Menopause Effects on Cortico-reticular Functioning

Study aim: To determine cortico-reticular functioning during low and high female sex hormone, estrogen and progesterone, concentrations. Hypothesis: Greater functioning/response during neurophysiological tests will occur in the presence of high compared to low estrogen concentrations accompanying greater force production capacity. In addition, pathways reliant on a greater number of synapses, i.e. cortico-reticulospinal, will demonstrate the greatest difference between hormone concentrations. Justification: Several studies in monkeys and humans suggest that the methodology employed is sensitive to distinguish between high and low force production capacity. Estrogen is a neurotransmitter agonist exerting its influence at least via glutamate and GABA interneuron functioning, respectively. The MENSA study is a locally administered trial where volunteers who request to be put on combined hormone replacement therapy will be recruited through cooperation with gynaecologists in the Jyväskylä area. Participants visit the University of Jyväskylä laboratories 1-5 days before beginning treatment (baseline), 2 months after beginning treatment and 5 months after beginning treatment having completed a 12-week non-supervised exercise intervention. The experimental sessions will be conducted in the morning (beginning at approximately 7 am) following an overnight fast, and the time of the day kept constant for each individual participant (± 1 h). The posteriori measurement of serum follicular-stimulating hormone, estradiol and progesterone concentrations will be used to verify the hormonal status of the participants. A recent study showed that a sample of 12-15 participants would be expected to lead to moderate-to-large (0.2-0.9) effect sizes in the tests of cortico-cortico and cortico-reticular functioning. The target muscle is the biceps brachii performing voluntary unilateral isometric elbow flexion actions. MENSA aims to recruit 20 females; this attempts to overcome potential reduced sample size through drop-out or measurement/technical error, as well as sufficiency for detection of possible changes in secondary outcome measures.