Electrical Stimulation With Different Currents: the Effects on Force, Tolerance and Fatigue in Healthy Subjects

Muscle strength is the amount of force generated by muscle contraction. It could be measured with an isometric dynamometer. This is a validated tool that could be used to measure Maximal Voluntary Isometric Contraction (MVIC) and Maximal Electrical Induced Contraction (MEIC). It is claimed that higher MEIC values will result in more force gained. If a current is more tolerated it will be easier to achieve better MEIC values. Tolerance to an electrical stimulation could be measured with the Visual Analogue Scale (VAS). A ratio between Normalized MEIC / VAS is often used, implying that the current is better with a higher ratio. Muscle fatigue is defined as a temporary loss or decrease in force-generating ability due to previous contractions. It is claimed that medium frequency neuromuscular electrical stimulation (NMES) generates more fatigue than low frequency currents. Aussie is a medium-frequency alternating current, sinusoidal waveform, 1 KHz carrier frequency. Neo-Russian is a medium-frequency current, rectangular biphasic symmetrical waveform, 2,5 KHz carrier frequency. Rectangular Biphasic symmetrical (RBS) waveform is a type of Low Pulsed Current (LPC), claimed to be better than classical Russian Current. Purpose: As it has been claimed that LPC is better in MEIC and tolerance, the aim of this study is to compare it with two newer medium frequency currents in terms of MEIC, tolerance and fatigue. Methods: Thirty male subjects, right leg dominant, will receive randomly the 3 types of electrical stimulation. Before that, the MVIC will be measured for data normalization. The MVIC and MEIC will be measured with an isometric dynamometer. In both measurements, subjects will be asked to perform three reps (5 sec work x 120 sec rest) and the best one will be used. Whenever the third one was the best, additional measurements will be taken until a decrease in torque will be obtained to determine the maximum. To apply Aussie electrical stimulation, an Aussie Sport (Ibramed) will be used. To apply Neo-Russian, a Neurodyn III (Ibramed) will be used. To apply RBS, a Genesy (Globus) will be used. The VAS will be used to assess tolerance to each treatment. One week later, the subjects will receive, randomly, a fatigue protocol that consists in 21 reps (5 sec work x 5 sec rest) of electrical stimulation with the three types of current. The data will be normalized with the MVIC and the reps equal or below 50 % of the first rep will be considered as a fatigue rep.