Experts bust common sports medicine myths

SAN DIEGO – Is it okay for pregnant women to attend CrossFit classes? Are patients who run for fun at increased risk for osteoarthritis? Does stretching before exercise provide any benefits to athletes?

Experts discussed these topics during a session titled “Mythbusters in sports medicine” at the annual meeting of the American Medical Society for Sports Medicine.
 

Does exercise negatively impact pregnancy?

The idea that strenuous exercise during pregnancy can harm a baby’s health is a myth, according to Elizabeth A. Joy, MD.

“Women having healthy, uncomplicated pregnancies should be encouraged to be physically active throughout pregnancy, with a goal of achieving 150 minutes per week of moderate-intensity activity,” she said. “Fit pregnant women who were habitually performing high-intensity exercise before pregnancy can continue to do so during pregnancy, assuming an otherwise healthy, uncomplicated pregnancy.”

Results from more than 600 studies in the medical literature indicate that exercise during pregnancy is safe for moms and babies, noted Dr. Joy, medical director for community health and food and nutrition at Intermountain Healthcare in Salt Lake City, Utah.

In fact, the 2008 Physical Activity Guidelines for Americans state that pregnant women who habitually engage in vigorous-intensity aerobic activity or who are highly active “can continue physical activity during pregnancy and the postpartum period, provided that they remain healthy and discuss with their health care provider how and when activity should be adjusted over time.”

Such advice wasn’t always supported by the medical profession. In fact, 1985 guidelines from the American College of Obstetricians and Gynecologists recommended that women limit exercise to no more than 15 minutes at a time during pregnancy and keep their maternal heart rate less than 140 beats per minute. ACOG also discouraged previously sedentary women from beginning an exercise program during pregnancy.

“Sadly, women are still getting this advice,” said Dr. Joy, who is also president of the American College of Sports Medicine. According to the 2005-2010 National Ambulatory Medical Care Survey, only 18% of pregnant women reported receiving counseling to be physically active during their pregnancies (Matern Child Health J. 2014 Sep;18[7]:1610-18). “That is just unacceptable,” she said.

In a prospective study of the association between vigorous physical activity during pregnancy and length of gestation and birth weight, researchers evaluated 1,647 births among primiparous women (Matern Child Health J. 2012 Jul;16[5]:1031-44).

They conducted telephone interviews with the women between 7-20 weeks gestation and assigned metabolic equivalent of task values to self-reported levels of physical activity. Of the 1,647 births, 7% were preterm.

Slightly more than one-third of the women (35%) performed first-trimester vigorous physical activity. The average total vigorous activity reported was 76 minutes per week, 38% of which was vigorous recreational activity.

Women who performed first-trimester vigorous recreational physical activity tended to have lower odds of preterm birth. They also tended to have lighter-weight babies, but this did not reach statistical significance (P = .08). The authors concluded that first-trimester vigorous physical activity “does not appear to be detrimental to the timing of birth or birth weight.”

In a separate analysis, researchers evaluated acute fetal responses to individually prescribed exercise according to existing physical activity guidelines in active and inactive pregnant women (Obstet Gynecol. 2012 Mar;119[3]:603-10).

Of the 45 study participants, 15 were classified as nonexercisers, 15 were regularly active, and 15 were highly active. The women underwent treadmill assessment between 28 weeks and 33 weeks, while fetal assessment included umbilical artery Doppler, fetal heart tracing and rate, and biophysical profile at rest and immediately post exercise.

The researchers observed no differences between the groups in mode of delivery, birth weight, and Apgar scores. During vigorous-intensity exercise, all umbilical artery indices showed decreases post exercise.

“Although statistically significant, this decrease is likely not clinically significant,” the researchers wrote. “We did not identify any adverse acute fetal responses to current exercise recommendations.” They went on to conclude that the potential health benefits of exercise “are too great for [physicians] to miss the opportunity to effectively counsel pregnant women about this important heath-enhancing behavior.”

In a more recent randomized study, Swedish researchers evaluated the efficacy of moderate-to-vigorous resistance exercise in 92 pregnant women (Acta Obstet Gynecol Scand. 2015 Jan; 94[1]:35-42).

The intervention group received supervised resistance exercise twice per week at moderate-to-vigorous intensity between 14-25 weeks of their pregnancy, while the control group received a generalized home exercise program. Outcome measures included health-related quality of life, physical strength, pain, weight, blood pressure, functional status, activity level, and perinatal data.

The researchers found no significant differences between the two groups and concluded that “supervised regular, moderate-to-vigorous resistance exercise performed twice per week does not adversely impact childbirth outcome, pain, or blood pressure.”

Despite all that’s known about exercise during pregnancy, a few practice and research gaps remain.

For one, Dr. Joy said, the relationship between performing physically demanding work during pregnancy in combination with moderate-to-vigorous exercise remains largely unknown.

“Even within health care, you have residents, nurses, and others working in hospitals,” she said. “That’s demanding work, but we don’t know whether or not moderate-to-vigorous exercise in combination with that kind of work is safe. Also, although women tend to thermoregulate better during pregnancy, we still don’t fully understand the impact of elevated core body temperature, which may occur with regularly performed vigorous-intensity exercise over the course of pregnancy.”