Sports supplementation for women - Women's Health Update

Townsend Letter for Doctors and Patients, July, 2003 by Tori Hudson, Laurie Cullen

Women have long been aware of the benefits of exercise in reducing the risk of heart disease, osteoporosis, diabetes, and breast cancer, not to mention weight management. Ever since title IX in the early 1970s, females have been participating in sports and athletic activities in ever increasing numbers. When women engage in regular physical activity or train for athletic events, women often require specific nutritional and herbal support for optimal performance. This nutritional support varies more by sport than by gender differences in body fat, hormonal influences and muscle mass. Those issues are more relevant in terms of dosing of nutrients rather than the nutrient selected and in some cases of lower body weight, nutrient depletion caused by the exercise may have a more adverse impact in women than in men. However, it is important to recognize that in general, women have lower muscle mass, greater body fat, and less upper body strength than do men. On the other hand, this body fat can be useful in endura nce activities as fuel for continued prolonged exertion. The greatest concern about the influence of women's menstrual cycles and exercise is the risk of underweight women and/or heavy exercisers. One or both of these can lead to infrequent or amenorrhea which in turn will significantly impact bone mass and an increased risk of osteoporosis later in life. All women should assure proper nutrient and caloric intake, in particular calcium and vitamin D. For women aged 14-16, 1,300 mg of calcium per day; for women aged 19-menopause, 1,000 mg per day, and for post menopausal women, 1200 mg per day. The current recommended dietary intake for vitamin D is 400 IU daily for women aged 51 to 70 years and 600 IU daily for women over 70. If these amounts are not achieved in the diet, then supplementation is required.

Exercise Physiology Basics

Exercise physiology takes into account the disciplines of biochemistry and biology in order to study the body under the stress of acute and chronic physical activity. Exercise physiology also studies the body and how it responds to intense demands of exercise and the changes that can occur as people participate in regular exercise training. As you can see, a discussion about exercise physiology can become incredibly extensive. Therefore, this review will only focus on sorting out the difference between aerobic and anaerobic exercise and the energy requirement for these different types of activities.

Exercise takes many forms. For example, exercise is as diverse as a slow stroll, a fast paced run, lifting weights, or a 20 mile run. Also, physical activity can range from sports performance to normal everyday activities in life. Therefore, the body needs to make physiologic adjustments to these different demands.

With exercise, there are acute responses to the activity and chronic adaptations to a training program. Acute responses refers to performing a single bout or session of exercise such as weight lifting or a long run. Under the particular metabolic demand, the body will adjust to the type of exercise and provide the specific energy for consumption. Chronic adaptations refers to how the body adjusts to the acute exercise sessions over a period of time, as with a training program. How the body adapts is measured as improvements in body function either at rest, during sub maximal exercise or during maximal exercise.

All types of exercise can be placed on a continuum. This is so the exercises can be classified in terms of the metabolic demand for a given activity. The range is from primarily anaerobic to those that are primarily aerobic. Power, speed, and endurance describe how intensely the exercise is performed over time. The figure below describes this in more detail.

Examples of power events are weight lifting, the shot put, the 50 meter dash.

Examples of speed events arc the 100, 200, or 400 meter runs.

Examples of endurance events are the 1 mile run or longer.

Keep in mind, all activities are not mutually exclusive to a certain type of metabolic demand. This means no one activity relies solely on a single energy system. For example, a soccer or basketball athlete interchanges between both ends of the spectrum and is for the most part somewhere in the middle.

Energy expenditure is a vital concept to understand when it comes to discussing how the body functions during exercise. Skeletal muscle contraction occurs when the biochemistry of the body causes one type of energy termed potential energy to be converted into another type called free energy. The potential energy for this conversion of energy for muscle contraction comes from the foods we consume. Food is where we get energy rich nutrients such as carbohydrates, fats, and proteins. Food is digested to its end products such as glucose, fatty acids, or amino acids. These products are then converted into the intermediate high energy compound, adenosine triphosphate (ATP). The pathways for this to occur are the following: the breakdown of creatine (an amino acid) phosphate for an immediate production of energy (anaerobic); the breakdown of sugar for a rapid production of energy (anaerobic or minimally aerobic); or the breakdown of stored sugar, fat or protein for a slower production of energy (aerobic).