Neuromuscular Electrical Stimulation and Isokinetic Training
Condition: Healthy
Study type: Interventional

Summary: 
      The purpose of this study was to assess the effects of Neuromuscular Electrical Stimulation
      (NMES) associated to an isokinetic training program in both young healthy men and women.
      Twenty subjects (10 men, 10 women; 21±1.5 years) submitted both quadriceps femoris muscles to
      a strengthening program (3 sets of 10 isokinetic concentric repetitions at 30°/s) two days
      per week for 4 weeks. One limb was submitted only to the strength training (EX) while the
      other underwent the same training program but with NMES added to each contraction (Ex+NMES).
      The current used for NMES was Russian Current (frequency of 2500 Hz, 50 bursts/s and pulse
      duration of 200 µs). The evaluation protocol included isometric and isokinetic concentric
      extensor torques at 30°/s. Men increased their torque in both tested modalities in both
      limbs, with no difference between them. The angle of peak torque increased for the EX limb,
      showing an altered tension-length relationship, which did not occur for the Ex+NMES limb or
      for women. Women increased their torque for EX limb in both modalities, which only occured
      for isometric mode in the Ex+NMES limb. However, they showed a decrease in their acceleration
      time in Ex+NMES limbs, showing they could produce a muscular contraction more readily than
      they did before training. The results of this study found that the association between NMES
      and isokinetic concentric voluntary strength training does not improve strength gains of
      voluntary training itself for young healthy subjects of both genders. However, it could
      improve neuromuscular readiness to produce torque in women.
    

Detailed description: 
      Subjects Twenty active and healthy undergraduate students (men: 21 ± 1.9 years; 1.77 ± 0.1 m;
      73 ± 8.4 kg; 23.3 ± 1.4 kg/m²; women: 20.9 ± 0.7 years; 1.64 ± 0.1 m; 56.3 ± 5.5 kg; 21 ± 1.0
      kg/m²) were selected for this study. All of them underwent physical examination before the
      study and had already participated in strength training programs before this study. All 10
      men selected concluded the study. Although 15 women were selected and began the training
      program, 5 were excluded: 3 reported episodes of pain in the knee joint during training
      sessions, and 2 of them could not conclude the training program for personal reasons.
      Therefore, the final data refers to 10 women.

      All procedures for evaluation and training were explained before and a consent term was
      signed. The project was approved by the Ethics Committee for Medical Research of Federal
      University of São Carlos and is in agreement with the Declaration of Helsinki.

      Evaluation protocol Before all evaluations, subjects were familiarized with testing and
      training procedures. All the evaluation and training procedures were applied for both right
      and left limbs of subjects before and after training program. To avoid possible dominance
      effects, volunteers were randomly separated to determine in which limb (right or left)
      training would be associated with NMES. The investigator who made the data analysis was blind
      to this randomization.

      After 5 min period of warm-up in a stationary bicycle at a speed of 20 km/h and load of 20 W,
      the subjects stretched the quadriceps femoris and the hamstring muscles of both limbs. Each
      muscle group was stretched 3 times of 30 s alternately. Afterwards, the subject was
      positioned in an isokinetic dynamometer (Biodex® Multi-joint System 3, Biodex, Shirley, NY),
      with the angulation of 100º on hips. Trunk, pelvis, and thigh of subjects were stabilized by
      strips, following equipment description36. Rotation axis of dynamometer was aligned with axis
      of the knee, at the level of lateral epicondyle of the femur, while the attachment was fixed
      at the distal part of leg of subjects, about 5 cm above medial malleolus. The gravity effect
      correction was calculated with the limb at 60° of flexion. The isokinetic device was
      calibrated before each evaluation and training session as requested by the manufacturer.

      After that, volunteers had their knees positioned at 60° and were familiarized to the action
      they would do. After that, they were asked to perform 3 maximum voluntary isometric knee
      extension contractions for 5 s, with 1 min of rest interval between the contractions. Three
      min after the last contraction, subjects were familiarized with the isokinetic contraction
      and then performed 5 maximum isokinetic concentric knee extension contractions at 30º/s
      speed, from 90° to 15°, 0° being full extension, totaling up 75° of Range of Motion (ROM).
      Verbal encouragement37 as well as visual feedback from the equipment38 were given in an
      attempt to achieve a maximal voluntary effort level during all contractions each subject was
      asked to perform. The same procedures were repeated with the contralateral limb.
    

Intervention name(s): NMES; Isokinetic exercise
Intervention type(s): Device; Other
Intervention description(s): In the contralateral limb, the same protocol was repeated; however, each contraction was associated with overlapped NMES (Ex+NMES limbs).For the NMES, a symmetric double-phase sine-wave was used. Bearing wave frequency was of 2500 Hz, modulated in 50 bursts/s, with pulse duration of 200 µs, interburst interval of 10 ms. This configuration is known as "Russian current".; Subjects realized training sessions twice a week with a 2-day minimum interval between the sessions, for 4 weeks. Each session included 5 min period of warm-up in a stationary bicycle, followed by 3 series of quadriceps stretching, as previously described. After being positioned at the isokinetic dynamometer, just as in the evaluation sessions, subjects firstly performed 3 sets of 10 maximum isokinetic concentric repetitions at the speed of 30º/s with one limb (EX limb), respecting the rest interval of 3 minutes between the sets.
Other intervention name(s): Current generator Physiotonus Slim (Bioset, Brazil); Isokinetic Dynamometer: Biodex Multi Joint System 3
Allocation: Randomized
Intervention model: Single Group Assignment
Masking: Single (Investigator)
Keywords: Electric Stimulation; Quadriceps Muscle; Muscle Strength; Neuromuscular Properties; Tension-Length Relationship; Healthy young adults