Prenatal Training: Part II, Strength Training

By Nina Clark, CSCS, RYT

Strength training is not as prevalent in the research as is cardiovascular exercise, but it has been shown to greatly benefit, if done correctly, many of the issues that women face during pregnancy. There have been no documented consequences to the fetus due to resistance training to date. (Ploutz-Snyder, 2001). Rather, strength training has been shown to improve posture and transiently improve glucose control. The numerous adaptations that the body goes through during pregnancy need to be taken into account when prescribing an exercise program. First, the weight gain that occurs during pregnancy leads to changes in posture and increases the force on the joints. The increase in weight can put a 100% increase in force across the knee and the hip joint during weight-bearing exercises such as running. (Artal & O'Toole, 2003). Therefore, previous exercise regimens might need to be altered. Lumbar lordosis and back pain also affects 50% of pregnant women and need to be taken into account when exercising. Resistance training focusing on the spinal extensors and increasing abdominal strength can help prevent these postural issues. However, conventional exercises targeting the low back will often need to be modified to protect the fetus. A woman's balance is also affected by the increase in laxity of the ligaments due to an increase in hormones being secreted and other musculoskeletal adaptations. Therefore, increasing balance and/or doing stable exercises will be more beneficial for maintaining strength and fitness. As Artal and O'Toole summarize, Despite a lack of clear evidence that musculoskeletal injuries are increased during pregnancy, these possibilities should nevertheless be considered when prescribing exercise in pregnancy. (Artal& O'Toole, 2003). Resistance training will increase the cross-sectional area of the muscle and will increase the strength of the tendon. Stronger muscles, tendons, and ligaments can increase the stability of the joint. However, exercises that have heavy loading at the end of the range of motion, despite providing an increase in strength, need to be avoided. The increase in the secretion of the hormone relaxin during pregnancy can predispose women to ligament injury if precaution is not taken. Furthermore, increasing the strength of the leg abductors and adductors can improve the woman's balance and hopefully prevent falls and other injuries. ACSM (American College of Sports Medicine) suggests that pregnant women follow the ACSM guidelines for healthy adults while being mindful of specific contraindications while performing specific exercises. Women are recommended to do a resistance-training program 2-3 times per week. It should include at least 1-3 sets of 10-15 repetitions of 8-10 full-body exercises. (Ploutz-Snyder, 2001). In 1994, the American College of Obstetricians and Gynecologists revised their exercise recommendations, and notwithstanding the special considerations that I mentioned above, women should follow the general adult guidelines by ACSM, which suggest at least three, preferably all, days per week of around 30 minutes of aerobic exercise. It should be at a moderate intensity (40%-60% VO2R or 12-14 RPE). (ACSM, 2010). Even with the benefits of exercise during pregnancy, it is important to know the warning signs to terminate an exercise program. Warning signs to terminate exercise during pregnancy include vaginal bleeding, dyspnoea before exertion, dizziness, headache, chest pain, muscle weakness, calf pain or swelling (women need to rule out rhrombohlebitis), preterm labor, decreasing fetal movement, and amniotic fluid leakage. (Artal & O'Toole, 2003). The absolute contraindications include hemodynamically significant heart disease, restrictive lung disease, incompetent cervix/ cerclage, multiple gestations at risk for premature labor, persistent second or third trimester bleeding, placenta previa after 26 weeks gestation, premature labor during the current pregnancy, ruptured membranes, and pregnancy-induced hypertension. The relative contraindications are more prevalent it is very important to monitor women during their pregnancy. These include severe anemia, unevaluated maternal cardiac arrhythmia, chronic bronchitis, poorly controlled type 1 diabetes, extreme morbid obesity, extreme underweight (BMI< 12), a history of extremely sedentary lifestyle, intrauterine growth restriction in the current pregnancy, poorly controlled hypertension/pre-eclampsia, orthopedic limitations, poorly controlled seizure disorder, poorly controlled thyroid disease, and being a heavy smoker. (Artal & O'Toole, 2003). Every pregnant woman and her trainer should consult on these possible contraindications. Strength Training during pregnancy, when done correctly, can help the expectant mother stay aligned,  get more comfortable, and build stamina for the labor and delivery ahead.