There’s tons of advice out there about how to lose weight, but what if you want to gain it? Anyone with a persistently scrawny build understands the struggle of trying to pack on pounds—especially pounds of bod-shaping muscle.

Just like losing weight, putting on the pounds has a lot to do with genetics—but with the right diet and exercise plan, you can forge that mystic muscle! Spoiler alert: You’re going to be spending a lot of time picking heavy things up and even more time chowing down. If you’re game, read on for some expert-backed body-building strategy.

The Gym

Putting on weight requires a very specific approach to exercise—and it can be tricky. You don’t want to end up actually losing weight when you ramp up your routine, says Brian Neale, C.S.C.S., performance coach and owner of Brian Neale Personal Coaching in Westchester, New York. And that’s even more likely to happen if you haven’t been exercising regularly for a while, he says.

The solution? “The best way to ensure you don’t create an inverse effect is to limit your cardio,” he says. (What you eat plays a big role, too—but we’ll get into that a little later.)

But why nix cardio? Cardio and metabolic conditioning-style exercise is considered a catabolic process, meaning it breaks down tissues in the body, says Neale. While it’s effective for breaking down fat, it often takes some muscle with it. Instead, you want to focus on lifting weights, which is considered an anabolic exercise and helps build tissues in the body, he says.

Find The Rep/Set Sweet Spot

You know you’re safe from endless bouts on the treadmill, but that doesn’t mean you should just start throwing around the heaviest weights in the gym. “There’s a very small window in which to maximize how much muscle size you build,” according to Neale. That means finding the perfect balance of weight and reps.

Lifting weight that’s too light or performing too many reps can put your body right into that cardio state you want to avoid, he explains. On the other hand, lifting weight that’s too heavy and performing too few reps might help you build strength, but not necessarily size.

Related: 6 Ways Building Muscle Benefits Your Health And Well-Being

The muscle-building sweet spot, according to Neale: Find a weight you can lift for 12 reps with good form, but that requires a seven-out-of-10 effort for the last couple of reps.

This moderate rep range allows your muscles to adapt maximally for size (instead of for endurance or strength) by triggering a hormone response that promotes muscle fiber growth. Neale recommends performing two to three sets of each exercise when you’re first starting out, and then progressing to four sets as you ramp up after a month or so of training.

Now, you may think that if four sets is good, eight sets is even better, right? But that’s where you can get in trouble, according to Neale. “When you work your body too intensely, you won’t have enough time to recover between workouts, which can ultimately hinder your performance in the gym and slow your progress,” he says.

To prevent your routine from getting stale, though, Neale recommends adjusting your reps from week to week. Try the following structure:

Week 1: 2-3 sets of 12 reps of each exercise
Week 2: 2-3 sets of 10 reps of each exercise
Week 3: 2-3 sets of 12 reps of each exercise
Week 4: 2-3 sets of 8 reps of each exercise

“Remember, you always want to keep your exertion level at a seven out of 10,” says Neale. So when you decrease your reps, up your weight slightly to maintain that level of intensity, he says.

Repeat this four-week cycle three times, for a total of 12 weeks. After those 12 weeks, you’ll focus purely on strength for four weeks. That means dropping your rep ranges down super low—like two-to-five reps total per set. (We’ve already got that strength-building plan ready for you, here.)

These four weeks will help you increase the weight you can lift in that eight-to-12 rep range. Then, you’ll restart the 12-week muscle-building cycle, using heavier weights and renewing the optimal stress put on your muscles to maximize growth.

Neale recommends hitting the gym no more than four to five times per week. “In some cases less is more,” he says, “in order for your muscles to grow, they need time to recover and repair between tough workouts.”

Use The Right Moves

That also means you shouldn’t be hammering the same muscle groups workout after workout. Neale recommends breaking up your training sessions by movement type instead of muscle group. Why? “You want to perform exercises that work more than one muscle group at a time, so you build muscle efficiently,” he says. So instead of focusing on hitting just your shoulders, pick upper-body exercises—like the overhead press, for example—that will hit your shoulders, upper back, and core.

Here’s what your weekly breakdown might look like:

Day 1: 2 upper-body horizontal push exercises (like bench press and pushups)
Day 2: 2 upper-body vertical push exercises (like overhead press and dips)
Day 3: 2 upper-body horizontal pull exercises (like barbell or dumbbell rows)
Day 4: 2 upper-body vertical pull exercises (like cable pulldowns or pullups)
Day 5: 3 lower-body exercises (like squats, deadlifts, and lunges)

Nutrition

Just as important as your work in the gym is how you fuel your body for building muscle. What you eat, when you eat, and how much you eat all come into play.

“While genetics play a role in how much muscle you gain and how quickly you gain it, the biggest impediment for most people is an insufficient intake of calories,” according to Mike Israetel, Ph.D., sports physiologist and co-founder of Renaissance Periodization.

How Much To Eat

If you’re working on a muscle-building program, you should be chowing down on enough grub to gain about a half-pound to a pound of weight each week, according to Israetel. No fancy calculator needed—just get on the scale! “If the number is going up week to week, you’re eating enough,” he says, “If it’s not, you need to take in more calories.”

Think of it like you do your money: If you make more than you spend, you start to build savings, while if you spend more than you make, you start to go into debt. So, if you consume more calories than you burn, you store the extra, while if you burn more than you consume, your body blows through those calories for fuel. Too few calories means muscles that are too starved to grow.

What To Eat

While eating enough is the most important part, what you eat plays a role too. Your muscles are made of protein, so one of the best ways to insure they grow is to add more protein to your diet. Most people should eat about one gram of protein per pound of bodyweight in order to gain muscle, suggests Israetel. You can bump your intake even higher, but all the protein in the world won’t do much good unless your total calorie-intake is high enough, he says

Related: How Much Protein Do You Really Need?

That’s where the other two macronutrients come into play. Carbs and fats will help you reach that higher calorie intake, says Israetel. Carbs have gotten a bad rap from recent fat-loss fads, but they’re crucial for your muscle recovery after a workout. Israetel recommends at least two grams of carbs per pound of bodyweight for hard-gainers. If you’re still not putting on weight with two grams, bump it up to three, he says.

If you’re finding it difficult to eat enough calories to put on weight (eating a lot more than you’re used to is harder than it sounds!) fats come to the rescue. Since fats contain nine calories per gram—carbs and protein contain four—adding some extra fat to your diet can really boost your caloric intake. So go ahead and smear an extra tablespoon or two of peanut butter on that toast.

When To Eat

If you’re really trying to pack on pounds, it’s incredibly unlikely that you’ll be able to consume as much food as you need to in only a few sittings per day, suggests Israetel. Eating four or five meals a day will make your big eating a little easier.

These don’t have to all be full-on dinner-type meals, Israetel says. Some might be as simple as a protein shake. The key is eating regularly throughout the day. “For individuals with a fast metabolism and a small appetite, getting enough food regularly to gain muscle is the toughest part,” he says.

Instead of focusing on specific times to eat—like immediately post-workout, for example—just try to spread your meals out evenly from when you wake up to when you go to bed. That’s a meal every three-to-four hours if you’re getting a good eight hours of sleep. And remember: protein, protein, protein!