The Pregnant Athlete

Lori Boyajian-O’neill

Pregnancy alters the female body in many significant ways. For the female athlete, it is an inevitable issue to face, and for years, pregnancy meant limited physical activity. Despite the anatomic and physiologic stresses associated with pregnancy, the pregnant athlete has become more active over the years to the point where she can run long distance and work out daily up until delivery. The body’s ability to adapt to and compensate for these stresses is a model of its inherent predisposition to maintain homeostasis. Seasoned athletes or those who are training to prepare for the physical stresses of labor and delivery may enjoy the benefits derived from exercise but will face physical challenges. These demands affect neuromusculoskeletal, circulatory, respiratory, gastrointestinal, and other physiologic functions, all of which have an impact on athletic participation. The pregnant athlete presents challenges to the physician as well, who must have knowledge of the anatomic and physiologic demands of pregnancy and sports medicine.

Improved understanding of the anatomic and physiologic changes that affect exercise during pregnancy and of maternal and fetal adaptation to exercise has led to recommendations for exercise in pregnancy (1,2). This greater understanding has led to guidelines for safe participation that have evolved from restrictive and extremely conservative (3) to those that encourage physical activity and exercise (1,4).

The application of osteopathic principles, including manipulation, provides comprehensive care for the pregnant athlete, and assists in restoring and maintaining homeostasis as well as optimizing anatomic and physiologic function, the goals of which are to enable continued participation in sport and exercise (5). I support the implementation of exercise prescription and manipulation into obstetric care.

Recent scientific evidence supports the use of manipulation for the treatment of acute low back pain (6). Improved understanding of the benefits of manual therapies, including manual medicine, has led to the development of guidelines related to the use of manipulation in obstetrics (7).

EPIDEMIOLOGY

In 1967, when emphasis on physical activity was much less than it is today, Sady and Carpenter reported that 15% of women of reproductive age exercised regularly and expressed a desire to continue exercise into pregnancy (8). Today, there are pregnant athletes who engage in exercise and sports activities such as marathon running, and the effects of these activities in pregnancy should be considered.

One aspect of pregnancy that may affect activity is musculoskeletal pain and dysfunction. More than 50% of all pregnant women report musculoskeletal pain during pregnancy (9). There are numerous studies investigating the incidence of musculoskeletal pain in pregnancy, especially back pain. Low back and pelvic pain are the most common musculoskeletal complaints during pregnancy. Overall, studies show that between 48% and 90% of pregnant athletes experience back pain at some time during pregnancy, most commonly after the sixth month (7,10).

FACTORS

There are many risk factors associated with low back and pelvic pain in pregnancy, including
prior history of low back pain, strenuous work, smoking, and multiparity. Women with a history of low back pain prior to pregnancy experience more severe low back pain during pregnancy (11).

Physically strenuous work coupled with a history of low back pain are factors associated with increased risk of developing low back and sacroiliac (SI) joint dysfunction and pain during pregnancy (12). Smoking is also associated with low back pain (12), among other side effects. The amount of maternal weight gain does not appear to be correlated with low back pain (9,13); neither does age, height, race, fetal weight, and socioeconomic status (13).

Multiparity has been identified as a risk factor. Some studies suggest that multiparity alone is a factor in predicting back pain, while other studies link multiparity and prior low back pain as predictors of low back pain during pregnancy (14). Fast et al. reported more disability caused by backache in multiparas versus primiparas (9). They suggest that change of posture or weaker trunk muscles (core body strength) may explain this observation.

Although exercise may predispose any athlete to increased musculoskeletal injury or pain, studies show that active pregnant athletes report fewer overall musculoskeletal complaints than their sedentary counterparts (15). There has been no reported increase in injury rates when exercising during pregnancy. The National Collegiate Athletic Association does not keep statistics on numbers of athletes who become pregnant, and there are no prospective randomized controlled studies tracking injuries and injury rates of pregnant women during athletic activity (16). There are, however, presumed risks of certain athletic activities to maternal and fetal well-being. The increased understanding of these risks, both quantified and hypothetical, guides the recommendations for exercise and manipulation during pregnancy.

MUSCULOSKELETAL ADAPTATIONS TO PREGNANCY

The average woman gains 10 to 12 kg (27.5 lb) during a singleton pregnancy. There is a 20% increase in body mass by the ninth month (17), which alters normal biomechanics of the spine and extremities. Increased weight and mass of the uterus cause increased stress on soft tissues and bony structures unaccustomed to carrying this extra load. Workload during pregnancy is increased, while load-bearing capacity of the musculoskeletal system is decreased (18). The center of gravity (COG) shifts, which is clinically obvious in the usual postural changes observed in pregnancy.

As pregnancy progresses, the pelvis tilts forward, which increases lumbar lordosis and moves the thoracic spine posteriorly (19). These slight alterations in biomechanics may cause primary low back pain and dysfunction and lead to compensatory or secondary changes in cervicothoracic spine and upper and lower extremity biomechanics, which can affect athletes engaged in sports and exercise.

There are no reports of increased incidence of falling during pregnancy. This may be due, in part, to athletes being more cognizant of the increased risk and adopting more safe activities. However, the potential for falls and subsequent maternal or fetal injury warrants athlete counseling regarding high-risk activities. Poorly compensated shifts in the center of gravity increase the risk of falling, especially in sports requiring balance such as martial arts, cycling, or downhill skiing. The degree to which an athlete can adapt to these inevitable musculoskeletal stresses will determine, in part, whether the athlete can engage safely in athletic activity during pregnancy.

The hormones relaxin, progesterone, and estrogen are believed to contribute to the increased ligamentous laxity observed in pregnancy (20). This laxity, which contributes to the widening of the pelvis in preparation for delivery, may lead to joint instability, pain, and dysfunction. The production of relaxin increases tenfold during pregnancy (19,21). After 3 months post partum, there is no detectable level of relaxin (22). There appears to be a correlation between relaxin levels and isolated symphysis pain; however, a correlation has not been shown between relaxin levels and pain intensity, joint dysfunction, or disability in athletes with low back pain (22). There is
theoretical concern for hormonally induced joint and ligamentous laxity leading to increased ligament and joint injuries such as sprains and tears (e.g., of the anterior cruciate ligament). However, scientific proof is lacking.

Biomechanical Changes of the Pelvis

Pelvic pain has been reported to be approximately 20.1% at 33 weeks of pregnancy (23) and refers to pain of the symphysis pubis and the SI joint. Joint laxity of the pelvis is most profound in the symphysis pubis and the SI joints, which suggests hormonal effects as a cause of pelvic instability (21). The symphysis pubis widens throughout pregnancy, from a normal width of 0.5 mm to a maximum width of approximately 12 mm (13). Symphysitis is associated with SI pain and dysfunction (12). There is increased risk of vertical displacement of the pubis, which may lead to increased rotatory stress at the SI joints, causing sacral torsions and unilateral sacral dysfunctions.

These primary changes may lead to compensatory changes causing altered biomechanics of the lower extremities. Widening of the symphysis pubis contributes to the increase in Q-angle observed in pregnancy, which can increase valgus stress and load on the medial knee. This may also lead to increased valgus stress at the medial ankle, possibly causing overpronation, potentially leading to conditions such as Achilles tendinitis, posterior tibial tendinitis, medial arch pain of the foot, and plantar fasciitis. Athletes engaged in running sports are particularly affected. These changes may prohibit continued participation in even low-intensity or low-impact activities such as walking, Tai Chi, or yoga, and the pregnant athlete may have to try non-weight-bearing activities such as water training or stationary cycling.

Biomechanical Changes at the Sacroiliac Joint

As the SI ligaments relax due to hormonal influence, the SI joints become more mobile during pregnancy, which increases instability of the joints. SI joint instability allows for increased movement, which can stretch pain-sensitive structures, causing SI inflammation and pain (13). Radiographic studies confirm the presence of anatomic changes and inflammation at the SI joints (24).

Pregnancy-related pelvic pain (PRPP) is caused by dysfunction at the SI joints and frequently radiates into the buttocks and thighs. This is the most common site of pain in pregnancy. Sacral torsion and flexion and extension dysfunctions are common causes of SI joint pain (25). Berg found that two thirds of pregnant athletes with severe low back pain have dysfunction of the SI joint (12). Asymmetrical SI joint laxity in athletes with moderate to severe pelvic pain during pregnancy is a predictor of moderate to severe PRPP, conferring a threefold higher risk that pelvic pain will persist into the postpartum period (26). Pelvic girdle syndrome, which refers to dysfunction and pain in all three pelvic joints, that is, the symphysis pubis and both SI joints, occurs in 6% of pregnant athletes and has the worst prognosis and most severe symptoms (10,23,27).

Biomechanical Changes of the Lumbar Spine

In the lumbar spine, joint laxity is evident in the anterior and posterior longitudinal ligaments. The static supports become weakened and are less able to withstand shearing forces as the center of gravity shifts. Disc or facet pain may develop as a consequence of the altered spinal biomechanics. Lumbar spinal mechanics are influenced by the natural lordotic curve and the enlarging maternal-fetal mass. This load alters forces and stresses the lumbar vertebrae and supporting structures. Disc herniations are rare; LeBan et al. reviewed the records of 48,760 deliveries and reported only one incidence of herniated lumbar disc (28).

Stabilization of the lumbar spine is important in maintaining neutral posture and counteracting the shifts in the center of gravity. Ligaments and muscles provide stabilization for the spine, which works to maintain center of gravity and normal posture. The abdominal and iliopsoas
muscles contribute greatly to countering the shift in the center of gravity and providing stabilization of the low back. When the ability of the ligaments and muscles to compensate is overwhelmed, pain and dysfunction can develop.

Core Strength

Poor core strength may be a predictor of poor posture and low back dysfunction and pain during pregnancy. Core strength is a factor contributing to the stabilization of the spine and may, in part, account for those pregnant athletes who do not complain of pain (9,29). As pregnancy progresses, there is a reduction in the capacity of the abdominal muscles to counterbalance the increased weight and mass. Fast et al. reported that approximately 17% of pregnant women could not perform a single sit-up compared to 0% of matched nonpregnant women (30). CSEP and the Society of Obstetricians and Gynaecologists of Canada (SOGC) both recommend that women without contraindications be encouraged to participate in strengthconditioning exercises as part of a healthy lifestyle during their pregnancy (1).

The main stabilizing center is at L5-S1 with secondary centers at C7-T1 and T12-L1. These are balance points for the anterior-posterior curves of the spine and reference points for the longitudinal center of gravity (31). Chapter 13 discusses core stabilization in more detail.

FETAL RESPONSES TO MATERNAL EXERCISE

Most of the potential fetal risks in uncomplicated pregnancy are hypothetical (2). There are no reported increases in abdominal injuries among pregnant athletes. The possibility, however, for injury that may cause catastrophe such as abruptio placentae does exist and should be discussed during the exercise screening examination.

Basal metabolic rate and heat production increase during pregnancy. Intensity of exercise has the greatest impact on body temperature. In nonpregnant women, the core temperature increases by an average of 1.5°C during the first 30 minutes of moderate-intensity aerobic exercise in thermoneutral conditions (32). If exercise is continued for an additional 30 minutes, core temperature then reaches a plateau. The few studies on the fetal effects of maternal exercise and core temperature during human pregnancy are limited (33). In animal studies, an increase in maternal core temperature of more than 1.5°C during embryogenesis has been observed to cause major congenital malformations including increased neural tube defects (33). The first 45 to 60 days of gestation are particularly critical to neural tube development, and temperatures above 39°C have been shown to be teratogenic in animals and may also be teratogenic in humans (34). However, there have been no reports that hyperthermia associated with exercise is teratogenic in humans (35,36). There are no prospective studies to date that have found any association between increased maternal temperature induced by self-paced exercise and teratogenicity. It appears that sustained exercise does not increase maternal core body temperature to detrimental levels (37).

Physical exercise diverts blood flow to large muscles and has the potential to decrease uteroplacental perfusion and thus the transport of oxygen, carbon dioxide, and nutrients to the fetus. This raises concerns about the lasting effects, but the indirect evidence shows no lasting fetal effects. This concern mainly applies to out- of-condition women who begin a vigorous exercise program while pregnant. Such women should limit themselves to exercise that is no more strenuous than walking. Well-conditioned pregnant women generally are able to continue their exercise routines if their pregnancy is uncomplicated.

The fetus is well protected during exercise. Clapp and co-workers reported that fetal heart rate always increased in women who exercised regularly throughout pregnancy as long as the duration of the exercise was 10 minutes or longer and the intensity of the exercise exceeded 50% of maximum aerobic capacity (38). Minor decreases in PO₂ cause a fetal sympathetic response, which increases fetal
heart rate. There is also an increase in fetal baseline parasympathetic tone with advancing gestation, which causes a lower baseline fetal heart rate. Therefore, fetal sympathetic stimulation that occurs during maternal exercise causes an increase in fetal heart rate that is of greater magnitude due to the increased parasympathetic tone (39).

EXERCISE AND PREGNANCY

Louisa Burns, DO, supported exercise during pregnancy as far back as 1944, when she wrote, “Normal pregnancy and especially normal labor require strong muscles, both striated and non-striated. It is extremely important that all these muscles be strengthened during pregnancy. The striated muscles, which are completely voluntary, can be developed by well-planned exercises” (quoted in reference 7).

Active athletic women who are pregnant should be encouraged to continue their activities, and those who are not physically active should be encouraged (provided there are no contraindications) to begin an exercise program, particularly if they are planning a pregnancy. A moderate level of exercise on a regular basis has minimal risks for the fetus and beneficial metabolic, psychological, musculoskeletal, and cardiorespiratory effects for the mother during a low-risk pregnancy (15).

Women who exercise throughout pregnancy may require less medical intervention such as forceps or cesarean section (15,40), improved aerobic and muscular fitness, facilitation of labor (5), prevention of gestational glucose intolerance (5,41), and pregnancy-induced hypertension (5). Weekly physical exercise before pregnancy reduces risk for back pain in pregnancy. In fact, the American College of Obstetricians and Gynecologists (ACOG) (18,41) and CSEP (1) promote regular exercise during pregnancy for its overall health benefits (18). The Centers for Disease Control and Prevention and the American College of Sports Medicine recommend at least 30 minutes of moderate physical activity daily three times per week (42). Moderate intensity is defined as activity with an energy requirement of 3 to 5 metabolic equivalents (METS), equivalent to walking at a rate of 3 to 4 miles per hour.

Exercise prescriptions are useful for setting parameters and guidance for safe participation and providing encouragement for exercise as well as security. Maternal adaptations to pregnancy occur throughout the trimesters. These adaptations necessitate ongoing adjustments in physical activity and exercise prescription. Pregnant athletes should be counseled that modifications in type, frequency, intensity and duration of physical activity are expected in order to address the changing conditions of pregnancy.

Pregnant athletes need to adapt their training to maintain sport-specific fitness and conditioning. Cross-training can be beneficial in maintaining the athlete’s aerobic and anaerobic capacity to avoid environments unsafe for a pregnant athlete. For example, cross-country runners should be discouraged from running on uneven terrain, which may be unpredictable and predispose to falls. Water training may be particularly beneficial. It provides for continued aerobic activity in a relatively weightless environment where there is less stress and strain on joints and muscles. Non—weight-bearing or low-impact endurance exercises using large muscle groups (e.g., walking, stationary cycling, swimming, aquatic exercises, low-impact aerobics) are generally safe and should be recommended and included as part of the exercise prescription (43).

Exercise Screening

Athletes should be screened for any contraindications to exercise including medical, obstetric, and neuromusculoskeletal that may become problematic as pregnancy progresses. Ideally, this occurs at a preconception visit where the athlete can be assessed for medical problems and for current levels of fitness and athletic participation. Preexisting conditions, including neuromusculoskeletal, may worsen during pregnancy and may lead to pain or dysfunction that may prohibit the pregnant athlete from engaging in athletic activity or even light activity.

Screening should also include inquiry into the use of supplements. Ten percent of all Americans use dietary or herbal supplements or neutraceuticals along with prescription medications (44), yet almost 50% of athletes studied did not report their use of herbal medicines, even when specifically asked on written forms (45). This has the potential for serious health consequences (45) including herb-drug interactions and teratogenicity.

Contraindications to Exercise

There are some sports that are too threatening to maternal and/or fetal well-being, even in low-risk pregnancies. These include sports where contact or collision is a concern and those that require balance or otherwise place the athlete at increased risk of falls and abdominal injury. Abdominal trauma can cause direct placental and fetal injury, including abruptio placentae. Contact-collision and limited contact sports that are contraindicated include basketball, ice hockey, soccer, downhill skiing, and horseback riding (46). Environment must be controlled when formulating exercise prescription and advising athletes on safe activity. Hyperbaric, hyperthermic, humid, or hypoxic environmental conditions should be avoided (43). The athlete should limit activities to those occuring in a climate-controlled environment (indoors) and run on flat, even surfaces. High-altitude climbing (6,000 ft or higher) is contraindicated because of the risk of acute mountain sickness and the limitations pregnant women have in performing high-intensity physical activities at that elevation (47). The development of high-altitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE) could be disastrous. No adverse fetal response has been noted in activity below 2,500 meters. Scuba diving is contraindicated because of the risk of fetal decompression sickness (4).

Certain medical and obstetric conditions prohibit or limit physical activities. Ongoing assessment and evaluation for these conditions are important in adapting exercise prescriptions. Both ACOG and CSEP have issued absolute and relative contraindications to aerobic exercise during pregnancy based on medical and obstetric conditions. Pregnant athletes should be screened for these conditions and be aware of them should they develop during exercise (Tables 45.1 and 45.2). The CSEP recommendations in Tables 45.1 and 45.2 are also listed on the PARmed-X for Pregnancy (48) documents for convenience, which CSEP developed and which is endorsed by SOGC as the basis of safe and practical exercise prescription in pregnancy.

TABLE 45.1. ABSOLUTE CONTRAINDICATIONS TO EXERCISE IN PREGNANCY