灰男的健身網誌

要推介這篇關於胸部的英文文章：

Anatomy

The general shape of the pectoralis major is that of a "fan", meaning it has a wide origin on the clavicle, ribs 2 through 6 and sternum and tapers into a narrow insertion on the humerus. In addition, the pectoralis major is a cruciate muscle.

This means that the fibers originating from the upper half of the muscle cross over those originating from the lower half on their way to the humerus, forming an anatomical "twist" in the muscle. Due to these characteristics, the muscle fiber angles fluctuate by as much as seventy degrees from the most superior to the most inferior portions of the muscle.

Kinesiology

The result of this unique shape and varying fiber angles of the pectoralis major is the superior and inferior portions of the muscle have somewhat different actions on the arm. Hence, certain exercises involve the upper "head" of this muscle more than the lower and vice versa. This has significance in your training because you can select exercises that will train the portion of the pectoralis major, specific to your goals. This can be more effective than a general training approach of exercising the whole muscle as one unit.

Although the pectoralis major has some influence on the movement of the shoulder girdle, its main action is on the arm. We now know that the upper and lower portions of the muscle have somewhat different actions on the arm, although they share some functions. Below is a list of the specific actions of the two heads of the pectoralis major.

Upper fibres -- Flexion
Lower fibres -- Extension, adduction
All fibres -- Horizontal adduction

Exercise & Development

The pectoralis major has a tremendous capacity for development in both strength and size. The reason for this lies in the fact that humans have evolved to walk on two legs. When we were quadripeds (if you believe in evolution), the pectoralis major played a significant role in our everyday lives of walking with our arms and legs.

Nowadays, the muscle gets much less opportunity to contribute to our daily activities, and thus lies in a state of atrophy in your average person. For this reason, detrained people who begin a strength training program incorporating the pectoralis major have a lot of genetic room to work with and typically show great improvement in this muscle in a short time period.

A general approach to training the entire pectoralis major is the best choice for beginners, general fitness enthusiasts, and athletes looking for general improvements in strength of the arms. If this is you, the flat bench press is a great way to go. The only limitation to this exercise is that it does not allow a full range of motion in the upper portion of the movement.

To get a better range of motion, try a dumbell press. You will see that your hands get closer together at the end of the movement, indicating a more complete range of motion. A dumbell or cable fly (lateral) on a flat bench is a great way to isolate the pectoralis major from the tricep and provides an even more complete range of motion. All of these exercises are pure horizontal adduction of the arm.

If you are interested in developing the upper portion of the pectoralis major for aesthetic reasons, or want improved strength in arm flexion (raising the arm in front of the body), doing the above exercises on an incline bench will introduce some flexion of the arm into the movement. A front barbell or dumbell raise is pure arm flexion and also a great way to train the upper head of the pectoralis major. A less common and more creative way to train this portion of the muscle is to do a cable cross-over using the bottom instead of the top cables of the apparatus. This exercise is a very good combination of arm flexion and horizontal adduction and very effective in exercising the upper head of the pectoralis major.

If you are interested in developing the lower portion of the pectoralis major for aesthetic reasons or a need for improved strength in arm extension (lowering the arm from in front of the body) or adduction (pulling the arm towards the body from an out-to-the-side position) performing the general pectoralis major exercises discussed above on a decline bench is a effective way to train.

Using the decline bench incorporates arm adduction into the movement, increasing the stress on the lower head of the pectoralis major. Ironically, a lat pull-down is as much a lower pectoralis major exercise as it is a latissimus dorsi exercise due to the adduction involved. The dumbbell pull-over is a good arm extension exercise and also effective for the lower pectoralis major.

Special Considerations

It is important when training any muscle to be sure to train that muscle's antagonist(s). Failing to do this will likely result in muscular imbalance, which will alter the mechanics of the joint involved. Muscle imbalances resulting form a strong pectoralis major and weak rear deltoid/rhomboids are very common. To avoid this condition in the shoulder area, incorporate just as much time training with reverse flies, seated rows, T-bar rows and other mid back/ rear deltoid exercises as you do training the pectoralis major to maintain agonist/ antagonist balance.

How do you tell if you or your client already has a muscle imbalance in the shoulder? Stand to the side of your client (or have someone stand to the side of you) and look at the alignment of the center of the shoulder with the ears. Proper alignment will be identified when the center of the shoulder is inline on the vertical axis with the ear. If the center of the shoulder is forward of direct alignment with the ear (slumped shoulder), you are likely looking at the muscle imbalance discussed here. What if you are too late? To correct an existing muscle imbalance of this type, you need to stretch, not strengthen the pectoralis major and spend a lot of time doing mid back/rear deltoid exercises.