An interventional study of Exercise and Exercise in Achilles Tendon Rupture, Strength Training Adaptations and Neuromuscular Adaptations, sponsored by Federal University of Rio Grande do Sul. Recruiting at 1 site in Brazil. Open to male participants aged 18 Years to 64 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-01-30.
Sponsored by Federal University of Rio Grande do Sul · Not applicable, Interventional, and Treatment
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.
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.
Federal University of Rio Grande do Sul is the lead sponsor of 121 studies on the registry; 20 are open to participants now.
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Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
A condition in which the immune system attacks the body’s own tissues, such as rheumatoid arthritis, lupus, psoriasis, type 1 diabetes or inflammatory bowel disease.
Immunotherapy studies often leave out active autoimmune disease, and some name exceptions, such as thyroid disease on replacement hormone. Check the exceptions this study lists.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Autoimmune disease
A condition in which the immune system attacks the body’s own tissues, such as rheumatoid arthritis, lupus, psoriasis, type 1 diabetes or inflammatory bowel disease.
Immunotherapy studies often leave out active autoimmune disease, and some name exceptions, such as thyroid disease on replacement hormone. Check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
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Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
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Twelve weeks of strength training program for the calf muscles, with low load intensity
Other: Exercise
Twelve weeks of strength training program for the calf muscles, with moderate load intensity
Other: Exercise
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.
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.
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.
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.
Time frame: 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).
Time frame: 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.
Time frame: 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).
Time frame: 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.
Time frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
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.
Time frame: 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).
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
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.
Time frame: 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.
Time frame: From baseline measurements up to 13 weeks after (i.e., one week after the end of the training program)
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