Do you ache for a body like Sylvester Stallone's? How big your muscles grow depends on your body type, as well as the amount of exercise you do. There are three basic body shapes.
Endomorph
Tendency towards small bones, large chest or breasts, pear shape, large head, short neck. Will gain weight easily.
Mesomorph
Tendency towards heavy bones, triangular shape, broad chest and shoulders. Little excess body fat.
Ectomorph
Tendency towards long bones, long neck and limbs, short trunk, narrow chest and buttocks. Little excess body fat.
Whatever weight training you do, the eventual size of your muscles will depend on your body type.
Many people's muscles are made up of equal percentages of "slow twitch" fibres (for long-term, low intensity activity) and "fast twitch" fibres (for high intensity, short burst activity). A higher proportion of slow-twitch fibres will limit muscle growth. Ectomorphs tend to have a higher proportion of slow-twitch fibres. Mesomorphs tend to have a lower proportion.
In addition to assessing your body type, there is another test you can do to give you an indication of the extent of muscle development you can expect. Stand on one leg, supporting all your weight on your toes. Mark the end of your bulge of muscle near your heel. If your calf muscle bulges near your knee, you will have limited potential for growth. If your muscle stops mid-way down your calf, you have medium growth potential. A muscle that almost reaches your heel indicates the greatest growth potential.
If you have high or medium muscle growth potential, you will be able to build sizable muscles. A personal trainer or a good gym will be able to advise you on the right type of frequency of exercise to maximise the size of your muscles (if you want to look like Arnold Swarzchenegger!!).
If you have a low muscle growth potential, do not lose heart. Whilst you are unlikely to win the Mr. Universe competition, you will still be able to achieve good muscle definition and get that six-pack stomach!
