Improving Foot Strength in Vocational Ballet Dancers

March 25, 2025 updated by: University of Bern

The Effects of Two Foot Strengthening Interventions on Toe Flexor Strength and Jumping Performance in Vocational Ballet Dancers: A Randomized Controlled Trial

Professional dancers subject their feet to high forces through frequent jumping, repeated heel rises, insufficient shoe cushioning, and a high degree of foot mobility. To prevent injuries and improve jumping performance, dancers are recommended to strengthen the muscles of the lower extremities.

The foot muscles, especially the toe flexors, play an important role as shock absorbers and motors for the foot by absorbing and generating mechanical energy, which is essential for human locomotion. Furthermore, they serve as a link between the powerful leg extensor muscles and the ground, transmitting the energy generated by the larger muscle groups. This makes them essential components of overall athletic performance. However, the impact of foot muscle strength on dancers´ jumping performance remains uncertain. Therefore, the aim of this study is to investigate the effectiveness of two training programs designed to strengthen the toe flexor muscles in dancers. For this project, a 6.5-week intervention with ballet students from a vocational ballet school is planned. Before and after the intervention, all study participants will perform tests to assess foot muscle strength and jumping performance.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

This study aims to develop two different toe flexor (TF) exercise programs for vocational dancers to enhance TF strength and jumping performance. It is hypothesized that i) both training programs increase TF strength and jumping performance, ii) horizontal jumps are more affected than vertical jumps, and iii) the TF exercise program with the TF strengthening device has a greater impact on TF strength.

Participants

Participants will be recruited from a vocational ballet school via an email detailing the study outline. They and their legal guardians (for participants under 18 years old) will be informed of the potential risks and benefits of the study. They will provide written informed consent prior to the measurements. Participants will then be assigned to either a control group, a toe flexor device experimental group, or a heel rise experimental group. The schedule includes three and a half weeks of training, a 12-day break due to the school schedule, followed by another three weeks of training. This will result in a total of 26 training sessions. An experienced trainer will supervise all training sessions. The control group will continue with the ballet school´s normal training schedule.

Data collection and management

An intervention protocol will be kept to collect information on compliance and progression of the training, such as the number of repetitions and the resistance applied. Data analysis will be performed according to the intention-to-treat (ITT) principle, in which participants are analyzed according to their original treatment group assignment. An additional researcher will manage reporting for adverse effects (such as delayed onset muscle soreness) and adverse events. All data collected in this study will be anonymized, personal identifiers removed, and data coded to protect the identities of the participants.

Sample size

Due to the study´s novel character, no sample size calculations have been conducted. To the researchers' best knowledge, no comparable protocols to improve TF strength have been investigated, so a sample size calculation was not warranted. The study is, therefore, exploratory.

Statistical analysis

Variables will be presented as the mean ± standard deviation. The Shapiro-Wilk test will be performed to assess the normality of the measured variables. Repeated-measures Analysis of Variance (ANOVA) with Bonferroni correction will be used to analyze variables across different times and groups. Non-normally distributed variables will be analyzed using Friedman ANOVA and Kruskal-Wallis ANOVA, with multiple comparisons of mean ranks for individual comparisons. Statistical analyses will be performed using IBM SPSS Statistics for Windows (Version 29.0), and the statistical significance level will be set to .05. If the primary and/or secondary outcomes yield null findings, equivalence testing will be conducted to determine whether the intervention is equivalent to the usual training (control group). The two one-sided tests (TOST) procedure will be applied, using either standardized differences (e.g., Cohen's d) or raw differences.

Study Type

Interventional

Enrollment (Actual)

49

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United Kingdom
      • Birmingham, United Kingdom, B57UH
        • Elmhurst Ballet School

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child
  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria

  • Being a ballet student at the Elmhurst Ballet School.
  • Aged 14 to 19.
  • Written informed consent (by the participant and/or their legal guardian).

Exclusion Criteria:

  • Any recent lower leg or foot injuries.
  • Chronic pain in the lower extremities.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Basic Science
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: "Toe flexor device" experimental group

Participants will complete:

  • 3 sets of 15 repetitions with a 90-second break between each set.
  • Tempo 2-0-2-0
  • 4 times per week
  • Progression will be achieved by increasing the stiffness of the elastic band whenever the participant can perform 15 repetitions without great effort.
Other: "Toe flexor device" experimental group
This intervention group will perform toe flexion using a toe flexor (TF) device, which facilitates the shortening and stretching of the TF muscle-tendon units (MTUs) against resistance bands. While seated, participants will push a pedal down with their toes over two counts and release it over two counts.
Experimental: "Inclined Heel Rise" experimental group

Participants will complete:

  • 3 sets of 10 to 15 repetitions with a 90-second break between each set.
  • Tempo 2-0-2-0
  • 4 times per week
  • Progression will be achieved by increasing the number of repetitions to 15 and then adding weights to be held in the ipsilateral hand.
Other: "Inclined Heel Rise" experimental group
This intervention group will perform single-leg heel rises on an inclined platform. Participants will place their hands against a barre for balance support, lift their heels over two counts, and lower them over two counts.
No Intervention: Control group
The control group will continue with the ballet school's normal training schedule.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Maximal voluntary isometric contraction (MVIC) of the toe flexors muscles
Time Frame: Measurements will be performed one week prior to and one week after the intervention.
The post-intervention difference between the three groups in MVIC of the toe flexors measured with a custom-made toe flexor dynamometer in a seated position (90° angle in the hips and knees) where the foot is secured with a strap. Participants will push with their toes against a pedal and hold this isometric contraction for 2-3 seconds. The strength will be normalized by body weight (N/kg).
Measurements will be performed one week prior to and one week after the intervention.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Vertical jump - Countermovement jump (CMJ) - Jump height (cm)
Time Frame: Measurements will be performed one week prior to and one week after the intervention.
Participants will perform three CMJs on a Hawkin Dynamics force plate. They will stand upright on the plate and be instructed to jump as high as possible with their hands positioned on their hips.
Measurements will be performed one week prior to and one week after the intervention.
Vertical jump - CMJ - changes in force parameters
Time Frame: Measurements will be performed one week prior to and one week after the intervention.
Participants will perform three CMJs on a Hawkin Dynamics force plate. The variables collected will be peak power (W), peak propulsive force (N), and peak landing force (N).
Measurements will be performed one week prior to and one week after the intervention.
Vertical jump - Sauté jump - jump height (cm)
Time Frame: Measurement will be performed one week prior to and one week after the intervention.
Participants will perform three sautés on a Hawkin Dynamics force plate. They will perform a ballet-specific jump in an upright position with the legs externally rotated. Participants will be instructed to jump as high as possible.
Measurement will be performed one week prior to and one week after the intervention.
Vertical jump - Sauté - changes in force parameters
Time Frame: Measurements will be performed one week prior to and one week after the intervention.
Participants will perform three sautés on a Hawkin Dynamics force plate. The variables collected will be peak power (W), peak propulsive force (N), and peak landing force (N).
Measurements will be performed one week prior to and one week after the intervention.
Horizontal jump - Long jump - jump distance (cm)
Time Frame: Measurements will be performed one week prior to and one week after the intervention.
Participants will perform three horizontal long jumps with their hands positioned on their hips. The distance of the jumps will be measured (cm).
Measurements will be performed one week prior to and one week after the intervention.

Other Outcome Measures

Outcome Measure
Measure Description
Time Frame
End User Questionnaire
Time Frame: After the intervention, up to one hour.
The questionnaire features questions on participant satisfaction, the perceived effectiveness of the program, and the clarity and ease of following instructions. It invites suggestions for improvement and assesses the overall impact of the intervention. Scores range from 1 to 5, with higher scores indicating better clinical outcomes.
After the intervention, up to one hour.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University of Bern

Collaborators

German Sport University, Cologne
Elmhurst Ballet School, Birmingham

Investigators

  • Principal Investigator: Anna Schrefl, MSc, University of Bern
  • Study Chair: Daniel Erlacher, PhD, University of Bern
  • Study Chair: Andrea Schaerli, PhD, University of Bern
  • Study Chair: Nico Kolokythas, PhD, Elmhurst Ballet School

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

September 10, 2024

Primary Completion (Actual)

December 5, 2024

Study Completion (Actual)

December 15, 2024

Study Registration Dates

First Submitted

September 5, 2024

First Submitted That Met QC Criteria

September 5, 2024

First Posted (Actual)

September 19, 2024

Study Record Updates

Last Update Posted (Actual)

March 26, 2025

Last Update Submitted That Met QC Criteria

March 25, 2025

Last Verified

March 1, 2025

More Information

Terms related to this study

Keywords

Other Study ID Numbers

  • 5/24/AS/UOW

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

Sensitive data of the students and the school.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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