Menstrual Cycle Physiology and Effects

Menstrual Cycle Phases and Hormonal Changes

The menstrual cycle consists of two major phases - follicular and luteal - separated by ovulation, with characteristic hormonal fluctuations that affect metabolism, energy utilization, and various physiological functions throughout a woman's reproductive years 1
The follicular phase is characterized by rising estrogen levels and low progesterone 1
Early follicular phase is optimal for muscle glycogen storage when combined with high carbohydrate intake 1
Ovulation occurs following a sharp increase in luteinizing hormone (LH), estrogen, and FSH levels 1
Typically, ovulation happens around days 12-14 in a standard 28-day cycle, but varies with cycle length 2
For shorter cycles (25 days), ovulation occurs earlier, with fertile periods typically between days 6-11 2

During the luteal phase, high estrogen levels improve glucose metabolism by increasing glucose availability and glycogen storage in skeletal muscle 1
Estrogen increases the availability of free fatty acids and enhances oxidative energy metabolism 1
Women have higher rates of lipid oxidation and lower rates of carbohydrate and protein metabolism during exercise compared to men, particularly during the luteal phase 3
Protein requirements may be higher during the luteal phase due to increased progesterone levels causing higher rates of protein catabolism 3

Increased ventilatory drive occurs during the luteal phase 1
Estrogen has complex effects on the respiratory and cardiovascular systems 1
Despite these changes, menstrual phase generally does not significantly influence exercise performance at low altitudes 1

Normal menstrual cycles typically range from 23-38 days in length 1
Menopause typically begins around age 51, characterized by gradual loss of estrogen and absence of the menstrual cycle 1
Menopausal changes affect glucose and fatty acid metabolism, impacting multiple organ systems including adipose tissue, bones, gut microbiome, and skeletal muscles 1

Estrone-3-Glucuronide (E1G) levels rise again during the mid-luteal phase, approximately 7-10 days post-ovulation peak, reaching levels that are approximately 2-3 times higher than early follicular phase baseline values 4

The elevated estrogen during the luteal phase has important metabolic effects, including protein-sparing during exercise, improved glucose metabolism, and increased lipid oxidation 4
Estrogen during this phase improves muscle strength and bone mineral density 4
The combination of elevated estrogen and progesterone leads to increased fluid retention 5

Individual cycle length significantly affects the timing of both E1G peaks: women with shorter cycles will have earlier peaks compared to those with longer cycles 6