ScienceDaily (Apr. 22, 2009) — Exercise has many benefits for adults, teens, and youngsters. It is less clear what benefit, if any, exercise may have during fetal growth during gestation. Now that scientists have determined that, generally speaking, maternal exercise poses no significant risk to a fetus, studies are underway to examine the mother/fetus/exercise/health connection.

One important study is now complete.

Study and Background

The primary aim of the pilot project was to test the theory that maternal exercise imparts a cardiovascular benefit to the fetus. The secondary aim was to determine if exercise-exposed fetuses have increased breathing movements compared to non-exercise exposed fetuses. Fetal breathing movements are a marker of fetal well-being and reflect functional development of the respiratory system and central nervous system control.

The researchers used a non-invasive, dedicated fetal biomagnetometer to measure maternal and fetal magnetocardiograms (MCG) along with fetal movements (breathing, body movements, hiccups and non-nutritive suck). Unlike an ultrasound, which takes static measurements of anatomy, MCG records the physiology of the developing fetus.

The investigators looked at the results from pregnant women between 20 and 35 years of age. The mothers were classified as exercisers if they performed moderate intensity aerobic exercise at least 30 minutes three times per week (moderate to vigorous walking, stationary bicycling and running). Mothers in the control category did not partake of a regular exercise routine. The MCG was measured between 24-36 weeks gestational age.

Between 36-38 weeks gestational age, breathing movements were identified using specific criterion. Measures of fetal heart rate and autonomic control were analyzed during episodes of fetal breathing and non-breathing movements. Although there was no difference in the number of breathing episodes, differences were noted between the groups.

Results

The researchers found:

• Fetal HR was significantly lower in the exercise group during both breathing and non-breathing movement periods.
• Fetal short-term and overall heart rate variability were higher in the exercise group during breathing movements.
• Three independent measures of vagal control were higher in the exercise-exposed fetuses during breathing movements.
• During periods of fetal non-breathing, there were no significant differences in measures of vagal control between groups. There were no group or breathing period differences in sympathetic heart rate control.

Conclusion

According to Drs. May and Gustafson, “These findings suggest a potential benefit of maternal exercise on fetal development because of the link between fetal breathing movements and the developing autonomic nervous system.” Their next step is to use exercise as a potential intervention to improve short and long term outcomes in children born to women at risk for gestational diabetes.

The study was entitiled “Fetal Responses to Maternal Exercise: Effect on Fetal Breathing and Body Movement,”  and was conducted by Stephanie Million and Linda E. May, Kansas City University of Medicine and Biosciences (KCUMB), Kansas City, MO; and Kathleen M. Gustafson, University of Kansas Medical Center (KUMC), Kansas City, KS. The researchers will discuss their findings at the 122nd Annual Meeting of the American Physiological Society, which is part of the Experimental Biology 2009 scientific conference. The meeting will be held April 18-22, 2009 in New Orleans.

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Led by Kinesiology and Health Studies professor Ian Janssen, the new study supports Canada’s Physical Activity Guidelines for Children and Youth, which call for children to accumulate at least 90 minutes of  moderate-to-vigorous physical activity over the course of the day, in bouts of at least five to 10 minutes’ duration. Until now there has been no scientific evidence to support the recommendation of sustained, rather than sporadic exercise.

“Even in 60-minute physical education classes or team practices, children are inactive for a large portion of the time and this would not necessarily count as sustained exercise,” says Dr. Janssen. “When children engage in longer periods of sustained physical activity, there is a smaller likelihood that they will be overweight or obese.”

The findings appear in the May issue of the American Journal of Preventive Medicine.

Conducted by Dr. Janssen and graduate student Amy Mark, the study analyzed data from 2,498 youth aged eight to 17, who participated in the National Health and Nutrition Examination Survey. Sporadic (one to four minutes), short (five to nine minutes) and medium-to-long (10 minutes and longer) bouts of moderate-to-vigorous physical activity were measured using motion sensors. Participants’ body mass index (BMI) was used to classify them as normal weight or obese.

Two-thirds of the physical activity measured in the young people took place in short, sporadic sessions that lasted less than five minutes. Within the most active children, 25 percent of those who tended to accumulate their physical activity in bouts were overweight or obese, compared with 35 percent in those who tended to accumulate their activity in a sporadic manner.

“Our findings have important public health implications with respect to the promotion of physical activity in young people,” says Dr. Janssen, noting that current U.S. and international guidelines do not stipulate how daily physical activity should be accumulated.

The researchers say that further studies will be required to determine the optimal length of exercise time, and to examine the influence of bouts of physical activity on other aspects of health.

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