α levels increased in the parietal cortex and hippocampus with voluntary exercise. In rTBI rathletes, the rTBI+Immed group showed impaired social behavior, memory impairment in novel object recognition, and increased immobility compared to rathlete shams. All rats showed greater neuropathic mechanosensory sensitivity than previously published uninjured adults, with rTBI+3dd showing greatest sensitivity. These results demonstrate that voluntary exercise changes baseline functioning of the brain, and that among rTBI rathletes, delayed return to activity improved cognitive recovery.

Evaluation of General and Musculoskeletal Health Literacy Disparities in Pediatric Sports Injury Patient and Guardian Populations.

BACKGROUND: Increased participation of adolescents in organized sports has led to an increase in pediatric sports injury. Limited health literacy puts patients at risk for worse outcomes through decreased compliance. We aim to evaluate the extent of health literacy disparities in pediatric sports medicine populations. METHODS: Patients aged 10 to 17 years and their consenting guardians visiting clinic for treatment of a sports-related injury completed a unique questionnaire including self-reported health literacy measures and direct assessment of knowledge regarding care for musculoskeletal injuries. Statistical analysis based on socioeconomic factors and demographics was performed using t tests. RESULTS: A total of 268 patient surveys (14.37±1.94 y) and 251 guardian surveys (43.62±9.08 y) were collected. In self-reported general health literacy scores for guardians, all categories except ethnicity played a statistically significant role, with higher health literacy scores associated with higher education, use of English as the primary language at home, private insurance, and female guardians (P<0.001, <0.001, <0.001, 0.011). In contrast, age was the only factor affecting scores in the patient population (P=0.015). Among self-reported musculoskeletal health literacy and directly measured musculoskeletal literacy scores, there were significant differences in groups by age, primary language, and level of education (P=0.020, 0.003). CONCLUSIONS: Significant disparities in general and musculoskeletal health literacy exist within pediatric sports medicine populations, most notably between guardian groups. Improving disparities in health literacy for these populations may best be aimed at guardians, using medical education through verbal/written instruction in multiple languages. LEVEL OF EVIDENCE: Level IV.

Anabolic-androgenic steroid abuse and cognitive impairment: Testosterone IMPAIRS biconditional task performance in male rats.

Our goal is to understand the consequences of anabolic-androgenic steroid (AAS) abuse on cognitive function, using rats as a model. There is relatively little research on how AAS abuse impacts cognition. In the present study, rats were tested for their ability to use contextual information to guide decision-making in biconditional discrimination. The Stroop task is a classic human test for contextual decision-making. In rodents, biconditional discrimination challenges subjects to use contextual cues in the operant chamber to resolve the correct lever response when auditory and visual cues are incongruent. The hypothesis is that chronic high-dose testosterone impairs biconditional discrimination. Rats were trained in 24 trials/day over 14 days, in alternating sessions with each environment. On a flat floor with houselight illuminated, auditory cues (clicker vs tone) signified the active lever. On a barred floor with no light, visual cues from 2 stimulus lights (constant vs blinking) identified the active lever. Rats treated chronically with testosterone (7.5 mg/kg) were unimpaired in task acquisition, and all rats learned to select the correct lever in response to auditory or visual cues. During extinction, controls made significantly more correct than incorrect responses in congruent trials (p < 0.05 by paired t-test), but testosterone-treated rats failed to show a similar preference. This was reflected by significant interactions of drug x cue agreement (F1,18 = 5.21, p < 0.05) and drug x cue agreement x response accuracy (F1,18 = 8.95, p < 0.05). These results suggest that testosterone impairs cognitive flexibility, and demonstrates potential for AAS abuse to impair cognitive function in humans.

Repeat Mild Traumatic Brain Injury in Adolescent Rats Increases Subsequent ß-Amyloid Pathogenesis.

Single moderate-to-severe traumatic brain injuries (TBIs) may increase subsequent risk for neurodegenerative disease by facilitating ß-amyloid (Aß) deposition. However, the chronic effects on Aß pathogenesis of repetitive mild TBIs (rTBI), which are common in adolescents and young adults, remain uncertain. We examined the effects of rTBI sustained during adolescence on subsequent deposition of Aß pathology in a transgenic APP/PS1 rat model. Transgenic rats received sham or four individual mild TBIs (rTBIs) separated by either 24- or 72-h intervals at post-natal day 35 (before Aß plaque deposition). Animals were euthanized at 12 months of age and underwent immunohistochemical analyses of Aß plaque deposition. Significantly greater hippocampal Aß plaque deposition was observed after rTBI separated by 24 h relative to rTBI separated by 72 h or sham injuries. These increases in hippocampal Aß plaque load were driven by increases in both plaque number and size. Similar, though less-pronounced, effects were observed in extrahippocampal regions. Increases in Aß plaque deposition were observed both ipsilaterally and contralaterally to the injury site and in both males and females. rTBIs sustained in adolescence can increase subsequent deposition of Aß pathology, and these effects are critically dependent on interinjury interval.