Is It Safe to Work Out Twice in One Day?

More isn't always more when it comes to exercise.

If one workout a day is generally a good thing, two workouts a day should be even better, right? Not exactly. You've probably heard the term "two-a-days" tossed around, and maybe even been tempted to work them into your own routine in the name of accelerated fitness results. In New York City, for example, it’s not uncommon to see someone in a fitness class who has just come from another similar class, or overhear someone planning their evening workout before they’ve even cooled down from their morning one.

But whether two-a-days are safe—or even worth the extra time (and laundry)—depends on a few factors, including your fitness level, your goals, and most importantly, the type of two-a-day workout routine you've got in mind.

"Typically, two-a-days mean a cardio session and a resistance training session," exercise physiologist Jonathan Mike, Ph.D., C.S.C.S., tells SELF. Professional athletes regularly have two-a-days on their training schedules, and they’re set up so that the athlete can safely work on different parts of their physical fitness in one day.

If you’re not a professional athlete, working out twice in one day could mean fitting in two cardio sessions, two resistance training sessions, one cardio session and a hot yoga get the picture. Usually, people do one workout in the morning and one in the afternoon or evening, but they could be done back-to-back.

Not all two-a-days are created equal, though. Some of these approaches might be helpful, while other types of two-a-days may actually hinder your fitness results. Here's what you need to know about doubling your daily sweat.

Working out twice in one day increases the chances you’ll overdo it and end up injured.

When it comes to two-a-days, overtraining and injury are the biggest concerns. And keep in mind, you can still run into these issues if you're just hardcore working out above your fitness level without taking enough rest—even without implementing two-a-days, there's such a thing as too much exercise. (You should always talk with your doctor before starting a new exercise routine, especially if you are concerned about how it might impact a pre-existing health condition or injury.)

It all comes down to whether or not you're giving your body a chance to recover. "Exercise, especially high-intensity exercise, is a stressor to the body," Nathan Jenkins, Ph.D., associate professor of exercise physiology at the University of Georgia and sports nutrition consultant with Renaissance Periodization, tells SELF. In normal conditions, this stress is a good thing, because it pushes your body to adapt so that it gets better at handling the stress the next time you put it through the paces—that's pretty much what getting fitter is.

But if you don't allow your body enough time for this adaption to happen, you end up doing yourself a disservice. When you do resistance training, for example, you actually create little micro tears in the muscle fibers, and it's when they repair and rebuild that you see increases in size and strength. But if you don't give them the opportunity to recover, you're just continuing to break your muscle fibers down over and over again.

Not only will you potentially stop seeing improvements in, say, how much you can lift, but you can also end up with nagging aches, pains, and even injuries when your muscles are overworked.

Over-doing it on cardio, especially high-intensity cardio (like high-intensity interval training, or HIIT, where you're pushing yourself to your max) is also a recipe for trouble. While you may also notice muscular consequences with excessive cardio, the bigger thing to watch out for here is more systemic overtraining: When you're constantly revving up your body with too much high-intensity work, your central nervous system can get so overwhelmed that it basically starts to pump the breaks a bit on some of its duties, which results in classic symptoms of overtraining, exercise physiologist Joel Seedman, Ph.D., owner of Advanced Human Performance in Atlanta, Georgia, tells SELF.

There are a few telltale sign to be on the lookout for that suggest you may be putting too much stress on your central nervous system. "Sleep will be one of the first things that will be noticeably impacted if you start to go into overtraining. You'll notice that you're having poor quality sleep, or you're feeling like you just can't get enough sleep no matter what," says Seedman. You may also notice your moods or mental state changing, or your digestion not functioning as well as it should, he adds.

"Of all the types of two-a-days you could possibly do, [high-intensity cardio twice a day] is the one that should be avoided," says Seedman. "High-intensity cardio is pretty intense on the body, so there's a lot of recovery demands. Usually, I recommend every other day at most of high-intensity training, [or] you're just not going to be able to recover well." Many experts suggest even limiting high-intensity cardio to every three days.

While there's no one-size-fits-all limit for how much working out will lead you into overtraining, two-a-day intense cardio sessions or strength sessions that hit the same muscle groups are certainly playing with fire.

For most people, adding in a second workout isn’t always the best way to reach their health and fitness goals.

Traditionally, two-a-days have been designed for athletes and people training for challenging events or very specific performance goals—an A.M. session might be conditioning-focused, while a P.M. session might be dedicated to honing specific skills or strength training.

For most people, though, training twice a day for goals like improving overall health, building strength, or weight loss, isn't really necessary—most people don’t need to be working out that much to reach their goals. In fact, while exercise is really good for your health, its ability to facilitate weight loss is complicated and questionable at best, so keep that in mind before doubling down on exercise for weight loss reasons.

Generally, for overall health, the CDC recommends adults log at least 150 minutes a week of moderate-intensity aerobic activity (when your effort is about a 4 or 5 on a scale of 1 to 10) or 75 minutes a week of vigorous-intensity aerobic activity (about an 8 or higher on that scale of 1 to 10). And if you’re spreading that out over the week, you shouldn’t need to schedule two hour-long sessions a day to meet those suggestions.

As for building strength, for most people, three days of total-body resistance training is a great approach, Seedman says. Or, you could do four days a week and switch off between upper-body training and lower-body training. The goal is to be able to fit at least 48 hours of rest between training specific muscle groups again so they have time to recover (we’ll explain why that’s important shortly).

The truth is that working out twice a day simply isn’t realistic for many people long term. “Most individuals can't sustain this, and once they begin to miss a few workouts, mentally they feel defeated and often end up giving up,” says Seedman.

Even if you're not overtraining, you can still hit a point of diminishing returns—meaning all that extra work may be for naught.

Even if you're in good shape and are working out a "safe" amount for your body, there's likely a point where you may not see extra benefits from adding in more exercise on any given day.

"If you're doing a 45-minute, moderate- to high-intensity cycling class and then you turn around six or seven hours later and do a resistance-training session, you're likely not going to be able to exhibit the same amount of intensity in the second training session as you did on the first," says Mike. And if you can't push yourself as far the second time around, you're probably not getting the same benefits as you would if you'd gone in feeling fresh.

It's not that these second workouts are doing nothing, per se—and as long as you're still below a point of overtraining, it's definitely not worthless. But if you're pretty tuckered out, the benefits of a workout you can barely get through may not be worth the time or energy you're spending.

If you do want to make two-a-days a part of your regular routine, there are a few things you should keep in mind.

You should only do two workouts in one day when there’s a clear purpose for both. Maybe you're training for a long-distance race and you want to work in some strength training in the afternoon after you already went on a morning run. Or, maybe you have some yoga pose goals that you're inching toward at an occasional afternoon class, but you love your heart-pumping cardio sessions those same mornings.

The key is that your two workouts in one day should be different. "If you're going to make the two-a-day thing work on a consistent basis, the only way to really feasibly make it happen is doing strength in one portion of the day and cardio in the other portion," says Seedman. If you are doubling up on high-intensity cardio sessions or full-body strength training workouts five or six days a week, you may end up doing more harm than good.

Mike suggests starting with just two days a week. "It's always better to start conservative, because you can always add," he says. Space your double workout days several days apart to make sure you’re getting adequate rest in between.

You should also try to put as much time in between every workout as possible (so, back-to-back classes aren't the best plan). While there hasn't really been much research on the ideal amount of rest time to put between two-a-day workouts, "the longer the better, generally speaking, to maximize the quality of the second session," says Jenkins.

Again, most people just don’t need to be working out twice daily. If you want to add two-a-days to your routine, first think about why you’re doing it and if there might be better ways to reach your goals. (It’s not a bad idea to talk with your doctor or trainer to get their input on that.) And if you definitely want to try doubling up, just be sure to always listen to your body when it tells you it's too much.