If you want to build more muscle:
There's a popular gym notion that doing 8 to 12 reps is the best way to build muscle. However, the origin of this recommendation might surprise you: It's from an English surgeon and competitive bodybuilder named Dr. Ian MacQueen, who published a scientific paper in which he recommended a moderately high number of reps for muscle growth. The year? 1954. Now this approach most certainly works. But we've learned a lot about muscle science in the last half-century. And it makes more sense that using a variety of repetition ranges—low, medium and high—will lead to even better muscle growth. For the best results, you can switch up your rep ranges every two to four weeks, or even every workout.

I like this simple, three-day-a-week, total body scheme I learned from strength coach Alwyn Cosgrove, C.S.C.S., a longtime fitness adviser to Men's Health:
  • Monday: 5 reps
  • Wednesday: 15 reps
  • Friday: 10 reps
And after all, this approach is supported by 21st-century science. Case in point: Arizona State University researchers discovered that people who alternated their repetition ranges in each of three weekly training sessions—;a technique called "undulating periodization"—gained twice as much strength as those who performed the same number of repetitions every workout.

How much weight should I use?
This question pops up a lot in my email. Now, I used to reply: "How should I know? I can't tell how strong you are over the Internet!" But I've come up with a much better answer: Choose the heaviest weight that allows you to complete all of the prescribed repetitions. That is, the lower the repetitions, the heavier the weight you should use. And vice versa. For instance, if you can lift a weight 15 times, it's not going to do your muscles much good to lift it only five times. And if you select a weight that's difficult to lift five times, there's no way you can pump out 15 repetitions.

So how do you figure out the right amount? Trial and error. You just have to make an educated guess and experiment. This is second nature for experienced lifters, but if you're new to training, don't stress over it; you'll catch on fast. The key is to get in there and start lifting. If you choose a weight that's too heavy or too light, just adjust it accordingly in your next set.

Of course, you'll realize pretty quickly if you're using a weight that's too heavy for your rep range. After all, you won't be able to complete all the reps. But gauging if a weight is too light is a little trickier. One simple way: Note the point at which you "start to struggle."

Let's say you're doing 10 repetitions. If all 10 seem easy, then the weight you're using is too light. However, if you start to struggle on your 10th repetition, you've chosen the correct poundage. What does "start to struggle" mean? It's when the speed at which you lift the weight slows significantly. Although you can push on for another rep or two, the struggle indicates that your muscles have just about had it. This is also the point when most people start to "cheat" by changing their body posture to help them lift the weight.

Remember, the idea to complete all the repetitions in each set with perfect form, while challenging your muscles to work as hard as they can. Using the "start-to-struggle" approach will help you do this. Go hard, and when you start to struggle, you've completed the set. This is also a great strategy to use when you're directed to do as many repetitions as possible on bodyweight exercises such as push-ups, chin-ups and hip raises.

How long should my workout last?