Achilles Tendon Adaptation to Neuromuscular Electrical Stimulation: Morphological and Mechanical Changes

Area of Science:

• Biomechanics
• Exercise Physiology
• Rehabilitation Science

Background:

• Neuromuscular electrical stimulation (NMES) is used in rehabilitation, but its capacity to induce tendon adaptations is debated.
• Understanding NMES effects on tendon mechanical properties is crucial for optimizing therapeutic applications.

Purpose of the Study:

• To investigate the impact of high-frequency NMES on the morphological and mechanical characteristics of the Achilles tendon.
• To determine if NMES can induce sufficient tendon stress for adaptation.

Main Methods:

• Eight men underwent a 12-week high-frequency NMES training program for the triceps surae muscle under isometric conditions.
• Ultrasonography assessed Achilles tendon morphology (CSA, length) and myotendinous junction elongation pre- and post-training.
• Maximal isometric ramp contractions measured plantar flexion force.

Main Results:

• NMES training did not alter Achilles tendon morphology (CSA, length) or maximal elongation capacity.
• Significant increases were observed in maximal tendon force (+25.2%), Young's Modulus (+12.4%), and maximal stress (+23.4%) post-training.
• These findings indicate improvements in tendon mechanical properties.

Conclusions:

• High-frequency NMES effectively enhances Achilles tendon mechanical properties, particularly strength and stiffness.
• NMES induces sufficient stress to promote tendon adaptation, challenging previous assumptions.
• This training modality shows promise for tendinopathy rehabilitation and mitigating effects of hypo-activity.