Central and Peripheral Changes in Quadriceps Femoris Function After Different Types of Isometric Strength Training
Condition: Quadriceps Muscle Function
Study type: Interventional

Summary: 
      The purpose of this investigation is to examine the effects of 6-week unilateral isometric
      training interventions over quadriceps femoris on maximal strength and RFD-SF parameters and
      cortical excitability. Isometric strength training involved either electromyostimulation,
      voluntary activation, or the combination of both. The second aim is to investigate the
      potential cross-over effect on a non-trained leg.
    

Detailed description: 
      A longitudinal pre-post design with random assignment of the participants to one of three
      experimental groups or the control group was used. Quadriceps femoris (QF) function and
      cortical excitability were assessed on four occasions: prior to the intervention (pre-test),
      after 3 weeks of training (served for the adjustment of exercise intensity), after 6 weeks of
      training (post-test), and three weeks after the competition of training intervention
      (detraining) (Figure 1). Isometric strength training involves activation of QF applying EMS,
      VOLUNTARY, or the combination of both EMS and VOLUNTARY (COMBINED). The pre-test also served
      to familiarize participants with the training protocols and to determine the intensity of EMS
      needed to achieve 60%MVC. Quadriceps femoris (QF) function was assessed by MVC and RFD-SF.
      Cortical excitability was assessed with transcranial magnetic stimulation applied over the M1
      region. Prior to the pretest, body mass and percent of body fat were assessed using a
      bioelectric impedance method (In Body 720; USA) and body height with a standard stadiometer.
      After the pretest, the participants were randomly assigned to either one of the experimental
      groups (EMS, VOLUNTARY, or COMBINED) and the control group (CONTROL). Experimental groups
      performed unilateral isometric strength training three times per week for 6 weeks. All
      participants were advised to refrain from all resistance training targeting the legs between
      pre-test and post-test.
    

Intervention name(s): Isometric training with electromyostimulation; Isometric training with voluntary activation; Isometric training with combination of electromyostimulation and voluntary activation
Intervention type(s): Other; Other; Other
Intervention description(s): Each training session (18 in total) consisted of forty 4-s contractions separated by 20 s inter-contraction intervals. The exercise intensity was close-to-identical among the sessions (60 %MVC). The force intensity was determined individually during pretest where EMS was delivered at maximal tolerable dose. Electrical stimulation was 6.25-second long and was followed by a rest period of 20-second (duty cycle 15%). Stimulation characteristics were selected among the "Compex" commercially available strength programs. The stimulation intensity was monitored on-line and determined by the subject at the start of each EMS session according to his/her pain threshold to produce a force corresponding to at least 60% of the pretest MVC score.; Each training session (18 in total) consisted of forty 4-s contractions separated by 20 s inter-contraction intervals. The exercise intensity was close-to-identical among the sessions (60 %MVC). Participants were required to reach the proscribed force level only through voluntary activation of QF. To attain the same contraction/rest ratio as in EMS, automated audible signals were delivered in accordance with the contraction-rest pattern produced by the muscle stimulation device. To ensure participants produced 60% of individual MVC during each contraction the force level was measured with a force transducer and real-time feedback was provided on a computer screen.; Each training session (18 in total) consisted of forty 4-s contractions separated by 20 s inter-contraction intervals. The exercise intensity was close-to-identical among the sessions (60 %MVC). The proscribed force level was reached by the simultaneous action of EMS and VOLUNTARY. Each contraction was 6.25-second long and was followed by a rest period of 20-second (duty cycle 15%). Electrical stimulation corresponded to 30% of MVC, while the remaining 30% was achieved through voluntary muscle activation. To ensure participants produced a force corresponding to 60% of MVC during each contraction the force level was measured with a force transducer and real-time feedback was provided on a computer screen.
Allocation: Randomized
Intervention model: Factorial Assignment
Masking: None (Open Label)
Primary purpose: Basic Science