Physiological conditions that affect women divers are discussed. Among these are physical fitness, temperature adaptation, menstruation and pregnancy. Studies that clarify these issues are cited and their implications on dive safety are stressed.
Over the last few decades, there has been a steady increase in women entering scuba diving, both for recreational and professional purposes. The topic of women in diving, therefore, is becoming more relevant, not only to divers but to professionals who train and medically evaluate divers. Whereas diving ability and safety are not defined by gender, there are physiological considerations of specific concern for the female diver. These include: physical fitness, thermal stress, bends susceptibility, diving during menstruation, PMS and pregnancy. Historically, there have been very few studies that addressed these issues.
Table of Contents
Physical fitness is a topic to which all divers should give more import, but particularly women. Whereas a physically fit woman is a better candidate for diving than an unfit man, inherent anatomical and physiological differences give an untrained woman less aerobic capacity, speed and upper body strength than an untrained man.
Women are usually smaller in mass, height, weight, leg length and surface area than men. Women tend to have more fat and less lean muscle fiber, a lower center of gravity and greater tendon laxity. Women also generally have a faster pulse and respiration and lower blood pressure.
Some of these characteristics are advantageous in diving – small lungs need less air, so women usually have good air consumption. Fat stores give women insulation and positive buoyancy, which is a big plus for maintaining a comfortable horizontal body position both underwater and when swimming on the surface. Women also have natural grace, dexterity and flexibility.
Many women, however, have low “maximal oxygen consumption,” which is a disadvantage in diving. Maximal oxygen consumption measures how efficiently oxygen is carried by the hemoglobin in the blood to fuel the body’s muscles during aerobic exercise. Because a woman inherently has a small blood volume and a small hemoglobin component, the blood’s oxygen carrying capacity is limited.
Scuba diving requires above average and sometimes exceptional aerobic power and stamina. Equipment intensive activities, such as commercial diving, cave diving, etc., require not just cardiovascular fitness but significant muscle strength. It is also important to anticipate unforeseen physically stressful situations during any dive, such as suddenly being forced to swim against a strong current or conduct an emergency rescue. A female diver, therefore, should augment her fitness level to be fully prepared. There are a variety of training programs readily available to help women achieve these goals. An excellent regime, for example, would be one that combines a low fat diet and regular weight training and cardiovascular exercise (i.e., running, stair climbing, bicycling, etc.).
There are other ways in which a woman (as well as her male buddy) can enhance overall fitness for diving:
1) Learning and maintaining good water skills
2) Wearing comfortable, well-fitting diving equipment
3) Pacing yourself to conserve energy when diving
4) Staying well-nourished and maintaining adequate fluid intake
It has generally been believed that because women have a high percentage of body fat they will stay warm in cold water. Unfortunately, this is only true in certain obese individuals with very thick subcutaneous fat layers. In reality, heat loss is primarily determined by the ratio of exposed surface area relative to body mass (weight). Because of their curves, women, particularly slender ones, have a high ratio of surface area to mass and therefore lose significant body heat when exposed to a cold environment. Heat loss is also determined by basal metabolism rate (BMR), heat generated by muscle tissue and the individual’s health, nutritional and hydration levels. Vascular function is also a factor (for example, heat is lost when blood vessels dilate, from, for example, consumption of alcohol).
An interesting exception are the Ama divers of Japan and Korea. These professional free divers work six hours a day all year long, including winter, when the water temperature is 50oF (10oC). Even though the Ama usually wear only thin cloth suits, the women tolerate the cold better than their male counterparts. Female Ama divers, many of whom are lean, develop an exceptional degree of acclimatization. In other words, their bodies undergo adaptive changes that allow them to tolerate lower core temperatures. Unfortunately, acclimatization is rare in sport divers.
A female sport diver, therefore, should always wear an adequate thermal suit, even in temperate climates, to avoid hypothermia (lowering of the body’s core temperature below 95|degrees~F). Women should also be aware of the potential for heat stress – hyperthermia – when the body’s core temperature is elevated. Because women have fewer functional sweat glands per unit area and begin to sweat at a 3oF higher temperature than men, early studies indicated that women were more prone to hyperthermia. But, the women studied were not comparable in fitness to the male subjects. In subsequent studies using comparable subjects, women were shown to acclimatize just as well as men to heat stress.
Menstruation And PMS
A question many women ask is, “If I dive during my period, will I attract sharks?” Shark expert Dr. Eugenie Clark estimates that the chances of any diver being attacked by a shark are only one in 10 million and studies have demonstrated that sharks show no particular interest in menstruating women. This may be owing to the fact that menstrual secretions, which are actually a combination of hemolyzed or “old” blood, cellular debris, mucus and water, are distinctly different from fresh blood. In fact, some species of sharks are actually repelled by menstrual secretions. Additionally, the amount of blood that might enter the water during a dive, particularly if a woman wears a tampon, is negligible.
A dilemma that does merit concern, however, is whether a woman should dive if she is experiencing mental or physical impairment from PMS (premenstrual syndrome) or during menses. PMS usually occurs seven to ten days before the beginning of the menstrual cycle but it can last as long as two out of every four weeks and affects nine out of ten premenopausal women. PMS is commonly believed to be the result of a hormonal imbalance and may have as many as 150 signs and symptoms (i.e., bloating, sore breasts, insomnia, fatigue, vertigo, cardiac palpitations, hypoglycemia, headaches, mood swings, etc.) that can range in intensity from mild to incapacitating. (Note: There are various prescription medications for PMS but many have side effects that warrant serious precaution.) Also, a woman who loses a lot of blood during her period may suffer anemia, weakness, exercise intolerance and other associated problems. Depending on the severity of her symptoms, each woman should make a responsible decision as to whether she can dive safely during PMS and menstruation.
Women have traditionally been believed to be at greater risk for bends than men. However, recent studies reveal that this belief may not be accurate. The navy tables that established safe decompression limits were based on studies of male subjects, most of whom were young, physically fit SEALs. It was not known how applicable these parameters were for women, whose proportion of body-fat, hormones and fluid shifts are very different. In particular, the issue of fat has always raised concern. Even though accident statistics show no proof that fat, in and of itself, has ever caused decompression sickness, the fact that fat has a five-fold affinity for nitrogen and relatively low blood flow has been the subject of much speculation.
Air force studies and a survey of recreational divers conducted in the 1970s indicated a significant bends susceptibility in women but the validity of these findings was subsequently challenged because male/female subjects were not comparable in fitness and experience or because the DCS hits were not medically confirmed.
Comparative DCS studies conducted since 1980 conclude that women are no more susceptible to DCS than men and may be less likely to have bubbling following dives. The Naval Diving and Salvage Training study in 1987, for example, reported that eight male divers but no females developed DCS after making deep mixed gas dives. Most medical experts today agree that DCS susceptibility is a complex of individual, not sex specific factors. However, we still do not have definitive answers and we need more research on this insidious diving malady.
Diving during pregnancy has been a highly controversial topic, complicated by the fact that studies done on animals (sheep, dogs, rats, etc.) may not accurately simulate human physiology and studies done on humans rely on anecdotal reporting, which may not be scientifically accurate. Additionally, there is disparity in the results of the research.
Nevertheless, there are clear contraindications for diving during pregnancy, both for the mother and her fetus. Problems for the mother include: morning sickness that involves nausea, vomiting and gastric reflux, an increased risk of both hypothermia (owing to vasodilation) and hyperthermia (owing to increased metabolic rate), fatigue, back pain, increased fluid retention (making ear and sinus clearing difficult), increased fat stores and difficulty in wearing and ditching a weightbelt.
Dangers for the fetus: Some animal and human studies have shown that if a female dives during pregnancy, particularly if she gets bent, her fetus may be stillborn or suffer birth defects. Other concerns are the effects of hyperbaric oxygen if the mother has a diving accident that necessitates hyperbaric treatment (newborns exposed to 100 percent O2~ can develop retrolental fibroplasia, resulting in blindness) or the effects on the fetus if the mother is envenomated by a marine creature.
The most dramatic concern involves bubble formation in the fetus. In an adult’s circulatory system, the entire cardiac output passes through the lungs, which act as an effective bubble filter. But, since a fetus’ lungs are not functional until birth, any bubble(s) that may develop in the fetal circulation travel directly to the heart and brain, which can result in a fatal arterial gas embolism.
The consensus among diving medical professionals, therefore, is that women should never dive during pregnancy.
Practical experience has shown that women who are physically fit, well trained and responsible make excellent and safe divers. Hopefully, in the future we will gain a more comprehensive knowledge of issues in diving physiology and medicine that address the female diver.
Anatomical differences, women vs. men
- 3 to 4 inches shorter
- 25 to 30 pounds lighter
- 20 percent less mass
- 33 percent less lean body mass
- Smaller bones
- Leg length
- 51 vs. 56 percent in a man 10 to 15 pounds more fat
- 40 to 45 percent less fat free weight
- 18 percent less surface area