Isometric Training and Fast Twitch Muscle Fibers

Isometric Exercises using the Resistance Band – The little known ‘secret formula’ for speeding past your competition.

The word ISOMETRIC is defined as follows: “Iso” means equal or the same, and “metric” means length. Combining these two definitions we get “equal or the same length.”

Isometrics, as it pertains to muscle training, involves tensing muscles against other muscles or against an immovable object while the length of the muscle remains unchanged. For isometric training to be effective, this muscular tension must be maintained over a certain period of time.

Therefore, isometric training is best defined as follows: The sustained contraction of a muscle over a certain period of time where the length of the muscle remains unchanged.

The following are a few examples of an isometric contraction:

Example 1. Take a 20 pound weight and perform biceps curl. Hold a position halfway between the repetition for 10 seconds.

The length of your biceps muscle doesn’t change during this time. A force is still being applied. See Figure 1-1 below:

Fig. 1- 1 Isometric Hold Position

Example 2. Push against a wall for 10 seconds. The wall doesn’t move and neither does the length of the muscles in your arms pushing against it. A force is still being applied. See Figure 1-2 below:

Fig 1-2 Isometric Position

Isometric training has been around for a long time and so it is nothing new. Many extraordinary results in muscle size and strength have been achieved in a very short period of time with this type of training.

However, because of the number of new training products and techniques out on the market today, its use by athletes is often overlooked.

In order to help you fully appreciate the value of isometrics training to increase your speed, agility and power, let’s take a quick look at some basic principles of muscular contraction.

To start with all skeletal muscles consist of three main fiber types. These fiber types are:

1) Slow twitch fibers- Responsible for the strength and endurance of a muscle.

2) Intermediate twitch fibers- Possess qualities of both slow and fast twitch fibers.

3) Fast twitch fibers- Responsible for the speed of muscular contraction.

The fast twitch muscle fibers are responsible for giving the athlete his speed, agility, quickness, and power. Fast twitch fibers are up to 10 times faster than slow fibers.

In most muscles, these fibers are intermingled. However, there is usually a predominance of one or the other. For example, in postural muscles of the spine, the slow twitch fibers dominate. This is because slow twitch fibers can undergo extensive repetitive contractions without fatigue.

In non-postural limb muscles like the arms and legs, the fast twitch fibers dominate. This allows for powerful forces to be generated over a short period of time.

Because the fibers are intermingled it is not possible to isolate out a single fiber type during a muscular contraction. All of the fibers contract together, though at times one of the fibers may be dominant during the contraction.

All of these fiber types are arranged into groups known as motor units. A motor unit is defined as one motor neuron and all the muscle fibers it supplies. There are many motor units within the overall muscle. When a muscle begins to contract, an action potential is carried down the motor neuron across the motor endplate to the muscle fibers it supplies.

Initially, only some of the motor units become active. As the demand on the muscle increases, more and more motor units are recruited to help support this demand. As the demand on the muscle decreases, the number of motor units also decreases. This is a general description of muscular contraction.

With isometric training, a muscle opposes some form of resistance and is contracted to a certain length and then held for a certain period of time, usually 10 seconds or more. There are no repetitions required here as in weight training.

The biggest advantage to this type of training is twofold. First, by forcing your muscles to hold a position for a certain length of time, your body starts to recruit more and more motor units to help maintain this contraction. Motor units that are rarely exercised within a muscle are now brought into use, perhaps for the first time.

Second, the motor units that are recruited are forced to contract continuously, time after time, until your muscles achieve a state of maximum intensity safely and effectively.

The end result is that the entire muscle matures very quickly.

Resistance band training with an isometric strategy adds additional benefits to the athlete beyond traditional isometrics.

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