How do sports injury epidemiological outcomes vary depending on athletes' response rates to a weekly online questionnaire? An analysis of 39-week follow-up from 391 athletics (track and field) athletes.

OBJECTIVE: To explore how sports injury epidemiological outcomes (i.e., prevalence, average prevalence, incidence, burden, and time to first injury) vary depending on the response rates to a weekly online self-reported questionnaire for athletes. METHODS: Weekly information on athletics injuries and exposure from 391 athletics (track and field) athletes was prospectively collected over 39 weeks (control group of the PREVATHLE randomized controlled trial) using an online self-reported questionnaire. The data were used to calculate sports injury epidemiological outcomes (i.e., prevalence, average prevalence, incidence, burden, and time to first injury) for sub-groups with different minimum individual athletes' response rates (i.e., from at least 100%, at least 97%, at least 95%, … to at least 0% response rate). We then calculated the relative variation between each sub-group and the sub-group with a 100% response rate as a reference. A substantial variation was considered when the relative variation was greater than one SD or 95% CI of the respective epidemiological outcome calculated in the sub-group with a 100% response rate. RESULTS: Of 15 249 expected weekly questionnaires, 7209 were completed and returned, resulting in an overall response rate of 47.3%. The individual athletes' response rates ranged from 0% (n = 51) to 100% (n = 100). The prevalence, average weekly prevalence, and time to first injury only varied substantially for the sub-groups below a 5%, 10% and 18% minimum individual response rate, respectively. The incidence and injury burden showed substantial variations for all sub-groups with a response rate below 100%. CONCLUSIONS: Epidemiological outcomes varied depending on the minimum individual athletes' response rate, with injury prevalence, average weekly prevalence, and time to first injury varying less than injury incidence and injury burden. This highlights the need to take into account the individual response rate when calculating epidemiological outcomes, and determining the optimal study-specific cut-offs of the minimum individual response rate needed.

Does the sequence of plyometric and dynamic stretching exercises influence subsequent sprint performance? A randomized crossover intervention study.

The objectives of this study were to evaluate the acute effects of the sequence order of drop jumps (DJ) and dynamic stretching (DS) on sprinting performances in competitive athletes and to investigate the relationships between post-activation performance enhancement (PAPE) in sprint performance and lower limb power. Thirteen male jumpers and sprinters participated in this study (19 ± 2 years; 177 ± 7 cm; 71.7 ± 5.6 kg). Through a randomized crossover design, the athletes were exposed to three different conditions after a standardized warm-up: DS+DJ, DJ+DS, and control. Sprinting performance over 40 m was analysed with consideration of initial (0 to 20 m) and final acceleration (20 to 40 m) phases. The effect of intervention was examined by two-way repeated-measures of ANOVA. Pearson's correlation test was used to determine the association between PAPE during sprinting and jump performance. There was no effect of any factor on 40-m sprint performance. Meanwhile, the performance at 20-40 m was higher after the DS+DJ condition when compared to baseline (8.79 ± 0.43 vs. 8.91 ± 0.35 m/s; p = 0.015). However, the initial acceleration was worsened in the DJ+DS condition when compared to baseline (6.26 ± 0.25 vs. 6.22 ± 0.26 m/s; p = 0.002). There was a negative correlation between CMJ height and the improvement in final acceleration (r = -0.741; p = 0.004). The use of DS prior to DJ is an effective strategy to improve performance in the final acceleration phase (20-40 m). The athletes with lower levels of lower limb power benefited the most from this PAPE strategy.

Changes in running biomechanics during the 2017 IAAF world championships men's 1500 m final.

The aim of this study was to analyze key kinematic, spatiotemporal, and global mechanical characteristics in world-class middle-distance racing. Eight men were recorded halfway along the home straight on the second, third, and final laps in the 2017 IAAF World Championship 1500 m final. Video data (150 Hz) from three high-definition camcorders were digitized to calculate relevant variables, subsequently analyzed in relation to running speed and finishing position. Better-placed finishers had greater hip extension at initial contact and through late stance, greater knee excursion throughout stance, and longer overstriding distances. Step length did not change with faster speeds as runners relied on increasing step frequency, but the highest-finishing athletes had longer contact phases and greater fluctuations in speed through the step cycle, which were related to higher normalized peak horizontal forces. The best athletes also had lower leg stiffnesses and vertical stiffnesses. The extended contact phase and greater compression could allow for more sustained force production, enabling better acceleration and maintenance of sprinting speed, indicating a trade-off between aerobic energetic efficiency and anaerobic power capacity. Coaches should note that these factors, as well as the best athletes' greater overstriding distances, show that elite 1500 m runners might prioritize a technique that favors running speed over economy.

Characterising coordination strategies during initial acceleration in sprinters ranging from highly trained to world class.

Identifying coordination strategies used by sprinters and features that differentiate these strategies will aid in understanding different technical approaches to initial sprint acceleration. Moreover, multiple effective coordination strategies may be available to athletes of similar ability, which typical group-based analyses may mask. This study aimed to identify sub-groups of sprinters based on thigh-thigh and shank-foot coordination during initial acceleration, and assess sprint performance across different combinations of coordination strategies. Angular kinematics were obtained from 21 sprinters, and coordination determined using vector coding methods, with step 1 and steps 2-4 separated for analysis. Performance was assessed using metrics derived from velocity-time profiles. Using hierarchical cluster analysis, three distinct coordination strategies were identified from thigh-thigh and shank-foot coordination in step 1 and two strategies in steps 2-4. Coordination strategies primarily differed around early flight thigh-thigh coordination and early stance shank-foot coordination in step 1, while timing of reversals in thigh rotation characterised differences in later steps. Higher performers tended to have greater lead thigh and foot dominance in step 1 and early swing thigh retraction in steps 2-4. The novel application of cluster analysis to coordination provides new insights into initial acceleration technique in sprinters, with potential considerations for training and performance.

Relative age effect reversal on the junior-to-senior transition in world-class athletics.

The relative age effect (RAE) is a selection bias resulting from the interaction between the selected dates and birthdates. Nevertheless, the impact of birthdate on the junior-to-senior transition in international track and field is unclear. This study aimed to quantify the RAE's magnitude and test if birthdate affects the junior-to-senior transition rate. The birthdate and performances of 5,766 sprinters (female: 51.0%) and 5,863 jumpers (female: 45.9%) were collected. Elite athletes (operationally defined as the World's all-time Top 200, 100 and 50 athletes) were identified according to Under 18 and Senior categories. Skewed quartile distributions were observed in the Under 18 (effect size ranged = 0.15-0.10) but not in the Senior category. RAE magnitude increased according to performance level (i.e., from Top 200 to Top 50) and was higher in males than females. Relatively younger athletes showed significantly higher transition rates with a higher chance of maintaining top level in the senior category (odds ratio (OR) ~ 1.64). The probability of maintaining success was lower for sprinters than jumpers (OR ~ 0.70), influenced by decade of birth and continental place but similar for male and female athletes. Data corroborate that relatively younger athletes are disadvantaged in the junior category but advantaged when transitioning to the senior category.

[Robotic mechanotherapy in a complex of procedures for the functional state recovery of the neuromuscular system and peripheral hemodynamics in track-and-field athletes]. / Robotizirovannaya mekhanoterapiya v komplekse protsedur dlya vosstanovleniya funktsional'nogo sostoyaniya nervno-myshechnogo apparata i perifericheskoi gemodinamiki legkoatletov.

The background of the study is caused by the need to develop methods of drug-free neuromuscular system and peripheral hemodynamics recovery of athletes to optimize their functioning after intense physical activity in current conditions of high sporting competition. OBJECTIVE: To develop a program of comprehensive recovery of neuromuscular apparatus and hemodynamics of the lower limbs of track-and-field athletes during intense physical activity, including mechanotherapy on the robotic biomechanical complex with biological feedback and to evaluate its efficacy, comparing with a standard recovery program. MATERIAL AND METHODS: The study involved 23 track-and-field athletes (the mean age 24.6±3.8 years) with qualification «master of sports¼ and «master of sports of international class¼. The athletes were randomly divided into two groups (study and control). In the study group athletes received hydro-, presso- and magnetotherapy procedures, as well as mechanotherapy procedures on a robotic biomechanical complex with biological feedback. The athletes from control group received only traditional rehabilitation with hydro-, press- and magnetotherapy. The examination of the functional state of the neuromuscular apparatus and peripheral hemodynamics was performed with the use of stimulation electroneuromyography, robotic dynamometry and rheovasography. RESULTS: When registering a motor response from a foot extensor digitorum brevis, innervated by the deep fibular nerve, after conduction of procedures set, a decrease in the residual latency parameters of study group's athletes was found. The dynamometric investigation showed a decrease in the fatigue coefficient of knee joint's flexors and extensors, as well as an increase in the strength of knee joint's extensors in the athletes from the study group. During the rheovasography the decrease of the rheographic index in the «foot¼ and «lower leg¼ segments in the study group was revealed. The decrease of the geographic index in the «lower leg¼ segment and normalization of the rheographic waves distribution time in the «foot¼ segment in control group were identified. CONCLUSION: The study results showed the efficacy of both the standard recovery program for athletes and the program, supplemented by mechanotherapy. It has been found that the use of hydro-, presso- and magnetotherapy is more conductive to the normalization of the blood flow, while the inclusion of mechanotherapy, in addition to the action on peripheral hemodynamics, improves the neuromuscular transmission, reduces fatigue of muscular system and increases its strength indicators.

Time to return to full training and recurrence of rectus femoris injuries in elite track and field athletes 2010-2019; a 9-year study using the British Athletics Muscle Injury Classification.

Rectus femoris (RF) injuries are common in sports requiring maximal acceleration and sprinting. The British Athletics Muscle Injury Classification (BAMIC) describes acute muscle injury based on the anatomical site of injury and has been associated with return to play in hamstring and calf muscle injury. The aim of this study was to describe and compare the time to return to full training (TRFT) and injury recurrence for BAMIC-classified RF injuries sustained by elite track and field (T&F) athletes over a 9-year period. All rectus femoris injuries sustained by elite T&F athletes on the British Athletics World Class Program between September 2010 and September 2019 that were investigated with an MRI within 7 days of acute onset anterior thigh pain were included. Injuries were graded from the MRI by a specialist musculoskeletal radiologist using the BAMIC, and TRFT and injury recurrence were determined by evaluation of the Electronic Medical Record. Athlete demographics and World Athletics event discipline were recorded. Specific injury details including mechanism, location of injury, and whether surgical or rehabilitation management was undertaken were recorded. There were 38 RF injuries in 27 athletes (24.7 ± 2.3 years; 10 male, 17 female). Average TRFT for rehabilitation managed cases was 20.4 ± 14.8 days. Grade 1 injuries had significantly shorter TRFT compared with grades 2 (p = 0.04) and 3 (p = 0.01). Intratendinous (c) and surgically managed RF injuries each had significantly longer TRFT compared with other injury classes (p < 0.001). Myofascial (a) injuries had reduced repeat injury rates compared with b or c classes (p = 0.048). Grade 3 injuries had an increased repeat injury rate compared with other grades (p = 0.02). There were 4 complete (4c) proximal free tendon injuries sustained during sprinting and all in female athletes. The average TRFT for RF injuries in elite T&F is similar to that previously identified in elite football and Australian Rules. Similar to previous research in hamstring and calf injury, RF injuries extending into the tendon (BAMIC class c) had delayed TRFT which may reflect the longer duration required for tendon healing and adaptation. Grade 3 injuries had in increased repeat injury rate compared with grades 1 and 2. The BAMIC diagnostic framework may provide useful information for clinicians managing rectus femoris injuries in T&F.

Relationships between kinematic characteristics and ratio of forces during initial sprint acceleration.

In track sprinting, acceleration performance is largely determined by the ability to generate a high ratio of forces (RF), but the technical features associated with this remain unknown. This study therefore investigated the relationships between selected kinematic characteristics and RF during the initial acceleration phase. Fourteen male sprinters completed two maximal 60 m sprints from a block start. Full-body kinematic and external kinetic data were obtained from the first four steps, and the relationships between selected kinematic characteristics and mean RF over the first four steps were determined. Placing the stance foot further behind (or less far in front of) the whole-body centre of mass at touchdown was significantly related to greater RF (r = -0.672), and more anterior orientation of the proximal end of the foot (r = -0.724) and shank (r = -0.764) segments at touchdown were also significantly related to greater RF. Following touchdown, greater ankle dorsiflexion range of motion during early stance was significantly related to greater RF (r = 0.728). When aiming to enhance RF during initial acceleration, practitioners should be encouraged to focus on lower leg configurations when manipulating touchdown distance, and the role of dorsiflexion during early stance is also an important consideration.

Squat and countermovement jump performance across a range of loads: a comparison between Smith machine and free weight execution modes in elite sprinters.

The aims of this study were to: 1) provide and compare the height achieved during Smith machine (SM) and free weight (FW) loaded jumps executed over a wide spectrum of loads (40-120% of body mass [BM]); and 2) test the difference between loaded and unloaded squat jump (SJ) and countermovement jump (CMJ) attempts in ten highly trained male sprinters. On the first visit, athletes performed unloaded SJ and CMJ, loaded SJ with loads corresponding to 40, 60, 80, 100, and 120% BM, and loaded CMJ at 100% BM using an Olympic barbell (FW). On the second visit, they performed loaded SJ and CMJ tests under the same loading conditions on the SM device and, subsequently, a half-squat one-repetition maximum (1RM) assessment. The relative strength (RS = 1RM/BM) of the athletes was 2.54 ± 0.15. Loaded SJ performance was similar between SM and FW, and across all loading conditions. Differences in favour of CMJ (higher jump heights compared with SJ) were superior in the unloaded condition but decreased progressively as a function of loading. In summary, sprinters achieved similar SJ heights across a comprehensive range of loads, regardless of the execution mode (FW or SM). The positive effect of the countermovement on jump performance is progressively reduced with increasing load.

Bone parameters of elite athletes with oligomenorrhea and prevalence seeking medical attention: a cross-sectional study.

INTRODUCTION: Since the definition of secondary amenorrhea is cessation of regular menses for more than 3 months, it is likely that athletes with irregular menstrual cycles, including oligomenorrhea, do not consider the condition as serious. However, the consequences of untreated oligomenorrhea have not been investigated in elite track and field athletes. MATERIALS AND METHODS: The cohort consisted of 91 elite-level track and field athletes. Body compositions, including bone parameters and bone turnover markers (BTMs), were measured. RESULTS: Among the 91 participants, 52 were eumenorrheic and 33 were oligomenorrheic. The eumenorrheic athletes had significantly higher bone mineral density (BMD) and bone mineral content (BMC) of the lumbar spine, lower extremities, and whole body than had the oligomenorrheic athletes (p < 0.01). There were no significant differences in BTMs between the two groups, but oligomenorrheic athletes had significantly lower percent body fat. CONCLUSION: More than 40% of the elite-level female track and field athletes in this study reported menstrual disorders with oligomenorrhea as the most common. However, none sought medical attention. As compared to the eumenorrheic athletes, the oligomenorrheic athletes had lower BMC and BMD. Hence, if an athlete is oligomenorrheic, bone parameter measurements are considerably important.

Apparent temperature and heat-related illnesses during international athletic championships: A prospective cohort study.

International outdoor athletics championships are typically hosted during the summer season, frequently in hot and humid climatic conditions. Therefore, we analyzed the association between apparent temperature and heat-related illnesses occurrence during international outdoor athletics championships and compared its incidence rates between athletics disciplines. Heat-related illnesses were selected from illness data prospectively collected at seven international outdoor athletics championships between 2009 and 2018 using a standardized methodology. The Universal Thermal Climate Index (UTCI) was calculated as a measure of the apparent temperature based on weather data for each day of the championships. Heat-related illness numbers and (daily) incidence rates were calculated and analyzed in relation to the daily maximum UTCI temperature and between disciplines. During 50 championships days with UTCI temperatures between 15℃ and 37℃, 132 heat-related illnesses were recorded. Average incidence rate of heat-related illnesses was 11.7 (95%CI 9.7 to 13.7) per 1000 registered athletes. The expected daily incidence rate of heat-related illnesses increased significantly with UTCI temperature (0.12 more illnesses per 1000 registered athletes/°C; 95%CI 0.08-0.16) and was found to double from 25 to 35°C UTCI. Race walkers (RR = 45.5, 95%CI 21.6-96.0) and marathon runners (RR = 47.7, 95%CI 23.0-98.8) had higher heat-related illness rates than athletes competing in short-duration disciplines. Higher UTCI temperatures were associated with more heat-related illnesses, with marathon and race walking athletes having higher risk than athletes competing in short-duration disciplines. Heat-related illness prevention strategies should predominantly focus on marathon and race walking events of outdoor athletics championships when high temperatures are forecast.

Meso-pacing in Olympic and World Championship sprints and hurdles: Medallists save their best for the final.

The aim of this novel study was to analyse performance changes across qualifying heats, semi-finals and finals in world-class sprinters and hurdlers. Finalists' finishing positions, times and rankings at the Olympic Games and IAAF World Championships (2012-2019) were obtained. 78% of gold, 67% of silver and 38% of bronze medallists won their qualifying heat and semi-final, and in most events final placings were associated with finishing positions in the qualifying heats (P ≤ 0.006), but not with finishing times. Medallists ran faster in each successive round (P < 0.001), whereas those finishing between 4th-6th did not improve on their semi-final times. Most athletes finishing last and second-last ran the final slower than both their semi-final and qualifying heats. The short hurdles events, with fixed barrier heights and distances, differed from the other races as the medallists were faster than most rivals in the qualifying rounds (P < 0.05), and their race times did not improve from the semi-final to the final. Coaches should note that the world's best athletes were able to conserve energy for the final within a meso-pacing strategy throughout the championships, which was more important in the short hurdles, and requires preparation within their training regimens.

Corrective procedures remove relative age effect from world-class junior sprinters.

This retrospective study investigated whether corrective adjustment procedures can remove the relative age effect (RAE) from world-class junior sprinters at the beginning of their career. A total of 2,918 male and 3,029 female athletes competing in sprint races (100 m, 200 m, and 400 m) of the World Athletics lists between 2000 and 2018 were considered. Longitudinal quadratic trendline equations across ages 16-25 yrs were calculated considering athletes' exact age and respective performance. Corrective adjustment calculations from the estimated longitudinal quadratic equations were applied at 16 yrs and 17 yrs. RAE was investigated for the whole sample and top-level athletes (i.e., first Top50 and Top100) considering the uncorrected and corrected performance. Moderate to large RAE was observed in Top50 and Top100 at 16 yrs. Differently, a lower RAE was observed at 17 yrs. When re-examining the data using the corrective adjustment calculations, the RAE disappeared in all sprint events and both genders at 16 yrs, while a more equal distribution was observed at 17 yrs. Corrective adjustment procedures can remove or at least reduce the RAE in world-class sprinters. Applying simple equations based on exact age might improve the accuracy of performance evaluation and talent identification in international track and field sprint competitions.

Prevalence and burden of health problems in competitive adolescent distance runners: A 6-month prospective cohort study.

To describe all health problems (injuries and illnesses) in relation to type, location, incidence, prevalence, time loss, severity, and burden, in competitive adolescent distance runners in England. Prospective observational study: 136 competitive adolescent distance runners (73 female athletes) self-reported all health problems for 24-weeks between May and October 2019. Athletes self-reported health problems using the Oslo Sports Trauma Research Centre Questionnaire on Health Problems. The incidence of running-related injury per 1,000 hours of exposure was markedly higher, compared to previous research. At any time, 24% [95% Confidence Intervals (CI): 21-26%] of athletes reported a health problem, with 11% [95% CI: 9-12%] having experienced a health problem that had substantial negative impact on training and performance. Female athletes reported noticeably more illnesses, compared to male athletes, including higher prevalence, incidence, time loss, and severity. The most burdensome health problems, irrespective of sex, included lower leg, knee, and foot/toes injuries, alongside upper respiratory illnesses. The mean weekly prevalence of time loss was relatively low, regardless of health problem type or sex. Competitive adolescent distance runners are likely to be training and competing whilst concurrently experiencing health problems. These findings will support the development of injury and illness prevention measures.

Static postural balance between male athletes with intellectual disabilities and their sedentary peers: A comparative study.

BACKGROUND: Previous reports showed that athletes without disabilities have better postural skills than their sedentary peers. This finding has not been elucidated in athletes with intellectual disabilities despite their decreased postural balance. This study aims to investigate static postural balance in track and field athletes with intellectual disabilities compared to their sedentary peers. METHODS: Eighteen track and field athletes with intellectual disabilities (23.5 ± 4.52 years) and 18 sedentary peers (20.3 ± 3.4 years) participated in this study. A stabilometric platform was used to assess static postural balance in bipedal and unipedal stances with open (OE) and closed (CE) eyes. RESULTS: In OE, the result showed significantly better static postural balance (CoPVm : p < .001; CoParea : p < .001) in athletes compared to the sedentary ones in both stances. In CE, this difference was not observed in the unipedal stance. CONCLUSION: Track and field experience may improve static postural balance in athletes with intellectual disabilities, mainly when visual input is available.

Performance and reference data in the jump squat at different relative loads in elite sprinters, rugby players, and soccer players.

The aims of this study were to compare the outcomes and provide reference data for a set of barbell mechanical parameters collected via a linear velocity transducer in 126 male sprinters (n = 62), rugby players (n = 32), and soccer players (n = 32). Bar-velocity, bar-force, and bar-power outputs were assessed in the jump-squat exercise with jump-squat height determined from bar-peak velocity. The test started at a load of 40% of the athletes' body mass (BM), and a load of 10% of BM was gradually added until a clear decrement in the bar power was observed. Comparisons of bar variables among the three sports were performed using a one-way analysis of variance. Relative measures of bar velocity, force, and power, and jump-squat height were significantly higher in sprinters than in rugby (difference ranging between 5 and 35%) and soccer (difference ranging between 5 and 60%) players across all loads (40-110% of BM). Rugby players exhibited higher absolute bar-power (mean difference = 22%) and bar-force (mean difference = 16%) values than soccer players, but these differences no longer existed when the data were adjusted for BM (mean difference = 2.5%). Sprinters optimized their bar-power production at significantly greater relative loads (%BM) than rugby (mean difference = 22%) and soccer players (mean difference = 25%); nonetheless, all groups generated their maximum bar-power outputs at similar bar velocities. For the first time, we provided reference values for the jump-squat exercise for three different bar-velocity measures (i.e., mean, mean propulsive, and peak velocity) for sprinters, rugby players, and soccer players, over a wide range of relative loads. Practitioners can use these reference values to monitor their athletes and compare them with top-level sprinters and team-sport players.

Do changes in middle-distance running kinematics contribute to the age-related decline in performance?

OBJECTIVES: The aim of this study was to assess ageing-related changes in middle-distance running kinematics and performance in master athletes. METHODS: Male athletes (n=157; 57±13.3 years) competing in the 800- and 1500-m runs at the German Master Athletics Outdoor Championships 2018 were filmed and the bending-over angle, brake angle, leg-stiffness angle, propulsion angle and hip-flexion angle measured. RESULTS: Leg-stiffness and propulsion angle decreased with age (all p<.001), while bending-over, brake and hip-flexion angle increased (all p<.001). Bending-over, propulsion and hip-flexion angles were smaller in 800- than 1500-m races, while the brake angle was larger in 800- than 1500-m races (all p<.001), with no significant difference in leg-stiffness angle between disciplines. In the last round, hip flexion was lower compared to earlier rounds in both distances (p<.001). Age was the major predictor for performance in both races (800-m Radj2=0.74; p<.001, 1500-m Radj2=0.80; p<.001), with a minor impact of technique (improved Radj2 to 0.84 and 0.86, respectively). CONCLUSIONS: The study revealed that the ageing-related decline in running performance of master athletes was primarily explicable by age with only a small contribution of changes in sprint kinematics.

The effect of biological maturity status on ground reaction force production during sprinting.

Sprint ability develops nonlinearly across childhood and adolescence. However, the underpinning ground reaction force (GRF) production is not fully understood. This study aimed to uncover the kinetic factors that explain these maturation-related sprint performance differences in Japanese boys and girls. A total of 153 untrained schoolchildren (80 boys, 73 girls) performed two 50-m maximal effort sprints over a 52-force-platform system embedded in an indoor track. Maturity offset (years from peak height velocity; PHV) was estimated using anthropometric data and used to categorise the children into six-year-long maturation groups (from group 1 [5.5-4.5 years before PHV] to group 6 [0.5 years before to 0.5 years after PHV). Maximum and mean step-averaged velocities across 26 steps were compared across consecutive maturation groups, with further GRF analysis (means and waveforms [statistical parametric mapping]) performed when velocity differences were observed. For boys, higher maximum velocities (effect size ± 90% CI = 1.63 ± 0.69) were observed in maturation group 2 (4.5-3.5 years before PHV) compared to group 1 (5.5-4.5 years before PHV), primarily attributable to higher antero-posterior GRFs across shorter ground contacts. Maximum velocities increased from maturation group 4 (2.5-1.5 years before PHV) to group 5 (1.5-0.5 years before PHV) in the girls (effect size ± 90% CI = 1.00 ± 0.78), due to longer ground contacts rather than higher GRFs per se. Waveform analyses revealed more effective reversal of braking forces and higher propulsive forces (e.g. 14%-77% of stance 4), particularly for comparisons involving boys, which suggested potentially enhanced stretch-shortening ability. Youth sport practitioners should consider these maturation-specific alterations when evaluating young athletes' sprint abilities.

Developing web-based health guidance for coaches and parents in child athletics (track and field).

The aim of this study was to develop athletics health guidance (AHG) aimed at supporting coaches and parents involved in organized child athletics by providing practical advice and tools for the management of the most common health problems experienced in athletics by the 12- to 15-year olds. The study used participatory action research (PAR) and an established health service guideline development procedure modified to fit AHG development in child athletics. A sequential process consisting of four steps with associated subgoals was employed. The collected data were structured according to the AHG development steps and analyzed using qualitative methods. The most common health concern identified was injuries related to growth and overuse. No randomized controlled studies investigating injury prevention programs or any existing concepts/guidelines in child athletics were found that could be used in the development of the AHG. A requirements document was instead defined in a nominal group process and used for the AHG development. The areas included in the final AHG were as follows: training youth athletes, growth and puberty, recovery, injury prevention, injuries and illnesses, mental illness, safe sport, and anti-doping. The evidence regarding health issues in child athletics is limited, indicating that actions to support good health in the sport are currently based essentially on best practice. The long-term aim of the AHG and associated website is to systematically create and introduce conditions that can bridge the "know-do gap" and provide coaches and parents with easy-to-access and up-to-date knowledge in the field of child athlete health in athletics.

Skeletal maturation and growth rates are related to bone and growth plate injuries in adolescent athletics.

Injuries are common in elite adolescent athletics, but few studies have addressed risk factors for injury. Growth and maturation are potential risk factors in this population; however, the current body of literature is both inconclusive and considered at high risk of bias. The aim of this study was therefore to examine whether growth rate, maturity status, and maturity tempo are associated with injury risk in an elite sports academy. Anthropometric, skeletal maturity and injury data collected prospectively over four seasons (117 athlete-seasons) were included in the analyses. Growth rate for stature was associated with greater risk of bone (incidence rate ratio (IRR): 1.5 per one standard deviation increase above the mean; 95% CI: 1.1-1.9) and growth plate injuries (IRR: 2.1; 1.5-3.1). Growth rate for leg length was associated with greater overall injury risk (IRR: 1.3; 1.0-1.7) as well as the risk of bone (IRR: 1.4; 1.0-1.9) and growth plate injuries (IRR: 2.1; 1.4-3.0). Athletes with greater skeletal maturity, expressed as skeletal age (IRR: 0.6 per year; 0.5-0.9) and percentage of predicted mature height (IRR: 0.8 per percent increase; 0.7-1.0), were less prone to growth plate injuries. Rate of change in skeletal age was associated with an increased risk of bone injuries (IRR: 1.5; 1.0-2.3). The results of this study suggest that rapid growth in stature and leg length, skeletal maturity status, and maturity tempo represent risk factors for certain injury types in adolescent athletics.