"Active rest" sounds like a contradiction in terms. Unless you're a chronic sleepwalker, you might not be used to being active while you rest. But active rest is a technique trainers implement to maximize the benefits of a workout. Active rest takes advantage of the period between sets of exercises in which you'd typically do nothing other than rest. It not only makes the most of your workout, but it increases the efficiency, too.
Active Rest Within a Workout
If you don't over-think the term, implementing active rest into your workout is easy. You simply design your workout with exercises that function in a complementary way so you can do one right after another without having to rest in between. Organize the exercises so as you move from one exercise to the next, the exercise you're doing works muscles other than the ones you've just worked. For example, do a set of abs immediately after doing a set of pushups. The ab exercises serve as the "active" part of your rest from the pushups.
If you've ever performed intervals or super sets, you should have no problem doing an active rest workout. They're all similar in the aspect that you don't take an actual rest but continue exercising throughout your entire workout. One way to structure an active rest workout would be to do pullups until failure, immediately followed by one minute of pushups. Then do a set of crunches until failure, and then get on the stationary bike or the treadmill for one minute before starting the circuit over with pullups again, going through all exercises five times. Alternatively, you could do increasing reps of the exercises, starting out with five of each for your first set, increasing to 10, 15, 20 and finally 25. You'd also increase the amount of time you spend on the treadmill by 30 to 60 seconds with each set.
Active rest helps with muscle and cell recovery during your workout, but it helps in general, too. It's a useful way to get the most out of your workouts, help get you past plateaus and improve strength and performance. When recovering from an injury, active rest workouts can be used to work around the injured muscle while still getting an intense workout. And when you're feeling the "burn" of lactic acid from going to failure on one exercise, active rest is more effective than sedentary rest at dispersing it from your muscles, according to Matt Siaperas, a personal trainer at Hardbodies Gym in Idaho.
Active Rest as Maintenance
Sometimes active rest workouts are considered maintenance workouts, and are used to help athletes recover from intense training without taking time off from working out. In his article on active rest workouts for Stack.com, Mark Roozen, strength and conditioning coach with the Cleveland Browns, outlines three ways he uses them to give help his players "rest" and help them recover from extreme workouts. The first way is to maintain the intensity level but only perform one set of each exercise. The second way is to lower the intensity but do your usual number of sets and reps. The third way Roozen recommends using active rest as maintenance is to change the workout entirely by doing different exercises, or just by switching from free weights or other equipment to only using your body weight for resistance.