Origins and insertions

We use the words "origin " and "insertion " to indicate where muscles are attached to bones in relation to the most common movement at a joint. The origin of a muscle is on the bone that is relatively (or usually) stationary, and the insertion of a muscle is on the bone that is most generally moved Flexion of the elbow is again a good example. Since ordinarily the arm is fixed and the forearm is moved, at least in relative terms, we say that the

24 ANATOtfo OF HATHA I <X,yl biceps brachii and triceps brachii take origin from the arm and shoulder, and that they insert on the Forearm (fig. 1.1).

The origins and insertions of a muscle can be functionally reversed. When the latissimus dorsi muscle (figs. 8.9-10) pulls the arm down and back in a swimming stroke, its textbook origin is from the lower back and pelvis, and its insertion is on the humerus in the arm. But when we do a chin-up the arm is the relatively stable origin, and the lower back and pelvis become the insertion for lifting the body as a whole. In the coming chapters we'll see many examples of how working origins and insertions are reversed.

agonist and antagonist muscles

The muscles surrounding a joint act cooperatively, but one of them—the agonist—ordinarily ser-ves as the prime mover, assisted in its role by functionally related muscles called synergists. While the agonist and its synergists are acting on one side of the joint, muscles on the opposite side act as antagonists. As suggested by the name, antagonists monitor, smooth, and even retard the movement in question. For example, when the biceps brachii and the braehialis in the arm (the agonist and one of its synergists) shorten to flex the elbow, the triceps brachii (on the opposite side of the arm) resists flexion antagonistically while incidentally holding the joint surfaces in correct apposition (fig. l.l).

Muscles also act in relation to the force of gravity. In the lower extremities extensor muscles act as antigravity muscles to keep you upright and resist crumpling to the floor. Examples: the quadriceps femoris muscle (figs. 1.2, 3.9, and 8.11) on the front of the thigh (the segment of the lower extremity between the hip joint and the knee joint) extends the knee joint as you step onto a platform, and the calf muscles extend the ankles as you lift your heels to reach an object on a high shelf. Flexor muscles are antagonists to the extensors. They can act in two ways. They often aid gravity, as when you settle into a standing forward bend and then pull yourself down more insistently with your hip flexors—the iliopsoas muscles I figs. 2.8, 3.7,3.9, and 8.13). But they also act to oppose gravity: if you want to run in place the iliopsoas muscle complex flexes the hip joint, lifting the thigh and drawing the knee toward the chest; and if you want, to kick yourself in the buttocks the hamstrings (fig. 3.8, 3.10, 8.10, and 8.12) flex the knee, pulling the leg (the segment of the lower extremity between the knee and the ankle) toward the thigh. Even so, the flexor muscles in the lower extremities are not classified as antigravity muscles, because under ordinary postural circumstances they are antagonists to the muscles that are supporting the body weight as a whole.

For the upper extremities the situation is different, because unless you

/. MOVEMENT AMI POSTURE 25

are doing something unusual like taking a walk in a handstand with slightly bent elbows (which necessitates a strong commitment from the triceps brachii muscles), the extensor muscles do not support the weight of the body. In most practical circumstances, it is likely to be the flexors rather than extensors that act as antigravity muscles in the upper extremities, as when you flex an elbow to lift a package or complete a chin-up.

(Technical note: Throughout this book, in order to keep terminology simple and yet precise, I'll stick with strict anatomical definitions of arm, forearm, thigh, and leg, which means never using ambiguous terms such as "upper arm," "lower arm," "upper leg," and "lower leg." The same goes for the careless use of the term "arm" to encompass an undetermined portion of the upper extremity and the careless use of the term "leg" to encompass an undetermined portion of the lower extremity.)

infraspinatus musde teres major muscle medial border of scapula —

triceps brachii muscle; extends forearm at elbow as prime mover

Origins Insertions Simple Simply

brachialis muscle: synergist for flexion of forearm deltoid muscle clavicle biceps brachii muscle: flexes forearm as prime mover supraspinatus muscle spine of scapula upper part of forearm

Figure 1.1. View of the right scapula, arm, and upper part of the forearm from behind and the side (from Sappey; see "Acknowledgements" for discussion of credits regarding drawings, illustrations, and other visual materials).

brachialis muscle: synergist for flexion of forearm teres major muscle deltoid muscle teres minor muscle clavicle biceps brachii muscle: flexes forearm as prime mover olecranon: bony tip of elbow and insertion of triceps brachii infraspinatus musde supraspinatus muscle medial border of scapula —

spine of scapula triceps brachii muscle; extends forearm at elbow as prime mover upper part of forearm

Figure 1.1. View of the right scapula, arm, and upper part of the forearm from behind and the side (from Sappey; see "Acknowledgements" for discussion of credits regarding drawings, illustrations, and other visual materials).

The Newbies Guide To Yoga

The Newbies Guide To Yoga

Yoga is extensively know as a form of exercise that stretches and strengthens the body through various poses know as ASANA. For other people yoga is the realization of inner self satisfaction. For other it is a religion that the believe and must follow. Learn more within this guide by downloading today.

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Responses

  • taija
    Why is it important to know the origih and insertion of a muscle in yoga poses?
    7 years ago
  • betty
    Which muscle is acting as the synergist?
    7 years ago

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