Transcranial static magnetic field stimulation (tSMS) is a novel brain stimulation technique that has been shown to be safe and effective in modifying biological parameters when applied to the cerebral cortex. Its application decreases cortical excitability, regardless of the polarity of the magnetic field, reducing the amplitude of motor evoked potentials (MEP). tSMS is presented as a potentially useful tool in the management of the interhemispheric inhibition, a condition present in neurological pathologies such as stroke or multiple sclerosis. Despite having demonstrated neurophysiological effects in previous studies, the effects of tSMS application on force production and manual dexterity, have not yet been clearly established.

The present study aims to evaluate changes in force production, manual dexterity, and fatigue after unilateral application of a tSMS session on the primary motor cortex (M1). It is hypothesized that the application of tSMS will momentarily decrease the parameters of strength and manual dexterity in the upper limb contralateral to the stimulated cortex, without changes in the strength and dexterity of the unstimulated hemibody. These parameters may show an increase in the unstimulated hemibody. If the hypothesis is confirmed, it could be considered a valid treatment for health conditions presenting interhemispheric inhibition.

Inclusion Criteria:

• Age between 18 and 60 years.
• Absence of cognitive impairment.
• Adequate understanding of verbal and written information, sufficient to complete the tests.

Exclusion Criteria:

• Presence of metallic implants (e.g., neurostimulator, pacemaker, cochlear implant, or metallic elements in the head or around the eyes).
• Diagnosis of epilepsy or being under treatment with antiepileptic drugs.
• Diagnosis of unstable cardiovascular disease.
• Diagnosis of any disease or condition that may interfere with this study.
• Use of drugs that may influence with neuromuscular function (muscle relaxants or some analgesics...).

Several devices (helmets) were available for the active and sham intervention. An investigator outside the study intervention labeled the active and sham helmets with an alphabetic code (A or B). The investigator applying the stimulation did not know which type of intervention was applying (A or B). Neither the investigator performing the intervention, nor the participant knew which intervention corresponded to each group. The data were analyzed by another researcher who was not involved in the assignment and intervention.