Lower Limb and Foot Health in Danish Paediatric Ballet Dancers and Foot-ballers

Background and Rationale

Participation in organized sports during childhood is associated with substantial physical, psychological, and social benefits. However, intensive training during skeletal growth may also be associated with adaptations in joint mobility, lower limb alignment, and foot morphology, as well as musculoskeletal pain and overuse-related conditions.

Ballet and football impose different mechanical demands on the developing musculoskeletal system. Ballet requires substantial hip external rotation, ankle plantarflexion, and specific postural control, whereas football involves repetitive running, kicking, jumping, and rapid changes of direction.

Despite these differences, comprehensive data on lower limb anthropometrics, rotational profiles, foot morphology, functional characteristics, and pain in young athletes remain limited.

A previous Danish study established reference data on lower limb and foot characteristics in 501 typically developing schoolchildren aged 6-17 years. The present study will extend this research by examining children participating in ballet and football.

Study Objectives

The primary objective is to compare passive external hip rotation between ballet dancers and an age- and sex-frequency-matched reference cohort of typically developing children.

The primary hypothesis is that ballet dancers demonstrate greater passive external hip rotation than children in the reference cohort.

Secondary objectives include:

1. Evaluating ankle range of motion, particularly plantarflexion, in ballet dancers compared with the reference cohort.
2. Characterizing lower limb rotational profiles, anthropometric measurements, and foot morphology in ballet dancers and football players.
3. Investigating associations between clinical and biomechanical characteristics, musculoskeletal pain, functional measures, and patient-reported outcomes.
4. Exploring sport-specific movement characteristics, balance, and loading patterns.
5. Examining how children experience, communicate, and manage lower limb pain and soreness within ballet and football training environments.

Comparisons involving football players and sport-specific functional assessments will be considered exploratory.

Study Design and Participants

This is an observational, cross-sectional study involving approximately 148 children aged 7-16 years, including 74 ballet dancers and 74 football players.

Participants will be recruited from the Royal Danish Ballet School and selected Danish football clubs. Eligible children will belong to predefined age groups (7-8, 11-12, or 15-16 years) and meet age- and sport-specific minimum training requirements.

Clinical findings will be compared with an existing reference cohort of 501 typically developing Danish schoolchildren. Comparisons with the reference cohort will account for age group and sex.

Clinical and Functional Assessments

Each participant will undergo a standardized clinical examination, including:

• Lower limb anthropometric measurements.
• Hip internal and external rotation.
• Ankle and foot range of motion.
• Lower limb rotational and angular alignment.
• Generalized joint hypermobility.
• Clinical foot posture and morphology.
• Assessment of common foot conditions.

Sport-specific functional assessments will examine movement characteristics, joint mobility, balance, and neuromuscular control. These assessments will include evaluation of active turnout in ballet dancers and functional movement tasks relevant to the participants' sports.

Three-dimensional foot scanning will be performed using a Volumental scanner to obtain standardized measurements of foot morphology, including foot length, width, arch height, instep dimensions, and other anatomical parameters.

Footwear dimensions and fit will also be assessed.

Patient-reported outcome measures will evaluate musculoskeletal pain, ankle and foot function, health-related quality of life, and sport-related overuse problems. Instruments will include age-appropriate pain rating scales, the Oxford Ankle Foot Questionnaire for Children (OxAFQ-C), the Pediatric Quality of Life Inventory (PedsQL), and the Oslo Sports Trauma Research Centre (OSTRC) questionnaire.

Qualitative Component

A complementary qualitative component will explore children's experiences of lower limb pain, soreness, and training culture.

Short-term observations will be conducted during regular ballet and football training sessions over approximately 3-4 weeks.

Subsequent focus group interviews will involve selected children and their teachers or coaches. Interviews will examine experiences of pain, communication about symptoms, and attitudes toward physical discomfort during training.

Qualitative data will be evaluated using reflexive thematic analysis.

Statistical Analysis

The primary analysis will compare passive external hip rotation between ballet dancers and the reference cohort using linear regression.

The participant-level mean of the right and left hip measurements will be used as the primary outcome. Results will be presented as mean differences with 95% confidence intervals.

Secondary analyses will evaluate associations between anthropometric measurements, range of motion, functional characteristics, pain intensity, and patient-reported outcomes.

Multivariable regression models will account for relevant potential confounders, including age, sex, body mass index, and training volume, where applicable.

Generalized estimating equations will be used when bilateral measurements are analyzed separately to account for within-participant correlation.

Multiple secondary and exploratory comparisons will be addressed using the Benjamini-Hochberg false discovery rate procedure.

Study Significance

The study will provide detailed descriptive and comparative information on lower limb and foot characteristics in young ballet dancers and football players.

The findings may help distinguish normal developmental variation and sport-related adaptations from characteristics associated with musculoskeletal symptoms.

Because the study is cross-sectional, it cannot establish causal relationships or predict future injuries.

The results may contribute to future longitudinal studies and inform clinical assessment, injury prevention, training recommendations, and musculoskeletal health promotion in physically active children.