Danny O’Dell’s

Explosivelyfit Training News

Strength and power knowledge

15-April-07

ISSN: 1550-2643: Library Of Congress, Washington D.C.,

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Topic discussed:

Dynamic muscle activity-concentric and eccentric

A dynamic muscle action indicates a change in muscle position and fiber activity. The following paragraphs briefly describe the activity of the muscles during concentric and eccentric muscle actions.

In concentric muscle actions the muscle fibers are shortening in length. Lifting the bar upward and off the chest in the bench press is an example of a concentric muscle action.

More energy is required from the muscle fibers during concentric movements than the other types of motion. The greater the concentric speed on the bar the less force that is developed. This is due to the relationship expressed by the force velocity curve.

Eccentric muscle action

The activity of the muscle fibers during an eccentric movement is that of lengthening; each fiber is being stretched out as the limb or joint moves or tends to collapse under the weight of gravity or a load that is much greater than a one repetition maximum. Eccentric contractions take place during the negative phase of an exercise.

The opposite effect of speed on the bar (compared to concentric muscle action) relative to the force potential takes place with an eccentric action. A faster eccentric speed will generate greater force. The weight on the bar can be as high as 130-150% greater than a 1RM for experienced athletes when using eccentrics as a training method. This will increase strength. It also can create muscle fiber damage which is expressed as DOMS-delayed onset muscle soreness.

DOMS is believed to result from a combination of damage that occurs to the membranes in the muscle fibers and an inflammatory reaction within the muscle.

The strength gains are similar between concentric and eccentric muscle activity.

Isotonic muscle movement

As was previously stated, isotonic means the muscle tension remains the same. However, in any activity this is patently false due specifically to the lever systems of the human body. When the joint angles change during the movement, the degree of force available to move the weight also changes. The load on the bar may remain the same but the tension placed on the muscles throughout the entirety of the motion will not.

The greatest amount of force or tension occurs at the weakest point in the lift, i.e. the sticking point. This position in the maneuver is where gravity has its greatest influence on the bar. This spot is when the bar or load is parallel to the floor in relation to the lever arm of the limbs moving the weight. For example, in the barbell curl this point is when the arms are flexed ninety degrees. The muscles are exerting maximum tension on the bar. Earlier and later in the movement the lever positioning is more advantageous and the weight feels lighter. Because it feels lighter the bar is moved faster through the range of motion. Momentum carries the load through the sticking point and deprives the muscles of an opportunity to develop more strength in their weakest point.

This is not all as bad as it may seem. Speeding up the lift enables the athlete to move the sticking point to a different place in the lift. This allows more weight to be lifted which after all is the name of the game.

Isokinetic activity

Isokinetic (1), as does concentric and eccentric muscle action, involves motion. The term means having the same non variable, non changing speed of motion or movement during these actions. The speed remains the same throughout the motion but the resulting muscle tension varies as the exercise progresses from start to finish. Again this is due to the differing lever positions and the varying physiological states (actin and myosin cross bridge connections) of the muscles during the movement.

Except in a rehab situation the Isokinetic machine is rarely used in strength training for sports. The machines are not fast enough to duplicate the velocity required in sports movements to be successful on the field or platform so are seldom used.

The latter two descriptions refer to isotonic muscle actions where ‘iso’ means constant and ‘tonic’ which in this case means tension and ‘kinetic’ meaning speed.

Muscle isolation seen in lab tests and espoused in isotonic theory assumes the muscle is producing tension without a variance in the force as the length of the muscle shortens during the exercise movement while using a constant load. However this is not the case in the real world because the muscle tension does change as the exercise progresses throughout the range of motion. This deviation in tension is brought about by the consistently changing lever angles observed during the exercise movement. At all angles in the bar path the muscles encounter various advantages and disadvantages due to the pull on the bones resulting from these lever angles. This is commonly referred to as muscle moment arm change. The more favorable this arm position (joint angle) the less force that has to be applied to move the load.

Isokinetic dynamic exercise training keeps the movement constant while at the same time disregarding muscular tension throughout the range of motion. Speed, in this instance, is ill defined. It may refer to the rate of muscle length change, the velocity of speed on the bar, or the angular velocity of the joint during the motion. Training and testing this dynamic muscle activity takes expensive equipment which few gyms have on hand. This is not something that is used very often in sports training because the speed of movement is not at a high enough velocity in any category to compare to the speed of movement seen in competition.

That’s all for this time. I hope your training is going well and wish you happiness in your life.

(1) This is also known as accommodating resistance because of the change in the resistance that takes place at various positions during the range of motion of the exercise.

Stay strong, and remain passionately committed to your hearts chosen path.

By Danny M. O’Dell, MA. CSCS*D

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