How to Build Muscle if Your Arms Are Skinny

There's nothing wrong with having skinny arms — in fact, some people would be thrilled to have them. But if you find yourself thinking "My arms are too skinny," adding just a little bit of muscle can give them a sleek, defined shape. And if you want to build bigger muscles, you can do that, too, using the same exercises. The only thing you need to change is how you're organizing your sets and repetitions.

Skinny or not, you have two relatively large muscles that give your arms most of their shape: Your biceps brachii on the front of your arm and your triceps brachii on the back of your arm.

None of your muscles work in isolation, but each of those muscles has a motion — or motions — that they're chiefly responsible for, and knowing which muscle does what will help you choose the right exercises to work them.

• If you're flexing (bending) your arm at the elbow, your biceps is doing most of the work. It also helps with some forearm and shoulder movements.
• If you're extending (straightening) your arm at the elbow, your triceps is doing most of the work. It also helps with some shoulder movements.

People sometimes default to thinking of the biceps muscle as the only arm muscle they need to work — probably because that's the only arm muscle you see when you look straight into a mirror. But in order to build truly strong, healthy arm muscles, you need to develop balanced strength in both your biceps and your triceps.

There are literally dozens of exercises from which you can choose to work your biceps and triceps, using a variety of equipment. Don't worry about choosing exercises like a bodybuilder; whole-body strength training is important for your health, so there's no need to spend all day working just these two muscles. Instead, choose two or three exercises you enjoy for each muscle, and then work those into your regular strength-training program.

To work your biceps, you're always going to be doing some form of a curl — but you can vary your choice of resistance tool.

Move 1: Dumbbell Biceps Curls

1. Hold a dumbbell in each hand, and sit or stand so that you can let both arms hang straight beside your body, palms facing forward.
2. Stabilize your core and your upper arms as you bend each arm at the elbow, curling the weights up toward your shoulders.
3. Lower the dumbbells back to the starting position; this constitutes one repetition.

Move 2: Barbell Biceps Curls

1. Hold a barbell in both hands, palms facing up (or to put it another way, thumbs facing out). You can use a straight barbell or a curl bar (sometimes called an EZ-curl bar).
2. Stabilize your core and upper arms, as before, as you bend your arms and curl the barbell up toward your shoulders.
3. Straighten your arms, lowering the bar, to complete the repetition.

Move 3: Resistance Band Biceps Curls

1. Hold one end or handle of a resistance band in each hand, letting the length of the band dangle.
2. Use one or both feet to pin the middle of the band to the floor. Make sure the band is well and truly pinned beneath the ball of your foot/feet so it doesn't snap back at you.
3. As before, stabilize your core and upper arms as you bend your arms, curling the handles of the resistance band toward you.
4. Smoothly release the contraction, lowering the handles until your arms are straight. This completes the repetition.

As with the biceps, you can vary your choice of resistance mechanism for working your triceps. You can also vary your body position quite a bit when working this muscle.

Move 1: Overhead Triceps Extensions

1. Grasp a single dumbbell with both hands, either by the handle or by wrapping both hands around the "bell" at one end.
2. Position the dumbbell overhead — this is the starting position. If you're holding the weight by one end, the other end should hang down below your hands, not stick up above them.
3. Keep your arms close to your head, elbows pointing forward, as you bend your arms to lower the weight behind your head.
4. Straighten your arms, pressing the weight back overhead, to complete the repetition.

Move 2: Supine "Headbangers"

1. Lie face-up on a weight bench, a yoga mat, or even your bed will do. Hold a dumbbell in each hand or a single barbell in both hands with your palms facing away from you.
2. Extend both arms straight up, so the weight is above your head.
3. Work to keep your elbows stable as you bend your arms at the elbow, lowering the weight toward your forehead but slightly beyond (above) it. The weight should never actually contact your head.
4. Extend your arms, lifting the weight back to the starting position. This completes one repetition.

Move 3: Triceps Pushdowns

1. Place a rope handle, a V handle or even a straight handle on the high pulley of a cable machine.
2. Stand close to the pulley, facing it, with both hands on the handle. Your arms should be bent, elbows pointing down, with tension on the cable when you hold at the handle at about face level.
3. Squeeze your abs to stabilize your body as you straighten your arms, pressing the handle down in front of you.
4. Complete the repetition by releasing the handle back to the starting position in a smooth, controlled motion.

Read more: 10 Resistance Band Exercises to Tone and Tighten

Once you've chosen a couple of exercises that focus on the muscles in your arms, you need to put them in action. If you're new to weightlifting, doing one set of eight to 12 repetitions for each exercise is enough to start building strength. Since being skinny means you have relatively little body fat to hide the muscles you develop, you'll start seeing the fruits of your labor fairly quickly.

Your body will adapt quickly to the exercises you've chosen. If you want your muscles to keep developing, you need to continue presenting them with new challenges. One way of doing this is to simply increase the amount of weight you're lifting; getting that last repetition done with good form should always be at the limit of what you can do.

Read more: 16 Exercises From the World's Best Trainers

If you have the time and motivation, you can also increase the number of sets you lift. A meta-analysis published in the July 2016 issue of the Journal of Sports Sciences found that as your volume of strength-training sets goes up during the week, so does the size of your muscles. Just make sure that you always allow at least one full day between workout sessions for any given muscle group. So if you're doing full-body workouts, it means you should only do dedicated strength training two or three days a week.