Weight lifting exercises cause your muscles to generate heat and strength. Your muscles need to be strong, in order to help you move, breathe and so on.

This article on weight lifting exercises will look at the relationship between the exercises you use when weight lifting and your muscles.

Your actual muscle tissue is made up of 2 types of muscle fibers, actin, which are a slim fiber and myosin which are substantially thicker. Both of these fiber types help to give your muscles a striated look about them.

When performing any exercises used in weight lifting the muscle being exercised must be able to contract properly. To do this they need to become stimulated by motor neurons. These are simply nerves.

One motor neuron and the muscle fibers stimulated during exercises used during weight lifting activities are called a motor unit. These motor units or muscle fibers play a large part in the force your muscles can produce during a contraction.

The more motor units you can activate during your weight lifting exercises the stronger the contraction. Meaning you'll be able to lift a greater amount of weight for an increased number of repetitions.

Your muscle fibers are categorized as Type I, Type IIa and Type IIb muscle fibers. The more common term for muscle fibers are "fast" and "slow" twitch.

When performing high rep weight training exercises it's your slow twitch muscle fibers (Type I) that will be recruited to do the majority of the work. Your body uses this type of muscle fiber when endurance activities, aerobic activity or high rep sets are used.

Fast twitch muscle fibers (Type IIa and Type Iib) are used by your body during explosive contractions. It's these fibers that have the greatest potential for growth resulting from the weight lifting exercises you perform.

Your body will used fast twitch muscle fibers during high-intensity, short-duration exercises such as weight lifting exercises that use heavy weight for very low reps, or sprinting.

People who seem to be able to build muscle at will when performing almost any weight lifting exercises, usually will have an unusually large number of fast twitch muscle fibers in their body.

In the majority of people the muscle fiber make-up in each muscle group will be relatively equal in most muscle groups. Therefore you need to recruit both slow twitch and fast twitch fibers at some point in your exercise program.

One exception to the rule of equal types of muscle fibers is when it comes to your hamstrings. The hamstring muscles in the vast majority of people tend to be made up of mostly fast twitch muscle fibers.

For that reason, when performing weight exercises for your hamstrings, you should try to use heavier weights for a lower number of reps.

Now, when executing any weight training exercises your muscles will go through a few different actions. There are isometric, eccentric, concentric, and isotonic portions of most weight lifting exercises;

Isometric contractions can best be described as the same stress your muscle would go through when pushing against a wall.

The lifting portion of weight training exercises such as a dumbbell bicep curl is known as the concentric contraction. Lowering the dumbbell in a controlled fashion is the eccentric portion.

The more common terms for this part of weight training exercises are positive (concentric) and negative (eccentric).

The fourth type of contraction that can occur during weight exercises is the isotonic contraction. This can occur more commonly during plyometric training.