Effects of Strength Training on the Plantar Flexors' Properties After Achilles Tendon Rupture

January 28, 2026 updated by: Jeam Marcel Geremia, Federal University of Rio Grande do Sul

Effects of Strength Training at Different Intensities on the Plantar Flexors' Functional, Neuromuscular, and Tendon Properties After Achilles Tendon Rupture

Among the injuries that affect the Achilles tendon, rupture is one of the most frequent. This injury can generate functional, neuromuscular, and tendon deficits that can last for long periods or even be permanent. In the long term (i.e., more than a year after the injury), individuals present functional impairments related to the lower limb, deficits in the capacity to produce muscle force, as well as higher levels of muscle activation (as a compensatory response). Such changes may be due to injury adaptations in the plantar flexor muscles' architecture, which may have shorter, more pennate fibers, leading to reduced muscle thickness. Furthermore, the Achilles tendon may be elongated, with a greater cross-sectional area, presenting lower stiffness and quality (i.e., lower Young's modulus). Strength training can play an important role in recovering from Achilles tendon ruptures, as it promotes functional, neuromuscular, and tendon adaptations that can minimize deficits caused by the injury. However, there is a gap in the literature regarding strength training, as well as the dose vs response relationship, regarding functional, neuromuscular, and tendon adaptations after Achilles tendon rupture. Thus, the aim of the present study is to compare the effects of a strength training program of different intensities on plantar flexors' functional, neuromuscular, and tendon outcomes after Achilles tendon rupture. Men aged between 20 and 50 years old who suffered a total unilateral rupture of the Achilles tendon between one and five years after the rupture will be included in the study, as well as healthy men who did not suffer the rupture (control group). Participants who have suffered an Achilles tendon rupture will undergo a progressive lower limb strength training program twice a week for a total duration of 12 weeks, which will be randomized between two groups: low intensity (G55 - 55% of 1-RM) and moderate intensity (G70 - 70% of 1-RM). The following outcomes will be evaluated: a) Achilles tendon's morphological (length and cross-sectional area), mechanical (force-elongation relationship and stiffness) and material (stress-strain relationship and Young's modulus) properties; b) triceps surae muscles' morphological (architecture [fascicle length, pennation angle and thickness] and quality [measured by echointensity and specific tension]) properties; c) ankle functionality (maximum height in the heel raise test); d) the plantar flexors' force production capacity (peak and rate of torque development in different joint positions); e) the plantar flexors' muscle voluntary activation; and f) triceps suraes' neuromuscular capacity (i.e., recruitment curves). Assessments will be performed at two times (pre-training; and after 12 weeks of training [post-12]) through functional tests, ultrasound techniques, isokinetic dynamometry, electromyography, and percutaneous electrical stimulation. An intraclass correlation coefficient will be used to verify the test-retest reproducibility of ultrasound measurements. The Chi-Square test will be used to compare the level of physical activity (pre-training) between the groups. The results of the intervention will be expressed using descriptive statistics (mean, standard deviation, and standard error). The normality and sphericity of the data will be tested using the Shapiro-Wilk and Mauchly tests, respectively. A generalized estimating equation, followed by Bonferroni post-hoc, will be used to compare the effects of groups (G55 and G70) and times (pre-training, Post-6, and Post-12). A one-way ANOVA, followed by a Bonferroni post-hoc, will be used to compare the control group participants' limbs with the healthy and injured limbs from both intervention groups (G55 and G70) in the Pre and Post-12 times. The effect size will be estimated for each outcome. All statistical analyzes will be performed using SPSS software.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

Among the injuries that affect the Achilles tendon, rupture is one of the most frequent. This injury can generate functional, neuromuscular, and tendon deficits that can last for long periods or even be permanent. In the long term (i.e., more than a year after the injury), individuals present functional impairments related to the lower limb, deficits in the capacity to produce muscle force, as well as higher levels of muscle activation (as a compensatory response). Such changes may be due to injury adaptations in the plantar flexor muscles' architecture, which may have shorter, more pennate fibers, leading to reduced muscle thickness. Furthermore, the Achilles tendon may be elongated, with a greater cross-sectional area, presenting lower stiffness and quality (i.e., lower Young's modulus). Strength training can play an important role in recovering from Achilles tendon ruptures, as it promotes functional, neuromuscular, and tendon adaptations that can minimize deficits caused by the injury. However, there is a gap in the literature regarding strength training, as well as the dose vs response relationship, regarding functional, neuromuscular, and tendon adaptations after Achilles tendon rupture. Thus, the aim of the present study is to compare the effects of a strength training program of different intensities on plantar flexors' functional, neuromuscular, and tendon outcomes after Achilles tendon rupture. Men aged between 20 and 50 years old who suffered a total unilateral rupture of the Achilles tendon between one and five years after the rupture will be included in the study, as well as healthy men who did not suffer the rupture (control group). Participants who have suffered an Achilles tendon rupture will undergo a progressive lower limb strength training program twice a week for a total duration of 12 weeks, which will be randomized between two groups: low intensity (G55 - 55% of 1-RM) and moderate intensity (G70 - 70% of 1-RM). The following outcomes will be evaluated: a) Achilles tendon's morphological (length and cross-sectional area), mechanical (force-elongation relationship and stiffness) and material (stress-strain relationship and Young's modulus) properties; b) triceps surae muscles' morphological (architecture [fascicle length, pennation angle and thickness] and quality [measured by echointensity and specific tension]) properties; c) ankle functionality (maximum height in the heel raise test); d) the plantar flexors' force production capacity (peak and rate of torque development in different joint positions); e) the plantar flexors' muscle voluntary activation; and f) triceps suraes' neuromuscular capacity (i.e., recruitment curves). Assessments will be performed at two times (pre-training; and after 12 weeks of training [post-12]) through functional tests, ultrasound techniques, isokinetic dynamometry, electromyography, and percutaneous electrical stimulation. An intraclass correlation coefficient will be used to verify the test-retest reproducibility of ultrasound measurements. The Chi-Square test will be used to compare the level of physical activity (pre-training) between the groups. The results of the intervention will be expressed using descriptive statistics (mean, standard deviation, and standard error). The normality and sphericity of the data will be tested using the Shapiro-Wilk and Mauchly tests, respectively. A generalized estimating equation, followed by Bonferroni post-hoc, will be used to compare the effects of groups (G55 and G70) and times (pre-training, Post-6, and Post-12). A one-way ANOVA, followed by a Bonferroni post-hoc, will be used to compare the control group participants' limbs with the healthy and injured limbs from both intervention groups (G55 and G70) in the Pre and Post-12 times. The effect size will be estimated for each outcome. All statistical analyzes will be performed using SPSS software.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
67

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • 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 Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Locations

  • Brazil
    • Rio Grande do Sul
      • Porto Alegre, Rio Grande do Sul, Brazil, 90690-200
        • Recruiting
        • Exercise Research Laboratory (LAPEX) - School of Physical Education, Physiotherapy, and Dance
        • Contact:

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

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Men aged 18 to 64 who have ruptured their Achilles tendon unilaterally no more than 5 years ago;
  • Who are not performing systematic and regular calf strength training.

Exclusion Criteria:

  • Non-surgical treatment for Achilles tendon rupture;
  • History of postsurgical complications (infection or re-rupture);
  • Presence of any type of ankle injury in the last six month;
  • Participation in a strength training program for plantar flexors in the last six months prior to participation in the study;
  • Having heart failure; autoimmune diseases; and/or diabetes;
  • Systematic use of antibiotics or steroids within the last 12 months;
  • Presence of any other clinical contraindication for performing maximum strength tests.

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: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: Strength training (low intensity)
Twelve weeks of strength training program for the calf muscles, with low load intensity
Other: Exercise
A progressive calf strength training program lasting 12 weeks (twice weekly sessions), with a total of 25 visits to the gym. Specific exercises for ankle flexors: standing unilateral plantar flexion (on the machine) and seated unilateral plantar flexion (adapted on the Smith machine) will be performed. Participants will use progressive load from 55% of one repetition maximum load for the specific plantar flexion exercises.
Other: Exercise
A progressive calf strength training program lasting 12 weeks (twice weekly sessions), with a total of 25 visits to the gym. Specific exercises for ankle flexors: standing unilateral plantar flexion (on the machine) and seated unilateral plantar flexion (adapted on the Smith machine) will be performed. Participants will use progressive load from 70% of one repetition maximum load for the specific plantar flexion exercises.
Experimental: Strength training (moderate intensity)
Twelve weeks of strength training program for the calf muscles, with moderate load intensity
Other: Exercise
A progressive calf strength training program lasting 12 weeks (twice weekly sessions), with a total of 25 visits to the gym. Specific exercises for ankle flexors: standing unilateral plantar flexion (on the machine) and seated unilateral plantar flexion (adapted on the Smith machine) will be performed. Participants will use progressive load from 55% of one repetition maximum load for the specific plantar flexion exercises.
Other: Exercise
A progressive calf strength training program lasting 12 weeks (twice weekly sessions), with a total of 25 visits to the gym. Specific exercises for ankle flexors: standing unilateral plantar flexion (on the machine) and seated unilateral plantar flexion (adapted on the Smith machine) will be performed. Participants will use progressive load from 70% of one repetition maximum load for the specific plantar flexion exercises.
No Intervention: Healthy subjects
A control condition composed of healthy individuals (i.e., without any injury), who will not receive any training, will be used as a comparison at the beginning and end of the intervention.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Changes in foot and ankle joint function
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
The foot and ankle joint function will be assessed through Foot and Ankle Outcome Score, which evaluate five different domains: pain, other symptoms, activities of daily living, sports and recreational activities, and quality of life related to the ankle and foot.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in Achilles tendon function and symptom
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Achilles tendon post-rupture function and symptoms will be assessed through Achilles Tendon Rupture Score (ATRS).
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in ankle functional performance
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
The ankle functional performance will be assessed using the heel raise test. With this test, the maximum height of the heel lift will be assessed, corresponding to the measurement of functionality of the ankle plantar flexors.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in plantar flexors' muscle strength
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
The plantar flexors' muscle strength will be assessed by the peak torque in different ankle joints (i.e., -10º, 0º, and 20º of plantar flexion - 0º neutral position).
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in Achilles tendon stiffness
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Tendon stiffness will be obtained by calculating the slope in the last 10% of the linear region of the force-deformation curve.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Changes in Achilles tendon Young's Modulus
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Tendon stiffness will be obtained by calculating the slope in the last 10% of the linear region of the stress-strain curve.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in Achilles tendon morphological properties
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Tendon morphological properties will be obtained by the total tendon length (distance between medial gastrocnemius muscle-tendon junction and tendon distal insertion in the calcaneous bone), free tendon length (soleus muscle-tendon junction and tendon distal insertion), and tendon's cross sectional area (measured at 2, 4, and 6cm from the tendon distal insertion).
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in plantar flexors' muscle arquitecture
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
The muscular architecture of the plantar flexor muscles will be evaluated using B-mode ultrasound images. Imagem analyses will be performed to identify the pennation angle and length of the muscle fascicles, and the muscle thickness of each triceps surae muscle.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in plantar flexors' muscle activation
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Muscle activation will be captured during muscle voluntary isometric contraction (MVIC) testes, at different joint positions. The maximum root mean square (RMS) values of each plantar flexor muscle will be calculated for each of the MVICs produced during the isometric peak torque assessments. These RMS values will be obtained by means of 1-s duration cuts (corresponding to 2000 points) of the MVICs during the torque signal plateau.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in neuromuscular recruitment capacity
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Muscle activation parameters evoked by percutaneous neuromuscular electrical stimulation techniques will be obtained through neuromechanical responses. Recruitment curves will be constructed to evaluate the neuromuscular capacity of the plantar flexors, based on the peak-to-peak amplitudes of the M waves and H reflexes, which will be mapped and recorded simultaneously.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)

Other Outcome Measures

Other Outcome Measures

For clinical trials, a planned measurement described in the protocol that is used to determine the effect of an intervention/treatment on participants. For observational studies, a measurement or observation that is used to describe patterns of diseases or traits, or associations with exposures, risk factors, or treatment. Types of outcome measures include primary outcome measure and secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Changes in plantar flexors' muscle power
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
The torque values obtained during the maximal voluntary isometric contractions (MVICs) tests will be used to determine the peak torque, as well as for the analysis of the rate of torque development (RTD). The active torque values produced in the torque-time curve obtained during the MVICs will allow the analysis of the RTD, which will be calculated in each joint position from the derivative of the torque-time curve (Nm s-1), from the beginning of the contraction (onset = 0-ms) to 50, 100, 200 and 400-ms, in addition to the interval between 200 and 400-ms.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
Changes in plantar flexors' muscle quality
Time Frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
In addition to the analysis of the muscle architecture, the images obtained for each plantar flexor muscle will allow the simultaneous analysis of the muscle quality measured by echointensity. During this analysis, the region of interest that includes the largest muscle area between the deep and superficial aponeuroses (avoiding wrapping tissues and bone) will be considered, for which the mean values of a histogram corresponding to the values in gray scale [scale from 0 (black) to 255 (white)] will be calculated. In addition, muscle quality will also be estimated by specific tension, expressed as force/torque per unit of muscle mass, which will be calculated by the ratio between the peak torque of the plantar flexors, obtained during isometric tests with the ankle in the neutral position (i.e., 0º of plantar flexion), and the amount of muscle mass representative of the triceps surae.
From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)

Collaborators and Investigators

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

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Federal University of Rio Grande do Sul

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Study Director: Jeam M Geremia, PhD, Federal University of Rio Grande do Sul
  • Principal Investigator: Marcelo H Glänzel, MSc, Federal University of Rio Grande do Sul

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)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
October 10, 2024

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
August 20, 2026

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
August 30, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
October 10, 2024

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
March 28, 2025

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
April 4, 2025

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
January 30, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
January 28, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 6786944

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

UNDECIDED

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

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