The Effects of Cathodal tDCS on Muscle Strength in Healthy Adults

Study Overview
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Brief Summary
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To investigate the effects of different intensity of cathodal tDCS on muscle strength in healthy adults.

Detailed Description
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Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that can modulate cortical excitability. In 2000, Nitsche and Paulus reported the polarity-dependent effect of tDCS in humans, i.e., anodal tDCS facilitates cortical excitability while cathodal tDCS decreases it. (Nitsche & Paulus, 2000). TDCS studies have been replicated by many researchers and reported similar effects of tDCS in humans when using anodal and cathodal tDCS with an intensity of 1 mA. The linear effect of tDCS also has been reported by various studies, i.e., when increase intensity, the polarity-dependent effect of tDCS also enhances. However, conflicting results of cathodal tDCS efficacy have been reported. Cortical excitability has been used to represent the efficacy of tDCS on neuroplasticity. The linear effect of cathodal tDCS on cortical excitability have been reported by researchers when using intensities at 1, 2, and 3 mA stimulated at the primary motor cortex in healthy participants (Batsikadze et al., 2013; Jamil et al., 2017; Kuo et al., 2013; Mosayebi Samani et al., 2019; Nitsche et al., 2003). Nevertheless, some studies showed the non-linear effects of cathodal tDCS (i.e., when increases intensity, cathodal tDCS enhances the cortical excitability) when using intensities at 1.5 and 2 mA in healthy participants (Batsikadze et al., 2013; Jamil et al., 2017; Mosayebi Samani et al., 2019). Hence, cathodal tDCS efficacy on cortical excitability is still controversy. Muscle performance is an outcome that represents clinical change induced by tDCS. Previous studies reported the tendency of cathodal tDCS efficacy in decreasing muscle performance of both upper and lower extremities in healthy participants (Cogiamanian et al., 2007; Tanaka et al., 2009). However, previous studies used a single intensity of tDCS in each study. Hence, there was no direct comparison between different intensities of cathodal tDCS on muscle performance in healthy participants. In our study, we aim to investigate the effect of different intensities of cathodal tDCS on muscle strength in healthy participants.

Official Title
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The Effects of Cathodal tDCS on Muscle Strength in Healthy Adults

Conditions
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Healthy Participants

Intervention / Treatment
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* Device: Transcranial direct current stimulation


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Male and female healthy adults Age range between 18 - 60 years old Right-handed dominant identified by the Edinburg Handedness Inventory No recent muscle injuries of both limbs for a past 6-months Exclusion Criteria: Consumed caffeine within 24 hours prior the experiment History of neurological symptoms i.e. seizures, weakness, loss of sensation or unclear history of pass illness Presence of metal implantation, intracranial shunt, cochlear implantation or cardiac pacemakers Presence of opened wound or infectious wound around scalp Presence of pain in evaluating muscle groups History of surgery in evaluating limbs

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 60 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: Other
Allocation: Randomized
Intervention Model: Factorial Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Sham Comparator: Sham tDCS<br>Sham transcranial direct current stimulation (tDCS) will be applied for 20 mins. Cathode on the primary motor area (M1) and Anode on the supraorbital area of contralateral side. Current intensity will be at 2 mA (sham mode). The scope of intervention is to investigate effect of sham tDCS on muscle strength. | Device: Transcranial direct current stimulation<br>* Cathodal tDCS will be applied for 20 mins.<br>|
| Experimental: Cathodal-tDCS 1 mA<br>Cathodal transcranial direct current stimulation (tDCS) will be applied for 20 mins. Cathode on the primary motor area (M1) and Anode on the supraorbital area of contralateral side. Current intensity is fixed at 1 mA and current will flow continuously. The scope of intervention is to investigate effect of cathodal tDCS on muscle strength. | Device: Transcranial direct current stimulation<br>* Cathodal tDCS will be applied for 20 mins.<br>|
| Experimental: Cathodal-tDCS 1.5 mA<br>Cathodal transcranial direct current stimulation (tDCS) will be applied for 20 mins. Cathode on the primary motor area (M1) and Anode on the supraorbital area of contralateral side. Current intensity is fixed at 1.5 mA and current will flow continuously. The scope of intervention is to investigate effect of cathodal tDCS on muscle strength. | Device: Transcranial direct current stimulation<br>* Cathodal tDCS will be applied for 20 mins.<br>|
| Experimental: Cathodal-tDCS 2 mA<br>Cathodal transcranial direct current stimulation (tDCS) will be applied for 20 mins. Cathode on the primary motor area (M1) and Anode on the supraorbital area of contralateral side. Current intensity is fixed at 2 mA and current will flow continuously. The scope of intervention is to investigate effect of cathodal tDCS on muscle strength. | Device: Transcranial direct current stimulation<br>* Cathodal tDCS will be applied for 20 mins.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change from baseline muscle strength after tDCS | Muscle strength will be measured in Newton by using a hand-held dynamometer. | Baseline (Pretest) and 40 minutes ( posttest) |