The gastrocnemius (G. gaster, belly ; kneme, leg.), or “gastroc” for short, is the largest muscle in the calf, which acts on both the ankle and knee joints. It shares the role of prime mover in ankle plantarflexion with the soleus, but only when the knee is straight. The gastroc becomes less active the more the …
The biceps brachii (L. biceps, two-headed [bis, twice ; caput, head] ; G. brachion, arm.), commonly known as the biceps, is the prominent two-headed muscle of the arm. It acts on the elbow, forearm and shoulder, with it’s main role being a synergist in elbow flexion. Note: The biceps is most active in elbow flexion …
The rectus abdominis (L. rectus, straight ; abdo, to hide) is a long muscle pair located front and center on the torso. It’s named after the straight, vertical direction of its fibers relative to the midline of the body. It acts on the spine, with its main role being the prime mover in spinal flexion. …
The soleus (L. solea, sandal.) is the smaller of the two major calf muscles; the other muscle being the gastrocnemius (gastroc). Fun fact: It was originally named after its resemblance to the flat, sandal-shaped sole fish, whose name also comes from the Latin word, solea. The soleus and gastroc are both prime movers in ankle plantarflexion when …
The supraspinatus (L. supra, above ; spina, spine [of scapula].) is the uppermost muscle of the rotator cuff. It is a synergist in shoulder abduction, being most active during the initial 15° of the range of motion. It also stabilizes the shoulder joint by compressing the humeral head into the glenoid fossa, counteracting the shearing …
The brachialis (G. brachion, arm.) is a lesser-known arm muscle located on the front of the humerus. It is the prime mover in elbow flexion. Since it only crosses one joint, its contribution to elbow flexion is always the same, no matter the position of the shoulder joint or rotation of the forearm. It’s the …
The upper trapezius (G. trapeza, four-sided or four-legged table.) refers to the uppermost section fibers on the trapezoid-shaped muscle pair known as the trapezius. The upper trapezius fibers span from the top of the upper back to the base of the skull, and act on the scapula and cervical spine, with their biggest role as …
The middle trapezius (G. trapeza, four-sided or four-legged table.) refers to the middle section of fibers in the trapezius, between the upper and lower trapezius fibers. It acts on the scapula and is the prime mover in scapular retraction. The middle trapezius is grouped as a superficial posterior axioappendicular (extrinsic shoulder) muscle. It’s situated between …
The lower trapezius (G. trapeza, four-sided or four-legged table.) is not an individual muscle, itself, but rather it is the lowermost section of fibers in the trapezius muscle. It acts on the scapula, with its main role as the prime mover in scapular depression. Also worth noting is its important role as a scapular stabilizer: …
The teres minor (L. teres, round and long ; minor, smaller.) is a small rotator cuff muscle, which is hidden from the surface of the physique. It acts on the shoulder joint and is a prime mover (along with the infraspinatus) in shoulder external rotation. Like all rotator cuff muscles, it also helps stabilize the …
