**2. Benefits of and recommendations for exercise during pregnancy**

Prenatal exercise has a plethora of benefits for both pregnant women and the fetus(es) they carry. Exercise during pregnancy has been shown to increase the incidence of vaginal delivery as well as lower the incidence of cesarean delivery, excessive gestational weight gain, gestational diabetes, gestational hypertensive disorders, preterm birth, and lower birth weight [1–6]. Additionally, prenatal exercise has a positive impact on healthy growth and improved cognition and intelligence of the baby after birth [3].

The American College of Obstetrics and Gynecology (ACOG) recommends 30 minutes of physical activity 5 days a week for pregnant women [1, 6–9]. Pregnant women with uncomplicated pregnancies, or pregnancies free of medical conditions that are deemed unsafe by their obstetrician, are safe to engage in both resistance training and aerobic activities. Contraindications for prenatal exercise will be further discussed in Section 2.4. It is important to note that according to the CDC, only 15% of American women meet these recommendations for prenatal physical activity [1]. Identified barriers to prenatal exercise include lack of energy and becoming too uncomfortable especially in the third trimester in addition to lack of education in safe prenatal exercise practices [1, 10, 11]. Despite its safety, only 11% of pregnant women engage in resistance training during their pregnancy [4, 12]. Acute bouts of resistance exercise are consistently associated with increased feelings of energy and decreased feelings of fatigue in pregnant women during the second and third trimesters [11].

Historically, physical activity was deemed unsafe for pregnant women for fear that it would cause a miscarriage or have negative impact on the developing fetus [1, 6, 8]. This view could be largely attributed to the lack of understanding of the physiological maternal adaptations throughout the 40 weeks of pregnancy. Physiological maternal adaptations include 50% increase in plasma, 40% increase in red blood cell volume, 40% increase in cardiac output in the late second trimester that remains stable until delivery, 40–50% increase in renal blood flow starting at 6 weeks gestation, 35–50% increase in tidal volume, 5% increase and lung capacity, and 10–20% increase in oxygen consumption [8]. All of these adaptations demonstrate the ability of the pregnant body to accommodate the growing fetus while also maintaining physical activity.

#### **2.1 Strenuous exercise during pregnancy**

While physical activity is both safe and beneficial, there are consequences for strenuous activity (95–100% Vo2max to the point of exhaustion) [8]. Such strenuous activity may result in elevated maternal sympathetic response, reduced maternal placental blood flow, elevated maternal lactic acid, reduced glucose delivery, lowered maternal pH, increased uterine contractility, and reduced fetal oxygen [8]. Therefore, it is not recommended that pregnant women perform repeated bouts of extremely strenuous exercises at 95–100% of their Vo2max or continue long duration workouts at a high level of perceived effort [8].

Women who are considered "untrained" can safely exercise at a moderate intensity 70–75% of Vo2max, while trained women can handle up to 85–90% of Vo2max [8].

#### **2.2 Prenatal general medical conditions and their impact on physical activity**

Two common prenatal medical conditions that can impact a pregnant woman's ability to continue safe exercise are gestational diabetes and preeclampsia [13–15]. These conditions can develop during pregnancy and should be carefully monitored by the pregnant woman's primary care physician or obstetrician.

Gestational diabetes is impaired glucose intolerance that is diagnosed for the first time during pregnancy and is associated with other prenatal conditions such as preeclampsia, hypertension, preterm birth and higher incidence of induced labor

and cesarean delivery [13, 14]. It occurs in 2–10% of pregnancies and does not have any symptoms. Healthcare providers routinely test for gestational diabetes around 24–28 weeks gestation. If diagnosed, the pregnant woman will be advised to check her blood sugar, modify her diet, and partake in physical activity.

Moderate-intensity exercise training during pregnancy is associated with a lower incidence of gestational diabetes and reduced maternal weight gain [3, 6, 13, 14]. Prenatal physical activity yields the best results in managing gestational diabetes and maternal weight gain when performed in a combination aerobic and resistance training. Additionally, the benefits of physical activity are greater when started in the first trimester [6].

Preeclampsia is a serious high blood pressure condition that develops during pregnancy usually after 20 weeks gestation. It occurs in 3–7% of pregnancies and is more commonly seen in 1st time mothers, mothers who are black or of African descent, and those with a history of high blood pressure or thyroid conditions [15]. Preeclampsia can develop without symptoms and can change suddenly and drastically so it is important to regularly monitor maternal blood pressure throughout pregnancy. This condition should be closely monitored by the pregnant woman's healthcare provider and exercise may or may not be recommended depending on the severity of the condition. Blood pressure medication may be prescribed to lower pressure during pregnancy and preeclampsia usually resolves after birth.

#### **2.3 Contraindications and warning signs to terminate prenatal exercise**

ACOG outlines absolute contraindications to prenatal exercise that include; significant heart or lung disease, incompetent cervix, multiple gestations at risk for premature labour, persistent second or third trimester bleeding, placenta previa after twenty-six weeks, premature labour during this pregnancy, ruptured membranes, and pregnancy-induced hypertension [9]. All of these conditions pose significant risk to maternal and fetal health and therefore should be considered absolute contraindications for exercise unless otherwise determined by the pregnant woman's obstetrician (**Table 1**).

There are also environmental conditions that should be considered as they can have adverse impacts on prenatal exercise. Higher altitude creates challenges in


#### **Table 1.**

*Contraindications to and warning signs to stop prenatal exercise [9].*

handling exercise load for the pregnant woman and warrants caution. It is recommended that pregnant women stay in a more moderate heart rate zone, 50–60% max heart rate, for a shorter duration- about 20 min [8, 9]. Prenatal exercise in high temperatures can have adverse effects on maternal and fetal health. Because increased fetal heart rate correlates with higher maternal body temperatures, maternal body temperature, especially with strenuous exercise, should be closely monitored. Prolonged exercise of more than 45 min can result in elevated core maternal and fetal temperature and increased uterine contractions, leading to preterm labor [8].

While physical activity is safe for most pregnancies, there are definitive warning signs to terminate or cease prenatal exercise. Some warning signs are those that are applied to any person working out such as shortness of breath before exercising, dizziness, headache, chest pain, calf pain or swelling. Others are very specific to pregnancy; vaginal bleeding, preterm labor, decreased fetal movement, amniotic fluid leakage, muscle weakness. All of these symptoms should be treated as indicators that exercise should be stopped immediately and reported to the pregnant woman's obstetrician [9].

### **3. Exercise modification for pregnant women**

The 40 weeks of pregnancy are commonly broken down into three trimesters that serve as mile markers for both fetal development and maternal changes. In regards to prenatal exercise, the trimesters serve as general time frames for when modifications need to be made for safe exercise practice.

#### **3.1 The first trimester**

In general, women experiencing healthy, uncomplicated pregnancies do not require much exercise modification in the first trimester. For most women, the first trimester is marked by mild to extreme fatigue [11]. Scaling back on exercise volume to reduce fatigue can be a useful strategy until energy levels return in the second trimester. Nausea is also very common in the first trimester making maintenance of adequate nutrition and physical activity difficult.

#### **3.2 The second trimester**

Upon entering the second trimester, more exercise modifications are necessary to accommodate the expanding uterus and pregnant belly. Modifications are also necessary to help manage the development of diastasis recti and bearing down into the pelvic floor which can ultimately lead to pelvic organ prolapse.

Diastasis recti, or abdominal separation, is a normal and necessary adaptation for the pregnant body. As the uterus expands and the fetus grows, the two rectus abdominal muscles will separate to create more space. Diastasis recti also involves the thinning and stretching of the linea alba, or the connective tissue between the two rectus abdominal muscles [16, 17]. It is measured by both the width between the two separated rectus abdominis muscles and the degree of tissue thinning of the linea alba. Diastasis recti is prevalent in 33% of pregnant women at 21 weeks gestation and 100% of pregnant women at 35 weeks gestation [16]. While diastasis recti is necessary prenatal accommodation, it should be managed appropriately to limit the amount of separation and thinning.

Important considerations in limiting diastasis recti during pregnancy include posture, body awareness, and intra abdominal pressure management. Pregnant women should be coached on being more mindful of how they are carrying themselves and maintaining posture throughout the day. Pregnancy tends to invoke an anterior pelvic tilt, therefore placing additional stress on the anterior core and the separating rectus abdominis muscles and thinning linea alba [18]. Placing unnecessary pressure on these structures when getting up from the seated position or utilizing a "crunch" to sit up can also exacerbate diastasis recti.

Specific modifications that need to be made starting in the second trimester to help manage diastasis recti include removing front loading exercises from the pregnant woman's workout routine. Front loading exercises include crunches, planks, pull-ups, push-ups, and leg lifts. Front loading exercises generate excessive intra abdominal pressure that presses on the linea alba and rectus abdominis muscles causing a more significant diastasis recti [19].

Pelvic organ prolapse, or more commonly referred to simply as prolapse, occurs when pelvic floor muscles and ligaments stretch and weaken and no longer provide enough support for the uterus. As a result, the uterus slips down into or protrudes out of the vagina [20]. The pelvic floor muscles and connective tissues are responsible for supporting pelvic organs such as the bowels and bladder and uterus and vagina in females. Additionally they provide the contractor mechanism for the anal canal, urethra, and vagina.

As a pregnancy progresses, the uterus expands and becomes heavier placing increased strain on the pelvic floor. If the pregnant woman exerts additional downward pressure into the pelvic floor such as excessive pushing to have a bowel movement or bracing and bearing down with lifting a heavy object, the pelvic floor tissue may not be able to withstand the pressure and prolapse can result. Prolapse can be avoided during pregnancy by properly managing intra abdominal pressure when lifting, removing front loading exercises from the workout routine, and consulting a healthcare provider if persistent constipation occurs during the pregnancy.

Another modification to consider upon entering the second trimester is performing exercises in the supine position. Extended time spent in the supine position can cause venous obstruction in some pregnant women [21–23]. The weight of the uterus and fetus can compress both the superior vena cava and the aorta while in the supine position. This can reduce blood flow to the uterus and make the pregnant woman feel dizzy, light headed, and possibly nauseous. Therefore it is recommended that pregnant women do not lie flat on their back after the first trimester but rather utilize an inclined position in lieu of the full supine position. Some modifications that can be made for exercises commonly performed in the supine position include; seated deadbugs, incline chest press, and being creative with the kneeling or half kneeling positions for different shoulder fly movements.

#### **3.3 The third trimester**

Further modifications are needed throughout the third trimester as the uterus expands, the fetus grows larger and heavier, abdominal separation increases, the pelvic floor undergoes more stress, hormones change to relax ligaments to prepare for delivery, movement becomes more challenging for the pregnant woman, and fatigue increases.

If the pregnant woman has been running throughout her pregnancy, she is welcome to continue to do so but it may be beneficial to phase out running as the stress it imposes on the pelvic floor may become more problematic as her due date approaches. Urinary incontinence, or the involuntary leaking of urine, becomes more likely in the third trimester. An estimated 37% of women experience urinary incontinence during pregnancy and it is most common in the third trimester [24]. Running and jumping will increase the incidence of urinary incontinence during pregnancy as it significantly increases the stress on the pelvic floor [2] which is already undergoing increased stress from the weight of the uterus and growing fetus. Other lower-impact modes of cardiovascular training should be considered to replace running such as walking, swimming, stairmaster, elliptical, upper body ergometer, etc.

There are six key pregnancy hormones that help regulate the female body to maintain a normal pregnancy. The six key hormones are human chorionic gonadotropin (hCG), progesterone, estrogen, prolactin, oxytocin, and relaxin. For the purposes of this chapter we will focus only on relaxin and its role during pregnancy as it has the most direct impact on exercise and resistance training.

Relaxin, a peptide hormone of the insulin-like growth factor family, has been associated with collagen remodeling. It is secreted by the corpus luteum in the ovary and by the placenta beginning around the 10th–12th week of pregnancy [25]. In addition to inhibiting uterine contractions to prevent preterm birth, relaxing blood vessels, increasing blood flow to the placenta and kidneys, and softening and lengthening the cervix during birth, relaxin relaxes the joints of the pelvis in preparation for delivery [25, 26]. It is believed that relaxin increases pelvic laxity, and predisposes separation of the pubic symphysis, by altering the structure of collagen [25].

Pelvic and sacroiliac joint (SIJ) pain are common complaints of pregnant women particularly in their third trimester and may be attributed to the changes in the pelvic region due to increased relaxin levels [25, 27, 28]. This will lead to a need for exercise modification to reduce pelvic and SIJ pain. Modification suggestions include decreasing or eliminating single leg exercises such as single leg deadlifts and decreasing exercises performed with wide legs such as plie squats. It is also recommended to increase glute and hamstring strength to help stabilize the pelvis.

Lastly, for women still engaging in resistance training in the third trimester are encouraged to continue pending that they feel comfortable and motivated to do so. Scaling back is also appropriate as the pregnant woman will be experiencing greater challenges with movement, discomfort, and lack of energy. General guidelines to help maintain resistance training include decreasing barbell lifts especially if she is experiencing difficulties navigating her large belly and maintaining balance, and utilizing free weights and bands as necessary.

#### **3.4 Guidelines for prenatal resistance training**

Resistance training is a safe mode of physical exercise for women experiencing uncomplicated pregnancies and have been cleared by their healthcare provider to do so [12–14, 29]. It can be beneficial in maintaining current strength, posture, and mood during pregnancy. When done properly, without creating excessive intra abdominal pressure or bearing down into the pelvic floor, it can prepare the body for labor and help maintain pelvic stability.

When designing a prenatal resistance training program, it is important to consider that not only does each woman experience pregnancy differently, it can also vary widely with each pregnancy in the same woman. This makes it exceedingly difficult to create an all-encompassing prenatal resistance training plan that is appropriate and realistic for all women and all pregnancies. Some women will be able to continue resistance training at a high level for their entire pregnancy. Some will feel the need

#### *Guidelines for Prenatal and Postpartum Resistance Training DOI: http://dx.doi.org/10.5772/intechopen.109230*

to scale back almost immediately. While it varies widely, there are some concepts and components that can be applied to all prenatal resistance training.

Front loading exercise, as previously mentioned, should be removed from physical activity and lifting routines by the start of the second trimester. This will help decrease unnecessary pressure on the linea alba and pelvic floor to manage diastasis recti and prevent pelvic floor dysfunction and prolapse during pregnancy.

Equipment selection will also be an important consideration as pregnancy progresses. As the pregnant belly continues to grow, lifting a barbell may not be comfortable or safe- ensuring that there is adequate clearance from the belly while lifting and lowering the barbell will need to be a top priority to prevent dropping the bar on the pregnant belly [2]. Balance will also be altered as the pelvis tilts anteriorly and the pregnant belly expands 18]. It may not be advisable for some pregnant women experiencing balance changing to lift the barbell even if she is an experienced lifter. Proper monitoring of balance changes should be completed periodically to determine if specific equipment selections are safe. Dumbbells and resistance bands are safe alternatives to heavier equipment if balance issues are present [2].

The intensity of prenatal exercise will vary from woman to woman depending on her level of physical fitness before becoming pregnant and the goals she has in maintaining that fitness. The American College of Sports Medicine (ASCM) defines moderate exercise as d as exercise of 3–4 METS or any activity that is equivalent in difficulty to brisk walking without any reason to alter the recommendation for pregnant women [30]. It should be noted that the allowance for intensity for pregnant women wishing to maintain or progress physical fitness throughout pregnancy is increased without cause for safety concerns in uncomplicated pregnancies. The ACSM recommends that intensity should be 60–90% of maximal heart rate or 50–85% of either maximal oxygen uptake or heart rate reserve. The lower end of these ranges (60–70% of maximal heart rate or 50–60% of maximal oxygen uptake) appears to be appropriate for most pregnant women who did not engage in regular exercise before pregnancy, and the upper part of these ranges should be considered for those who wish to continue to maintain fitness during pregnancy [30].

ACOG recommends the use of ratings of perceived exertion (RPE) in addition to heart rate suggesting the use of Borg's conventional 6–20-point scale, with 12–14 (a rating of 13 corresponds to a subjective rating of "somewhat hard") identified as the RPE range to apply in pregnancy [30, 31]. Occasional higher intensity cardiovascular activities may be completed for short time periods, but time spent exceeding the RPE ranges of 5–7 should be limited as the increased pressure directly impacts the health of the pelvic floor [2]. Historically there was a prenatal maximum heart rate limit of 140 bpm that has since been discredited by ACOG. Observing this unsupported heart rate maximum is not necessary [32].

While no universal prenatal resistance training protocol currently exists due to the wide variability in previous lifting experience, pre-pregnancy physical fitness levels, and prenatal medical conditions, The ACSM does provide basic guidelines for safety measures. In general, the ACSM does not recommend using a one repetition maximum (1-RM) with pregnant women [31]. It is suggested that clinicians, coaches, and trainers use the Oddvar Holten diagram to make a 1-RM prediction to guide resistance training. For example, the clinician, coach or trainer, makes an estimation of the weight that can be lifted for 10–20 times; the number of repetitions that can be maximally performed is registered; the percentage of intensity can than be looked up in the Oddvar Holten diagram, seen in **Figure 1**, at the number of repetitions and 1RM can be computed by the formula as seen in **Figure 2** [31].

**Figure 1.** *Oddvar Holten diagram.*

#### **Figure 2.** *Formula. A: lifted weight; B: percentage of intensity.*

The most important consideration for prenatal resistance training is determining if the pregnant woman is properly managing intra abdominal pressure and is not bearing down into the pelvic floor. Pregnant women who engage in prenatal resistance training should be educated on how to manage intra abdominal pressure by utilizing proper breathing and bracing technique rather than a breath-holding technique. Pregnant women should breathe through their lift without holding their breath or simulating a valsalva maneuver as it generates significant pressure in the abdomen [33]. This pressure also can go directly down into the pelvic floor leading to dysfunction or prolapse. It is estimated that 46% of women had some degree of prolapse at 36 week gestation [34], making it a common concern especially if continuing resistance training throughout pregnancy.

Generally, resistance training movement selections should be made with the intention of focusing on the outlined goals of the pregnant woman and with respect to her energy levels, nausea, and other common pregnancy symptoms. If the goal is to maintain a moderate level of physical activity during pregnancy, the focus of resistance training should be on postural endurance and endurance with full body movements. Resistance training should take place at least 2 days in a week with a selection of movements desired by the patient and clinician, coach, or trainer [2]. Movements that focus on pelvic stabilization such as squats and lunges, postural strength and endurance such as rows and flys, and work in the quadruped position such as bird dogs are all encouraged to be utilized in prenatal resistance training [2].
