Muscle names have their origins in Latin or Greek and either describe the function, location, or the shape of the muscle. For example:
- Function: Flexor Digitorum is a muscle that flexes digits (fingers or toes). Erector Spinae straightens the spine.
- Location: The interossei are muscles between bones of the hands or feet. The Tibialis Anterior lies on the front of the shin bone (Tibia).
- Shape: The Rhomboid muscle is shaped like a rhombus. The Deltoid muscle is shaped like the capital version of the Greek letter Delta.
Tendons attach muscles to bones causing the bones to move when the muscle is active.
Many of our muscles are redundant, meaning there may be more than one muscle that can cause the same motion, but because of their attachment site, one might be weaker or stronger than another. (see Bending the Elbow). The advantage of the redundancy is that if one muscle is seriously injured, another might be able to take over its function. In these commuting exercises, although I have included movements of most joints in the body, I have not credited all the redundant muscles that also might be involved in a given movement.
There are other small muscles that don’t have any significant movement function in humans, but most of us still have them. An example is a muscle that could retract claws if we had claws.
The deltoid muscle actually has 3 sections, front, middle, and back. The front lifts your arm in front of you, and the back lifts your arm behind you. The middle section can lift your arm to the side, but only after another muscle, part of your rotator cuff, has lifted the arm the first 30 degrees to the side. If the rotator cuff isn’t functioning properly, the middle section of the deltoid pulls the top of the arm straight up and it hits another bone causing pain.
Rotator cuff muscles: Raising arm 30 degrees to the side-Supraspinatus
The tendons of 4 muscles make up the rotator cuff. The muscle that raises the arm the first 30 degrees to the side is called the Supraspinatus. After the Supraspinatus has done its job, the deltoid muscle takes the arm the rest of the way out to the side and up toward your ear. When you hear about a rotator cuff tear, the most common part of the cuff that is torn is the Supraspinatus tendon.
Bending elbow - Biceps and Brachialis
Most people think that the Biceps muscle is solely responsible for bending the elbow. Think about the Popeye pose. However, actually it is the Brachialis muscle, which lies deep to the Biceps, that is doing most of the work. The Biceps works mainly to rotate your forearm to a palm up position. Prove this to yourself by putting your forearm on your thigh with your palm down. Keeping your elbow resting on your thigh lift your forearm so that your elbow bends more. Look at and feel your biceps. There won’t be much to see or feel. You bent your elbow with your Brachialis. If you now start with your palm up and then bend your elbow, you will see and feel your Biceps working. There is a smaller “back-up” muscle called the Brachioradialis that can also bend your elbow, especially when your forearm is neither palm down nor up, but rather in a neutral position with your thumb pointing toward the ceiling. You might be able to see it working if you look at your forearm just below your elbow, especially if you resist the bending movement with your other hand.
Making a fist
To make a really strong fist that has a great grip on something, your wrist (with palm facing down) has to be bent slightly upward. This puts tension on the muscles and tendons that bend your fingers. If your wrist is bent down, the tendons of these muscles are slack and they can’t hold on to something tightly. IN THEORY, If you wanted to disarm someone holding a knife as a weapon, and you could get close enough safely to force the attacker’s wrist down, the weapon might be released. DO NOT TRY THIS. If you want to grasp (pun intended) the concept, try holding a spoon in your fist and then push down on that hand till it is at a 90 degree angle with your forearm. Notice that you can’t hold the spoon quite as tightly as you could when your wrist was up.
Spreading the fingers
In the exercise drawing we showed you only the small interossei muscles that spread your fingers apart. There are other similarly small muscles between the bones of the hand that are responsible for bringing your fingers back together again and a third set of muscles between the bones that allow you to wave bye- bye by keeping your fingers straight while moving them down from the knuckles where they attach to your hand.(see “lumbricals” in Spreading Your Toes).
Bending hips with knees bent
There are two muscles that bend (flex) your hips, the Iliopsoas (which is hard to work in a seated position) and the Rectus Femoris, which is part of the Quadriceps muscle. The Rectus Femoris is the only part of the Quadriceps muscle that attaches above your hip joint. When you’re sitting you use your Rectus Femoris to bend your hip. The iliopsoas (pronounced ill’ e o so’ ass) is a much stronger hip flexor when you’re standing. It helps dancers lift and hold their straight leg up in the air in front and helps athletes kick a long distance starting with their leg behind their body and using their entire leg to transmit energy to a ball.
Moving hips to the side - Gluteus Medius and Minimus
Although the Gluteus Medius can move the leg out to the side, its main function is to keep the ball and socket joint of the hip together. Along with the Iliotibial band (ITB) the Gluteus Medius muscle stabilizes the lower limb when standing on one leg. The ITB is the longest tendon in the body. It starts on the Iliac bone of the pelvis (your waist, where you put your hand when you’re angry, where you hold a child on your side) and goes all the way down to attach to a small bump just below the knee, at the outer side of your shin bone (Tibia).
Straightening knees - Quadriceps
In the anatomical picture you only see three parts of the four-headed Quadriceps muscle. The fourth part of the Quadriceps muscle is lying deep to the Rectus Femoris. All 4 parts of the quadriceps muscle join together into a tendon that surrounds your knee cap, except on its underside, and attaches to your shin bone just below the knee. This allows the Quadriceps muscle as a whole to straighten your knee as well as directing the movement of your kneecap.
Bending knees - Hamstrings
You have 3 hamstring muscles, one of which has two heads (Biceps Femoris). The upper attachment of the long head of the Biceps and the other 2 hamstring muscles is on the Ischial tuberosity, known to you as your “sit bone.” The hamstrings’ main function is to bend the knees. They can also act as weak extensors of the hip, moving your leg toward the back. The main hip extensor is the Gluteus Maximus. You can feel these muscles working when you climb stairs as you put all the weight of your leading leg up to the next step and straighten (extend) your hip.
Lifting heels - Calf Muscles - Gastrocnemius and Soleus
The big muscle visible on the back of your calf is the Gastrocnemius. Deep to it is the Soleus muscle. Both of these become the Achilles tendon and help you to lift your heels, stand on your toes, and propel you forward when you walk and run. The upper end of the Gastroc is attached to bone above the back of your knee, whereas the Soleus begins below the knee. This is why you should do Achilles stretches with your knees bent and also with your knees straight so that you stretch both muscles. “Tennis leg” is a partial tear of the Gastrocnemius muscle.
Other than muscles related to movement of your thumb, you have essentially the same muscles to move your toes as you have to move your fingers. In the drawing, we’ve shown you the Lumbricals, “wormlike” muscles that are interesting because they only have a tendon at their far end where they attach to the toes (or fingers). At the other end the lumbricals don’t attach to bone but rather attach to tendons belonging to another muscle. As in the hand we also have two sets of Interossei muscles. So why can’t we spread our toes like we can our fingers? Mainly because most of us wear shoes all the time and don’t use these muscles. (Use it or lose it.) The functional loss of these small toe muscles contributes to various toe deformities.