CENTENNIAL, CO – APRIL 15: Fit through menopause at Curves, 7424 S. University Blvd. in Centennial on Wednesday, April 15, 2015 coach Joyce Myers works the leg press machine as she helps customers on the floor of the gym use the hydraulic equipment to maintain strength. (Photo by Cyrus McCrimmon/The Denver Post )

No one’s ashamed of their hot flashes at Krissy O’Brien’s women-only exercise programs.

“My ladies like to call them ‘personal summers,’ ” says O’Brien, who owns and manages threeCurves fitness centers in Denver, Centennial and Lone Tree. “They say, ‘I’m having a personal summer. Turn the fans on!’ “

Though the joke breaks the tension, the exercise probably won’t relieve the hot flash, a common symptom caused by dropping levels of estrogen during menopause. But in terms of menopause’s more subtle and serious health concerns — weight gain, bone-density loss, increased risk for heart disease and diabetes — these women also are recruiting the best possible weapon: muscle.

The first, weight gain, might be at the top of the concerns for menopausal or perimenopausal women — especially increased fat around the midsection, or pounds that show up despite keeping up with past exercise programs. Before, some of these women may have simply jogged farther or done aerobics more often, but science is now showing how strength-building exercises are key.

“The anecdotes we often hear about weight — there is real biology behind why it becomes more difficult for women to lose weight or to prevent gain after menopause than before,” says Dr. Wendy Kohrt of the Division of Geriatric Medicine at the University of Colorado Hospital.

In fact, as director of the hospital’s IMAGE program (Investigation into Metabolism, Aging, Gender and Exercise), Kohrt describes menopause as a sort of perfect storm for weight gain. As dropping estrogen causes your metabolism to slow, it may also change the body’s ability to regulate appetite, so you crave more and burn less.

“It’s insidious,” she says. “In our studies, the magnitude of that change (in metabolism) is about 50 calories a day. That doesn’t seem like a lot, but when you add that up over time, and if you don’t compensate for it by decreasing your eating or increasing your exercise, that magnitude would equate to gaining a pound of fat about every 12 weeks.”

To up the ante of the perfect storm, this is dangerous fat we’re talking about. Rather than gain fat on the hips and thighs, the places women tend to store it most of their lives, the hormonal change often relocates the fat to the belly, the type of fat that nests among your organs and ups the risk of heart disease and diabetes.

That’s where muscle comes in to help level the metabolic playing field, and why doctors are currently recommending strength training more than or in addition to traditional “fat-burning” cardio activities like stair machines, running or cycling. The latter certainly wasn’t cutting it for athlete and chiropractor Joanie DeBever of Boulder, who went through menopause around the age of 51.

Due to always-painful periods, “Menopause was something I was looking forward to,” says DeBever, founder of Healing Touch Chiropractic. But as an elite competitive cyclist who once participated in Olympic trials, she says, “I was not able to maintain and hold onto the musculature that allowed me to do so much for so many years.”

The answer was not more cardio, but instead high-intensity, short-duration exercise focused on strength training. She says, “It’s going from that competitive push-hard, gotta-go, gotta-train mentality to truly training smarter, not harder.”

The smart part is knowing more about how muscles work. Think of muscle mass as an investment and metabolism as the payout. The more money/muscle you have in bank, the more you earn/burn. As estrogen falls along with metabolism and muscle mass, a menopausal woman’s investment of muscle will develop a slow leak, meaning she needs to constantly replenish muscle just to maintain it. (Doctors also recommend weight-bearing exercise for bone health.)

It’s a cycle that’s certainly not fair, but by counteracting that reduction of lean muscle, it also makes it is possible to wrest your metabolism back, at least partially.

For those who’ve been absent from or never took up exercise, it’s never too late to put more muscle in the bank and reap the rewards, but this transition can be especially challenging for women who are already quite fit.

“The expectations of people who have a history of exercise might not be well aligned with reality in terms of how much weight it should take off, or how much they should lose (during menopause),” says researcher Kohrt, because they’re not accounting for that slow drain.

“Maintaining a lifetime of fairly vigorous activity does not prevent you from gaining excess fat or losing bone mass.”

High-performing athletes might also benefit from a change in activity or sport, because they’re used to how their bodies performed at that activity and how it responded in terms of weight maintenance — and neither will be unchanged. DeBever, for instance, switched from cycling to power hiking with trekking poles, which works the body differently and has helped her regain muscle mass without forcing a comparison with her highly competitive past self.

No matter what your history with fitness, with enough renewed or even increased muscle mass, you can close that 50-calorie metabolic gap back up to your previous “normal,” even if it takes more effort to stay in that zone.

Even so, most experts believe the goal should be to counteract negative health outcomes, like that dangerous belly fat or osteoporosis, rather than focusing on your figure. When menopausal symptoms level out and stabilize, it’s totally natural to have a slightly higher fat-to-muscle ratio than you did in youth. In fact, it’s a ratio that can be healthier, says Kohrt.

“It’s something we refer to as the obesity paradox,” she says. Whereas young and middle-aged adults’ health outcomes are precipitously worse when they’re overweight or obese, “once you’re over the age of 60 or so, that doesn’t seem to happen. Older adults who are a little overweight might be a little better off than those who are underweight, and we don’t understand why yet.”

DeBever believes that changing the menopausal conversation from one about losing the new inches around your tummy into one about weight maintenance for long, healthy life is welcome.

“We tend to get so caught up in being beautiful and staying beautiful, and we beat ourselves up to meet a myth we can’t attain,” she says. “(Menopausal age) is a time to enjoy life and relish our accomplishments and what we’re doing, not to go down the path of beating ourselves up.”

O’Brien also loves seeing this shift in fitness goals among her clients, some of whom are in their 70s and are holding planks or doing jumping jacks.

“I’m hearing that more now, that ‘my doctor is encouraging me to go to strength training,’ ” says O’Brien. “Doctors are giving a prescription for exercise and education over a pill, and that makes me ecstatic. That’s the direction we should be moving.”

Kate Jonuska: kate.jonuska@gmail.com or twitter.com/kjonuska