Effect of different stretching strategies on the kinetics of vertical jumping in female volleyball athletes

Purpose： The present study aimed to examine the effect of static stretching （SS） and a sport-specific dynamic stretching （DS） session at two specific post-stretch time intervals in highly trained female athletes （age 19.90 ± 1.60 years; height 1.80 ±0.06 m; mass 76.87 ± 9.95 kg） on kinetic parameters of peak force, time-to-takeoff, and rate of force development. Methods： The data were collected over 3 days （randomized within subject design with control session）. Following each stretch session （SS vs. DS vs. control） of equal duration （7 min total： 30 s per targeted muscle group） participants performed countermovement jumping on a force platform at 1 and 15 rain after stretching. Results： The DS session significantly improved upon kinetic variables of rate of force development, peak force, and time-to-takeoffrelative to SS at 1 min after stretching. No significant effect was found at 15 min. Conclusion： Together these findings suggest that when training and competing to jump quickly and maximally the female athlete should incorporate DS instead of SS as part of their pre-competition warm-up, but conduct performance within 15 min of their warm-up to elicit maximal gains

Vitamin D Status and Bone Mineral.Density in Female Collegiate Dancers and Cheerleaders

Bone mineral density reflects an athlete＇s cumulative history of energy availability, physical activity, and menstrual status, as well as nutritional and environmental factors. Although sports with high-impact loading are associated with higher bone mineral density than low-impact or non-impact sports, confounding variables are differences in the athletes＇ body size and sport-specific training. The purpose of this study was to determine if bone mineral density （BMD） and vitamin D status are different between two groups of female collegiate athletes who have comparable body size/weight requirements, but who engage in qualitatively different training regimens. Full body, spine and dual femur BMD was assessed by dual energy X-ray absorptiometry （DXA） in members of a university pep-dance team （n = 10） or cheer team （n = 9）, ages 18-22. Plasma vitamin D status was assessed by ELIZA. There was no significant difference between the groups for total body BMD （1.23 g/cm^2 dance vs 1.22 g/cm^2 cheer, P = 0.70）, spine BMD （1.39 g/cm^2 dance vs 1.36 g/cm^2 cheer, P = 0.72） or dual femur BMD （1.20 g/cm^2 dance vs 1.11 g/cm^2, P = 0.23）. Insufficient serum vitamin D status （20-32 ng/mL） was found in 74% of the athletes （27 ± 4 ng/mL, dance and 25 ± 8 ng/mL, cheer）. In addition, estimated daily vitamin D and calcium intakes were less than the RDA for both dancers and cheerleaders. Despite nutritional insufficiencies, BMD was not significantly different between the low-impact activity pep dance team and high-impact activity cheer team, suggesting that the type of physical activity was not as important for BMD in these athletes as participating in 20＋ hours a week of physical activity, which could have counteracted the negative effects of the nutrient insufficiencies on their bone health.

Comparison of the‘Seattle’and‘International’Criteria Electrocardiogram Interpretation in Division II Female Collegiate Athletes:A Preliminary Study

Purpose A 12-lead electrocardiogram(ECG)is a screening tool to detect abnormalities that may predispose athletes to sud-den cardiac death.Newer standardized criteria have been introduced to better interpret ECG data,however this research has predominantly focused on male athletes.It is important to include female athletes in research to better define ECG character-istics in this population.The purpose of this study was to compare the Seattle and International Criteria ECG abnormalities in Division II female collegiate athletes of various ethnicities.Methods Fifty-six females(age 20.2±1.4 years;height 1.70±0.7 m;weight 69.5±8.9 kg)completed a resting 12-lead ECG protocol.ECG data was classified as‘normal’and‘abnormal’according to the parameters of each criterion and abnormal conditions were noted.Chi-square analysis was used to assess statistical comparisons between criteria.Results There was a significant difference in abnormal classifications as the total number of ECGs identified as abnormal using the Seattle Criteria decreased from 12(21.4%)to 2(3.6%)when using the International Criteria(P<0.05).African American athletes had a higher number of abnormal ECG’s compared to White and Latina athletes using the Seattle Criteria(P=0.03).Conclusions The International Criteria significantly reduces the total number of abnormal ECG readings in female collegiate athletes compared to the Seattle Criteria and did not overly identify African American athletes with abnormalities.Further research is necessary to expand on this study and clearly define criteria for female athletes of various ethnicities.

The Rise of China’s Women’s Basketball Team:An Exploration of Gender Equality in Professional Basketball

This article explores the rise of the Chinese women’s basketball team in professional basketball and its relationship to gender equality issues.In view of the gender differences in salary,market value,social status,and other aspects,the article proposes a series of strategies to promote the realization of gender equality for female basketball players in professional basketball.This article points out that the rise of the Chinese women’s basketball team will lead the process of gender equality and lay the foundation for a more equitable and inclusive future.To achieve this goal,this article highlights the importance of improving the competitive level of female athletes,improving basic education,promoting basketball culture,and promoting gender equality.

Pelvic region bone density,soft tissue mass,and injury frequency in female professional ballet dancers and soccer athletes

We recently observed a high prevalence of low pelvic bone mineral density(BMD)in female professional ballet performers.Because this population is susceptible to musculoskeletal overuse injuries,we aimed to determine which regions of the pelvis may be at greatest risk compared to general population females(GENPOP)as well as professional female soccer players(SOCCER,a comparison to other elite athletes regularly subjected to high degrees of loading).Three groups of age-matched females[(GENPOP;n=38,27±1yrs),(BALLET;single com-pany,n=36,26±3yrs),(SOCCER;single NWSL■club,n=34,25±1yrs)]consented to have their BMD and body composition assessed(DEXA,GE■).In addition to soft tissue and total and regional BMD analyses,a segmental analysis of the pelvis was performed to determine site-specific BMD for the iliac fossa,iliac fossa/iliac crest/ilium combined,pubic bone,ischium,and sacrum.A mixed-model ANOVA followed by a Tukey's post-hoc test was used to compare the groups(Type-I error;α=0.05).The BALLET group had lower pelvic BMD for all measures(Avg.%Diff.=15%-27%,p<0.001)compared to the SOCCER group and for the ischium(Avg.%Diff.=8%;p=0.007)and sacrum(Avg.%Diff.=7%;p=0.028)compared to the GENPOP group.The BALLET group had lower lean mass for all measures compared to the other groups(Avg.%Diff.=12%-18%;p<0.01).Professional ballet performers exhibit reduced pelvic region soft tissue and site-specific BMD not previously detected using standard DEXA analyses.These findings highlight which pelvic regions may benefit from preventative strength training and/or nutritional interventions.

Is it Possible to Protect the Adolescent Brain with Internal Mechanisms from Repetitive Head Impacts:Results from a PhaseⅡSingle Cohort,Longitudinal,Self-Control Study

Purpose To quantify the effects of an externally worn collar device for mitigating the influence of repetitive head impacts on alterations to diffusion tensor imaging(DTI)metrics of white matter.Methods Fifteen female high-school soccer athletes(age:14.00-16.98 yrs)completed pre-and post-season DTI over two consecutive years,including measures of diffusivity,changes in which may be associated with brain dysfunction.The collar was worn during year 1(Yr1)but not during year 2(Yr2).Athlete exposures(AEs)and head impact exposure were recorded over the competitive seasons.Results There were no significant differences in AEs or head impact exposures between Yr1 and Yr2(P>0.05).In Yr2,there was significant pre-to post-season mean diffusivity and/or axial diffusivity reduction in multiple WM regions(cor-rected P<0.05).Pre-to post-season mean diffusivity,axial diffusivity,and radial diffusivity decreases were 3.04%±2.53%,2.97%±2.19%,and 3.37%±3.34%,respectively,significantly greater than pre-to post-season changes in Yr1(mean dif-fusivity:-0.31%±1.78%,P=0.0014;axial diffusivity:-0.02%±2.25%,P=0.0014;radial diffusivity:-0.63%±2.10%,P=0.0030).Conclusions Mild bilateral compression to athletes'internal jugular vein through collar application may have increased intracranial blood volume and spatially redistributed head-impact-derived brain energy absorption.However,future research is needed to elucidate the potential clinical significance of WM changes of various degrees.Clinical trails registration NCT03014492.

Effects of a soccer-specific vertical jump on lower extremity landing kinematics

Anterior cruciate ligament(ACL)injury frequently occurs in female soccer athletes during deceleration movements such as landings.In soccer,landings mostly occur following jumping headers.Little research has been done to determine the mechanics that follow and how they compare to standard drop vertical jumps(DVJ).The purpose of this study was to analyze differences in kinematics between the DVJ and the soccer-specific vertical jump(SSVJ)in female soccer athletes to better assess the sport-specific risk for ACL injury.A secondary aim was to compare second landings(L2)to first landings(L1).Eight female recreational soccer athletes performed DVJs and SSVJs initiated from a 31 cm height.Motion capture was performed during landings and data were analyzed using repeated-measures ANOVA.SSVJs produced less peak hip flexion(p=0.03)and less peak knee flexion(p=0.002)than DVJs.SSVJs also demonstrated increased ankle plantarflexion at initial contact(IC)than DVJs(p=0.005).L2s produced less peak hip(p=0.007)and knee flexion(p=0.002)than L1s.SSVJs and L2s displayed a more erect landing posture than the DVJs and L1s at the hip and knee,a known ACL risk factor.The significant results between jump styles show that the SSVJ displays mechanics that are different from the DVJ.The SSVJ may be a better sport-specific screening tool for ACL injury mechanisms than the DVJ in soccer athletes as it has a more direct translation to the sport.