The traditional push-up is generally considered a chest exercise, not one that you would focus on to increase your arm muscles. However, push-ups do target the triceps brachii, located on the back of the arm, as well as the coracobrachialis, a small muscle on the front of the arm. Therefore, a standard push-up can increase strength in these muscles. When you combine push-ups and additional upper-body exercises, you can increase the size of your arms.
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Read More: Proper Push-Up Technique
Targeting the Triceps
The triceps brachii assist in extending the arm outward during a push-up, and just happen to be the most exerted muscle during the move. However, if you want to focus on this muscle even more, modify your push-up to a narrow-grip version. A small study published in 2005 in the Journal of Strength and Conditioning found that muscle activation during a narrow-grip push-up for both the triceps and the pectoralis muscles was greater than during a wide-based position.
To properly do a narrow-grip push-up, get into the standard push-up plank position. Move your hands so your thumbs and index fingers are about 2 inches apart from their companions on the other hand. Your hands will be almost in a triangle position. From there, complete a push-up by lowering your chest to the ground and pushing back up.
You can further activate your triceps during a push-up by elevating your feet on a bench or exercise ball. This requires your triceps to lift a greater percentage of your body weight, as well as creates instability that the triceps and core must manage in tandem.
Additional Arm Exercises
Push-ups don't target the biceps because it's what's known as a "pulling" muscle, while the triceps are a "pushing" muscle. You should do an equal number of a pulling and pushing exercises to balance your upper body and increase the muscles in your arms.
Biceps Curls: Use a dumbbell, resistance band or other heavy object for this exercise. Hold the dumbbell or heavy object in both hands with the palms facing outward. If you're using a resistance band, loop it under your foot and hold the ends with each hand. Slowly lift your hands toward your chest while bending your elbows. Keep your arms close to your body. Return the hands to the starting position to complete one rep.
Hammer Curls: Work your forearms, as well as your biceps with this exercise. Start in the same position as a biceps curl, but turn your wrists so your palms face inward, toward each other. Bring your hands up to your chest, bending your elbows. Keep your wrists straight, palms facing each other and arms close to your body. Return the hands to the starting position to complete one rep.
Inverted Rows: Lie on the ground underneath a bar —whether it's a Smith Machine at the gym or a steady horizontal bar at home — and grab the bar with an overhand grip, meaning your palms are facing away from you. Engage your core and, while keeping your body in a straight line, lift yourself up toward the bar. When you chest touches the bar, lower yourself back down to complete one rep.
Read More: How to Increase Arms and Chest Size Fast