Some days you may feel as if there’s nothing in the gym that you can’t conquer; other times the only thing you feel like lifting is the blanket over your head. What’s behind these dramatic swings in mood and energy? For many women, hormones rightfully bear the brunt of the blame, since they influence everything from cramps and bloating to junk-food cravings. The good news: You actually can boost your fitness regimen and maximize your performance by tuning in to what’s happening in your body, then adjusting your training and nutrition to match. Here’s how to take control of your monthly cycle and stay fit every day.

The average woman’s cycle is 28 days, though some are shorter or longer than others. “Estrogen and testosterone levels are rising from rock bottom beginning on the first day of your period, so you’ll feel a bump in mood and energy,” says Mary Jane Minkin, M.D., clinical professor of obstetrics and gynecology at the Yale School of Medicine. “In general, the hormone estrogen makes you feel good, while testosterone boosts libido.”

● Fitness Fundamentals: “Your feel-good hormones are starting to kick in, so your energy levels will be a bit higher and your appetite slightly suppressed,” says Kim Oddo, a certified personal trainer, nutritionist, and owner of Body By O. Take advantage by dedicating a little more time to longer weight-training and cardio sessions.

● Nutrition Know-How: “You don’t want to do anything to elevate blood sugar levels and trigger cravings, so stick with foods that are lower on the glycemic index,” Oddo says. To tame a sweet tooth without sending glucose levels soaring, try having a cup of low-sugar, nondairy coconut (or goat’s milk) yogurt topped with berries. For something savory, go for roasted chicken with a baked yam.

DAYS 8–14
You’re still flying high from the euphoric effects of rising estrogen and testosterone, both of which peak during this week leading up to ovulation and which can help boost your energy. This is also when you’re most focused on your appearance, according to a study in the Journal of Consumer Psychology. The same study also found that your appetite is lower at this time.

● Fitness Fundamentals: “Use your extra energy to push your training above and beyond what you’d typically do,” Oddo advises. “If you’re looking to lose weight, do supersets and pick up the pace to make your workout more aerobic. If you want to boost lean muscle mass, lower your reps and increase your weights.”

● Nutrition Know-How: Now is the time to have smaller, more frequent meals. “Instead of eating four meals a day, aim to consume the same amount of calories in six smaller meals,” Oddo says. If your appetite is smaller, a plate filled with food may look daunting and even turn you off from eating, but mini meals keep your metabolism revved without making you feel stuffed, he explains.

DAYS 15–21
When your body ovulates at the beginning of this week, estrogen levels take a dive, which can make you slightly irritable. And when estrogen—a natural fluid retainer—surges again toward the end of the week, you may feel bloated. At the same time, progesterone is steadily increasing, which can make you feel more tired than you probably felt in the first half of your cycle, Minkin says.

● Fitness Fundamentals: It’s all about maintenance during this low-energy phase. “Feel free to scale back on your intensity when you are lifting so you still have enough energy left over for your cardio workouts,” Oddo says. “If you’re trying to maintain lean muscle mass, reduce the number of sets you do but keep your weights the same.”

● Nutrition Know-How: Switch the balance of carbs and fats at this point in your cycle. “Fats don’t spike blood sugar and trigger cravings the way carbs do, and they can actually help you fight PMS cravings by making you feel more satiated,” Oddo explains. Try snacking on a handful of mixed nuts, peanut butter with celery sticks, or avocado slices sprinkled with lemon juice.

DAYS 22–28
At this point in your cycle, progesterone peaks before it tumbles. The hormone may also be linked to an increase in body temperature, which can elevate metabolism slightly. Levels of estrogen, testosterone, and progesterone all plummet by the end of this week, though, and you may experience PMS symptoms such as bloating and insomnia. No surprise: Your appetite and cravings for high-calorie foods peak during this week. Stay strong!

● Fitness Fundamentals: Your hormones are at an all-time low and so are levels of the feel-good neurochemical serotonin. “You may not feel like working out now, but don’t skip your training regimen, because exercise triggers the release of endorphins to naturally help boost your mood,” Oddo says. The more you work out, the more those happiness-helping endorphins are released. To add a little intensity, try lowering your reps but increasing your weights, or keep weights the same and do more reps.

● Nutrition Know-How: This is the time to watch your sodium intake, since salty foods such as soy sauce and condiments compound water-weight gain. “You really have to watch your nutrition, because you could set off a cycle where you feel bloated and reach for food for instant comfort, only to trigger a binge or pattern of unhealthy eating,” Oddo says. “Also, be sure to drink plenty of water. Natural diuretics such as asparagus, cucumbers, and dandelion tea can fight water retention by flushing out your system.”

Fine-Tune Your Fitness
Here’s a week-by-week training guide to feeling strong all month long.

Week 1: Estrogen levels start to increase. Try high-energy fitness with amped-up cardio, such as a tough kickboxing boot camp, a spinning class, or a Zumba session.

Week 2: Hormone levels are still rising, giving you maximum workout power. Tune in to this amped-energy phase with some high-intensity interval training (HIIT) or plyometric circuit training.

Week 3: This transitional week typically begins with high energy levels but then dips as the days go on. Opt for slow and steady strength-training sessions, or try a core-focused Pilates class.

Week 4: Hormone drops leave you feeling exhausted. Take the week off from hardcore workouts and treat yourself to a long walk, or hit the mat with a rejuvenating yoga class.

Supps for Your Cycle
PMS hits some women hard in the week before their period starts. To minimize both physical and emotional changes, try these vitamins, minerals, herbs, and other supplements, advises Paul Dell’Aquila, M.D., director of the Preventative and Restorative Center of New Jersey.

› Magnesium (300–600mg daily) and calcium (600–1,000mg daily) have both been shown to help reduce tension, cramps, and fluid retention. Also helpful are omega-3 fatty acids (200mg daily), which lower levels of prostaglandin 2, an inflammatory substance associated with fluid retention and cramps.

› Taken as part of a B-complex supplement (100mg daily), vitamins B3 and B6 have a natural diuretic effect, helping to ease cramps while also boosting mood by assisting in the formation of certain neurotransmitters.

› For herbal remedies, borage oil, Angelica sinensis, evening primrose, and chasteberry, available in most health food stores, are often recommended the week before your period to help with changes associated with the early part of the menstrual cycle. Start taking them one week before your period begins and continue taking until your period ends.

› Finally, a high-potency multivitamin taken daily is a great way to supplement a healthy diet, since we don’t always get all the nutrients we need from food sources, adds Dell’Aquila.