Hey girls!! I am not pregnant but I am an OB nurse and I work in an Obstetrical and Gynecological Emergency Department at Winnie Palmer Hospital in Orlando,Fl . I can answer a few of these questions for you. The reason they say no laying on your back especically once you get into your 2nd and 3rd trimester is because when you lay on your back the baby puts pressure on a major artery that supplies oxygen to your brain. If you are being deprived of oxygen so is your baby. A lot of times you may feel short of breath or dizzy laying on your back and that is why. If the baby is not getting the oxygen it can cause their heart rate to drop. Sleep on your side or wedge yourself with a blanket so you are not flat on your back.
As far as not getting your heart rate above 140bpm, I found this on Mayoclinic.com:
If you exercised regularly before your pregnancy, don't be too concerned about your heart rate during pregnancy.
In the past, the American College of Obstetricians and Gynecologists (ACOG) recommended a heart rate of no more than 140 beats a minute for exercise during pregnancy. Today, however, the ACOG recommends 30 minutes of exercise a day during pregnancy for most women without any specific heart rate limits.
I found this on the ACOG website:
The extra weight you are carrying will make your body work harder than before you were pregnant. Exercise increases the flow of oxygen and blood to the muscles being worked and away from other parts of your body. So, it's important not to overdo it.
Try to exercise moderately so you don't get tired quickly. If you are able to talk normally while exercising, your heart rate is at an acceptable level.
Still, reasonable precautions for exercise during pregnancy are important. Get your health care provider's OK for any exercise during pregnancy — especially if you have a history of preterm labor or certain medical conditions, such as diabetes or high blood pressure. Also be careful to pace yourself appropriately. In general, you should be able to carry on a conversation while you're exercising. If you can't speak normally while you're working out, you're probably pushing yourself too hard. This could lead to overheating, dehydration or other problems.
Staying well hydrated during your workouts is super important...Becoming dehydrated can cause you to contract.
Your doctor probably told you no deep knee bends or toe touches because The extra weight in the front of your body shifts your center of gravity and places stress on joints and muscles, especially those in the pelvis and lower back. This can make you less stable, cause back pain, and make you more likely to lose your balance and fall, especially in later pregnancy.
Certain sports are safe during pregnancy, even for beginners:
-Walking is a good exercise for anyone. Brisk walking gives a total body workout and is easy on the joints and muscles. If you were not active before getting pregnant, walking is a great way to start an exercise program.
-Swimming is great for your body because it works so many muscles. The water supports your weight so you avoid injury and muscle strain. It also helps you stay cool and helps prevent your legs from swelling.
-Cycling provides a good aerobic workout. However, your growing belly can affect your balance and make you more prone to falls. You may want to stick with stationary or recumbent biking later in pregnancy.
-Aerobics is a good way to keep your heart and lungs strong. There are even aerobics classes designed just for pregnant women. Low-impact and water aerobics also are good exercise.
Other exercises, if done in moderation, are safe for women
who have done them for a while before pregnancy:
-Running. If you were a runner before you became pregnant, you often can keep running during pregnancy although you may have to modify your routine. Talk to your doctor about whether running during pregnancy is safe for you.
-Racquet sports. In some racquet sports, such as badminton, tennis, and racquetball, your changing balance may affect rapid movements. This can increase your risk of falling. You may want to avoid some racquet sports.
-Strength training will make your muscles stronger and may help prevent some of the aches and pains common in pregnancy.
I hope this helps.
Here is the ACOG website if you would like to read more.
http://www.acog.org/publications/patient_education/bp119.cfm