From Time, exerpts from the article “The Science of Exercise“:

“There are so many misconceptions about strength and resistance training,” says Larry Tucker, a professor in exercise sciences at Brigham Young University. “One is that you’ll become muscle-bound”—so bulked up that your body becomes rigid. That myth was somewhat dispelled when athletes who started strength-training saw that they could hit a ball farther, jump higher and run faster, Tucker says. “Gradually we started realizing there are benefits beyond sports.”

But women in particular are neglecting strength training at their own peril. It’s the only kind of exercise that makes muscles bigger, which lets them generate more strength and force, faster. “Muscle mass allows us to move,” Tucker says. Young people tend to take for granted the day-to-day parts of life that require strength, like walking up stairs or picking up a baby. “But a sedentary lifestyle means that people are gradually becoming weaker over time,” he says. Building muscle can fight back against that process.

It’s also one of the very few ways to make bones denser, a perk that is especially important for women. Lifting something heavy, like a dumbbell, makes bones bear more weight, and in exercise, stressing your bones is a good thing (to a point of course). Bones are constantly remodeling, explains Anthony Hackney, an exercise physiologist at the University of North Carolina. “Your body is always adding calcium to your bones and taking calcium away from your bones,” he says.

This delicate balance starts to tip as people age, and “they lose more mineral from the bone than they’re able to lay down,” Hackney says. Over time, bone gets less dense and more brittle and prone to osteoporosis, a condition that affects about 10 million Americans—80% of whom are female. Women have smaller, thinner bones than men from the start, and after menopause they lose estrogen, a hormone that protects bones.

Strength training also comes with the less visible benefit of lowering risk for several diseases. “The only real way we can increase our metabolism, unless we take drugs, is to lift weights and maintain or increase our lean mass,” says Tucker. Doing so makes the body more sensitive to insulin, and therefore more durable against certain diseases.

Recent research suggests that strength training may lower a woman’s risk for Type 2 diabetes and cardiovascular disease. In a 2016 study, researchers from Harvard Medical School and the National Institutes of Health used data from nearly 36,000 older women, who ranged in age from 47 to 98. The women filled out questionnaires for about a decade detailing their health and exercise levels, and one question asked women to estimate how much weightlifting or strength training they had done per week in the past year. The researchers then tracked which of the women had a heart attack or stroke and which developed Type 2 diabetes.

Whether or not a woman did muscle-strengthening exercises indicated a lot about her health. Compared with women who avoided it, those who did any amount of strength training were more likely to have a lower body mass index and a healthier diet and less likely to be a current smoker.

They also had a Type 2 diabetes risk that was 30% lower and a cardiovascular disease risk 17% lower than those who did no strength training, even after the researchers controlled for other variables like age, diet and physical activity.

Adding aerobic exercise helped drive both risks down even more. Those who did at least 120 minutes a week of aerobic exercise and some strength training had a Type 2 diabetes risk 65% lower than women who didn’t do either.

Most people should do both kinds of exercise for the biggest gains. But if you had to choose one, Clark advises, pick strength training. “Cardio is more digestible, it’s less intimidating, but people also get less and less out of it over time,” she says. As you grow fitter, you have to do more and more aerobic exercise to see the gains, she explains. Strength training, in her view, is the most efficient exercise for those with limited time.

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