The design aims to investigate the value of direct current, specifically the polar effects this has, and its influence on neuromuscular changes described in the literature. This research proposal seeks to assess the influence of application anode and cathode pole in muscle strength when testing handgrip dynamometry by healthy subjects. The study will evaluate changes in muscle strength when performing a manual dynamometer test in a group exposed to the application of cathode, another exposed to the application of anode, compared with a control that will not receive the intervention will be evaluated. Subsequently the investigators proceed to compare the maximum force obtained from the dynamometry test in each of groups and between the groups .

1. Methodology

This research has the characteristics of a random analytical experimental design (ECA). The study was conducted in the laboratory of physiotherapy, room 401, 4th floor, building C5 University Andres Bello (UNAB), Faculty of Rehabilitation Sciences, Campus Casona, Nº700 Street Fernández Concha, Santiago, Chile. The sample was selected from the university population that is part of the faculty. The study was submitted to the ethics committee of the East Metropolitan Health Service (SSMO) of Salvador Hospital. Once approved by the ethics committee began the investigation. It was taken as population all students of the Faculty of Rehabilitation Sciences, made up of races Physical Therapy, Speech Therapy and Occupational Therapy. The study group was determined through a simple random sampling process, which was conducted through a questionnaire with closed questions. This questionnaire allowed select participants according to the inclusion and exclusion criteria proposed in the work. The number of participants was taken for the convenience of researchers. The final sample included 150 participants. Student population share similar characteristics, so that most made them compatible for the sample. Inclusion criteria were established: participants aged 18 years and people that they should not discomfort or pain on the handgrip. Moreover Exclusion criteria were considered: muscle pathologies skeletal hand, wrist or elbow in the last 6 months, the presence of materials osteosynthesis or endoprosthesis in areas of application, peripheral neurological diseases such as neuropraxias or nervous cuts, skin disorders application areas, such as burns, wounds, scars, apprehension or fear of the application of electrotherapy, non-completion of the evaluation protocol / intervention designed for studio or away from it, and do not sign the consent for participation.

3 stages of conducting the study were designated. Stage 1 called "The Sample Phase", had a duration of one week. This Phase consisted of the implementation of the survey to students, followed by analysis of the collected information and registration for a first filter potential participants. The survey was applied to all courses of the Faculty of Rehabilitation Sciences. The first filter was given with the survey questions that has specifics questions with the inclusion and exclusion criteria. Participants who met the characteristics of participation and were invited to join the study. The students will be contacted personally. Students interested will be explained in detail the study and were asked to give their written consent. Informed consent reflected the 4 principles of bioethics so as to safeguard the integrity of each person.

The second stage of design called "Evaluation Phase" lasted 5 days. In this phase the ability to perform hand grip on the participants according to the protocol established in the investigation was assessed. The strength assessment will be probe in the same conditions in which they worked on the study. At this level, people explained everything concerning the characteristics of electrical stimulation used, and as applicable. This stage marked a second filter instance dismissing students who had discomfort or inability to perform the handgrip. After this phase had the final number of participants who made up the final sample of the study, giving way to step 3.

The stage called "Experimentation Phase" had a duration of 3 weeks. The sample was randomly so as to establish three working groups, a group called "Cathode Stimulation", another group called "Anode Stimulation" and a third group called "Control Group". The group "Cathode stimulation" includes 48 participants, while the "Anode Group" had 52 participants and the "Group Control" 50 participants.

The designation of each group participants, was conducted by the director of the study, by simple randomization process, through Microsoft Excel® program. This allowed decrease selection bias. After this process the director conduce each student to the box in which the force will be evaluated. A first evaluator (Evaluator 1) analyzed the demographic characteristics of each group, including age, body mass index (BMI), and gender, which allowed determine the characteristics per group. This would establish any comparisons at the end of work, taking the results. This information is obtained by the survey. The participants of the 3 groups were evaluated by another evaluator (Evaluator 2), who recorded the average maximum handgrip force developed by the dominant limb of the participants. Grip strength was evaluated according to the evaluation protocol proposed by manual torque test, registering kilograms (kg) of force developed by understanding. The evaluation included 3 executions leaving a rest interval of 15 seconds between each attempt (measurement protocol). The evaluator 2 recorded in an Excel spreadsheet the initial 3 attempts, leaving the best maximal force value of them as definitive. This was considered as the maximal handgrip Force value prior the intervention. After the director derived each participant according to the particulary group, Cathode, Anode or Control. The design featured participation of three therapists, one for each working group.

Therapist did not know the data obtained from the evaluation of strength, and the students that belonged the groups. Physiotherapists executors were familiar with the application of electric current. Each therapist worked using direct current with 500 COMBI GYMNA® equipment company. In the application we worked with one channel team, applying an electrode on the engine of the flexor muscles of the forearm dominant point and the other electrode closing the circuit on the side face of the opposite arm. It was taken as described by the motor point SENIAM corporation, who recommend specific motor points for the application surface electromyography. For the Cathode group the black electrode was used in the forearm muscle flexor of the dominant side for the anode group red electrode was used in the forearm muscle flexor of the dominant side, while for the control group the black electrode was used in the same musculature. The first two groups were given a current intensity of 2mA (based on the safety recommendations when applying direct current), while the control group was not applied current. With these parameters a current density of 0,04mA /cm2 was obtained. (rubber electrodes coal rectangular area 48cm2). Each therapist was masked output color channel electrode by a black tape, so that it was not known what was the black or red electrode. The treatment time for each group was 10 minutes, according to the protocol established for the investigation. This generated a dose of current 5mA/min. Participants of the three groups were installed on wooden stretchers sitting in Fowlers position maintaining a 45 ° angle. The electrode was placed on the side of the dominant limb with the device screen facing towards the foot of the participant, so the person could not display the current value set. After the application of the current, the participants left the room intervention and were led by the director to the force assessment room. In this room would register the best post maximum grip strength. The evaluator recorded three attempts, leaving the same time of 15 seconds between each. The evaluator 1 record average of the 3 values in an Excel spreadsheet. This is the value designated as post test (maximal strength post intervention).

After completing the measurements two weeks were available to sort the data and the analysis of the recorded information. This task was driven by the research director who was responsible for storing and sorting data received by the evaluators. The Microsoft Excel program was used for this process register all data. Descriptive statistics for the maximum strength was represented in the form of averages, frequencies and standard deviation. This information is also represented as graphs of boxes comparing IMC, gender and age per group. Inferential statistics was development with the Shapiro Will test to determinate a normally distributed data, then using ANOVA test or T-test. For data not normally distributed Kruskal-Wallis test was applied. The statistics was perform with de STATA program. Once the statistical analysis done within 3 weeks for the analysis of results, and approach the discussion and results are considered.

2. Measurement handgrip strength protocol pre and post electrotherapy

Measuring handgrip strength will be conducted in the laboratory of physiotherapy, room 401, 4th floor, building C5 University Andres Bello (UNAB), Faculty of Rehabilitation Sciences, Campus Casona, Las Condes, Street Fernández Concha Nº700, Santiago, Chile. Initially, participants were instructed to sit in a straight chair with dimensions of 42cm high, 46 cm wide by 40 cm long, back tilt of 10 ° and dimensions of 43 cm high by 46 cm wide, the participant shall be placed with his feet flat on the floor, erect trunk in contact with the back, head and neck in a neutral position, shoulder adducted, in neutral rotation, elbow bent at 90, forearm prone neutral supination, unsupported any surface and wrist position neutra.67 for the test, a hydraulic hand dynamometer model Dynatron® which has a weight of 600g, dimensions of 26 cm long by 13 cm wide, with reading will be used dual measurement scale up to 200lbs / 90kg, also has five levels of manual adjustment, which will be set at the second level. The estimated time measuring participant is 2 minutes.

The handgrip strength was measured on 3 occasions, the break between measurements is 15 seconds, taking an estimated 54 seconds net force measurement by participant time. Participants will be instructed to position themselves correctly in the workstation and apply maximum force for 3 seconds and work at maximum effort in each test returning the marker measuring instrument 0 lbs / after each measurement kg. The evaluator register the average maximal handgrip strength between the 3 attempts. For the data registration we will use Microsoft Excel® program. The division consist in 3 categories of participants, Cathode Group, Anode Group and Control Group. The pre electrotherapy application data will be recorded immediately after the measurement of palmar force dynamometry.

2. Electrotherapy Protocol

The intervention will take place in the laboratory of physiotherapy, room 401, 4th floor, building C5 University Andres Bello (UNAB), Faculty of Rehabilitation Sciences, Campus Casona, Las Condes, Street Fernández Concha Nº700, Santiago , Chile. After the initial force measurement participants will be placed in the particular station for applying electrotherapy, where each participant will be instructed to position themselves in a sitting position 45º on a stretcher fixed two bodies, with dimensions 190cm long by 70cm wide and 80cm high, each participant must support the trunk on the top of the table, inclined at 45 degrees, with both elbows, forearms and arms bare skin, well supported on the stretcher.

For the application of electrotherapy was applied with the devise Gymna® Combi 500 model, which it is characterized by having a unit of electrotherapy, ultrasound and laser.

It was also be used carbon electrodes which measurements are 7.5cm long x 6cm wide with their respective terminals, 2 driving pads 9.5 cm long by 8 cm wide and 2 fasteners with velcro for electrodes, 47cm long by 5 cm wide.

During the intervention, it proceeds to plug the equipment into an outlet 220v conventional power, then connect the electrodes in one of the two channels available on the device. Once the participant is correctly positioned in the workstation, the therapist will place correctly the electrodes, applying an electrode on the belly of the flexor muscles of the forearm (established on the recommendation of SENIAM project point), and the other electrode closing the circuit laterally on the other forearm. For the Cathode Group the black electrode is used in the flexor muscles of the dominant hand, for the Anode Group red electrode is used in the flexor muscles of the dominant hand, while the Control Group the black electrode will be used in the same muscles, procedure will be repeated for the 3 groups of participants, once completed this procedure. The Therapist applied to the first two groups a current of 2mA, thereby determining a density 0,04mA current /cm2 considering a size of 48cm2 electrode, while the control group will not be applied any intensity keeping the power on but without emission. For the 3 groups of participants application time is 10 electrotherapy minutes.

Inclusion Criteria:

• Participants older than 18 years
• Do not manifest discomfort or pain when performing the handgrip.

Exclusion Criteria:

• Skeletal muscle pathologies in hand, wrist or elbow in the last 6 months.
• Materials osteosynthesis or endoprosthesis in areas of application.
• Peripheral neurological pathologies as neuropraxias or nerve sections.
• Changes in the skin of the application areas, such as burns, wounds, scars.
• Apprehension or fear of the application of electrotherapy.
• No completion of the evaluation protocol / intervention, designed for study or abandonment.

Serious and/or Other (Not Including Serious) adverse events were not collected/assessed.

Serious and/or Other (Not Including Serious) adverse events were not collected/assessed.