Pulsed Current Versus Russian Current Effects in Healthy Young Subjects.
Condition: Healthy Young; Electric Stimulation Therapy
Study type: Interventional

Summary: 
      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.
    

Detailed description: 
      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.
    

Intervention name(s): Pulsed current; Russian Current
Intervention type(s): Device; Device
Intervention description(s): For stage 1 of the study, which corresponds to analysis of the evoked torque, evaluation of the discomfort level, current intensity, analysis of neuromuscular efficiency and clinical efficiency, 2 configurations (PC1 and PC2) will be used.
PC1, will be set at a frequency of 100 Hz, phase duration of 1000 microseconds, ON-OFF time of 5s:10s.
PC2, will be set at a frequency of 100 Hz, phase duration of 200 microseconds ON-OFF time of 5s:10s.
For stage 2 of the study, which corresponds to the analysis of the fatigability level, only the PC1 configuration will be used.; For stage 1 of the study, which corresponds to analysis of the evoked torque, discomfort level, current intensity, neuromuscular efficiency and clinical efficiency, 2 configurations (RC1 and RC2) will be used.
RC1, will be set to a frequency of 100 Hz, burst duty cycle of 20%, ON-OFF time of 5s:10s.
RC2, will be set at a frequency of 100 Hz, burst duty cycle of 50%, ON-OFF time of 5s:10s.
For stage 2 of the study, which corresponds to the analysis of the fatigability level, only the RC2 configuration will be used.
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Other
Keywords: Muscle Strength; Fatigue; Neuromuscular efficiency; Discomfort level; Electric Stimulation