How Much Exercise You Need Totally Depends on Your Goals

With our crazy busy lives, it can be hard to squeeze in a sweat sesh. And when you do, you might wonder: How long should I sweat for? Well, even experts argue over that very question—but it turns out, you might not be doing enough. A new study published in Circulation found that 30 minutes of exercise a day (the previously recommended amount) might not be enough to keep your heart healthy.

In fact, you might need four times that. Researchers found that the amount of exercise we get has a direct dose relationship to our heart health—the more you get, the healthier your heart will be—and they suggest two full hours a day should be the new goal. (Excuse us while we go clear our calendars...)

But what about a higher intensity workout like your favorite HIIT class—don't you get more bang for your buck with that? While you'll certainly burn more calories going harder for short periods of time, moderate exercise does have its value, says Noam Tamir, C.S.C.S. and owner/founder of TS Fitness in New York City. "You will get a nice steady flow of blood flowing into the left ventricle, which needs to be strong because it pumps blood to the rest of the body." When you get your heart pumping at a slower and steadier pace, it allows the ventricles to fully expand and contract with each beat. "High-intensity training, on the other hand, doesn't do this as effectively, although it is more effective at burning calories." When you go hard, your heart beats too fast to get the same effect—think of it like the difference between taking short quick breaths versus long deep ones.

The bottom line: How long you work out for might depend on what your goals are. And while every body is different, science does have some stats on how long you should sweat for depending on what you're after.

Time at the Gym Per Week: 10 hours
To reap the most heart health benefits, the researchers of this new study are on to something. They found an exercise regimen of 30 minutes a day only reduces your risk of heart disease by about 10 percent. Up your daily workout to two hours a day, though, and you reduce the risk by 35 percent. Two hours seems like a ton, but study authors were only looking at moderate exercise—so your walk to and from the subway counts! To score more steps, take walking meetings, do a couple laps around the office at lunch, or go for a sunny stroll with your bestie instead of feasting on brunch.

Tamir recommends his clients seeking a healthier heart regimen do a combination of high intensity and moderate intensity cardio like these HIIT workouts. "This has been shown to significantly improve your body's VO2 max, which is the body's ability to utilize oxygen," says Tamir. A higher volume of blood flow expands your arteries and minimized the chance of blockages.

Time at the Gym Per Week: 40 to 60 minutes
Obviously, one of the benefits of every gym session is torching major calories. Lucky for us (and our abs), there's a totally time efficient way to do this: Researchers from the University of Wisconsin tested Tabata-style workouts and found that this high-intensity interval training torched 15 calories per minute. Talk about burn!

Try a 20-minute Tabata session two to three times a week—giving yourself at least two rest days in between—to reap the most calorie burning benefits.

Time at the Gym Per Week: 30 minutes
Strength training is about way more than just getting big guns. Studies have shown that regular resistance training reduces your risk of type 2 diabetes and blood pressure and improves your cardiovascular health, not to mention your self-esteem (why, hello there, Jillian Michaels-level abs).

The great thing about strength training is that you don't have to devote a lot of time to reaping these benefits. "In many cases, increasing strength can take as little as training once a week," says Tamir. "The difference in gains between training one, two, or three times per week is very minimal."

Time at the Gym Per Week: 3 to 4.5 hours
Whether you're in the midst of marathon training or just want to run a 5K without stopping, building endurance is key to a well-rounded workout. To up your endurance, it's all about quality over quantity of gym time. A study published in the Journal of Medicine and Science in Sports and Exercise found that HIIT is more effective than doing the same amount of total work but at a lower intensity.

But don't bank on settling into just one routine if you want to improve endurance. "The body will adapt and need to be challenged by a more rigorous routine," says Tamir. "Otherwise, the benefits associated with the exercise will give a low return." He recommends the following endurance plan to keep things fresh:

• Day 1: Short run: 20 to 30 minutes; strength training: 20 to 30 minutes
• Day 2: Interval HIIT run: 20 to 30 minutes
• Day 3: Strength training: 40 to 50 minutes
• Day 4: Rest day or brisk walk: 20 to 30 minutes
• Day 5: Hill run: 20 to 30 minutes
• Day 6: Strength training: 40 to 50 minutes
• Day 7: Swim/bike: 30 to 40 minutes

Time at the Gym Per Week: 2 to 4 hours
As Elle Woods once famously said, exercise gives you endorphins and endorphins make you happy. Studies have long shown that regular physical activity can help decrease depression and anxiety, and it can even score you a serious natural high with the cocktail of serotonin and dopamine released every time you exercise.

"Workouts that are as little as 20 minutes per day can create a 12-hour mood boosting benefit," says Tamir, who often sees mood boosts happen within five minutes of starting your training session. For optimal mood boosting benefits, aim for 20 to 40 minutes of moderate exercise a day.

Time at the Gym Per Week: 2.5 to 3.5 hours
All sleep is not created equal. Your body needs what experts call "slow-wave sleep," which is responsible for body repair and maintenance in order to fully recharge and keep you from feeling sluggish. According to the National Sleep Foundation, exercise is excellent for increasing not just the amount of sleep you get, but the quality.

To get the best zzz's, make time in the morning for a 30- to 45-minute run five times per week. Exercise too vigorously or too close to bedtime, and it could actually have the opposite effect, says Tamir—since exercise also produces adrenaline, hitting the gym right before you hit the mattress may leave you lying wide awake.

Time at the Gym Per Week: 2.5 hours
All those squats are doing more than just building you a butt like Beyoncé's—they're also helping you stay sharp. According to researchers at Stanford, exercise immediately boosts your cognitive skills. Researchers have also found that regular exercise, especially between the ages of 25 and 45, decreases your risk of dementia and Alzheimer's. Say hello to a stronger brain! Thirty minutes of high intensity exercise a day should be enough to help you stay sharp.