For years, fitness experts and exercise scientists have said that if you want your muscles to grow, then you must put them under tension for 40 to 70 seconds at a time.

But there’s nothing magical about 40 to 70 seconds, says Men’s Health fitness advisor Brad Schoenfeld, Ph.D., C.S.C.S. What really matters is 1) the degree of tension—which is dictated by the amount of weight you’re lifting—and 2) the total time a muscle group is under tension in any given work session. Schoenfeld says that should add up to several minutes, and that how you go about it may not matter.

For instance, Schoenfled claims that shorter 10-second work bouts with heavier weights work just as well as sets that last 40 seconds—as long as you do an appropriate number of total sets.

Let’s break that down: Traditionally, you might perform enough reps of an exercise so that you work for 40 seconds or so without stopping. That’s about the time it takes to complete 10 to 12 reps, says Schoenfeld.  Since that rep range is high, you’d most likely choose a light to moderate weight.

But when you perform only 10 seconds of work—or about 3 to 5 reps—you can obviously go significantly heavier with the weights. That extra load actually puts your muscle under greater tension, but for less time.

However, Schoenfeld says you can simply rest as long as needed after that first 10-second set, and then do several more sets the same way. The result: You achieve the same time under tension as you would when doing fewer sets of more reps.

Two very different ways to lift, and one method isn’t necessarily better than the other for building muscle size, Schoenfeld explains. However, lifting heavier loads for shorter amounts will make you stronger in the long run.

So why shouldn’t you always lift like this? It’s a lot of wear and tear on your joints. “In terms of longevity and injury prevention, lifting lighter for longer definitely is the better option,” he says.

That’s why Schoenfeld recommends combining both methods, instead of pitting one against the other. “Mixing shorter, heavy bouts with lighter, longer periods of work will allow you to reap the strength benefits, and spare your joints in the process.”

There are endless ways to do this, but Schoenfeld suggests combining them in the same circuit during your workout to maximize your strength and size gains.

Follow his example below, which alternates between heavier multi-joint lifts and lighter supplemental exercises. You’ll target the same major muscle groups back-to-back, so you can reap the maximum muscle-building benefits of both methods. Complete it 2 to 3 times a week for best results.

How to Do It
Perform the following exercises in the order shown. Do 3 sets of an exercise before moving on to the next movement on the list. Rest only as needed. (Note: Because you’re combining the methods, you’re accumulating your total time under tension for each muscle group from both.)

1.    Squat: 3 to 5 reps
2.    Leg Press: 10 to 12 reps
3.    Bench Press: 3 to 5 reps
4.    Chest Fly: 10 to 12 reps
5.    Barbell Row: 3 to 5 reps
6.    Lat Pulldown: 10 to 12 reps