Women, Hormones, Metabolism & Energy Expenditure

What trainers need to know about subtle differences in female physiology.

By Len Kravitz, PhD
Jun 28, 2013

When it comes to optimal endurance exercise performance, fuel source and utilization play a major role in success. The contribution and expenditure of fats and carbohydrates for the synthesis of ATP (adenosine triphosphate) during exercise are regulated by several factors, including activity, duration and intensity, as well as the person’s age, training status, diet and gender. Proteins contribute a minor 1%–8% of fuel needs during submaximal exercise (Isacco, Duché & Boisseau 2012).

Before puberty, there is no difference between males and females when it comes to substrate usage during exercise (Isacco, Duché & Boisseau 2012). This is not the case during adulthood, when women rely more on fats than men do for the same relative exercise intensity. Read on for an in-depth exploration of how metabolism, energy expenditure and hormonal changes affect women during exercise.

The Major Female Hormones and Their Functions

Hormones help cells communicate with each other. Two major female sex hormones—estrogen and progesterone—play essential roles in a woman’s reproductive system. Both derived from cholesterol, these hormones are often called ovarian hormones because they are produced and secreted primarily by the ovaries (D’Eon & Braun 2002). Estrogen, which is also secreted to a lesser extent by the adrenal glands, is actually a class of 18-carbon steroid hormones. A steroid hormone affects the growth and development of sex organs.

The most biologically active estrogen is 17ß-estradiol, or estradiol. Other estrogens include estrone and estriol, but these are less biologically active than estradiol (D’Eon & Braun 2002). McCarthy (2008) notes that estradiol is at its highest level in the brain prenatally, or during the first few days of life, suggesting that this estrogen has potent and wide-ranging effects on the developing brain. Hormones from the hypothalamus and pituitary gland regulate and control the release of estrogen and progesterone.

Overview of Metabolism

Metabolism represents all chemical reactions that sustain the life of cells, and thus of the organism. The process can be divided into two categories: catabolism, or the breakdown of molecules to obtain energy; and anabolism, the synthesis of compounds needed by the cells.

Carbohydrates, proteins and fats provide a variety of substances essential for the building, upkeep and repair of body tissues, and for the efficient functioning of the body.

  • Carbohydrates come in three forms: starch, sugar and cellulose. Starch and sugar are essential energy sources for humans. Cellulose is an indigestible carbohydrate known as dietary fiber, which provides volume or bulk in food. Cellulose has no caloric value, which makes it a popular bulking agent in diet foods.
  • Proteins are the chief tissue builders of every cell in the body. Proteins help make the blood’s hemoglobin, which carries oxygen to the cells; form antibodies to fight infection; and supply nitrogen for DNA and RNA genetic material.
  • Fats are considered concentrated sources of energy, providing more than twice as much of it as carbohydrates and protein do. Fats make up part of the structure of cells, form a protective cushion and heat insulation around vital organs, carry fat-soluble vitamins and provide reserve storage for energy.

Energy Regulation, Hormonal Influences and Carbohydrate Metabolism

A major role of carbohydrate metabolism in a resting state is to maintain a constant supply of glucose to the brain. Carbohydrate in the form of glucose traveling in the bloodstream is the fuel that powers the brain. Glucose is the only fuel that brain cells normally use. Neurons, the cells that send bioelectric messages to one another, have a large demand for glucose because these cells are always in a state of metabolic activity.

Even during sleep, neurons are at work repairing and rebuilding their structural components. Because neurons cannot store glucose, they depend on a constant supply of this precious fuel. From a health standpoint, repeatedly overloading the bloodstream with sugar (e.g., by consuming too many soft drinks) places extra demand on the pancreas to keep secreting more insulin. This condition, where excess levels of insulin are circulating in the blood, is called hyperinsulinemia, and it may lead to insulin resistance (Alemany 2011). Insulin resistance is a condition in which normal amounts of insulin are inadequate for transferring blood glucose into cells, and the risk of type 2 diabetes progressively increases.

The energy needs of the muscle are what primarily determine how quickly and in what quantity carbohydrates (glucose and glycogen, the stored form of glucose in the liver and muscle) are used during rest and exercise. Blood glucose and muscle glycogen are essential for vigorous and prolonged strenuous exercise. Development of hypoglycemia (low blood glucose) and muscle glycogen depletion highly influence exhaustion during exercise.

How Women Use Glucose and Glycogen

In respect to female use of glucose and glycogen during endurance exercise, the research consensus suggests that women have lower rates of glucose appearance and disappearance than men do (Tarnopolsky 2008). According to current findings, Tarnopolsky observes, this may be due to lower activation of the sympathetic nervous system (responsible for the fight-or-flight response) in women, and not due to ovarian hormones. Tarnopolsky adds that the slightly inhibited carbohydrate use observed in women during endurance exercise also reflects the influence of hormones on fat metabolism.

Energy Regulation, Hormonal Influences and Fat Metabolism

Exercise intensity is the primary factor determining the degree of fat or carbohydrate utilization during exercise. During very light exercise, most energy fuel in the form of ATP is derived from fat. However, fat oxidation increases as intensity rises—until it reaches about 65% of VO2max (Jeukendrup 2002). Beyond this intensity, notes Jeukendrup, a gradual decline in the rate of fat oxidation is observed until intensity goes above 80% of VO2max, at which point fat oxidation rapidly declines. Training can reduce this decline in fat utilization (in both women and men), however—thus demonstrating that with continual endurance training, the body becomes more efficient at using fat as a fuel.

Fat Factors for Women

Most studies show that females store slightly higher levels of intramuscular fat, which is stored in small lipid droplets in muscle, than men do; and women also have more lipid droplets as opposed to larger lipid storage depots (compared with men) (Tarnopolsky 2008). During moderately vigorous exercise that is sustainable for 90 minutes or longer (approximately 55%–75% of VO2max), there is a progressive decline in muscle glycogen use and greater reliance on fat oxidation (breakdown) for ATP synthesis (Holloszy, Kohrt & Hansen 1998). This adaptation during endurance exercise is often referred to as glycogen sparing. Most research indicates that total-body lipolysis (fat breakdown) is higher in women than in men, as women have higher levels of glycerol (the backbone molecule of triglycerides) than men during sustained endurance exercise (Tarnopolsky 2008; D’Eon & Braun 2002).

Research indicates that estradiol plays a role in why women use more fat and less carbohydrate to fuel exercise at any given submaximal cardiovascular intensity (Tarnopolsky 2008). Also, women are not as efficient in carbohydrate-loading protocols that result in supercompensation of glycogen storage; this may be a direct result of higher levels of estradiol (Tarnopolsky 2008) and may slightly compromise women’s performance in marathon and ultra-marathon–like events.

How Menstrual Cycles Affect Exercise Metabolism

Estrogen and progesterone levels fluctuate during the menstrual cycle, with inferences for exercise performance (Oosthuyse & Bosch 2010). Some studies show that endurance performance is affected by the menstrual cycle, while others report no difference (Oosthuyse & Bosch 2010). Nevertheless, the increase in estrogen concentrations relative to progesterone levels during menstruation’s luteal phase suggests that endurance performance can readily improve during the midluteal phase.

In addition, during menstruation’s late follicular phase, which is characterized by a surge in estrogen and suppression of progesterone, endurance performance may potentially be enhanced as well. Oosthuyse & Bosch state that estrogen alters fat, carbohydrate and protein metabolism, improving performance, whereas progesterone appears to act in opposition to estrogen. The researchers propose that increases in estrogen enhance glucose appearance and utilization by the slow-oxidative type I muscle fibers. The high estrogen content during the luteal phase augments glycogen storage, which additionally has a meaningful influence on exercise performance.

Lastly, Oosthuyse & Bosch note that both estrogen and progesterone suppress gluconeogenesis output during exercise.Gluconeogenesis is a metabolic pathway that results in the synthesis of glucose from substrates such as lactate, amino acids and odd-chain fatty acids. It is a primary mechanism the body uses to keep blood glucose levels from dropping too low during sustained exercise bouts. This suggests that toward the end of some ultralong endurance events, some women may need to enhance their fuel availability via energy (glucose) replacement supplements (Oosthuyse & Bosch 2010).

The Female Hormonal Response to Resistance Training

Resistance training is essential for the maintenance of musculoskeletal health. It also lowers the risk of bone deficiencies such as osteopenia (below-normal mineral density) and osteoporosis, and reduces the risk of bone fractures. Decreases in bone density and/or bone mass become a greater risk with age, especially for women. According to a review by Kaufman et al. (2013), women who have low bone mineral density have a lifetime fracture risk of up to 50%, as opposed to 13%–25% for men.

Estrogen plays a key role in bone metabolism. Estrogen deficiency tends to have a negative impact on bone turnover markers and bone mineral density (Moghadasi & Siavashpour 2013). Implementing a resistance training program may help increase levels of hormones associated with bone formation, especially in women of reproductive age. Women who are postmenopausal have lower estrogen levels, which can lead to negative effects on bone mass (Moghadasi & Siavashpour 2013).

Resistance exercise can also affect bone formation by promoting changes in growth hormone, insulin, insulin-like growth factor I, leptin and parathyroid hormone. Moghadasi & Siavashpour investigated the hormonal effects of resistance training in 20 sedentary women, aged 25 ± 3.2 years (all having normal menstrual cycles). Over 12 weeks, the women participated in a 50- to 60-minute resistance training routine 3 days per week. The program included 2–4 sets (8–12 repetitions) of eight exercises performed at 65%–85% of 1-repetition maximum (1-RM). Exercises included chest press, leg extension, shoulder press, leg curl, latissimus dorsi pull-down, leg press, arm curl and triceps extension. Before the 12 weeks, and after the study was completed, hormonal blood profiles were taken during the follicular phase of the menstrual cycle.

Results indicated significant increases in muscular strength by the end of the 12-week program, as well as increases in growth hormone, estrogen, testosterone and parathyroid hormone. The authors concluded that sedentary women who engaged in a multiset total-body resistance training program (similar in design and intensity to the present study) would experience an increase in bone formation hormones and gain other musculoskeletal health benefits.

How Menopause Affects Exercise Performance

The higher utilization of fat as a substrate in women decreases at menopause. According to Isacco, Duché & Boisseau (2012), this is most likely attributable to a decline in plasma estrogen (and progesterone) concentrations and a drop in fat-free muscle mass. However, the researchers note that obese, postmenopausal women training at approximately 50% of aerobic capacity use fat more efficiently than men of a similar age. These results were observed despite similar basal plasma estradiol concentrations in the women and men, and higher plasma free fatty acid levels in men. Thus the exercise-induced increase in plasma estrogen concentrations that is observed in premenopausal women induced may partially occur in postmenopausal obese women as well. More research is needed in this area to fully explain and understand the mechanisms involved.

Practical Applications

An extensive review of the literature shows clearly that compared with men, women oxidize more fat and less carbohydrate at various levels of submaximal endurance exercise. This research suggests that personal trainers should incorporate a combination of the following training programs to most effectively promote fat utilization for their female clients:

  1. low-to-moderate, long-duration, submaximal steady-state cardiovascular endurance exercise
  2. fast, continuous, maximal steady-state training (tell the client to train at her maximal steady-state pace)
  3. interval training with moderate and high-intensity intervals during the work bouts
  4. total-body resistance training (it improves several hormonal responses and adaptations that impressively improve muscloskeletal health)

Exercise reduces the risk of heart disease and diabetes for women while increasing stamina and improving numerous health outcomes. No other intervention can make such a strong health claim. Keep your clients moving!

´╗┐´╗┐´╗┐´╗┐´╗┐´╗┐Hormones 101: Altering Cell Function via Feedback Circuits

Hormones—the word is derived from the Greek root meaning “impetus”—are specialized molecules released via the endocrine system’s network of tissues and organs. Hormones are best thought of as chemical messengers released by cells (via the blood) to communicate with other cells throughout the body. Each cell has specialized receptor proteins that respond to specific hormonal signals, and these signals trigger changes in the cell’s growth, function or metabolism.

Feedback circuits are the major control mechanisms of the endocrine system. Negative feedback is much more common, although positive feedback circuits do occur in humans. A negative feedback circuit happens when a stimulus triggers a response that causes a decrease in the stimulus. In the human body, secretion of a hormone can prompt a reaction that causes a reduction in the hormone, as illustrated in the following illustration.

Glucose Pathways to Brain, Adipose Tissue and Muscle

´╗┐´╗┐´╗┐´╗┐´╗┐´╗┐´╗┐Fat Oxidation Regulation in Adipose Tissue and Muscle

´╗┐10 Questions and Answers About Women’s Hormones and Athletic Performance

´╗┐1. What hormonal changes are observed in boys and girls at puberty?

At puberty, girls develop more adipose tissue, owing to their estrogen levels, and boys develop more muscle mass, owing to their testosterone levels (Isacco, Duch├® & Boisseau 2012).

2. What is the menstrual cycle, and what are its distinct phases?

The human menstrual cycle, designed to prepare a woman’s body for pregnancy, takes an average of 28 days. Usually, once a month the uterus grows a new, thickened lining (endometrium) that can hold a fertilized egg. If there is no fertilized egg to start a pregnancy, the uterus then sheds its lining.

The menstrual cycle has three distinct phases: the follicular phase (FP), ovulation and the luteal phase (LP). The FP begins on day one of menstruation and lasts about 10-14 days, until ovulation (the monthly release of a mature egg from an ovary). The LP, or secretory, phase is the second half of the menstrual cycle, after ovulation. Estrogen and progesterone concentrations vary between the phases.

3. Does lactate accumulation during exercise inhibit fat breakdown?

No, lactate accumulation from higher-intensity exercise does not inhibit lipolysis (Jeukendrup 2002).

4. What is the female athlete triad?

The three components of the female athlete triad are lack of a menstrual cycle, low bone mineral density and eating disorders. The triad occurs in females whose training levels exceed energy availability. Health consequences include cardiovascular, endocrine, reproductive, skeletal, gastrointestinal, renal and central nervous system complications. Psychological problems include low self-esteem, depression and anxiety disorders.

The first goal of treatment for someone suffering from the female athlete triad is boosting energy availability by increasing intake of foodstuffs and/or reducing energy expenditure. Females with eating disorders or disordered-eating patterns should be referred for nutritional counseling (Nattiv et al. 2007).

5. What is menopause?

Menopause is the profound transition in a woman’s body when menstruation ceases. A fundamental etiology associated with menopause is the intricate link between estrogen metabolism and the autonomic nervous system. Irregular menstrual cycle changes are usually the first symptom.

Lower fertility during the perimenopausal stage (transition into menopause that begins 8-10 years before menopause) of a woman’s life results in significant drops in estrogen levels. The term vaginal atrophy refers to inflammation, thinning and shrinking of the vaginal tissues, as well as decreased lubrication caused by lack of estrogen.

Hot flashes—sudden feelings of heat in the upper body—may start in the face, neck or chest and then spread upward or downward (depending on where they started). Skin on the face, neck or chest may redden, and a woman usually starts to sweat. Heart rate may suddenly increase and may become irregular or stronger than usual. Hot flashes generally occur during the first year after a woman’s final period. Disturbed sleep problems are typically caused by night sweats, insomnia or anxiety.

Difficulties falling asleep and staying asleep increase as women go through menopause. Urinary problems tend to be more likely during this period. Moodiness often goes hand in hand with sleep disturbance. There may also be some hair loss or thinning during menopause (Nordqvist 2009).

6. Is walking as effective as vigorous exercise for the prevention of cardiovascular events in women?

Manson et al. (2002) compared walking and vigorous exercise, along with hours spent sitting, as predictors of the incidence of coronary events and total cardiovascular events among 73,743 postmenopausal women aged 50-79 who were part of the Women’s Health Initiative Observational Study.

Results indicated that walking and vigorous exercise were associated with substantially fewer cardiovascular events among postmenopausal women, irrespective of race or ethnic group, age and body mass index. Prolonged sitting predicts increased cardiovascular risk.

7. Are women at increased risk for cardiovascular disease after menopause?

Yes. Women who are peri- and post-menopausal are at an increased risk, owing to a decrease in the female sex hormones.

8. Does estrogen affect skeletal muscle damage, inflammation and repair?

Yes, estrogen may positively lessen skeletal muscle damage and inflammation from exercise. Theoretical evidence suggests estrogen may encourage recovery and repair of muscle as well. This finding is preliminary, and more research is needed to explore mechanisms and further applications (Tiidus 2003).

9. Does hormone replacement affect exercise performance?

Green et al. (2002) found an effect only during high-intensity aerobic exercise. Systolic blood pressure at peak exercise in women taking hormones was lower than in women not taking hormones at almost identical levels of oxygen consumption and cardiac output. Further research is needed in this area.

10. Is weight gain during menopause inevitable or preventable?

The years during menopause are associated with weight gain and increased central adiposity. Body fat distribution and body composition changes may be due to the hormonal changes and loss of muscle mass occurring during the menopausal transition. The one factor most consistently related to weight gain during menopause, however, is physical inactivity. To avoid weight gain, women should make regular physical activity a priority (Simkin-Silverman et al. 2003).

Considerations for Active Women
  • Physical activity should be a priority at all ages, particularly after menopause.
  • Women use less fat and more carbohydrate to fuel exercise at submaximal levels.
  • Endurance performance may rise during specific phases in the menstrual cycle.
  • Resistance training can boost the hormones affecting bone formation, especially for women of reproductive age.
  • Trainers should be on guard for the female athlete triad.

References

Alemany, M. 2011. Utilization of dietary glucose in the metabolic syndrome. Nutrition & Metabolism, 8 (1), 74.

D’Eon, T., & Braun, B. 2002. The roles of estrogen and progesterone in regulating carbohydrate and fat utilization at rest and during exercise. Journal of Women’s Health & Gender-Based Medicine, 11 (3), 225-37.

Green, J.S., et al. 2002. Menopause, estrogen, and training effects on exercise hemodynamics: The HERITAGE study. Medicine & Science in Sports & Exercise, 34 (1), 74-82.

Holloszy, J.O., Kohrt, W.M., & Hansen, P.A. 1998. The regulation of carbohydrate and fat metabolism during and after exercise. Frontiers in Bioscience, 15 (3), D1011-27.

Isacco, L., Duch├®, P., & Boisseau, N. 2012. Influence of hormonal status on substrate utilization at rest and during exercise in the female population. Sports Medicine, 42 (4), 327-42.

Jeukendrup, A.E. 2002. Regulation of fat metabolism in skeletal muscle. Annals of New York Academy of Sciences, 967, 217-35.

Kaufman, J.M., et al. 2013. Treatment of osteoporosis in men. Bone, 53 (1), 134-44.

Manson, J.E., et al. 2002. Walking compared with vigorous exercise for the prevention of cardiovascular events in women. The New England Journal of Medicine, 347 (10), 716-25.

McCarthy, M. 2008. Estradiol and the developing brain. Physiological Review, 88, (1), 91-134.

Moghadasi, M., & Siavashpour, S. 2013. The effect of 12 weeks of resistance training on hormones of bone formation in young sedentary women. European Journal of Applied Physiology, 113, 25-32.

Nattiv, A., et al. 2007. American College of Sports Medicine position stand. The female athlete triad. Medicine & Science in Sports & Exercise, 39 (10), 1867-82.

Nordqvist, C. 2009. What is menopause? What are the symptoms of menopause? Medical News Today. www.medicalnewstoday.com/articles/155651.php; retrieved Apr. 21, 2013.

Oosthuyse, T., & Bosch, A.N. 2010. The effect of menstrual cycle on exercise metabolism: Implications for exercise performance in eumenorrhoeic women. Sports Medicine, 40 (3), 207-27.

Simkin-Silverman, L.R., et al. 2003. Lifestyle intervention can prevent weight gain during menopause: Results from a 5-year randomized clinical trial. Annals of Behavioral Medicine, 26 (3), 212-20.

Tarnopolsky, M.A. 2008. Sex differences in exercise metabolism and the role of 17-beta estradiol. Medicine & Science in Sports & Exercise, 40 (4), 648-54.

Tiidus, P.M. 2003. Influence of estrogen on skeletal muscle damage, inflammation, and repair. Exercise & Sport Sciences Reviews, 31 (1), 40-44.

Len Kravitz, PhD

Len Kravitz, PhD

"Len Kravitz, PhD, is a program coordinator and professor of exercise science at the University of New Mexico where he received the Presidential Award of Distinction and Outstanding Teacher of the Year award. In addition to being a 2016 inductee into the National Fitness Hall of Fame, Len has received the prestigious Specialty Presenter of the Year and Lifetime Achievement Award from CanFitPro."

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