Yes, there's a difference and yes, you need both.
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By now, you know that strength training is important. Yes, it gives you sleek muscles, but research shows that regularly lifting weights has a bunch of health benefits that go way beyond aesthetics. Thankfully, more group fitness classes than ever are incorporating weights into their routines. Even cardio-focused classes don't shy away from giving clients a little extra oomph-but when you lift 3- to 8-pound weights on a spin bike for five or so minutes, you're training your muscles very differently than when you're busting out a single super-heavy bench press.

That doesn't mean one type of training is better than the other, and it certainly doesn't mean you should stick to one training style all the time. In fact, that would be detrimental to your progress, as you need both muscular endurance and strength in your day-to-day life. But what, exactly, is the difference between the two?

Examples: "Sitting up with good posture, or walking home on your commute with good stamina is a test of muscular endurance," says Corinne Croce, D.P.T., SoulCycle's in-house physical therapist (who helped design the programming behind the brand's new class, SoulActivate). Strength, on the other hand, is called on when you need to lift a heavy box, put a suitcase in the overhead bin, or carry a child without getting injured, says Darius Stankiewicz, C.S.C.S., SoulCycle's in-house strength coach.

Your best course of action: Incorporate both into your weekly routine. But in order to do that, you need to truly understand the difference between muscular endurance and strength. We'll explain.

What is muscular endurance?

When you head to, say, a spin class, there's usually an upper-body segment incorporated. It's typically near the end of class, and it lasts about five minutes. During that time, you rotate between various exercises-biceps curls, overhead presses, and triceps extensions-without rest for what often feels like forever. That, in a nutshell, is building muscular endurance, which is "the ability for the body to work for an extended amount of time," says Dyan Tsiumis, C.P.T., head instructor at SWERVE Fitness. The longer you can perform that action-whether it's continuous biceps curls, riding a bike, or running-the more muscular endurance you have.

And while you often use the same muscle groups when building both strength and endurance, depending on the action, different muscle fibers are recruited: "Slow-twitch muscle fibers (type 1) are responsible for endurance, and fast-twitch fibers (type 2) are responsible for strength and power," says Stankiewicz. When you do endurance activities that train slow-twitch fibers, you improve the ability of your muscles to use oxygen-which helps you perform longer before feeling tired.

Why do I need muscular endurance?

Whether it's a day-to-day life activity-like when you're playing with your kids and doing chores around the house-or you're in the midst of a workout, your body needs muscular endurance. When you have a lot of it, "fatigue will not set in as fast and you will be able to withstand more while using less energy," says Croce. Think of it like running, suggests Tsiumis. "Muscular strength is a sprint, and muscular endurance is a marathon," she says. The more endurance you have, the harder you'll be able to go for a longer distance.

How can I improve muscular endurance?

Cardio training is typically the go-to method, but lifting lighter weights for a higher number of reps can also boost endurance. Be it a barre class, climbing stairs, or swimming, choose something that challenges you and keeps you interested.

Just don't expect this type of training to make your muscles visibly bigger, explains Tsiumis. "There is little to no increase in the size or strength of the individual muscles themselves," she says. "Slowly, over time though (in typical studies, about 12 weeks), there is increased strength in individual muscles and a thickening of the muscles that occurs." So rather than focus on how you look, tune in to how your body feels. If you're able to run, say, a 10K (6.2 miles) in the amount of time it would normally take you to cover six miles, your endurance is headed in the right direction.

What is muscular strength?

While endurance is all about how long a muscle can perform, muscular strength is how hard it can perform. Or, in more scientific terms, it's "a measure of the greatest amount of force that muscles produce during a single maximal effort," says Michael Piermarini, M.S., director of fitness at Orangetheory Fitness. One of the most common ways to test muscular strength is the one-rep max: lifting as much weight as you possibly can during a given exercise (the chest press and deadlift are popular choices) for one rep, and one rep only.

If you're ever confused about whether you're working on strength or endurance, think about the amount of weight you're lifting and how many reps you're performing, as the relationship is inversely related, suggests Piermarini. Going for lighter weights and a bunch of reps (somewhere in the 15 to 20 range)? That's endurance. Lifting heavier weight and only a few reps (around 5 to 8)? That's strength.

Why do I need muscular strength?

For so, so many reasons. Research shows it can counter bone loss and fight osteoporosis, prevent injury, and maybe even decrease your risk of cancer. Plus, "the more muscles you have, the more calories your body burns at rest and over the course of a day," says Piermarini. (Here's more on the science of building muscle and burning fat.) Burning more calories with zero extra effort? Yes, please.

How can I improve muscular strength?

Don't shy away from the heavier side of the weight rack, plain and simple. Experts have said time and time again that women do not have high enough testosterone levels to "get bulky," so you can throw that excuse out the window.

To get the most bang for your (dumb)bell, Piermarini suggests focusing on functional movements that utilize your entire body. "Functional exercises are those that we, as human beings, perform regularly in our daily lives," he says. These are movements you perform all day (sometimes without even thinking about it) like squatting, lunging, pushing, pulling, rotating, and hinging. Exercises that translate well include squats, reverse and side lunges, push-ups, bench presses, Russian twists, and deadlifts, he says. "They'll all help make daily activities easier by improving strength, coordination, and balance."

While you're training, "don't get caught up in the mindset that more is always better," he warns. "Instead, focus on the quality of movement. A strength session could be done in anywhere from 15 to 45 minutes." Need some suggestions? Get started with this heavy kettlebell routine or this total-body strength and conditioning workout.

How often should I work on both?

Really, it depends on your goals and where your weaknesses lie. "We are often more adapted genetically to one versus another," says Stankiewicz, so if you're simply looking to feel more balanced, then adjust your schedule to favor your weak link. In general, though, three sessions a week for both is the standard recommendation, or two if you're new to training.