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

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: Recruiting
• Conditions: Achilles Tendon Rupture; Neuromuscular Adaptations; Strength Training Adaptations
• Intervention / Treatment: Other: Exercise; Other: 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: Interventional
• Enrollment (Estimated): 67
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Jeam M Geremia, PhD; Phone Number: +5505133085852; Email: jeam.geremia@ufrgs.br

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: Jeam M Geremia, PhD; Phone Number: +5505133085852; Email: jeam.geremia@ufrgs.br

Participation Criteria

Eligibility Criteria

• 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

How is the study designed?

Design Details

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

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
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

Outcome Measure	Measure Description	Time Frame
Changes in foot and ankle joint function	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	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	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	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	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

Outcome Measure	Measure Description	Time Frame
Changes in Achilles tendon Young's Modulus	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	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	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	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	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

Outcome Measure	Measure Description	Time Frame
Changes in plantar flexors' muscle power	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	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

• Sponsor: Federal University of Rio Grande do Sul
• Investigators: 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

Study Major Dates

• Study Start (Actual): October 10, 2024
• Primary Completion (Estimated): August 20, 2026
• Study Completion (Estimated): August 30, 2026

Study Registration Dates

• First Submitted: October 10, 2024
• First Submitted That Met QC Criteria: March 28, 2025
• First Posted (Actual): April 4, 2025

Study Record Updates

• Last Update Posted (Actual): January 30, 2026
• Last Update Submitted That Met QC Criteria: January 28, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Functionality; Stiffness; Triceps surae; Neuromuscular plasticity; Calcaneal tendon rupture
• Additional Relevant MeSH Terms: Wounds and Injuries; Rupture; Motor Activity; Movement; Musculoskeletal Physiological Phenomena; Musculoskeletal and Neural Physiological Phenomena; Exercise
• Other Study ID 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