Perspectives of Ballet Dancers on Causes of Their Injuries and Implementation of Injury Preventive Measures by Ballet Teachers and Masters.

OBJECTIVES: Ballet dancers have a high injury risk. We aimed to gain insight into the causes for acute and overuse injuries in ballet dancers and the level of implementation of injury prevention by ballet teachers/masters, as perceived by dancers. METHODS: An international cross-sectional online-survey was based on the Fit-to-Dance Questionnaire and literature. Adult amateur, pre-professional, and professional ballet dancers reported the perceived causes of their injuries sustained in the previous 2 years. Multiple answers per injury were possible. Also, dancers rated the level of implementation of measures to prevent injury by their ballet teachers and ballet masters based on 21 items using a 5-point Likert scale. Causes were analyzed per-injury as well as per-dancer. RESULTS: 188 ballet ensembles and 51 dance organizations were contacted, from which 192 ballet dancers (mean age 27 ±7.8 yrs, 83% females) responded. 119 dancers (62%) reported 203 acute and 164 (85%) reported 469 overuse injuries. Fatigue was the most frequently perceived cause for acute injuries in the per-injury (n=89, 43.8%) and per-dancer analysis (n=63, 32.8%). For overuse injuries, pressure from the teacher/master was most frequently perceived as cause in the per-injury analysis (n=240, 51.2%), specifically in pre-/professional dancers (n=233, 61.3%). In the per-dancer analysis, fatigue/overtraining scored highest for overuse injuries (n=107; 55.7%). Other causes were previous/repetitive injuries (acute-per-injury 26.1%, acute-per-dancer 22.4%; overuse-per-injury 46.3%, overuse-per-dancer 53.1%) or erroneous dance technique (acute-per-injury 24.6%, acute-per-dancer 21.9%; overuse-per-injury 47.8%, overuse-per-dancer 45.3%). With regard to perceived level of implementation of injury preventive measures by ballet teachers/masters to prevent musculoskeletal injuries, 2 items received high ratings, 12 moderate ratings and 6 low ratings. CONCLUSIONS: Fatigue and pressure accounted for the majority of perceived causes for injuries. Perceived support by ballet teachers/masters regarding injury prevention was moderate to low. Future research should focus on the awareness, attitudes, and the important role of ballet teachers/masters for injury prevention in dancers.

The potential value of observational studies of elective surgical interventions using routinely collected data.

PURPOSE: To assess the apparent validity of observational studies of elective arthroplasty interventions. METHODS: Data from the nationwide Dutch Arthroplasty Register were used. The first case study compared surgical approaches for total hip arthroplasty (posterolateral approach vs. straight lateral approach), where allocation of the intervention was assumed to be mostly independent of patient characteristics. The second case study compared fixation methods (cemented vs. uncemented), where choice of fixation method was expected to depend on patient characteristics. The potential for confounding was quantified by differences between intervention groups and the impact of confounding adjustment. RESULTS: The study of posterolateral approach versus straight lateral approach included 73,750 and 16,557 patients, respectively, and showed no meaningful differences in patient characteristics between treatment groups (standardized mean differences <0.1) and also no relevant impact of confounding adjustment (Z-scores <1). The study of cemented versus uncemented total hip arthroplasty (THA) included 29,579 and 79,360 patients, respectively. Several meaningful imbalances were observed in patient characteristic between the two treatment groups (standardized mean differences >0.1), as well as a relevant impact of confounding adjustment (Z-scores >2). CONCLUSIONS: This study provides insight in the reasoning behind the credibility of observational studies of surgical interventions using routinely collected data and when confounding is expected to have a major impact and thus additional precautions to limit confounding are needed.

Perceptions of Motivational Climate and Association with Musculoskeletal Injuries in Ballet Dancers.

OBJECTIVE: Sports science has identified the trainer-athlete relationship in the etiology of injuries. We aimed to investigate: 1) the association between empowering (EMC) and disempowering (DMC) motivational-climate and musculoskeletal injuries in ballet, and 2) if EMC moderates the association between DMC and injuries. METHODS: A cross-sectional cohort survey-study was conducted online among ballet dancers (>18 yrs old) reporting acute and overuse injuries of the previous 2 years. Motivational climate was assessed with the Empowering-and-Disempowering Motivational Climate Questionnaire (5-point Likert scale). The Oslo Sports Trauma Research Centre Overuse Injury Questionnaire assessed severity of overuse injuries. Linear regression was performed adjusted for the confounders age, sex, expertise, experience, and initiation-age with an interaction term between EMC and DMC to assess effect modification. RESULTS: An international sample of 189 dancers (26.7±7.9 yrs; 130 professionals) reported 197 acute and 465 overuse injuries (in the previous 2 years). Mean EMC was 3.1±1.07, DMC 3.3±1.08. EMC was associated with less acute (b=-0.22; 95%CI -0.40 to -0.04) and overuse injuries (b=-0.74; 95%CI -0.99 to -0.50), while DMC was associated with more injuries (acute: b=0.30; 95%CI 0.13 to 0.47; overuse: b=0.74; 95%CI 0.50 to 0.98). When tested together and adjusted for confounders, EMC lost its protective effect (acute: b=-0.15; 95%CI -0.19 to 0.49; overuse: b=-0.34; 95%CI -0.81 to 0.13). DMC was positively associated with injuries throughout all settings (acute: b=0.43; 95%CI 0.10 to 0.76; overuse: b=0.46; 95%CI 0.00 to 0.91). EMC showed no moderating effects on DMC in the adjusted models. CONCLUSION: To avoid injuries, it is not enough to create an EMC, because any disempowering nuances may negatively affect empowering climates. Teachers should avoid DMC altogether to prevent injuries in dancers.

The association of birth weight and infant growth with childhood autonomic nervous system activity and its mediating effects on energy-balance-related behaviours-the ABCD study.

BACKGROUND: The purpose of this study was to examine the association of birth weight and infant growth with childhood autonomic nervous system (ANS) activity and to assess whether ANS activity mediates the associations of birth weight and infant growth with energy-balance-related behaviours, including energy intake, satiety response, physical activity and screen time. METHODS: In 2089 children, we prospectively collected birth weight, infant growth defined as conditional weight and height gain between birth and 12 months and-at 5 years-indices of cardiac ANS activity and parent-reported energy-balance-related behaviours. A mediation analysis was conducted, based on MacKinnon's multivariate extension of the product-of-coefficients strategy. RESULTS: Birth weight and infant height gain were inversely associated with sympathetic, but not parasympathetic, activity at age 5. Infant weight gain was not associated with childhood ANS activity. Infant weight gain was predictive of increased childhood screen time and infant height gain of diminished childhood energy intake, but sympathetic activity did not mediate these associations. CONCLUSIONS: Low-birth-weight children have higher sympathetic activity, which is considered a risk factor for cardiovascular disease. Height gain in infancy seems to be beneficial for childhood sympathetic activity. However, sympathetic activity was no mediator of the associations of infant growth with childhood energy-balance-related behaviours. As individual differences in ANS activity predict increased risk of cardiovascular disease, these differences may offer insight into the early-life origins of chronic diseases and provide further basis for public health strategies to optimize birth weight and infant growth.