At the West Roxbury YMCA's Boot Camp fitness class, Wendy Rue Williams leads her charges through high-intensity cardio drills, weight training, and core strengthening.
She demonstrates a series of jumps on and off the bosu (an inflated apparatus that looks like half of an exercise ball), then tells the class to keep on going while she switches to a lower-impact variation, stepping on and off instead of jumping.
The reason for the modification is that Williams is in the final month of pregnancy.
"I feel great," says Williams, a 35-year-old Roslindale resident whose second child is due this week. "It's been a great pregnancy. I love teaching this class. The music and the women in the group make it so fun. It's my job, but also I love it."
Some people are alarmed when they first see Williams jumping, running, and doing calisthenics, all with the round, extended belly of someone far along in their pregnancy. But her classes, which often include a few other expectant mothers, show how attitudes toward exercise and pregnancy are evolving.
"Trends change," says Dr. Laura Riley, medical director of labor and delivery at Massachusetts General Hospital. "It used to be, in the 1980s, pregnant women were told to limit their heart rates while exercising. Basically, that meant they couldn't get much of a workout. That restriction no longer exists. The data did not support it."
Riley adds, "Exercise is the best thing during pregnancy. . . . Women who exercise throughout pregnancy tend to gain less weight, have shorter labors, lower their risk of having a Caesarian delivery, and usually feel better about themselves."
A hard-core fitness enthusiast since her teens, Williams has never feared doing things that raise eyebrows. In high school, for example, she lifted weights with the boys' football team.
"Not a lot of girls were lifting weights then," Williams recalls, "but I just loved seeing my muscles develop."
Years later, while teaching fitness classes and exercising throughout her first pregnancy, Williams remembers more stares and questions.
" 'Are you sure you should be doing that?' was a common one," says Williams. "People were watchful. They'd never seen a pregnant fitness instructor before. Even now, nearly three years later, it's rare.
"Exercise was so helpful during my first pregnancy," she recalls, "I couldn't not do it this time around."
Williams wasn't always a certified fitness instructor. Shortly after becoming a mother for the first time, Williams struggled with how to meet the demands of a new baby, maintain her career as a social worker, and find time for her own health and fitness needs.
"I knew I could work out hard during my pregnancy," she says. "I knew the benefits. I wanted to educate and encourage other women to safely exercise during their pregnancies as well."
And so Wendy Rue Williams Personal Fitness was born. Williams, who has an undergraduate degree in sports medicine and a master's in social work, finds her dual background incredibly helpful.
"There is a lot of pressure on women to look a certain way," Williams says. "It is important to me to be able to empower women, to help them feel good about their bodies and learn healthy ways."
West Roxbury resident Meghan Wagner, 30, is someone who gets the message loud and clear.
"I took classes with Wendy while she was pregnant with her first child," says Wagner. "Later, she spoke to a group of women triathletes I was training with. Her topic was 'Pre- and Post-Natal Fitness: Dispelling Myths.' It was amazing, and very helpful, especially now."
Wagner, a community health trainer, group fitness instructor, and accomplished athlete, is also in her ninth month of pregnancy, due to deliver this week, just a few days before Williams. She teaches aqua kickboxing at the Wang YMCA in Chinatown, and is a backup teacher for the West Roxbury YMCA's Boot Camp classes.
"We're fit and we're trained," Wagner adds. "We know our bodies and we know how to modify our workouts if we need to."
Wagner doesn't say this lightly. Born with a congenital heart defect known as aortic stenosis, or heart murmur, Wagner experienced shortness of breath and dizziness while training for a half-marathon two years ago, around the same time she and her husband were talking about starting a family.
Wagner consulted a cardiologist who sent her to an obstetrician who handles high-risk cases. The two doctors recommended Wagner undergo a valvioplasty. This procedure, possible because of Wagner's excellent physical condition, allowed her to have a lower-risk pregnancy that could safely include high-intensity exercise.
"For women who are in excellent shape, they can continue everything -- except contact sports -- during pregnancy," says Riley. "They may need to modify their workouts toward the end of the pregnancy, to accommodate for weight gain and balance shifts that come with a bigger belly. But they certainly do not have to stop exercising, unless there is a complication."
Riley adds that "for women who have never exercised, pregnancy is an OK time to start. Every woman should exercise a minimum of 30 minutes, five days a week. For new exercisers, swimming and walking are great."
Williams agrees, adding that it is important to "listen to your doctor and to your body."
In addition to teaching Boot Camp classes Monday evenings and Saturday mornings at the Y, Williams does individual, partner, and workplace training, fitness consulting, and exercise classes for women's sports groups and mothers' groups. She speaks on fitness topics, offering motivation and structure to people interested in the topic.
"I hope that some of the younger women in class will remember seeing me going strong through my entire pregnancy," says Williams.
"Hopefully, when they become pregnant, they'll know they can exercise through the whole nine months, too."
Anna G. Rubin can be reached at email@example.com