Fitness apps can help people get in shape - here's how to use one of the top science-backed workout apps

The initial interface is simple and clean.

When you open up the app, you can choose whether you want to focus on strength, cardio, yoga, or stretching.

All the exercises are bodyweight-based, so you don't need additional equipment for any of the workouts. While I wouldn't use this as my only fitness option, it's a nice way to get a varied workout that can be done at home or on the road.

There are a number of custom or sport-specific workouts, though many require payment.

If you want some variation from the initial options, there are a number of other custom workouts on the home screen.

Some are targeted towards beginners, older athletes, or people with a specific fitness goal.

But many of these routines are locked behind the Sworkit Premium option, which costs $9.99 a month or $6.66 a month if you pay by the year. This option offers much more customization and the option to message trainers with questions, but is somewhat pricey.

After choosing from one of the four main categories of workout — strength, cardio, yoga, or stretching — you get to select a focused workout from within that category.

Within the "strength" category, for example, you can choose between a full body workout, an upper body workout, core workout, or lower body-focused workout.

The full body workout is a great go-to option here. While I like to go for a run, bike ride, or climb when I can, this is a nice alternative for particularly hot or freezing days.

Still, if you are going to use the app regularly, it's good to switch things up to stress different parts of your body.

You can work up a good sweat and push yourself hard enough that you get the mental clarity that's one of the best benefits of exercise.

Once you choose a workout, you'll see a list of the included exercises.

There's a large number of exercises included in each workout, and the order of those exercises will vary — it's not the exact same routine or even the same exercises every time, even within one workout.

The full-body strength workout, for example, includes 72 exercises. These range from relatively easy exercises, like wall push-ups, to more demanding exercises like mountain climbers, diamond push-ups, and of course, burpees.

After you pick a workout, you can choose how long you want to exercise for.

You can time it to match up with the length of a podcast, TV show, or album.

A show you really want to watch isn't the best option, as it's hard to follow all the on-screen action while you're doing push-ups, burpees, and whatever other activities the program throws your way.

The ACSM review notes that a 30-minute workout on the app works well, with enough intensity and activity for a good session.

You can also tweak the amount of time in between exercises.

Ten seconds before you finish each exercise, the voice of your "trainer" will tell you what you'll be transitioning to next.

It's helpful to have a small buffer to move into position for your next exercise — the default time in between is five seconds, which works well.

The premium option again has more customization. But for a casual workout intended to make sure you fit in exercise on a busy day, these aren't necessary.

Each exercise comes with an animation that shows you exactly how to perform it, which comes in handy, since proper form is essential.

In the strength section, you do each exercise for 30 seconds before transitioning to the next one.

There are a number of different varieties of push-ups, planks, and and squats that you'll regularly encounter. Animations show exactly what you should be doing, so when you hear "Spiderman push-ups," you aren't left searching for an explanation.

After five exercises (or two-and-a-half minutes), you'll get a 30-second break.

There's a good variety of exercises, some easier or harder than others.

Randomization keeps it interesting, though you'll sometimes hit a hard set, with burpees followed by diamond push-ups, or something along those lines.

The 2015 review said that the variation of exercises contained within Sworkit is a particular strength of the app. Previous research has shown that variety is important for fitness because if someone gets accustomed to a particular training routine, they are more likely to plateau and not get as many benefits from their workouts. Additionally, researchers have shown that people are more likely to stick with a varied workout routine than one that includes the same plan all the time.

However, the review also notes that some of Sworkit's exercises may be too difficult for beginners, and that some recommended activities, like plyometric jump squats, may not be safe for beginners.

From the home screen, you can select the "My Sworkit" tab to see your recent progress.

In the settings options, you can also connect the app to Apple's Health app, Strava, or MyFitnessPal to track workouts, or (of course) upgrade to Sworkit Premium.

You can also set goals, reminders, and look at breakdowns of the workouts you've been doing, for free.

You can also create and save one custom workout for free.

Unfortunately, one custom workout doesn't give you a whole lot to work with. But it can be enough for you to create one sport-specific routine and then you can use the preset workouts to hit fitness goals for the rest of the week.

The exercise list, which you can use to create a custom workout, is impressive.

There's a long list of different activities you can include in any custom workout, including segments from cardio, strength, yoga, or stretching routines.

You can filter by type of activity, exercise category, and other options. When taking a look at individual exercises in the list, you can see how they're done, which muscles they work, and even how loud they are, which can be helpful if you live in an apartment building.

Other sections of the app, like the cardio section, work similarly to the strength workouts.

To meet fitness guidelines, you should do about 30 minutes of exercise a day, with two strength days and five days of at least moderate cardio exercise — though you can get by with less, if you work out at a higher intensity.

It's pretty easy to work hard enough to use these training programs as a sort of high intensity interval training program, and there are even custom workouts set up to be used that way.

The yoga section includes a few different sequences, including a sun salutation and an everyday option.

A caveat here is that learning the proper position for yoga poses is important. An app can't correct your posture like a teacher can if you are doing something that's likely to lead to an injury — and yoga injuries can be serious.

Still, these particular routines are not incredibly demanding — they feel good but don't push as hard as some of the strength-training drills.

There's a similar variety of stretching routines.

Flexibility is an important and often neglected aspect of fitness, according to the American College of Sports Medicine.

These routines can be a solid warmup or a good option for a day you are feeling sore. They're also a nice way to get started with your morning.

While the app is a great option to have, don't make it the only part of your exercise regimen.

Through an app like Sworkit, you can get a good set of activities that will help you fit workouts into your routine, but you may not want to rely on it as your only form of exercise.

There are good reasons to do other activities too. Running comes with a huge number of health benefits, for example. The strength exercises you can do as part of a bodyweight routine like Sworkit are great, but at a certain point, to further strengthen muscles and bones, you may need more resistance, like you get from weights.

Still, I've found that having a well-defined routine with some variety that you can do at home is invaluable. And since I know it's easy to do, it makes it hard to skip a workout, even if I can't leave the apartment.

It's a useful part of a fitness plan, even if it isn't a complete plan itself.