Immediate Effects of Neuromuscular Electrical Stimulation on Pain and Function in Achilles Tendon Disorders

Immediate Effects of Neuromuscular Electrical Stimulation on Pain and Functional Performance in Individuals With Achilles Tendinopathy and Tendon Rupture: A Randomized Crossover Clinical Trial

The Achilles tendon exhibits high tensile strength and can withstand extremely high loads. However, it is susceptible to injuries such as tendinopathies and ruptures, which are associated with structural alterations and loss of function. Strategies have been investigated to enhance clinical rehabilitation. Nevertheless, the effects of neuromuscular electrical stimulation on pain and functional improvement, as well as the optimal dosing parameters for the rehabilitation of Achilles tendon injuries, remain inconclusive. The aim of this study is to compare the immediate effects of two electrical stimulation protocols on pain, functional performance, peripheral oxygen extraction, and maximal tendon displacement during a single leg heel rise functional task in patients with Achilles tendinopathy and/or a history of Achilles tendon rupture. In addition, this study aims to characterize Achilles tendon structural properties and ankle plantarflexor muscle strength in this population.

Study Overview

• Status: Recruiting
• Conditions: Achilles Tendon Rupture; Achilles Tendinopathy (AT)
• Intervention / Treatment: Device: Neuromuscular Electrical Stimulation (NMES)

Detailed Description

All groups will be composed of participants with a primary complaint of pain and/or a history of previous Achilles tendon rupture. Participants will perform the interventions in two blocks separated by a seven-day interval (wash-out). Block A: (1) control without active intervention and (2) electrical stimulation applied at the maximum tolerated intensity. Block B: (3) control with sham stimulation and (4) sensory-level electrical stimulation. Block A will always be performed first, followed by Block B. Interventions within each block will be conducted in three sets of 10 repetitions, totaling six sets per day.

• Study Type: Interventional
• Enrollment (Estimated): 30
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: João LQ Durigan, PhD; Phone Number: +55 61 3107-8450; Email: joaodurigan@gmail.com
• Study Contact Backup: Name: José RS Júnior, PhD; Phone Number: +55 61 3107-8450; Email: joserobertofisio@gmail.com

Study Locations

• Brazil
  • Federal District
    • Brasília, Federal District, Brazil, 72220900
      • Recruiting
      • University of Brasilia
      • Contact: João LQ Durigan, PhD; Phone Number: +55 61 3107-8450; Email: joaodurigan@gmail.com
      • Contact: José RS Júnior, PhD; Phone Number: +55 61 3107-8450; Email: joserobertofisio@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Primary complaint of pain localized in the midportion (2-6 cm proximal to the calcaneus) or insertion of the Achilles tendon, and/or a history of Achilles tendon rupture occurring at least 3 months prior to assessment.
• Pain on palpation of the Achilles tendon.
• Pain during load-bearing activities

Exclusion Criteria:

• Exclusive diagnosis of bursitis confirmed by ultrasonographic assessment
• Any other lower limb injury
• History of lower limb surgery within the past year
• Previous Achilles tendon tenoplasty performed less than 3 months prior to assessment

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Single

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
No Intervention: Control without active intervention; In this group, participants will perform three sets of 10 repetitions of the single leg heel rise functional task without the application of electrical stimulation. Immediately after each set, pain level, functional performance, peripheral oxygen extraction, and maximal Achilles tendon displacement will be assessed.
Experimental: Electrical stimulation applied at the maximum tolerated intensity; Under this condition, participants will perform three sets of 10 repetitions of the single leg heel rise functional task with superimposed electrical stimulation applied at the maximum tolerated intensity, characterized by visible muscle contraction and associated with a self-reported discomfort level between 8 and 10 on the Numeric Rating Scale. Immediately after each set, pain level, functional performance, peripheral oxygen extraction, and maximal Achilles tendon displacement will be assessed.	Device: Neuromuscular Electrical Stimulation (NMES); Neuromuscular electrical stimulation-induced contractions will be delivered using an electrical stimulator connected to a pair of 5×5 cm self-adhesive surface electrodes. Stimulation will be applied in a superimposed manner during voluntary movement, at a frequency of 75 Hz and a phase duration of 400 µs.
Placebo Comparator: Control with sham stimulation; For this condition, participants will perform three sets of 10 repetitions of the single leg heel rise functional task with superimposed sham electrical stimulation. Electrical stimulation parameters will initially be configured identically to those used in the active intervention. However, to ensure adequate blinding, stimulation will be applied for approximately 40 seconds and then gradually reduced until complete cessation. From this point onward, no additional current will be delivered, although the device will remain on and the electrodes will remain in place throughout the test. Immediately after each set, pain level, functional performance, peripheral oxygen extraction, and maximal Achilles tendon displacement will be assessed.	Device: Neuromuscular Electrical Stimulation (NMES); Neuromuscular electrical stimulation-induced contractions will be delivered using an electrical stimulator connected to a pair of 5×5 cm self-adhesive surface electrodes. Stimulation will be applied in a superimposed manner during voluntary movement, at a frequency of 75 Hz and a phase duration of 400 µs.
Active Comparator: Sensory-level electrical stimulation; In this condition, participants will perform three sets of 10 repetitions of the single leg heel rise functional task with superimposed electrical stimulation applied at the sensory level, defined as the highest intensity that does not elicit visible muscle contraction. Immediately after each set, pain level, functional performance, peripheral oxygen extraction, and maximal Achilles tendon displacement will be assessed.	Device: Neuromuscular Electrical Stimulation (NMES); Neuromuscular electrical stimulation-induced contractions will be delivered using an electrical stimulator connected to a pair of 5×5 cm self-adhesive surface electrodes. Stimulation will be applied in a superimposed manner during voluntary movement, at a frequency of 75 Hz and a phase duration of 400 µs.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Pain level	Pain intensity during the single leg heel rise task will be assessed using the Visual Analog Scale, consisting of a numerical scale ranging from 0 to 10 points, in which 0 represents no pain and 10 corresponds to the worst pain ever experienced by the participant.	Immediately after the performance of the functional task

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Total time	The total time (s) during the single-leg heel rise task will be measured using the MuscleLab® system.	Immediately after the performance of the functional task.
Maximal displacement	The maximal displacement (cm) during the single-leg heel rise task will be measured using the MuscleLab® system.	Immediately after the performance of the functional task.
Total work	The total work (J) during the single-leg heel rise task will be measured using the MuscleLab® system.	Immediately after the performance of the functional task.
Total power	The total power (W) during the single-leg heel rise task will be measured using the MuscleLab® system.	Immediately after the performance of the functional task.
Number of repetitions	The number of repetitions completed during the single-leg heel rise task will be recorded using the MuscleLab® system.	Immediately after the performance of the functional task.
Peripheral oxygen extraction	Oxygen extraction of the periarticular ankle muscles will be assessed using near-infrared spectroscopy, with the sensor positioned on the skin over the lateral gastrocnemius muscle during the single leg heel rise task. Variations in oxy- and deoxy-hemo/myoglobin (O₂Hb and HHb, respectively) will be recorded in arbitrary units at a sampling frequency of 25 Hz.	Immediately after the performance of the functional task.
Maximal Achilles tendon displacement	Maximal Achilles tendon displacement (%) will be measured using a transducer positioned over the myotendinous junction of the gastrocnemius muscles, secured to a specific support, during the single leg heel rise task. Maximal displacement will be determined based on the change in Achilles tendon length relative to its resting length.	Immediately after the performance of the functional task.
Lenght of achilles tendon	The total and free length (cm) of the Achilles tendon will be measured using portable ultrasonography.	Baseline (prior to Block A only)
Thickness of achilles tendon	The thickness (mm) of the Achilles tendon will be measured using portable ultrasonography.	Baseline (prior to Block A only)
Cross-sectional area of achilles tendon	The cross-sectional area (cm²) of the Achilles tendon will be measured using portable ultrasonography.	Baseline (prior to Block A only)
Presence of neovascularization of the Achilles tendon	The presence of neovascularization of the Achilles tendon will be assessed using portable ultrasonography.	Baseline (prior to Block A only)
Elastic modulus	The median elastic modulus (kPa) of the Achilles tendon will be measured using shear wave elastography.	Baseline (prior to Block A only)
Shear wave velocity	The median shear wave velocity (m/s) of the Achilles tendon will be measured using shear wave elastography.	Baseline (prior to Block A only)
Depth	The measurement depth (cm) of the Achilles tendon during elastography assessment will be recorded using shear wave elastography.	Baseline (prior to Block A only)
Isometric strength	Isometric strength will be assessed using an isokinetic dynamometer, based on peak isometric torque (N/m) during plantar flexion at 0°.	Baseline (prior to Block A only)

Collaborators and Investigators

• Sponsor: University of Brasilia

Study record dates

Study Major Dates

• Study Start (Actual): January 6, 2026
• Primary Completion (Estimated): August 30, 2029
• Study Completion (Estimated): December 30, 2029

Study Registration Dates

• First Submitted: February 13, 2026
• First Submitted That Met QC Criteria: March 2, 2026
• First Posted (Actual): March 6, 2026

Study Record Updates

• Last Update Posted (Actual): March 6, 2026
• Last Update Submitted That Met QC Criteria: March 2, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Pain; Achilles tendinopathy; Achilles tendon rupture; Neuromuscular electrical stimulation; Achilles tendon; Functional performance
• Additional Relevant MeSH Terms: Neurologic Manifestations; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Pain
• Other Study ID Numbers: CAAE: 94397825.9.0000.8093

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No