Pulsed Current Versus Russian Current Effects in Healthy Young Subjects.

Low frequency pulsed current (PC) and medium frequency alternating current (Russian current - RC, 2.5 kHz) have been largely studied due to their clinical use. However, it is not clear which current is the most efficient due to the existente literature conflicts.Therefore, the purpose of this study is to compare the neuromuscular efficiency, evoked torque, current intensity, fatigability and level of discomfort between the PC and the RC in healthy young. The current types will be tested in the same participant by the intervention sequences randomization. On the first, second, third and fourth days, the maximum voluntary isometric contraction (MVIC), the current intensity level, discomfort level, evoked torque, and clinical and neuromuscular efficiency of each current will be evaluated. Anthropometric measurements will also be assessed on the first day. In addition, the current intensity required to produce a torque level of 20% of the MVIC, the current intensity required to generate a torque of 40 Nm and the maximum intensity tolerated by the participant will be evaluated. Three contractions will be recorded in each condition, and the level of discomfort will be assessed during the evoked contractions. Evoked torque will be evaluated at the maximum tolerated intensity level using the isokinetic dynamometer. Clinical and neuromuscular efficiency will be evaluated (1) at the current intensity necessary to evoke 20% MVIC, (2) at the current intensity necessary to generate 40 Nm, and (3) at the maximum tolerated current intensity. On the fifth and sixth days, muscle fatigue induced by the diferente current types will be evaluated. Fatigue will be evaluated with sufficient current intensity to generate 20% of the MVIC. MVIC will be performed before and after the fatigue protocol, and the fatigue will be determined by the relative variation of the MVIC before and after the fatigue protocol. Fatigue will also be evaluated through the evoked torque variation between the first and the last minute of the fatigue protocol, as well as by the total work generated in each protocol. Neuromuscular efficiency will be evaluated before and immediately after the protocol through (1) the ratio between input NMES current intensity and output evoked torque, (2) total work (area under the evoked force by time curves) generated during the fatigue protocol, and (3) by the changes in muscle architecture from rest to evoked contraction at the maximal current intensity.

This study is characterized by a quantitative approach, with a randomized crossover clinical study design, blinded to evaluators and participants. The objective is to compare the neuromuscular and clinical efficiency, evoked torque, current intensity, fatigue and discomfort level between the low frequency biphasic pulsed current (PC) and the median frequency sinusoidal alternating Russian current (RC) in healthy young participants. The effect of the two neuromuscular electrical stimulation (NMES) current types on the cited variables will be evaluated in the same participant, by means of the randomization of the interventions sequences for each participant. The evaluation protocols will be performed by 2 blinded raters for the current type and for the outcome variables. A blinded evaluator to the study will randomize the current type, which will be applied on the different evaluation days, through a lottery using opaque envelopes. A researcher blinded to the study groups will analyze the data. Participants will be blinded to the current type will be receiving. The evaluations will be performed in six days, and a minimum interval of 7 days will be observed between the evaluation days. On the first, second, third and fourth days, characterized as Stage 1, the currents' intensity levels, discomfort level, evoked torque, and neuromuscular and clinical efficiency of each randomized current will be evaluated. On the fifth and sixth days, characterized as Stage 2, the muscle fatigue level induced by the two electrical currents will be evaluated. The first evaluation day will be divided into two phases. Phase 1 corresponds to the initial evaluation, anthropometric data collection and physical activity level evaluation. In Phase 2, the quadriceps femoris motor point will be located with a pen-shaped electrode and a neuromuscular electrical stimulation unit, and the subcutaneous adipose layer thickness covering the motor point will be evaluated by means of ultrasonography. Subsequently, the ultrasound probe will be maintained on the vastus lateralis muscle (VL) to obtain muscle architecture data at rest, during the maximal voluntary isometric contractions (MVICs) and during the evoked contractions. Next, a warming up protocol will be performed and the participants will perform three MVICs at the knee joint angles of 60° and 90° of knee flexion (0° = full knee extension) on the isokinetic dynamometer. Subsequently, the investigators will evaluate (1) the current intensity required to produce a torque equivalent to 20% MVIC, (2) the current intensity required to produce a 40 Nm torque, the maximum current intensity (mA) tolerated by the subject (3) at an angle of 60° of knee flexion, and (4) at 90° of knee flexion. From these evaluations, the investigators will analyze the neuromuscular efficiency (ratio between current intensity and evoked torque). After each NMES test, participants will indicate, on the visual-analog scale, the discomfort level perceived with each NMES current type. Clinical efficiency will be evaluated by the ratio between the discomfort level and the evoked torque in the above-described situations. On the second, third and fourth evaluation day, participants will perform all the evaluations described in Phase 2 of the first evaluation day, but with different configurations of the type of current randomized being applied. On the fifth day, the fatigue protocol will be applied with appropriated parameters according to the randomized current type, and sufficient current intensity to generate 20% of the MVIC. The discomfort level during the fatigue protocol will be recorded immediately after the end of the fatigue test. Participants will conduct three pre- and post-fatigue protocol MVICs in order to assess the fatigue level. For the sixth evaluation day, the same evaluations reported for the fifth day will be carried out, but with the second randomized current.

Eligibility Criteria:
Inclusion Criteria:

* Young male
* Age between 18 and 35 years
* Physically active,
* Normal knee function and range of motion
* No pain complaints
* No presence of lower limb pathology at the dominant limb.

Exclusion Criteria:

* Health problems (neurological, musculoskeletal impairment),
* Contraindication to maximal exercise,
* Having been treated with NMES in the last 3 months in the lower limb
* Not meeting the inclusion criteria.