For the NMES group one portable stimulator (Compex 2, Medicompex SA, Ecublens, Switzerland) will deliver NEMS (15 min; 75 EMS contractions completed during the training session; rise time = 0.25 s and descending time = 0.75 s). In order to maximize muscle tension without accompanying detrimental effects on fatigue onset, biphasic symmetric regular-wave pulsed currents (85 Hz) lasting 400 μs will be delivered. Each 4-s steady tetanic stimulation will be followed by pause lasting 8-s, during which subjects will be submaximally stimulated at 4 Hz on the medial arch muscles. According to the recommendations, the two electrodes are placed behind the head of the first metatarsal to stimulate the medial arch intrinsic muscles. The goal is to attain the highest tolerable level of muscle contraction without discomfort during the 15 minutes and to provide a full tetanic contraction of the intrinsic foot muscles during the contraction time.

For the control group the one portable stimulator (Compex 2, Medicompex SA, Ecublens, Switzerland) will be used to apply a stimulation of 15 minutes considered by TENS at the lowest intensity detectable by the participant in order to not influence the outcomes of interest. Our aim is to strengthen IFM which is not the role of TENS. The two electrodes will be placed on the dominant foot, at the same place than those for the NMES group.

Neuromuscular Electrical Stimulation (NMES) is a non pharmacological intervention that sends electrical impulses to nerves leading to muscle contraction. The electrical stimulation can increase strength and is often used to re-educate or re-train muscles.

The change of foot strength that will be measured on a pressure platform on the dominant foot before and after intervention (NMES or TENS). This primary outcome will be also measured on the non-dominant foot to assess cross effects.

The secondary outcomes include the change of dynamic postural balance in the posterior direction on the dominant foot. All measurements will be performed on the non-dominant foot to assess cross effects. To assess dynamic postural balance performance, we will use the Star Excursion Balance Test (SEBT). The star excursion balance test (SEBT) is a measure of dynamic balance with good to excellent test-retest reliability. The test will be conducted in the anterior, posterior-lateral and posterior-medial directions. The SEBT will be performed with the subject standing barefoot so that the distal end of the longest toe of the stance foot will be placed at the center of the grid. They will have to maintain a single-leg stance while reaching with the contralateral leg to touch as far as possible along the direction by a light touch. The reached distances will be normalized to the respective stance-limb length (anterior superior iliac spine to the inferior border of the medial malleolus).