Weight or strength training improves muscle strength, increases muscle tone, and reduces weight in non-pregnant women. It is generally acceptable during pregnancy, although data are limited on its effects. If you want to do weight training during pregnancy, you should consult your doctor first. There are certain conditions that forbid exercise completely during pregnancy. Working with a trainer who understands the impact of weight-training on the body and the proper use of equipment also can be valuable during pregnancy.

Weightlifting involves three types of muscle contractions:

  • Concentric- the muscle shortens and produces the movement of a joint. Examples are picking up a sack of groceries, turning the pages of a book, and lifting a bowling ball.
  • Eccentric- the loaded muscle increases in length. An example is an attempt to hold up a large object that is too heavy.
  • Isometric- the loaded muscle attempts to contract but cannot. An example is flexing a muscle against an immovable object.

Concentric muscle contraction has not been studied during pregnancy. However, dynamic exercise such as riding a bicycle, running, or swimming, does involve concentric contractions. To understand this better, read about aerobic and anaerobic (or resistance ) exercise on this HealthMap.

Isometric and eccentric contractions often occur at or around muscle fatigue and potentially cause changes in blood pressure and heart function. Overall blood pressure increases during isometric exercise in late normal pregnancy, according to a few studies. However, this elevated blood pressure reverses during rest after exercise.

In planning your program, here are some things to keep in mind:

  • Blood pressure rises during weightbearing exercise. Consequently, women with cardiovascular disease, high blood pressure, or pregnancy-induced hypertension should avoid such exercise during pregnancy.
  • Weightbearing exercise affects balance. Pregnant women, who experience a shift in the center of gravity with the growth of the uterus and the breasts, should be careful when lifting. Such exercise can also overextend the spine. Good posture and body mechanics are vital.
  • Hormonal changes in pregnancy increase the instability of joints. This could result in increased risk for joint sprain, strain, or dislocation.
  • Drugs used for muscle and joint pain, such as aspirin and ibuprofen, are not recommended during pregnancy. That makes injury treatment and pain relief more difficult.

Always use weight-training equipment properly. Many beginning weightlifters, pregnant or not, have unnecessary injuries and strains from improper techniques or unrealistic goals. Working with a professional trainer is always advisable when starting out.

You also need to pay close attention to your body during exercise. Don't exercise past fatigue or to the point of pain. Never lift if you are dizzy or if the exercise causes you to be uncomfortable.

Use good judgment during weight training. Consistent effort and good technique are more important than goals you cannot achieve.