The Exercise Sweet Spot

50 minutes – make that your workout time and you’ll maximise your fitness, calorie burn and overall health from head to toe, research finds. Learn how to hit the gym smarter, not harder.

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50 minutes – make that your workout time and you’ll maximise your fitness, calorie burn and overall health from head to toe, research finds. Learn how to hit the gym smarter, not harder.
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As you head outside for a long run or crank up the resistance in a spinning class, you’re focusing on muscles you’re going to build and calories that are being burned. But it turns out you should also be thinking about how your hormones will be affected.

Oestrogen and progesterone, the two most important female sex hormones, have a surprising and strong connection to your workouts, research shows. And how hard and long you exercise changes these chemicals in a way that profoundly influences your health.

Done properly, working out helps keep your oestrogen and progesterone levels balanced. This is a big deal. It means, as doctors have discovered, that you have enormous control in maintaining your wellness from top to bottom.

“We tend to think of oestrogen and progesterone only in terms of ovulation and menstruation, but they’re actually critical for the health of every cell and organ in our bodies,” says Dr Jerilynn Prior, a professor of endocrinology and metabolism at the University of British Columbia, and the founder of the Centre for Menstrual Cycle and Ovulation Research in Vancouver.

For instance, studies show that oestrogen helps shield brain cells from damage caused by oxidative stress and beta-amyloid protein, which is thought to be a culprit in Alzheimer’s disease. And oestrogen and progesterone play crucial roles in women’s bone and cardiovascular health, says Dr Jennifer Ashton, the ABC News senior medical contributor for Good Morning America and an ob-gyn in New Jersey.

But keeping these hormones balanced is key to netting the benefits. Repeated sweat sessions that are too long or too intense can backfire, throwing oestrogen and progesterone out of whack, studies have found.

More than an hour of vigorous activity every day can have a negative impact on your reproductive system, according to research published in the journal Human Reproduction. Specifically, it affects the hypothalamus, a gland in the brain that directly influences your levels of oestrogen and progesterone, says Dr Raul Artal, the chairman emeritus of the Department of Obstetrics, Gynecology, and Women’s Health at Saint Louis University.

For fit women, the goal is simple: exercise enough to keep oestrogen and progesterone functioning normally without getting too gung-ho and going overboard.

Once you find that exercise sweet spot, you can keep your hormones on track and improve your health. And because you’ll be working out smarter, not harder, you’ll have more energy, motivation, and free time to boot. Here is your healthiest plan:

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Keep Your Workouts to 50 Minutes

That’s enough time to build muscle, burn calories, improve your fitness and get the results you want without going into overdrive. Do one or two days of high-intensity interval training a week for the biggest overall health and fitness benefits, says John Porcari, a professor of exercise and sport science at the University of Wisconsin–La Crosse.

The other days, stick with a moderately intense fitness routine, like strength training or hiking. Of course, you may sometimes need to do longer workouts, as you would when training for a race, say. In those cases, don’t go allout the entire time. Mix in a few minutes of slower, steady-pace jogging, and alternate between the two.

Fuel Up Properly

What you eat is important too. Make sure you’re consuming enough food to stay fueled. “If you ovulate during the week or two before your period, your ovaries produce more progesterone, which raises your core temperature, so you naturally burn more calories,” Dr Prior explains.

And that’s on top of what you’re already torching through your workouts. “That means you’ll need to eat about 300 extra calories a day,” she adds.

Maintain a Healthy Weight

Being too heavy or too thin can cause your hormones to fall out of sync. Fat tissue produces extra oestrogen, too much of which can eventually stop ovulation, impair fertility, and encourage the growth of cysts and tumours.

Without enough body fat, however, oestrogen levels drop and can harm your bone and heart health. Aim to keep your body fat at 21 to 24 per cent of your weight, which is what experts at the American Council on Exercise deem healthy.

Work out smartly, and eat meals that include a mix of protein, fibre and good-for-you fats – oatmeal topped with berries and walnuts, a salad with chicken and avocado, and salmon with brown rice and asparagus – and you’ve got the power of health in your hands. 

So, how do oestrogen and progesterone work again?

Both hormones are produced by your ovaries as part of your monthly cycle, which can last anywhere from 21 to 35 days and is divided into phases. During the first, known as the follicular phase, your brain signals your pituitary gland to send follicle-stimulating hormone (FSH) to your ovaries, so they step up the production of oestrogen to thicken your uterine lining.

During ovulation, the sharp rise in FSH is followed by an increase in luteinising hormone, which prompts your ovaries to release an egg. Next comes the luteal phase, when your levels of oestrogen and progesterone rise to keep your uterine lining intact so that an egg can implant itself there in case of pregnancy.

If you don’t become pregnant, oestrogen production halts, and this triggers your period. Even under ideal circumstances, all these hormonal fluctuations trigger a cascade of physical and emotional effects: During the follicular phase, for instance, increased oestrogen levels may cause breast tenderness.