Your potential to generate gains in strength and lean muscle is inherited from your genetics. The magnitude of your muscular gains is dictated by how favorable your genetic predisposition is for gaining strength and size. We all have an ultimate ability to gain strength and muscular size. The quality and intensity of exercise and the frequency of your workouts are the keys to reaching your full potential.
First off, do not get frustrated with your training regimen. Few men have the genetic ability to add massive amounts of muscle and ladies are even less likely. Injury protection and improved anaerobic muscular endurance are far more important to you than the amount of muscle you add. Train hard, eat a balanced diet and get the proper amount of rest. These factors will enable you to maximize your muscular gains, and be sure to thank your parents for the gains you make.
Your body type is primarily determined by your bone structure, the width of your hips and shoulders, and your body composition (ratio of muscle to fat). There are three major body types to include the ectomorph, the mesomorph and the endomorph.
A major factor in determining how big you can get is the length of each individual muscle belly. The longer the muscle belly the greater the growth potential. The muscle belly is responsible for contracting and does not include the tendons or bones. Only the muscle belly will grow larger.
Another trait that affects your ability to lift more weight is lever length. The body is a system of levers and pulleys. The length of a bone can create a leverage advantage or disadvantage in the weight room. Generally, a longer bone creates a distinct leverage disadvantage in the weight room when compared to a shorter bone. On the field, however, longer levers can create performance advantage. For this reason alone we should not compare athletes strengths while in the weight room. Each athlete is doing a different amount of work on each rep depending on the length of their limbs and where each tendon attaches to their bones.
The insertion point is the spot a muscle attaches to the moving bone. For example, all biceps attach in the same spot near the shoulder. The difference is where the biceps insert on the forearm. The farther away from your elbow the biceps inserts the better leverage you will have for performing a biceps curl. This same mechanical advantage or disadvantage exists for the most muscle groups in the body.