From HIIT, Tabata training, and CrossFit to fast-paced group fitness classes and even, uh, high-intensity yoga, incredibly demanding workouts that leave participants in a sweaty heap are popular and don't seem to be going away anytime soon. But should every workout leave you gasping for breath and jonesing for naptime? The answer depends on what your body can handle and your personal fitness goals.

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Intermittent bursts of maximal effort during any exercise—say, three to five 30-second sprints peppered throughout a leisurely, half-hour elliptical, StairMaster, or treadmill session—can boost strength, endurance, and fat loss compared to slower paced workouts Low-volume interval training improves muscle oxidative capacity in sedentary adults. Hood M.S., Little J.P., Tarnopolsky M.A., et al. Medicine and Science in Sports and Exercise. 2011 Oct;43(10):1849-56.. Such explosions of power (see also: jump squats or burpees) also greatly improve insulin sensitivity, which means better digestion, improved absorption of nutrients, and the ability to maintain stable blood sugar levels (which prevents weight gain) Acute high-intensity interval exercise reduces the postprandial glucose response and prevalence of hyperglycaemia in patients with type 2 diabetes. Gillen J.B., Little J.P., Punthakee, Z., et al. Diabetes, Obesity & Metabolism. 2012 June;14(16):575-7.. Best of all, high-intensity training fits nicely into most busy schedules, as workouts can often be accomplished in 30 minutes or (way) less! There’s a huge difference, however, between adding a few minutes of all-out exertion to your weekly regimen and feeling destroyed after every gym session.

“Many gym-goers falsely equate getting crushed by a workout with getting more benefit,” says physical therapist and Greatist Expert Eugene “Bo” Babenko, DPT. “But there’s far more to fitness than feeling the burn.”

This Is Your Body on Beast Mode

Every time we work out, we break down our muscles and challenge our heart and lungs. With adequate rest and refueling, our heart, lungs, and muscles repair themselves and grow stronger. This is, in a nutshell, what “getting fit” means: What initially wiped us out becomes increasingly easier to bounce back from as our bodies adapt.

“Walking away from a training session without feeling sore doesn’t mean you didn’t get anything done,” Babenko says. “A lot of progress is being made neurologically—the brain is also adapting to your routine.” And even if that routine no longer feels challenging, “your body’s still benefitting from moving through a full range of motion.”

While periodically dialing up the intensity of our workouts ensures we make ongoing progress, days of less strenuous exercise (where our exertion levels remain below 50 percent of our maximum heart rate) are equally crucial to our health—and to our happiness. Lower-intensity workouts still burn calories, get our blood flowing, bolster our endurance, and produce enough endorphins to leave us with a comfortable exercise high. Being active for longer periods of time at lower intensities throughout the day may in fact be better for our heart health, longevity, and metabolism than isolated bouts of 30 to 60 minutes of maximal effort exercise—especially if, outside the gym, our lives are predominately sedentary Too Much Sitting: The Population-Health Science of Sedentary Behavior. Neville Owen, Geneviève N Healy, et al. Exercise Sports Science Review. Jul 2010; 38(3): 105–113..

No Pain, No Gain? No Dice

Pacing ourselves is particularly important if we’re recovering from an injury, we haven’t been sleeping well, or we’re awash in stress. “Clients come to me exhausted and over-pressured from work, or overstimulated from living in a 24/7 world,” says Manhattan-based holistic trainer and Greatist Expert Jonathan Angelilli, founder of TrainDeep™-Exercise Alchemy. “They want to be pushed hard through a difficult workout but that’s often the last thing their bodies need.”

Heavy workouts atop a schedule jam-packed with chronic stress can easily lead to overtraining—a condition characterized by fatigue, irritability, excessive thirst, impaired sleep, and difficulty focusing or thinking clearly. “It’s amazing how many people become desensitized to the classic signs of overtraining and perpetually live in this state,” Angelilli says.

Even if your home and work life are relatively chill, going full force with every workout (especially if you exercise most days of the week) isn’t advisable. “Workouts that leave you breathless take longer to recover from,” Babenko says. “There needs to be adequate recovery from the damage being done to the body. Proper sleep, hydration, and mobilization all need to be factored in with a smart program design as well.”

Slowing down doesn’t mean less progress, it means building a baseline of what works for your body so you’re not at a disadvantage later on.

If you want to stay fit for life, certified personal trainer and Greatist Expert Jessi Kneeland, founder of Remodel Fitness, says you’re going to have to find workouts you enjoy. Sure, dropping a few sizes in time for that big event might galvanize you to hit the gym several times a week. But you’re more likely to quit when what’s keeping you going is superficial, or short-term.

To build a fitness routine you can stick to, Kneeland advises revisiting the basics. “Too many people jump into working out as hard as they can only to get injured and lose motivation. Slowing down doesn’t mean less progress, it means building a baseline of what works for your body so you’re not at a disadvantage later on.”

For exercisers who view “off days” with dread, trainer, registered dietician, and Greatist Expert Erica Giovinazzo recommends active recovery exercises designed to regenerate the body rather than break it down further. A 30-minute session on a bike, elliptical, or rowing machine at a pace easy enough that allows you to hold a conversation should do the trick. Leisurely walks or a gentle yoga class can also help move your body through a full range of motion without impeding recovery.

So how much high-intensity training should one do each week? The answer, like most things health-related, depends entirely on your fitness levels, your goals, and what else is going on in your life before and after any given workout. Trust your body to tell you when you’re overdoing it, as well as when you’re ready for a new physical challenge. Add high-intensity exercise to your weekly routine slowly, building up to harder workouts or multiple sessions.

The Takeaway

Yes, high-intensity training can boost heart, muscle, and bone health better than prolonged, moderate bouts cardiovascular activity, but not every single one of your workouts needs to be as intense as the next. Nor should they always crush you—especially if you get your fitness on frequently. (Remember, it’s better to be intermittently active throughout the day.) The body needs time to recover, so don’t be shy about opting for easier days when you’re feeling tired or stressed. By all means take on fitness challenges as you feel ready, but don’t push yourself if you’re not feelin’ it—you'll risk getting injured or start dreading the gym.

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