Improving Foot Strength in Vocational Ballet Dancers

NCT ID: NCT06589050

Last Updated: 2025-03-26

Basic Information

• Recruitment Status: COMPLETED
• Clinical Phase: NA
• Total Enrollment: 49 participants
• Study Classification: INTERVENTIONAL
• Study Start Date: 2024-09-10
• Study Completion Date: 2024-12-15

Brief Summary

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.

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.

Conditions

Toe Flexor Strength

Study Design

• Allocation Method: RANDOMIZED
• Intervention Model: PARALLEL
• Primary Study Purpose: BASIC_SCIENCE
• Blinding Strategy: NONE

Study Groups

"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.

Group Type: EXPERIMENTAL

"Toe flexor device" experimental group

Intervention Type: OTHER

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.

"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.

Group Type: EXPERIMENTAL

"Inclined Heel Rise" experimental group

Intervention Type: OTHER

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.

Control group

The control group will continue with the ballet school's normal training schedule.

Group Type: NO_INTERVENTION

No interventions assigned to this group

Interventions

"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.

Intervention Type: 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.

Intervention Type: OTHER

Eligibility Criteria

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.

• Minimum Eligible Age: 14 Years
• Maximum Eligible Age: 19 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

Elmhurst Ballet School, Birmingham

UNKNOWN

Sponsor Role: collaborator

German Sport University, Cologne

OTHER

Sponsor Role: collaborator

University of Bern

OTHER

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Principal Investigators

Anna Schrefl, MSc

Role: PRINCIPAL_INVESTIGATOR

University of Bern

Daniel Erlacher, PhD

Role: STUDY_CHAIR

University of Bern

Andrea Schaerli, PhD

Role: STUDY_CHAIR

University of Bern

Nico Kolokythas, PhD

Role: STUDY_CHAIR

Elmhurst Ballet School

Locations

Elmhurst Ballet School

Birmingham, , United Kingdom

Countries

United Kingdom

References

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Reference Type: BACKGROUND

PMID: 22747582 (View on PubMed)

Goldmann JP, Sanno M, Willwacher S, Heinrich K, Bruggemann GP. The potential of toe flexor muscles to enhance performance. J Sports Sci. 2013;31(4):424-33. doi: 10.1080/02640414.2012.736627. Epub 2012 Oct 30.

Reference Type: BACKGROUND

PMID: 23106289 (View on PubMed)

Chiu LZF, Daehlin TE. Midfoot and Ankle Mechanics in Block and Incline Heel Raise Exercises. J Strength Cond Res. 2021 Dec 1;35(12):3308-3314. doi: 10.1519/JSC.0000000000004145.

Reference Type: BACKGROUND

PMID: 34570059 (View on PubMed)

Jarvis DN, Kulig K. Kinematic and kinetic analyses of the toes in dance movements. J Sports Sci. 2016 Sep;34(17):1612-8. doi: 10.1080/02640414.2015.1126672. Epub 2015 Dec 21.

Reference Type: BACKGROUND

PMID: 26691227 (View on PubMed)

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Reference Type: BACKGROUND

PMID: 35872091 (View on PubMed)

Tourillon R, Gojanovic B, Fourchet F. How to Evaluate and Improve Foot Strength in Athletes: An Update. Front Sports Act Living. 2019 Oct 11;1:46. doi: 10.3389/fspor.2019.00046. eCollection 2019.

Reference Type: BACKGROUND

PMID: 33344969 (View on PubMed)

Willemse L, Wouters EJM, Pisters MF, Vanwanseele B. Plantar intrinsic foot muscle activation during functional exercises compared to isolated foot exercises in younger adults. Physiother Theory Pract. 2024 Aug;40(8):1656-1668. doi: 10.1080/09593985.2023.2204947. Epub 2023 Apr 26.

Reference Type: BACKGROUND

PMID: 37126537 (View on PubMed)

Other Identifiers

5/24/AS/UOW

Identifier Type: -

Identifier Source: org_study_id