Those of you who grew up in the 1960s may remember a television advertisement for Virginia Slims cigarettes. The cigarette was aimed at women, with a catch phrase entitled "you've come a long way, baby." Well, the same can be said for women who wish to exercise or perform regular physical activity during pregnancy. When it comes to recommendations for exercise during pregnancy and the postpartum period, women have, indeed, come a long way. In fact, a recent study has shown that most women (approximately two thirds) are doing some sort of exercise during pregnancy (7). Much of this may have to do with the fact that nearly 3 million girls are now involved with high school sports, and many of them choose to continue to exercise well into their childbearing years of adulthood. So regardless of whether a woman is an elite athlete, a recreational athlete, or someone who performs physical activity simply for health benefits, she can usually continue to maintain a regular exercise schedule throughout the entire duration of pregnancy.
A LITTLE HISTORY
The first U.S. guidelines for exercise during pregnancy were published in 1985 by the American College of Obstetricians and Gynecologists (ACOG) (1). Credible information was sparse at that time, and research on the topic was being published at less than one article per month since the early 1950s. Most investigators who performed these early studies mentioned exercise only in passing, included only a small number of subjects, or used animal models. Understandably, the ACOG guidelines were cautiously conservative, given the lack of research at the time. Of particular note was the recommendation that "strenuous activities should not exceed 15 minutes in duration" and the infamous "maternal heart rate should not exceed 140 BPM." Almost by definition, this upper heart rate limit excluded any vigorous activities such as running, where values will almost always exceed 140 BPM (unless the woman is extremely fit).
During the 10 years that followed the 1985 ACOG guidelines, more than 600 articles were published on the topic of exercise and pregnancy. More study participants were being included, comparisons were being made between endurance trained and sedentary pregnant women, and exercise interventions were begun in women who were previously sedentary. In 1994, ACOG revised its original guidelines to reflect the large increase in scientific evidence that had become available (2). The overall tone of the guidelines had shifted to a more positive message. No longer was the 140 BPM heart rate limit indicated, but rather, women were encouraged to limit their exercise routines based on maternal symptoms and perception of effort involved, rather than a single measured physiological response. Although the 1994 guidelines were less cautious than the original 1985 version, they were still very generic and did not address the specific needs and concerns of the female athlete. In 2002, another revision was published, and a significant amount of discussion focused on the female athlete (3). In particular, the authors recommended "recreational and competitive athletes with uncomplicated pregnancies can remain active during pregnancy and should modify their usual exercise routines as medically indicated." Not only were many of the previous restrictions removed from the ACOG guidelines, but virtually all women experiencing normal healthy pregnancies were now encouraged to perform some sort of physical activity on most, if not all, days of the week. Similar guidelines were published in Canada only a year later, and they also are very positive and encouraging for physically active women (5). In the research world, we have now shifted our focus away from studying the fears about exercise during pregnancy to evaluating the benefits to the mother as well as the offspring (11).
HONEST COMMUNICATION WITH THE HEALTH CARE PROVIDER IS ESSENTIAL
Although it should go without saying, we strongly urge any pregnant woman to be completely honest with her health care provider when it comes to physical activity and exercise routines during pregnancy. This discussion should include not only the typical activity/training schedule, but also exercise history, goals, and psychological benefits the woman believes she gains from her program. If a pregnant woman notices any of the typical warning signs for discontinuing exercise (Table 1), she should stop exercising and inform her physician or nurse midwife immediately (3). In addition, each woman should ask her health care provider if there are other specific warning signs that she should be aware of. If good communication is maintained, the physician, nurse midwife, and/or other health care providers are more able to offer the best advice and prenatal care possible.
It also is important to understand that most physicians do not receive significant training regarding the role of exercise in general, and even less as it pertains to pregnancy. Current medical school curricula typically do not provide significant time for such discussion. For example, more than one obstetric practice manager has told us that their patients are not allowed to exercise at an intensity greater than a heart rate of 140 BPM; a recommendation that was removed from the ACOG guidelines years ago. Thus, it is up to the pregnant woman and any fitness specialists she may work with to keep abreast of the latest research and discuss these topics during normal prenatal visits. Pregnant women, fitness specialists, and physicians may want to refer to the physical activity readiness questionnaire for pregnancy (PAR MedEx), published in the Canadian guidelines (5) as a starting point for conversations about exercise during pregnancy (http://www.csep.ca/communities/c574/files/hidden/pdfs/parmed-xpreg.pdf).
HOW MUCH EXERCISE IS OK?
The most recent ACOG guidelines indicate that most women can continue doing their normal exercise routines until symptoms indicate otherwise (3). Symptoms do not always need to be dramatic, as many women simply feel the need to decrease exercise intensity, duration, or frequency as pregnancy progresses. Even Paula Radcliffe, the world record holder in the marathon, eventually decreased running to every other day in the final weeks of her pregnancy. However, we also have had conversations with women who indicated that they kept running close to 50 miles per week until delivery and resumed only a few days later. The variability that exists in what a woman wants to do, and can do, supports the need for chronic exercisers to maintain open communications with their health care providers. Every case is different. We also would suggest cross training a bit more during pregnancy, and increasing the emphasis on non-weight-bearing activities such as swimming and cycling. Thus, a woman can maintain or increase her cardiovascular fitness while decreasing her risk of an overuse injury.
It is natural for some women, particularly those who are highly trained and competitive, to believe that their aerobic fitness levels will decrease significantly if exercise routines are reduced. However, research has shown this not to be the case (9,13,14). Even in studies that have shown slight decreases in fitness, women who resumed training promptly after delivery were able to regain their prepregnancy levels within a few weeks (15). The point is women who maintain a fairly regular exercise routine throughout gestation should not suffer the effects of detraining to any great extent.
Although women are now encouraged to continue their exercise routines during pregnancy until symptoms indicate otherwise, there are still precautions that should be followed. It never has been nor will it likely ever be a good idea for a pregnant woman to perform physical activities that pose a high risk of blunt trauma. Examples include water skiing and most contact sports. In addition, the risk of falling increases with a woman's change in center of gravity and an increase in her joint laxity. A woman's overall body awareness may be affected, particularly if she attempts new activities that require extreme balance and coordination.
Temperature regulation is another important issue because there is concern that maternal overheating may cause developmental abnormalities (teratogenesis) on the growing fetus, particularly during the first trimester. Although congenital malformations have been shown in laboratory animals under experimental conditions of excess heat, there is no published evidence that this has ever occurred in humans. Anecdotally, a former student who also served as a research study participant ran a marathon in Corpus Christi, TX, while she was in her first trimester (and did not know that she was pregnant). Upon realization of her condition some weeks later, she had natural concern. However, mom and baby were fine, as are many others who have had this experience. Despite the lack of human evidence for maternal temperature regulation issues, it is still prudent to avoid hot-weather exercise whenever possible during pregnancy. When working out indoors, a woman should do so with a cooling fan while she uses the treadmill, cycle ergometer, or other exercise machine.
ACOG guidelines have historically warned that a woman should not perform any supine exercises while pregnant. The main concern is the issue of blood flow. That is, with a growing fetus taking up more and more space in the enlarging uterus, the fear is that the additional weight and pressure may impede venous return of blood to the heart, making the woman lightheaded, and possibly reducing oxygen traveling through the uterine and placental circulation. Although it is still good practice to avoid supine exercises, particularly late in pregnancy, a woman should be pragmatic about the issue. For example, since sleeping on either the left or right side is recommended during pregnancy, a woman also can perform stretching and strengthening activities in either of these side-lying positions. She may have to briefly move through the supine position to do these, and there is no evidence that this will cause any problems. Abdominal exercises can be performed as long as they are not overdone. For instance, it is a good idea for a woman who wishes to perform sit-ups or crunches to do so with the head higher than the feet, rather than starting off completely supine and flat. Any abdominal exercises should be discontinued, and the physician should be notified, if bulging of the abdominal muscles occurs (this is known as diastasis recti). See Table 2 for a summary of common risks and exercise modifications during pregnancy.
WEIGHT GAIN CONCERNS
In addition to the fear of getting out of shape during pregnancy, women also are concerned with how much weight they should gain and how fast they might be able to lose it after delivery. In 1990, the Institute of Medicine (IOM) listed weight gain recommendations as part of a lengthy document devoted to prenatal nutrition (8). The IOM weight gain recommendations are based on a woman's prepregnancy weight for height status as measured by body mass index ([BMI] Table 3). The BMI can be calculated by dividing the woman's weight (in pounds) by her height (in inches) squared, then multiplying the answer by 703.
Although some women are concerned about gaining weight during pregnancy out of fear of not being able to lose it postpartum, they should temper any urge to curb their eating for "aesthetic reasons." The need for optimal weight gain should be obvious. In addition to maintaining normal bodily functions, the woman needs an energy source for the developing fetus and associated organs and blood vessels. It also should be noted that a pregnant woman's changing energy need is not simply a function of her increasing body size. Regardless of weight gain and body size, research from our laboratory showed that a woman's resting energy expenditure increased an additional 5% to 7% by the second trimester of pregnancy. So not only does a woman's body mass increase, but much of the weight gained during pregnancy is very metabolically active. (12).
As an example of how a woman's metabolic needs increase, a 132-pound woman who gains 25 pounds during the course of a pregnancy would require an additional 1680 kJ/day, (400 kcal/day) simply to maintain her bodily functions and those of the growing fetus. Granted that this increase in energy need occurs gradually throughout gestation, it must be considered as the woman plans her exercise routines in conjunction with her pregnancy-adjusted diet. If the woman mentioned in the previous example had been maintaining her weight prior to pregnancy, even while exercising, she would only need to account for the extra 1680 kJ. However, if she had been gaining or losing weight prior to pregnancy, her caloric intake should be accordingly adjusted up or down during pregnancy.
One of the most frequent questions we hear from pregnant women who exercise is "what do the guidelines say about weightlifting during pregnancy?" The short answer is "not much" because there is so little good research on this topic. We believe that the major concern by physicians is that heavy weightlifting can cause premature labor, just like heavy lifting in "real life" has been strongly discouraged historically for the same reason. Although we would not recommend beginning a power-lifting routine during pregnancy, there is no evidence that general resistance training will cause any harm. Decreasing resistance and increasing repetitions is a good idea, and shorter sets (perhaps more of them) also will prevent undue fatigue from strength training. Of most concern are breath holding/Valsalva maneuvers, which should always be avoided, pregnant or not, and balance issues, which may occur with heavily weighted barbells. Resistance bands are an excellent option, as are weight machines, in place of barbells and heavy dumbbells. See Table 4 for general recommendations concerning strength training during pregnancy.
Although most of this article focuses on exercise during pregnancy, the issue of postpartum exercise also must be addressed. Whether the woman is a highly trained elite athlete or someone who simply chooses to walk for physical activity, one question that always comes up is, "when can I resume my normal exercise routine?" The best answer we can give is, "it depends." It depends on how much the woman had been doing during pregnancy. It depends on the duration and intensity of labor and delivery, or whether a woman needed stitches or underwent a cesarean delivery. In short, there is no definitive period of time that a woman must wait before returning to her normal exercise routines. Some women may be out running within the first week, others may require several months. This is a time when a woman should closely listen to her body and honestly communicate with her health care provider. The most recent ACOG guidelines indicate that "pregnancy exercise routines may be resumed gradually as soon as it is physically and medically safe" (3).
Many barriers a woman may encounter to keep her from returning to prepregnancy exercise routine and/or athletic competition may be more psychosocial, rather than physiological. A first-time mother may be overwhelmed by her new responsibilities because she is inexperienced in newborn care. Women who did not particularly enjoy exercising before pregnancy may use motherhood as an excuse to slack off on their previous activity routines. Others who considered themselves finely tuned athletes less than 40 weeks before delivery may be frustrated if they believe that it might take some time to return to their former competitive levels. Research has shown that while highly trained athletes perceive many of the same postpartum exercise barriers (lack of time, lack of social support) as less active individuals, they are more likely to overcome them and successfully return to their previous training levels (4). Part of this is likely caused by positive perceptions for return to competition that the athletic women carried with them throughout gestation. In nearly all cases, strong social support at home seems to be the key to rapid return to normal exercise.
TO BREAST-FEED OR NOT TO BREAST-FEED
The choice of whether to breast-feed is obviously an important one, and very personal. It is true that breast-feeding can make it very difficult and inconvenient for some who wish to resume a very vigorous exercise schedule. However, given what we know about the benefits of breast milk, many women feel that they should at least attempt to breast-feed for as long as possible through their babies' first 2 years. Many women with whom we have worked have managed to compromise. That is, they are willing and able to rearrange their workouts to follow feeding time whenever possible. If feeding is not an option when women need to exercise, they opt for the breast pump instead. Although this effort takes planning and patience, many women feel that the result is worth it. From a comfort standpoint, there is no question that enlarged breasts coincident with lactation are an issue. Once again, we must defer to our experienced female colleagues who indicate that wearing two sports bras is an option worth considering! One thing that research has shown that should be comforting for postpartum exercisers is that milk volume and nutrient content are not negatively affected by workouts (11).
Another reason women may choose to continue breast-feeding is the belief that it will facilitate their ability to lose the weight that they have gained during pregnancy. This makes sense intuitively because of the additional caloric expenditure associated with breast milk production. However, many research studies have shown that this does not always occur (6). The most likely reason is that women increase their caloric intake an equivalent amount. Thus, postpartum weight loss may not always be greater in women who breast-feed compared with those who do not.
Although results from some previous studies may seem disheartening, particularly to overweight women, recent research indicates that it is indeed possible to increase postpartum weight loss with the help of exercise (10). However, this effort must be combined with a moderate caloric restriction (approximately 2100 kJ/day) to be effective. We would recommend that any woman with questions regarding the interaction of exercise, breast-feeding, and postpartum weight loss visit with a lactation support specialist recommended by her health care provider.
For women going through healthy pregnancies, there is no reason to make drastic reductions in workout routines as long as their health care providers are kept in the loop. Exercise is now strongly encouraged because research has shown that the benefits far outweigh the risks. Some adaptations will likely have to be made, and common sense should rule as a woman listens carefully to her body. But barring any medical issues that may arise, our overall advice to a pregnant woman would be to continue her workouts while enjoying the moment!
Trained fitness professionals should consider their work with pregnant/postpartum women the same way as a health care provider, that is, a continuum of care should be provided. Certified fitness professionals have the knowledge and practical experience to counsel a woman throughout all stages of her pregnancy experience. Knowledge of the woman's exercise history, goals, and potential barriers to performance will help ensure that the relationship between the fitness professional and pregnant/postpartum client is maximized.
CONDENSED VERSION AND BOTTOM LINE
Recommendations for exercise during pregnancy have significantly changed during the past 20 years. Women are now encouraged to perform some sort of physical activity or exercise on most, if not all, days of the week during a normal pregnancy and soon after delivery. Women can perform a variety of activities for cardiovascular fitness, muscular strength and endurance, and flexibility. Modifications can and should be made according to a woman's goals and her maternal symptoms. Despite the liberalization of recommendations, a woman should still be concerned with safety issues, temperature regulation, and proper nutrition to complement her exercise program. The health care provider should be included in exercise discussions from the very beginning of a woman's pregnancy to ensure appropriate prenatal care.
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