A neurosurgeon once said that there were more negatives for our bodies than positives when it comes to running in general. Of course many people are runners and they won't give it up. We know that exercise during pregnancy is essential to your overall well being. You should gain about 20 to 25 pounds during pregnancy though many people gain twice that. In any case you'll be talking with your doctor and asking her or him about running.
Pregnancy is a time to cut back on the intensity and duration of fitness activities. Stop your martial arts classes as soon as your doctor says so. Know when you can and cannot do certain exercises. Running can be hard on your knees as well as your back. Pregnancy causes joints to loosen, which makes you more prone to injury.
Avoid anything that is dangerous like roller blading or ice skating. Make sure you drink enough water especially if you are running outside during the warm months. Make sure you wear the best running shoes you can afford and wear a very supportive workout bra.
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As the weeks grow into months stay off hills and be very careful of falling. Perhaps you can find a track to run on even if tracks are not your favorite mode of running surfaces.
Rather than running why not jog or do a fast walk? Pushing yourself can be dangerous especially if you become very tired or breathless. Pregnancy often causes fatigue - give in to it and get pampered!
Your running schedule can resume after the baby is born and your doctor gives the ok. For now if you can stay away from running enjoy some gentle exercises such as a beginner's Yoga class or a low impact fitness class- though some Yoga and low impact exercises are dangerous as well. Toward the end you do not want to bend over, spin, or do any turning movements that may make you dizzy and cause you to lose your balance. Do not lie on your back, make sure you have clothes on that breathe, and warm up and cool down.
The rule of thumb is to know your body, know what you can and cannot do, and keep communication open between you and your doctor or midwife.