| Volume 1, No.4 October 1998
Pregnancy and Exercise
Pauline P. L. Poon, MA
The biological adaptations to
pregnancy strain the body beyond any other physiological event in a
healthy woman’s experience, and requires significant cardiovascular,
metabolic, hormonal, respiratory and musculoskeletal adjustments
(Sternfeld, 1997). In addition, psychological responses to pregnancy
(e.g., mood changes)
and during postpartum (e.g., depression) have been well documented
(Koltyn, 1997). Recent reviews and studies indicate that exercise not
only has a positive effect on psychological outcomes during pregnancy,
but moderate exercise can also have beneficial influence on ventilatory
demand, perceived breathing effort in the late gestation period (Ohtake
& Wolfe, 1998) and can contribute to significantly heavier birth
weight babies (Pivarnik, 1998).
The following are some of the physiological concerns regarding exercise
Hyperthermia: Maternal temperature appears to be the primary
regulator or thermostat of fetal temperature. If maternal temperature
is increased excessively, it could threaten the health of the fetus.
Research shows that when the level of exercise is self-paced, exercise
during pregnancy results in only relatively moderate changes in
temperature (Sternfeld, 1997). Hence, the thermoregulatory processes
during pregnancy seem to protect against hyperthermia when exercising
at moderate levels (Canadian Academy of Sports Medicine, 1998).
Uterine Blood Flow: Uterine blood flow is part of the internal
organs circulation system. Blood flow during moderate exercise in a
non-pregnant state is redistributed away from the internal organs to
the working muscles, up to 50% less than at resting values, and a
30% reduction during prolonged high intensity exercise (Canadian
of Sports Medicine, 1998). The concern about exercise during pregnancy
is a decrease in nutrient delivery to the fetus which may result in
low birth weight, fetal hypoxia, and fetal growth retardation. Research
shows that oxygen delivery to the fetus and fetal oxygen consumption
are maintained at relatively constant levels during exercise due to
the following mechanisms: a) increased oxygen-carrying capacity of
the blood; b) increased oxygen extraction as blood flow decreases;
and c) redistribution of the blood flow which benefits the placenta
over the uterus. A possible negative effect on birth weight is
only with high frequency (5 - 7 days/week) exercising. Moderate
and intensity exercise are found to have a positive effect on the
of healthy babies (Pivarnik, 1998).
Uterine Contractions: Norepinephrine is released during exercise
in both pregnant and non-pregnant states. Theoretically, norepinephrine
is an uterine stimulus which could trigger uterine contractions and
result in premature labour. Research evidence to date suggests that
the fetus is protected from this stimulatory effect (Sternfeld, 1997).
Exercise or other physical activity does not increase the risk of
labour, nor increase the occurrence of premature rupture of membranes
in a healthy pregnancy (Canadian Academy of Sports Medicine, 1998).
The Canadian Academy of Sport Medicine recently published the Position
Statement on Exercise and Pregnancy (Canadian Academy of Sports
Medicine, 1998) that reviews the risks and benefits, and also gives
specific recommendations on exercise prescription for this segment of
the population. In addition, the Canadian Society for Exercise
(CSEP) developed the Physical Activity Readiness Medical Examination
for Pregnancy (PARmed-X for Pregnancy). Physicians can use this form
for screening the health of pregnant patients prior to their
in exercise programs and for continual medical monitoring.
The following guidelines are endorsed by the Canadian Academy of Sport
Medicine (1998). See the Position Statement for a complete listing
of the recommendations. Please note that these recommendations are
largely based on studies of healthy, nonsmoking, Caucasian, previously
fit women with low risk pregnancies.
- Regular exercisers prior to
pregnancy may maintain their program during the first trimester and
use the PARmed-X for pregnancy guidelines throughout the pregnancy.
- Women who were not regular
exercisers prior to their pregnancies should not begin to exercise
until the second trimester.
- The frequency of exercise
per week is dependent upon the duration and intensity of the sessions.
However, it is recommended to begin with a 3 times/week frequency
and progress to a maximum of 4-5 times/week.
- Since the safe upper limit for
an exercising target heart rate in pregnancy is controversial, the
talk test (an intensity level where the exerciser can easily carry
on a verbal conversation) and the Borg’s 15-point Rating of Perceived
Exertion (RPE) scale (i.e., a target range of 12-14 points - moderate
to somewhat hard intensity) are recommended to assess exercise
- Cardiovascular exercise should
begin with 15 minutes in duration and slowly be increased by 2
minutes/week until a maximum of 30 minutes at the target heart rate.
- Non-weight bearing activities
(e.g., swimming and cycling) are ideal for women who were inactive
to their pregnancies.
- Holding your breath during
resistance training and exercises in the supine position after the
month of pregnancy should be avoided.
Recent reviews (Pivarnik, 1998; Sternfeld, 1997; Wang, 1998), studies
(Koltyn & Schultes, 1997; Ohtake & Wolfe, 1998) and exercise
guidelines (Canadian Academy of Sports Medicine, 1998) indicate that moderate
exercise during a healthy pregnancy can have
beneficial physical and psychological effects on the expectant mother
and offer few risks to the fetus.
- Canadian Academy of Sport
Medicine (1998). Position statement on exercise and pregnancy.
Gloucester, Ontario: Author.
- Koltyn, K. F., & Schultes,
S. (1997). Psychological effects of an aerobic exercise session
and a rest session following pregnancy. The Journal of Sports
Medicine and Physical Fitness, 37, 287-291.
- Ohtake, P. J., & Wolfe, L.
A. (1998). Physical conditioning attenuates respiratory responses
to steady-state exercise in late gestation. Medicine & Science
in Sports & Exercise, 30, 17-27.
- Pivarnik, J. M. (1998).
Potential effects of maternal physical activity on birth weight: Brief
review. Medicine & Science in Sports & Exercise, 30,
- Sternfeld, B. (1997). Physical
activity and pregnancy outcome: Review and recommendations. Sports
Medicine, 23, 33-47.
- Canadian Academy of
Sports Medicine. Tel: (613) 748-5851, e-mail: email@example.com
- Clapp III, J. F. (1998). Exercising
Through Your Pregnancy. Champaign, IL: Human Kinetics
- Exercises During
and Postpartum Poster - 16 x 20" full-color poster displays simple
exercises. $10.00 US from American College of Obstetricians and
Gynecologists. Tel: 1-800-762-2264, website: http://www.acog.org
- Hanton, R. (1996). Times
A Prenatal Guide for the Active Women. Ottawa, Ontario: Serious
- Physical Activity
Readiness Medical Examination for Pregnancy (PARmed-X for Pregnancy) -
4-page tear-off form, $2.00/single copy or $9.95/pad of 25 forms
from Canadian Society for Exercise Physiology (CSEP). Tel: (613)
234-3755, website: http://www.csep.ca