A guide to the free fitness app sports scientists just called the best

If you choose the five-minute workout, the app will select a series of cardio and strength exercises and have you do them for 30 seconds each.

While five minutes isn't a lot, it's enough for a quick morning wake-up routine at least. Even a small amount of exercise can have a huge impact on your life, especially if you keep your intensity level high.

The five-minute workout is also a good warm-up option before a yoga session.

If you opt for the strength routine, you can choose what type of workout you want.

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

It's easy and well-defined enough that you can make yourself do it, even if you are just relaxing around the apartment.

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.

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 though, 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 Sworkit's 30-minute workout sessions are a strength of the app, with enough intensity and activity for a good session.

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. While the exercises are randomized, there are a number of different varieties of push-ups, planks, and and squats that you'll regularly encounter.

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

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 review says 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 main menu, you can see your recent progress, connect the app to Apple's Health app to track workouts, or upgrade to Sworkit Pro.

There's also some sort of rewards program connected to the app, but I've mostly ignored that.

The Pro version of Sworkit costs $3.99 and allows users to save an unlimited number of custom workouts instead of just keeping three at a time. It also adds a few bonus workouts and interval features, and allows you to store your full workout history for longer than a month — though you can store workout history longer for free by importing that information to Apple's Health app or to MyFitnessPal. It also removes the ads that appear at the bottom of the screen at times, though I've only accidentally clicked on these once or twice.

The analysis based on ACSM guidelines didn't review paid apps, since their goal was to analyze options accessible to anyone.

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.

Or you can select a pre-built custom workout if you want some variety.

You can select "low impact," for example, if you think your downstairs neighbors don't appreciate the jumping jacks and burpees.

Keeping just three custom workouts at a time for free isn't bad, especially if you make use of the many pre-designed workouts.

The app also offers a variety of different cardio routines, which work similarly to the strength workouts — 30 seconds, with a break after each set of five exercises.

While this isn't specifically designed to function as a high-intensity interval training program, you could treat it that way — or create a custom workout with that specifically in mind.

There are stretching routines that function as warmups and others for your whole body. The yoga section includes a few different sequences, including a sun salutation, full sequence, yoga for runners, and a pilates workout.

I'll provide the caveat here that learning the proper position for yoga poses is important, and 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.

I haven't explored this section of the app as thoroughly, but the yoga workouts that I've tried through the app have been on the more mellow side — they felt good but didn't push as hard as some of the strength-training drills.

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

In their review, the American College of Sports Medicine noted that the vast majority of fitness apps don't come close to fitting their recommended guidelines.

Sworkit scored best, with a 9.01 out of 14, (the aerobic and resistance categories were worth six points each, the flexibility category was worth two), with the score based on how well the app follows evidence-based guidelines for criteria including safety, intensity, and frequency.

Sworkit scored highly by providing a good number and variety of workouts that covered those three main components of fitness, but lost points for not including a training program to help beginners get started safely. Because of that, even as the best-rated app by the ACSM, they write that Sworkit still didn't fit guidelines well enough to be used as an exercise prescription (there's no free app that does).

There's still clearly room for improvement — a beginner trying to get fit for the first time might want to go over safety information with a trainer.

Still, I've found that having a well-defined routine with some variety that you can do at home is invaluable. It's a useful part of a fitness plan, even if it shouldn't be the whole plan.