Impact of Transcranial Direct Current Stimulation Intensity on Leg Muscle Fatigability in Healthy Adults

Overview

Transcranial direct current stimulation (tDCS) is a painless,non-invasive means of increasing brain excitability. It has been used for several years and in many populations to improve physical and psychological outcomes. Although many tDCS devices are capable of a range of stimulation intensities (e.g., 0 mA – 5 mA), the intensities currently employed in most tDCS research are ≤ 2 mA, which are sufficient to elicit measurable improvements; but, these improvements might be expanded at higher intensities. In the beginning, when the safety of tDCS was still being established for human subjects, careful and moderate approaches to stimulation protocols were warranted. However, recent work using stimulation at higher intensities, i.e. up to 4 mA, has been performed in many populations and was found to have no additional negative side-effects. Now that the safety of tDCS at higher intensities is better established, work exploring the differences in performance between moderate (i.e. 2 mA) and higher (i.e. 4 mA) intensities is necessary to determine if increasing intensity increases the effectiveness of the desired outcome.

Prospective participants will include 40 healthy young adults (all right-side dominant) that will be recruited to complete four randomly ordered stimulation sessions (Baseline, 2 mA, 4 mA, and sham), separated by at least 5 days. Each session will involve one visit to the Integrative Neurophysiology Laboratory (INPL) and will last for approximately one hour. We expect data collection to last 6 months. The first session includes leg strength measurements and fatigue tasks of both legs, as well as a baseline 6 min walk test (6MWT) to determine fatigued walking characteristics. The following three sessions will include performing a random tDCS condition (2 mA, 4 mA, or sham) over the brain area that controls the participant's dominant leg for 15 minutes prior to and then throughout the duration of the fatigue task of the dominant leg (16-20 min total stimulation time). The fatigue task for the nondominant leg will be performed after a 10 minute energy recovery period. After the fatigue task has been completed for both legs, the participants will perform the 6MWT.

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: Randomized
    • Intervention Model: Crossover Assignment
    • Primary Purpose: Treatment
    • Masking: Double (Participant, Investigator)
  • Study Primary Completion Date: June 24, 2019

Interventions

  • Device: Sham transcranial direct current stimulation
    • Uses weak electrical current (2 mA intensity) at the beginning and the end of a given stimulation period to control for potential placebo-like effects or participant expectation bias.
  • Device: Transcranial direct current stimulation at 2 mA
    • Uses weak electrical current (2 mA intensity) to either increase or decrease brain excitability and improve functional or cognitive outcomes.
  • Device: Transcranial direct current stimulation at 4 mA
    • Uses weak electrical current (4 mA intensity) to either increase or decrease brain excitability and improve functional or cognitive outcomes.

Arms, Groups and Cohorts

  • Sham Comparator: Sham
    • Participants will have the anode (active electrode) placed over the brain area the controls their dominant leg and the cathode (return electrode) above the ipsilateral eyebrow. Stimulation is turned on (2 mA) for the 30 seconds at the beginning and the end of the trial, but stays at 0 mA in the intervening time.
  • Experimental: 2 mA
    • Participants will have the anode (active electrode) placed over the brain area the controls their dominant leg and the cathode (return electrode) above the ipsilateral eyebrow. Stimulation is ramped up to 2 mA over the first 30 seconds and stays at 2 mA for the remainder of the stimulation time.
  • Experimental: 4 mA
    • Participants will have the anode (active electrode) placed over the brain area the controls their dominant leg and the cathode (return electrode) above the ipsilateral eyebrow. Stimulation is ramped up to 4 mA over the first 30 seconds and stays at 4 mA for the remainder of the stimulation time.

Clinical Trial Outcome Measures

Primary Measures

  • Distance walked in the 6 Minute Walk Test
    • Time Frame: Through study completion, up to 6 months
    • Walk back and forth between two markers spaced 30 meters apart for six minutes
  • Fatigue index from the isokinetic fatigue test
    • Time Frame: Through study completion, up to 6 months
    • Perform 40 consecutive flexion and extension repetitions of the knee on the dominant leg. After a 10 minute rest, do the same task on the the non-dominant leg.

Participating in This Clinical Trial

Inclusion Criteria

1. Young adult (18-30 yrs)

2. right-side dominant

3. able to independently walk for 6 min

4. at least 30 min of moderate-intensity, physical activity on at least 3 days of the week for at least the last 3 months

5. without chronic neurological, psychiatric, or medical conditions

6. not taking any psychoactive medications

Exclusion Criteria

1. pregnant

2. known holes or fissures in the skull

3. metallic objects or implanted devices in the skull (e.g., metal plate)

4. current student of study personnel

5. under the direct supervision of study personnel

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: 30 Years

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • University of Iowa
  • Provider of Information About this Clinical Study
    • Principal Investigator: Craig D. Workman, PhD, Postdoctoral Scholar – University of Iowa
  • Overall Official(s)
    • Craig D Workman, PhD, Principal Investigator, University of Iowa

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