There are numerous views regarding training / exercise during pregnancy. Training enthusiasts claim that fit / well-trained women have fewer problems and troubles during pregnancy and childbirth. The cautious suggest that training for the fetus can be stressful and endanger the mother's health. Often it comes to an underweight of the baby.
It is difficult to give any general recommendations, although there is a lot of scientifically proven information on this topic. A large number of tests were performed on animals, but only relatively few on humans. The animal experiments give some hints, but you can not transfer them one to one. For what is good for a pregnant rat does not necessarily have to be good for a pregnant woman. A recent "meta-study" (in which the results of many studies are collected and analyzed) has only found 18 studies in humans.
Meanwhile, athletes tend to continue their training despite a pregnant belly. These are not just gentle exercises. (Sport in Pregnancy) Pregnant women have even participated in Olympic Games and a variety of women have been pregnant with a pregnant belly in a marathon, z. For example, an American ran a marathon without knowing that she was at the 4th month of pregnancy.
On the other hand, women who had little physical activity prior to pregnancy get the idea through pregnancy gymnastics to move more, as they have suddenly developed a new body and health awareness.
With regard to the evidence currently available, it is difficult to predict the optimal level and type of exercise for pregnant women. One can only give general recommendations and advise on precautions. This paper will look at the theoretical risks and benefits and present the latest research results.
Physiological changes during pregnancy
Research shows us what changes a woman undergoes during pregnancy. The higher the month of pregnancy, the more the respiratory rate tends to rise (this can also be described as stressfulness). For example, it has been found that the amount of oxygen consumed per minute increases by 10% at a given walking speed. This is probably related to the increased body weight. At no-load loads, the results are very irregular, although oxygen uptake generally tends to increase at a given load. By the 21st week can be seen no significant increases.
In some studies, an increase in resting heart rate as pregnancy progressed was determined, although the maximum heartbeat volume remained approximately the same. The metabolic rate at rest has also increased. Cardiac output begins to increase in the first three months (trimester) and increases by 30-50% by the second trimester, mainly due to increases in heart size and heartbeat volume, but also by a pulse rate increase of 70-85% Minute is triggered. In general, athletes and untrained women have hardly any difference in cardiac output by the third trimester (the last 3 months of pregnancy).
Potential risks to the fetus
1. Blood flow reduction to the uterus
There was a decrease in uterine blood flow during exercise. This argument prevented pregnant women from exercising during pregnancy. However, it appears that fetal oxygenation remains relatively constant due to compensatory measures such as increased oxygen recovery and redistributed blood flow.
2. Decreased supply of the fetus with glucose
During pregnancy, the mother's blood glucose is used by the growing infant as its main source of growth. It has been a long time worrying that the blood glucose level could be reduced due to training. Although there is some evidence for this, however, it has also been shown that the mother is under increased load able to access other sources of energy. Although the level of glucose in the blood may drop slightly under exercise, this does not present any danger, as it is only of short duration. However, there is some evidence that prolonged and intense exercise can affect the infant's growth.
It is believed that increased core body temperature carries a risk to the unborn child. For example, it was found in a study that there is an increased occurrence of neuronal tube effects, eg. Spina bifida, comes when the mother is exposed to heat in the first three months of pregnancy (bath, sauna, fever). Overheating in the second half of pregnancy was associated with lower birth weight in animals. According to the latest recommendations, a core temperature of 39 degrees Celsius or above is harmful to the baby.
As a result, there is concern that training may increase core body temperature, although training was not listed as a potential risk factor in the study cited above. Further investigation has been done with women who trained at normal speed. In these experiments, no increase in temperature up to the risk zone was found. For example, in one study, a temperature increase of 5 degrees Celsius to 37.3 degrees Celsius was detected in women exercising at a moderate to high speed for 20 minutes. Some scientists point out that the physiological adjustments, such as the tendency for increased blood pooling under the skin and increased blood volume, causes more efficient heat loss. There is little evidence that core body temperature rises to critical levels due to exercise.
Other work in this area has suggested that training in water at a standard pool temperature is preferable to training on land, as core body temperature can not increase so much. In general, a change in core body temperature depends on the intensity and duration of the workout. Of course, with higher outside temperature and humidity there is a greater risk of overheating, so dehydration should be prevented and lighter clothing should be worn.
The effects of exercise on pregnancy symptoms
It has been suggested that women who exercise are less likely to suffer from typical pregnancy-related symptoms, such as Nausea, heartburn, cramps, etc. In most studies, it was difficult to find the root cause of these problems. Do women suffer less from these problems because they do not feel so miserable or are the symptoms reduced by training? A recent study has attempted to shed more light on this ambiguity by capturing information about the level of training of women before and during pregnancy in terms of symptoms and level of exercise. (1)
About 400 women were interviewed in this study, which was conducted in San Francisco. Four different levels of training were set, Level 1 for the most active women participating in aerobic training, ie training three times a week at least 20 minutes above the level required for aerobic exercise.
The percentage of women who trained at level 1 before pregnancy decreased from 41 percent before conception to 14 percent in the last three months before birth. However, the middle level 2 and 3 remained relatively constant. The form of training changed as well. For example, nearly one-fifth (57) runners before pregnancy, but in the last three months ran only one. Swimming became even more popular.
The pregnancy symptoms were recalculated for each trimester (three months of gestation). This was done using a questionnaire that asked questions about 22 physical inconveniences, such as: Nausea, heartburn, leg cramps. Women who trained at level 1 or 2 during the first trimester reported fewer symptoms in that time than women who trained at level 3 or 4. The same pattern was found in the third trimester - those who trained at a high level showed fewer symptoms of physical discomfort.
Similarly, increased training in early pregnancy resulted in fewer late pregnancy symptoms. One of the most interesting findings was that women who trained at level 1 before pregnancy reported fewer symptoms in the first trimester. This reinforces the good effects of training on the symptoms. Comparing women who maintained their training at a high level (level 1) with those who were training less and less, it was found that decreasing the frequency of exercise led to different symptoms. The researchers concluded from the findings that the women did not train because they felt better, but they felt better because they were training. One possible mechanism for this effect is that training results in higher endorphin output (natural painkiller), thereby reducing the perception of pain and discomfort. In one study, increased endorphin levels were measured during labor in a women's group, which were randomized into a training program during labor.
One reason women might be tempted to exercise while exercising or maintain training is weight loss. The fat stores increase steadily until the third trimester. This is partly due to the effects of a chronically elevated blood insulin level, which signals the body to store more energy. Two main studies suggest that moderate condition training of women who were previously inactive during the second and third trimesters is the typical pregnancy-related increase in fat storage HALT. Because of this, hormonal changes during pregnancy seem to be the usual reduction in body fat normally found in aerobic condition training, OVERRIDE.
Effects of training on the pregnancy outcome
Factors that are said to be closely related to exercise / can be influenced by exercise include: risk of preterm labor, length of labor, birth weight, and Apgar points (the infant's first assessment), and complications during labor. A recent analysis combined the results of 18 studies with a total of 2, 214 pregnant women. (2)
This analysis showed that none of the variables studied differed significantly from the control group in the training women. The variables included maternal weight gain, duration of pregnancy, duration of contractions, labor complications, type of childbirth, infant birth weight, and Apgar scores. All results of these variables were within the normal range for both groups. Although different studies showed that one or more of these specific outcomes was more likely for the active than for the inactive pregnant women, the researchers noted that there was no consistent pattern within the studies and that the sample size was too small. These results gave an "average" result. Looking at the specific individual studies, there is some evidence that strenuous exercise, inappropriate nutrition, and prolonged standing can adversely affect fetal growth. Similarly, data from women training intensively or with weights late in the third trimester indicated an increase in prematurity.
The authors of the meta-analysis summarized that a pregnant woman can exercise up to 3 times a week for 43 minutes with a heartbeat of 144 beats per minute without endangering herself or her unborn child. The effects of a higher intensity than this could not be determined. The results showed no negative effects with regard to jogging or weight lifting exercises.
We are still a long way from knowing what level and type of exercise seems ideal for pregnant women. An American team of maternal and pediatric health experts concluded that pregnant women should not or should not exercise, but that they can exercise.
Practical recommendations for pregnant women