The retraction of the posterior leg muscles consists of a shortening of the muscle fibers that limits ankle dorsiflexion. The objective of this randomized controlled clinical trial (RCT) with a double-blind technique and longitudinal chronology is to evaluate the short-term effect of electrostimulation associated with muscle stretching (electrical muscle elongation technique or EME) compared to static stretching in adult subjects with shortening of the posterior leg muscles.

The main questions it seeks to answer are:

• Are there significant differences in the short-term effect of electrical muscle elongation versus static stretching exercises on the gastrocnemius complex and Achilles tendon in young adults?
• Does the ankle's range of motion increase in both weight-bearing and non-weight-bearing positions?
• Does muscle strength increase in ankle plantar flexion?

The researchers will compare the group receiving electrical muscle elongation with interferential current to the group receiving passive static stretching to assess whether there are significant differences in the effects on the ankle's range of motion and the muscle strength of the posterior leg muscles.

Participants in this study will perform the following tasks:

• Receive a session of electrical muscle elongation with TENS and static stretching performed by the researcher.
• Follow the instructions during the intervention.
• Undergo evaluations of ankle range of motion and plantar flexor muscle strength
• Record their level of satisfaction after the study.

Inclusion Criteria:

• Subjects affiliated with or related to the University of Seville.
• Those with muscular shortening of the posterior chain of the limb.

Exclusion Criteria:

• Subjects who engage in sports activity above the average of the sample or who follow an organized stretching program for the posterior leg muscles.
• Hyperlaxity
• History of musculoskeletal, neuromuscular injuries, joint disease, surgery on the lower leg, or serious illness.

This was a single-blind study. The Participants were blinded to the specific intervention they received, as both the Electrical Muscle Elongation (EME) technique and the Static Stretching (SS) technique involved similar positioning and physical manipulation of the ankle, making it challenging for them to distinguish the exact treatment modality.

However, the Investigator (A.C-M, responsible for allocation and data recording) and the Care Provider (L.R-F, the podiatrist who applied the corresponding technique) were not blinded to the group assignment due to the distinct nature of the two interventions (one involving electrotherapy equipment and the other not).