The 8 most effective workouts if you have only 20 minutes

• Short, intense workouts can be just as effective as longer, moderate workouts.
• That means that even if you live a busy life, you don't need to give up on the idea of being in shape.
• Use a few short workouts throughout the week to meet fitness goals — and build some moderate activity into your day too.

The hardest part of working out can be finding the time to do it in the first place.

The Centers for Disease Control and Prevention recommend that US adults get at least 2 hours and 30 minutes of moderate intensity aerobic exercise each week (or 75 minutes of vigorous intensity exercise) and that people do muscle-strengthening activities — like lifting weights or body-weight exercises — at least twice a week.

If you spend a lot of time sitting, you may need even more exercise than that.

Between busy workdays, social lives, and family demands, it can feel impossible to fit a gym routine into your day. But if you approach it the right, it's possible to meet fitness recommendations without taking up too much of your limited free time.

There are a number of studies showing that shorter, high-intensity workouts can offer the same benefits as longer, moderate exercise sessions. In many cases, those shorter workouts can actually be more effective in improving athletic performance than a long, slow jog.

Many of these routines include muscle-strengthening elements, helping you cover your bases while still getting in an aerobic workout.

Here's how to get into shape if you can dedicate only 20 minutes or so at a time to working out:

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A high-intensity interval workout can accomplish as much as a longer workout, and there are a number of different ways to get it done.

"High-intensity training is kind of perfect for the busy schedule — you don't need a gym, you can do it at your home, you're looking at about a 20- to 30-minute workout,"Jason Barone, a clinical director at Professional Physical Therapy, told Business Insider.

When Barone and other trainers talk about high-intensity workouts, a number of activities qualify. The idea is you work out at close to full-on intensity for short periods instead of doing longer workouts at more moderate exertion levels. Some of these workouts include short sprints, some involve circuits of body-weight exercises, and others use weights or kettlebells.

Pick an exercise program that'll work for you, or come up with a mix of routines you can do on different days.

According to Barone, there's no one best workout, and for many people picking a few workouts may be the easiest way to stay interested enough to work out once or twice a week.

Most short workouts will be based on the ideas of high-intensity interval training, though some call more for sustained activity throughout.

High-intensity interval programs involve a warmup followed by a few cycles of intense activity with short rest breaks in between. That activity could be sprinting, swimming, cycling, or body-weight exercises.

Researchers have found that it's possible to get in a good workout in less than 10 minutes doing only one minute of all-out exertion.

In one small study published in 2016, researchers had a group of men do workouts consisting of three 20-second bursts of all-out exertion, with some warmup, cooldown, and rest in between sets. The results suggested those participants' fitness levels improved as much as those of men who worked out for 45 minutes at moderate intensity.

To try this routine, do a two- or three-minute warmup. Sprint or cycle at full intensity for 20 seconds, then take it easy for two minutes. Repeat the sprint twice more, and then cool down for a few minutes after your third sprint. That's a 10-minute workout.