Negative Isotonic Contractions
Soreness is generally accepted as being a result of negative isotonic contractions especially by placing a great load upon the muscle causing damage to connective tissue. If the load is greater than can be moved positively then the strain upon the muscle is more likely to cause damage. The reason that this type of work is done at all is that it promotes strength gains. Muscle fibre recruitment is implicated again.
Keep in mind the picture of an elastic band held under tension. This corresponds to the normal resting state of a limb for the current training condition. Shortening the muscle by contraction will cause the tension in the connective tissue to be reduced as its elastic nature allows it to take up the slack - the connective tissue spans a shorter distance. In this positive concentric movement an increasing number of muscle fibres become involved in moving the load, which ensures sufficient contractile force is generated up to the maximum possible. This is the type of work to increase the neuromuscular efficiency and hence strength. The muscle working in this eccentric phase (negative contraction) is still the prime mover. When the limb is extended or stretched beyond the normal limit for range of motion then the tension increases until the limb can be moved no further.
Initially the mechanism involves selectively switching off muscle fibres to reduce the contractile force. When alpha-motorneurones stimulate muscle fibres, they contract in an "all or nothing" fashion. Some fibres may become fatigued during the slow movement so others are recruited to sustain the contractile power. This recruitment explains why negative contractions promote strength gains. The resultant reduction in force reaches a point where there are no longer sufficient fibres to overcome the load and the muscle extends, pulled down by gravity. The tension within the muscle and the surrounding connective tissue begins to rise as the muscle lengthens, the elastic band analogy.
Fibres still participating in the contractile mode are attempting, and failing, to resist the load and they become overloaded. Contraction is in the opposite direction to the movement of the limb as the muscle lengthens. This results in an increase in the tension in the connective tissue of the contracting (active) fibres because a greater number of fibres are not participating and the connective tissue around these fibres is pulling in the opposite direction. The stress receptors, golgi organs in tendons and gammamotorneurones in the muscle spindles, monitor this rising tension and inhibit the alphamotorneurones, those responsible for contraction. The muscle contracts less strongly and continues to lengthen.
The antagonist muscle becomes increasingly involved to control the limb as the alphamotorneurones are inhibited. Remember the agonist/antagonist muscles work together and in the positive phase as the agonist contracts the antagonist is inhibited. The reverse occurs in the negative phase - the agonist contraction is reduced in intensity so the inhibition of the antagonist is similarly reduced. The tension reached depends on the load used. Under normal circumstances, a load which has been moved in the positive phase is the same which is moved in the negative phase. However, the greatest stress possible is to use a load which cannot be moved positively at all and this is where most of the problems, and strength gains, occur.
An example is the a press up. This can normally be performed using the weight of the body as the load without a problem. If, however, with the arms almost in the fully extended position (elbows not locked out), a heavy weight was placed upon your back just too much that a press up to this position would not be possible - then the triceps and chest would not have sufficient strength to stay in this position and the elbows would begin to bend. Gravity pulls you down and a slow negative contraction of the triceps will occur. The point is that you do not have enough strength to stop it completely but can resist and slow it down. If a load is used especially in a negative contraction exercise where this load is too much to move positively then great care is needed if the movement is likely to cause muscle elongation beyond the normal range of motion. Injury could occur.
Keep in mind the picture of an elastic band held under tension. This corresponds to the normal resting state of a limb for the current training condition. Shortening the muscle by contraction will cause the tension in the connective tissue to be reduced as its elastic nature allows it to take up the slack - the connective tissue spans a shorter distance. In this positive concentric movement an increasing number of muscle fibres become involved in moving the load, which ensures sufficient contractile force is generated up to the maximum possible. This is the type of work to increase the neuromuscular efficiency and hence strength. The muscle working in this eccentric phase (negative contraction) is still the prime mover. When the limb is extended or stretched beyond the normal limit for range of motion then the tension increases until the limb can be moved no further.
Initially the mechanism involves selectively switching off muscle fibres to reduce the contractile force. When alpha-motorneurones stimulate muscle fibres, they contract in an "all or nothing" fashion. Some fibres may become fatigued during the slow movement so others are recruited to sustain the contractile power. This recruitment explains why negative contractions promote strength gains. The resultant reduction in force reaches a point where there are no longer sufficient fibres to overcome the load and the muscle extends, pulled down by gravity. The tension within the muscle and the surrounding connective tissue begins to rise as the muscle lengthens, the elastic band analogy.
Fibres still participating in the contractile mode are attempting, and failing, to resist the load and they become overloaded. Contraction is in the opposite direction to the movement of the limb as the muscle lengthens. This results in an increase in the tension in the connective tissue of the contracting (active) fibres because a greater number of fibres are not participating and the connective tissue around these fibres is pulling in the opposite direction. The stress receptors, golgi organs in tendons and gammamotorneurones in the muscle spindles, monitor this rising tension and inhibit the alphamotorneurones, those responsible for contraction. The muscle contracts less strongly and continues to lengthen.
The antagonist muscle becomes increasingly involved to control the limb as the alphamotorneurones are inhibited. Remember the agonist/antagonist muscles work together and in the positive phase as the agonist contracts the antagonist is inhibited. The reverse occurs in the negative phase - the agonist contraction is reduced in intensity so the inhibition of the antagonist is similarly reduced. The tension reached depends on the load used. Under normal circumstances, a load which has been moved in the positive phase is the same which is moved in the negative phase. However, the greatest stress possible is to use a load which cannot be moved positively at all and this is where most of the problems, and strength gains, occur.
An example is the a press up. This can normally be performed using the weight of the body as the load without a problem. If, however, with the arms almost in the fully extended position (elbows not locked out), a heavy weight was placed upon your back just too much that a press up to this position would not be possible - then the triceps and chest would not have sufficient strength to stay in this position and the elbows would begin to bend. Gravity pulls you down and a slow negative contraction of the triceps will occur. The point is that you do not have enough strength to stop it completely but can resist and slow it down. If a load is used especially in a negative contraction exercise where this load is too much to move positively then great care is needed if the movement is likely to cause muscle elongation beyond the normal range of motion. Injury could occur.
posted by Louis Brothnias @ 9:44 AM
0 Comments:
Post a Comment
<< Home