As a gym veteran, I frequently receive two types of questions from beginners. The question that does not relate to what protein powder they should choose focuses on a very different matter: How much weight should they be lifting on a given exercise?

It's a perfectly good question, and there's no simple answer. In fact, a number of variables are in play here, so let's go through them one at a time. Doing so will allow you to customize your training program to ensure you're using the right weight every time.

You can pick up a 20-pound bar, curl it 75 times, and, after a while, you'll become fatigued and your arms will get pumped. You'll certainly be sweating a lot. Conversely, you can pick up an 85-pound bar, curl it 8 times, then have to drop it because you can't do any more reps. In both cases, you trained "hard." But is one approach better than another?

It may surprise you to learn that the answer changes depending on your goal. If you're looking to get as strong as possible, you'll be using a heavier weight than someone who is trying to get as big as possible. And to improve muscular endurance, you'll use an even lighter weight.

• Strength training means choosing weights that allow you to train in a rep range of 1-6.
• Building muscle mean choosing weights that allow you to train in a rep range of 8-12.
• Focusing on muscular endurance means choosing weights that allow you to train for at least 15 reps.

Let's take a closer look at the three training protocols.

1. Training For Strength

The biggest, strongest men and women—powerlifters, Olympic lifters, Strongmen—have one thing on their minds: getting stronger. To lift heavy objects in competition means they have to likewise lift heavy objects in practice. That means, basically, lifting really, really heavy.

Focusing on strength requires doing multijoint movements like bench presses, squats, and deadlifts. Here, more than a single set of joints are working at once, such as the shoulder and elbow joints working together on a bench press. This multijoint action recruits more total muscle mass, thus allowing you to lift heavier weights.

The actual muscle fibers being recruited during very heavy sets are called fast-twitch muscle fibers; they're the ones that are more prone to growing bigger and stronger in response to resistance training as well. However, they run out of steam fairly quickly, which is why you can't lift a very heavy weight very many times.

Rest periods between sets for main lifts are fairly long (3-5 minutes) so that incomplete recovery doesn't inhibit succeeding sets. Of course, lifting heavy means warming up well beforehand, so a number of progressively heavier warm-up sets precede the maximal weights. Strength trainers also avoid taking sets to muscle failure, a technique used primarily by bodybuilders.

For a great introductory piece on strength training, read "Your First Strength Phase: A Beginner's Guide to Getting Strong," by Todd Bumgardner.

Here’s an example of a strength-building workout:

2. Training For Muscle Size

While those who train for maximizing strength do in fact get big, their methods may not be the most effective for maximally increasing muscle size (hypertrophy). Bodybuilders and gym rats who aim to increase the size of their muscles take a slightly different approach to determining how much weight they use. Here, choosing a weight in which they can do 8-12 reps has been shown to maximize muscle gains.

But there are a couple of caveats with that statement, so let's address those first.

• You must use good form. You've probably seen YouTube videos of guys bouncing the bar off their chest when benching because the weight is so heavy that they need to generate a little extra momentum to get it going. That doesn't count as good form. Each exercise has its own "good form checklist." Generally speaking, you have to control the weight, and only designated joints are supposed to be working. If it takes hip or knee action to curl a barbell, you're using joints that should not be involved. There's a name for it—cheating—and it violates the good form mantra.

• Perform a "true" set of 8-12 reps. Of course, you can just put a light weight on the bar and stop at 12 reps, but that's not a true set. A true set means that you're very near muscle failure—the point at which you can't do another rep on your own with good form. If you can do a 13th rep, the weight you used was too light. Similarly, if you can do only 4-5 reps, the weight is too heavy for maximum muscle-building. The sweet spot lies in choosing a weight in which you can just do 8-12 reps on your own.

Bodybuilders also train the fast-twitch muscle fibers, usually starting with multijoint movements sorted by body part. Here the recipe calls for higher volume (3-4 working sets of multiple exercises at different angles) and shorter rest periods (60 seconds for smaller muscle groups and up to 90 seconds for larger ones).

For more detail on how to maximize your size gains, check out the 8-Week Fast Track to Intermediate workout.

Here’s an example of a strength-building workout:

3. Training For Muscle Endurance

Not everyone trains to get as big or as strong as possible. You can also train at a lower level of intensity—that is, the weight you use relative to what you can maximally lift for one rep. This builds up the mechanisms within the muscle that make it more aerobically efficient, without increasing the size of the muscle. Hence, the muscle can do lots of reps for long periods of time without fatiguing. The classic marathon runner's musculature is designed to take him or her the distance.

Focusing on muscle endurance means choosing very light weights that can be done for 15-20 reps or more. The weight stimulus just isn't strong enough to maximize size or strength. That's because the muscles are engaging the slow-twitch rather than the fast-twitch fibers. These fibers are designed to be used for longer activities and don't typically grow significantly in size compared to the fast-twitch variety.

Here’s an example of a strength-building workout:

The Weight/Reps Relationship

If you know what your goal is, it's not difficult to figure out how much weight you should be using on a given exercise. What you see is an inverse relationship between the number of reps you can do and the amount of weight. When the weight goes up, you can complete fewer reps. With a lighter weight, you can do more reps.

For instance, if your max weight on the bench press is 225 pounds, the number of reps you can do with each weight increment might look something like this:

• 145 lbs, 12 reps
• 155 lbs, 11 reps
• 165 lbs, 10 reps
• 175 lbs, 9 reps
• 185 reps, 7 reps
• 195 lbs, 5-6 reps
• 205 lbs, 4 reps
• 215 lbs, 2 reps
• 225 lbs, 1 rep

Since a strength curve like this is unique to each individual for each exercise, you could prescribe a training protocol based on it. If this was your curve for the bench press, to focus on strength you'd train with poundages above 195; for size you'd train with about 145-185; and for muscular endurance you'd be using weights below the lower limit of this chart, around 120 pounds.

Everyone has their own strength curve for every exercise. You'll become familiar with your own through practice and repetition. The key is to make sure you use a weight that best corresponds with your goals. If you always start each exercise with a practice set, you can always rack the weight short of muscle failure and call it a warm-up if you don't think you're within the target rep range. Adjust the weight on your next set as necessary. Of course, logging your weights in a notebook, on your smartphone, or on BodySpace reduces the guesswork next time around.

Fine-Tuning Your Weights

The difficult part is behind you, but that doesn't mean an experienced lifter can't fine-tune the working weights. Here are a couple of tips to keep in mind.

1. Build in progressively heavier warm-ups

Some consider warm-ups a waste of time, but they actually enable you to lift more weight. Your tissue is more elastic, and you've practiced the motion before tackling the heavier weights. It's important to note that even though a bodybuilder trains to muscle failure, warm-up sets are never taken to failure. Stop all lighter-weight sets well short of muscle failure. For a bodybuilder who wants to bench with a working weight of 225 pounds, so that they fall within that 8-12-rep range, warm-up weights might start with 135, 185, and 205 pounds.

2. Go heavy earlier in your workout

Because your energy starts to sag over the course of a hard workout, choose the most difficult exercises early in your training session, when you're fresh. You can even train in the lower range of the hypertrophy zone, choosing a weight in which you can do just 8 reps. Over the course of your body-part workout, train with different relative intensities so that you're also including sets of 10 (near failure) and 12 later on as well. Warm-ups excluded, start your exercises in the lower rep range and keep your sets of 12 for later in your workout.

3. Be mindful of progressive overload

Muscles adapt to training by growing bigger and stronger. Strength trainers and bodybuilders know that the most adaptation occurs within their fast-twitch muscle fibers. In graphical terms, your strength curve has shifted outward, and you can now do more reps with any given weight.

How do you know when to go up in weight? Try this method: When you can do 2 more reps with a given weight than you started out with, for two consecutive workouts, increase your weight. So if you started on the bench press with 8 reps of 225 pounds, but can now do 10 reps, and you've been able to achieve 10 reps for two workouts in a row, increase the weight.

• For upper-body exercises like the bench press, increase the weight by approximately 5 percent. So instead of using 225 pounds, use 235.
• For lower-body exercises like the squat, increase the weight by approximately 10 percent. So instead of using 225 pounds, use 245.

Let's say you make gains in size and strength. To continue making more gains, you must increase the challenge to your muscles by once again increasing the resistance. As you can see, you must progressively increase the overload over time or you'll simply stall. Complacency is your biggest enemy no matter what your goal, so pushing yourself to do more reps or use a slightly heavier weight can help you continue making progress.

Even the most dedicated lifter hits a training plateau sooner or later. Advanced techniques in which you manipulate weight can further spur gains in size and strength, but should be done in a specific, intentional manner rather than randomly. Study various techniques that allow you to cycle your training over time.

You'll soon learn that the bigger and stronger you get, the less you'll see "accidental" results, and the more you'll have to plan your training. Seems counterintuitive, but you'll find you make greater gains the more you know.