I promised I would discuss the rest of the muscles in the biceps area as well as their respective actions so here it goes!!!
If you need to refresh your mind in regards to the actual biceps brachii muscle you should refer back to Curls for the Girls (Part 1). Now that you know what the biceps brachii does as well as the different ways to work it, lets move on to the other muscles in the region.
So if the biceps muscle (image 1) isn't working during a reverse curl, what muscle is? As a result of its attachment site on the forearm, the line of pull of the biceps is negated and thus, the muscle becomes virtually
inactive when during a reverse curl (image 2). However, the line of pull of the brachialis muscle (image 3-located deep to (underneath) the biceps brachii) allows it to flex the elbow when the hand/forearm is in a pronated position (image 4). In other words, when doing a reverse curl, the brachialis muscle does the majority of the work while the biceps is inactivated and thus, does not assist in the curl. However, the brachialis muscle still gets activated in other forms of curls
but is the only one activated in reverse curls. Thus, when doing a reverse curl, you are essentially isolating the brachialis.
Image 1. The biceps brachii muscle
www.breakingmuscle.com
Image 2. Reverse curl (pronated grip)
www.t-nation.com
Image 3. Brachialis muscle (located deep to the biceps muscle, which is removed in this picture)
http://medical-dictionary.thefreedictionary.com/brachialis
Image 4. Pronated grip on the far right
www.gustrength.com
Ok, so now that we have covered the biceps brachii and the brachialis, lets move on to the brachioradialis muscle. I know what you are thinking- why do all these muscles sound so similar. The reason for this is due to the terminology used in anatomy. The upper arm (humerus bone) is referred to as the brachium and thus, the muscles that surround it resemble its name (i.e. brachialis). Now that you understand the terminology for the musculuture, lets get back to the brachioradialis (BR). The "radialis" aspect refers to its distal attachment on the radius (1 of 2 bones that make up the forearm). Image 5 shows the two attachments of the muscle. Image 6 shows the BR when the muscle is flexed in. You can see this on yourself by simply bending your elbow to 90, making a tight fist in a neutral grip and pressing down on your wrist with your opposite hand (image 7).
Image 5. Brachioradialis (BR)
http://www.teachpe.com/anatomy/muscles/brachioradialis.php
Image 6. Brachioradialis (BR)-the view of this picture is as if you were looking down at your own right arm while sitting in a chair. The subject has his elbow flexed at 90 degrees and is making a tight fist in a neutral (refer to to image 4) grip.
http://www.teachpe.com/anatomy/muscles/brachioradialis.php
Image 7. The BR scan easily be seen by flexing your right arm to 90 degrees, closing your fist in a neutral grip, and then taking your opposite hand and pressing down on the closed fist.
Ok, so what does this muscle do? The brachioradialis is actually the most powerful elbow flexor in the body despite its relatively small and slender size. Again, because if it's attachment points, the BR is the most active elbow flexor when the wrist/forearm is in a neutral grip (refer to image 4). Thus, when you do a hammer curl (image 8), which requires a neutral grip, you are highly activating the BR. However, the biceps brachii and brachialis are still active when doing a curl with this grip, just not as much as the BR.
Image 8. DB hammer curls
http://www.menshealth.co.uk/building-muscle/28-day-six-pack-workout-1
Another small action of the BR is radial deviation (image 9). Because it attached near the wrist at the radius, it can thus move "or deviate" the wrist. By adding resistance to this exercise (i.e., holding onto a DB or using resistance band), you can add yet another way to isolate the BR and help "confuse" the muscle into growing.
Image 9. Radial deviation against resistance. Notice how the subjects wrist/hand is in neutral. As the wrist moves up towards the nose, the subject is demonstrating radial deviation, an action controlled by the BR. Ulnar deviation occurs as the wrist moves downward toward the floor (however, this is not controlled by the BR).
http://www.physioadvisor.com.au/8122850/wrist-strengthening-exercises-wrist-rehabilitati.htm
The brachioradialis (BR) is more powerful than the bigger biceps due to its much further distal attachment point. What does this mean? Treat your arm like it's a wheelbarrow, where the elbow is the wheel and the end of the forearm closest to the wrist is the end of the wheelbarrow handles. If you were to lift up on the loaded wheelbarrow at a point close to the wheels, it would be much harder than lifting it up all the way at the ends where the handles are- Right? So, if you were to lift the wheelbarrow at a point close to the wheel it would be similar to the biceps trying to flex the elbow because its attachment (image 1) is very close to the elbow (the wheel)- Understand? Now take into consideration the brachioradialis (BR). Its attachment is relatively far from the elbow (wheel) compared to the biceps and thus, when it contracts to flex the elbow it would be analogous to lifting the wheelbarrow at the very end off its handles, which makes your job very easy. Thus, you can see why the BR can generate much more torque than the biceps; because its long lever arm!!! Why does this matter? Well, it really doesn't matter to you but it does explain why its easier to carry a very heavy box by holding your wrist in neutral. Think about how milk crates are designed- they have small handles in the sides that require you to grip it with a neutral grip. It is easier to carry the crate this way rather than keeping your hands under the crate with your palms facing up, right? This is because when you have your hands in a neutral grip, you are maximally activating your BR, which is the strongest elbow flexor, and thus, carrying the crate is easier! Great job- you just passed physics!
One muscle I forgot to mention in Part 1 was the coracobrachialis (image 10). This is a small muscle that attaches to the coracoid process of the scapula (shoulder blade) and the humerus. Its action is essentially the same as the short head of the biceps (which hew discussed in part 1); it helps raise the arm straight out in front of you as if you were doing to shake somebody's hand. Thus, refer to part 1 to see how to exercise the short head of the biceps (which will also work the coracobrachialis).
Image 10. Coracobrachialis
https://www.kenhub.com/en/library/anatomy/coracobrachialis-muscle
Ok, I know that was a lot but I truly hope you learned something interesting by reading Parts 1 and 2. I believe everyone should know how the body works and thus, I tried to make these posts as direct, yet sufficient as possible. If you are confused feel free to contact me and I will help clarify! Again, the main purpose of these posts was to show you how to target specific muscles of the arm as well as tell you which muscles are active in different variations of exercises, specifically curls. By working the same muscle in different ways you are able to "confuse" the muscle and promote higher rates of growth so please, remember these posts when you are at the gym! Take care and let me know if you have any further questions!