Thesis
Higher levels of estrogen are associated with greater transcranial direct current stimulation-induced leg muscle fatigability in eumenorrheic young women
University of Iowa
Master of Science (MS), University of Iowa
Spring 2021
DOI: 10.17077/etd.005836
Abstract
Research into transcranial direct current stimulation (tDCS) continues to have issues with high inter-subject variability. One possible source of variability is female sex hormone fluctuations in young, healthy eumenorrheic women. One of the primary sex hormones, estrogen, is thought to increase cortical excitability, while the other primary hormone, progesterone, is thought to inhibit cortical excitability. The goal of this study was to evaluate the effects of fluctuating hormone concentrations throughout a normal menstrual cycle on fatigability in an isokinetic fatigue task (FT) after 4 milliampere (mA) anodal tDCS of the left (dominant) M1. We hypothesized that tDCS applied during phases with higher estrogen levels would be associated with increased leg muscle fatigability and diminished performance.12 young, healthy eumenorrheic women (23.3 ± 5.3 yrs) received 4 mA anodal tDCS of the left M1 during two time points of the menstrual cycle (late follicular (F2) and luteal phases (L)) and received sham stimulation during the early follicular (F1) phase. Blood draws were performed immediately before each session to measure hormone levels during each phase. Fatigue index (FI) was calculated from the FT to quantify fatigability, and EMG activity of the knee extensors and knee flexors were recorded during the FT. A positive correlation was found between estrogen levels and FI of the right extensors (r = 0.58, p < 0.01), in other words as estrogen concentration increased, FI increased. A repeated measures ANOVA revealed significant differences in average EMG activity of the right extensors during all phases (p < 0.01). Further post-hoc testing revealed significant differences between F1, F2, and L (F1 < L < F2). These results indicated that estrogen may play a significant role in the muscle fatigability response to tDCS in healthy females, specifically estrogen may have a significant effect on EMG activity of the leg muscles and on fatigability during an isokinetic fatigue test of the right extensors.
Details
- Title: Subtitle
- Higher levels of estrogen are associated with greater transcranial direct current stimulation-induced leg muscle fatigability in eumenorrheic young women
- Creators
- Justin Deters
- Contributors
- Thorsten Rudroff (Advisor)Warren Darling (Committee Member)Anna Stanhewicz (Committee Member)
- Resource Type
- Thesis
- Degree Awarded
- Master of Science (MS), University of Iowa
- Degree in
- Health and Human Physiology
- Date degree season
- Spring 2021
- Publisher
- University of Iowa
- DOI
- 10.17077/etd.005836
- Number of pages
- ix, 36 pages
- Copyright
- Copyright 2021 Justin Deters
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 31-36)
- Public Abstract (ETD)
One of the most popular forms of non-invasive brain stimulation is transcranial direct current stimulation (tDCS). tDCS is thought to either facilitate or hinder the brain’s ability to generate action potentials. tDCS has been used to treat different diseases like multiple sclerosis and Parkinson’s disease, and might be beneficial as an ergogenic aid for athletes and healthy subjects. One of the biggest issues plaguing tDCS research is inconsistency in results, with some finding beneficial effects while others reported either no effects or negative effects. One potential source of this inconsistency is sex-specific hormonal variations. The purpose of this study was to investigate the effects of the fluctuating levels of the female sex hormone estrogen throughout a normal menstrual cycle on exercise performance of leg muscles in a fatigue task after tDCS administration. We hypothesized that tDCS applied during menstrual cycle phases with high estrogen would be associated with poorer exercise outcomes in the leg muscles. Twelve young, healthy females with normal menstrual cycles were recruited and had either tDCS or a placebo treatment during specific phases of their menstrual cycle. After tDCS they performed a fatigue task. A positive association was found between estrogen levels and poorer exercise outcomes of the leg muscles along with increased muscle activity. This suggests estrogen may have a significant effect on exercise outcomes and electrical activity of the leg muscles during a fatigue task after tDCS was applied.
- Academic Unit
- Health and Human Physiology
- Record Identifier
- 9984097075302771
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