Central and Peripheral Changes in Quadriceps Femoris Function After Different Types of Isometric Strength Training

Study Overview
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Brief Summary
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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
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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.

Official Title
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Central and Peripheral Changes in Quadriceps Femoris Function After Different Types of Isometric Strength Training

Conditions
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Quadriceps Muscle Function

Intervention / Treatment
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* Other: Isometric training with electromyostimulation
* Other: Isometric training with voluntary activation
* Other: Isometric training with combination of electromyostimulation and voluntary activation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: young healthy, physically active participants of both genders Exclusion Criteria: no history of injuries, muscle-skeletal or neurological disease, or medications intake

Ages Eligible for Study
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Minimum Age: 19 Years
Maximum Age: 30 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Factorial Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Electromyostimulation - EMS<br>Experimental group comprised of healthy young adults that undergoes unilateral isometric training using electromyostimulation over quadriceps femoris | Other: Isometric training with electromyostimulation<br>* 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.<br>|
| Experimental: Voluntary activation - VOLUNTARY<br>Experimental group comprised of healthy young adults that undergoes unilateral isometric training based on voluntary activation of quadriceps femoris | Other: Isometric training with voluntary activation<br>* 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.<br>|
| Experimental: Combination of EMS and VOLUNTARY - COMBINED<br>Experimental group comprised of healthy young adults that undergoes unilateral isometric training that combines electromyostimulation and voluntary activation of quadriceps femoris. | Other: Isometric training with combination of electromyostimulation and voluntary activation<br>* 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.<br>|
| No Intervention: Control group - CONTROL<br>Group of healthy young adults who received no intervention. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| MVC | Maximal isometric force and Rate of Force Development of quadriceps femoris muscle during isometric contractions with maximal effort | Baseline | 
| MVC | Maximal isometric force and Rate of Force Development of quadriceps femoris muscle during isometric contractions with maximal effort | After 3 weeks | 
| MVC | Maximal isometric force and Rate of Force Development of quadriceps femoris muscle during isometric contractions with maximal effort | After 6 weeks | 
| MVC | Maximal isometric force and Rate of Force Development of quadriceps femoris muscle during isometric contractions with maximal effort | After 9 weeks | 
| The slope of the rate-of-force development scaling factor (RFD-SF) | The slope of the relationship (RFD-SF) between muscle force and rate of force development during rapid isometric contractions of varying intensities | Baseline | 
| The slope of the rate-of-force development scaling factor (RFD-SF) | The slope of the relationship (RFD-SF) between muscle force and rate of force development during rapid isometric contractions of varying intensities | After 3 weeks | 
| The slope of the rate-of-force development scaling factor (RFD-SF) | The slope of the relationship (RFD-SF) between muscle force and rate of force development during rapid isometric contractions of varying intensities | After 6 weeks | 
| The slope of the rate-of-force development scaling factor (RFD-SF) | The slope of the relationship (RFD-SF) between muscle force and rate of force development during rapid isometric contractions of varying intensities | After 9 weeks | 
| Motor Evoked Potentials (MEP) | MEPs were elicited in quadriceps femoris by transcranial magnetic stimulation (TMS) over M1 area. Motor cortex excitability was estimated by measuring the MEP amplitude (Input-Output, IO) peak to peak, caused by 20 randomized individual TMS stimulates with 100% (IO1), 120% (IO2) and 130% (IO3) of active motor threshold (AMT) intensity. | Baseline | 
| Motor Evoked Potentials (MEP) | MEPs were elicited in quadriceps femoris by transcranial magnetic stimulation (TMS) over M1 area. Motor cortex excitability was estimated by measuring the MEP amplitude (Input-Output, IO) peak to peak, caused by 20 randomized individual TMS stimulates with 100% (IO1), 120% (IO2) and 130% (IO3) of active motor threshold (AMT) intensity. | After 3 weeks | 
| Motor Evoked Potentials (MEP) | MEPs were elicited in quadriceps femoris by transcranial magnetic stimulation (TMS) over M1 area. Motor cortex excitability was estimated by measuring the MEP amplitude (Input-Output, IO) peak to peak, caused by 20 randomized individual TMS stimulates with 100% (IO1), 120% (IO2) and 130% (IO3) of active motor threshold (AMT) intensity. | After 6 weeks | 
| Motor Evoked Potentials (MEP) | MEPs were elicited in quadriceps femoris by transcranial magnetic stimulation (TMS) over M1 area. Motor cortex excitability was estimated by measuring the MEP amplitude (Input-Output, IO) peak to peak, caused by 20 randomized individual TMS stimulates with 100% (IO1), 120% (IO2) and 130% (IO3) of active motor threshold (AMT) intensity. | After 9 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| The linearity of the rate-of-force development scaling factor (RFD-SF) relationship | The linearity, described by coefficient of determination (r-squared) of the relationship (RFD-SF) between muscle force and rate of force | Baseline | 
| The linearity of the rate-of-force development scaling factor (RFD-SF) relationship | The linearity, described by coefficient of determination (r-squared) of the relationship (RFD-SF) between muscle force and rate of force | After 3 weeks | 
| The linearity of the rate-of-force development scaling factor (RFD-SF) relationship | The linearity, described by coefficient of determination (r-squared) of the relationship (RFD-SF) between muscle force and rate of force | After 6 weeks | 
| The linearity of the rate-of-force development scaling factor (RFD-SF) relationship | The linearity, described by coefficient of determination (r-squared) of the relationship (RFD-SF) between muscle force and rate of force | After 9 weeks | 
| M-wave | The tracing of the earliest electromyography (EMG) response to the stimulation of femoral nerve | Baseline | 
| M-wave | The tracing of the earliest electromyography (EMG) response to the stimulation of femoral nerve | After 3 weeks | 
| M-wave | The tracing of the earliest electromyography (EMG) response to the stimulation of femoral nerve | After 6 weeks | 
| M-wave | The tracing of the earliest electromyography (EMG) response to the stimulation of femoral nerve | After 9 weeks |