Your upper arms and forearms comprise many muscles on the superficial and deep levels. The superficial muscles are those you can clearly see, such as your biceps -- and the deeper muscles you can't see as well are the brachialis. Possessing basic anatomical knowledge could help you better design your workout programs to work all the needed muscles to make your arms look bigger.
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Front Upper Arms
The bicep is one of the most popular muscles. This muscle is noticeable at the front of the upper arm. If you are lean enough, with a body fat percentage below 10, you may be able to see the distinct parts of the muscle. These are the inner head and the outer head of the biceps. But the biceps is not the only muscle at the front of your upper arms. There's a deeper muscle called the brachialis, which is located below the lower half of the biceps.
Looking to the Back
The lone major muscle located at the back of your upper arms is the tricep, which comprise three parts: outer, inner and long heads. If you've been exercising for a number of years, you will clearly be able to see the outer head and the long head. But the inner head is difficult to locate unless you have low body fat. Together, the three parts of the triceps make up two-thirds of your upper arm muscle mass, with the biceps and brachialis making up the other one-third.
Down to the Forearms
The muscle that is most noticeable in the forearm region is called the brachioradialis. This muscle actually begins in your lower upper arm area, but it extends down your forearm all the way to your wrist. It doesn't surpass your wrist joint, rather ending just short of it. You can feel the muscle by bending your elbows and palpating the outer region of your forearms.
Other Forearm Muscles
Dozens of other small muscles lie in your forearms. These muscles are termed the wrist flexors and wrist extensors. The flexors reside on the inside of your forearms while the extensors lie on the outer side. You can't see each individual muscle while looking at your forearms directly, but you can see their tendons. To do so, make a fist and press your fingers against your palm. The tendons will appear as long and cord-like tissues in your lower forearms. Although each individual muscle isn't large, together they all contribute significantly to forearm size.