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

Not Applicable

Recruiting

• Conditions: Achilles Tendon Rupture; Strength Training Adaptations; Neuromuscular Adaptations

• Registration Number: NCT06912269
• Lead Sponsor: Federal University of Rio Grande do Sul

Brief Summary

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.

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 Timeline

• Study Start: 2024-10-10
• Study First Submitted: 2024-10-10
• Study First Submitted QC: 2025-03-28
• Study First Posted: 2025-04-04
• Status Verified: 2025-07
• Last Update Submitted: 2025-07-03
• Last Update Posted: 2025-07-09
• Primary Completion: 2025-12-20
• Study Completion: 2026-08-30

Recruitment & Eligibility

• Status: RECRUITING
• Sex: Male
• Target Recruitment: 67

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 & Design

• Study Type: INTERVENTIONAL
• Study Design: PARALLEL

Primary Outcome Measures

Name	Time	Method
Changes in foot and ankle joint function	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.
Changes in Achilles tendon function and symptom	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).
Changes in ankle functional performance	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.
Changes in plantar flexors' muscle strength	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).
Changes in Achilles tendon stiffness	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.

Secondary Outcome Measures

Name	Time	Method
Changes in Achilles tendon Young's Modulus	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.
Changes in Achilles tendon morphological properties	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).
Changes in plantar flexors' muscle arquitecture	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.
Changes in plantar flexors' muscle activation	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.
Changes in neuromuscular recruitment capacity	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.

Trial Locations

Locations (1)

Exercise Research Laboratory (LAPEX) - School of Physical Education, Physiotherapy, and Dance; 🇧🇷 Porto Alegre, RS, Brazil