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- Oct 1, 2004
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Here's something interesting that I read last night from Dr. Tudor Bompa (the man who introduced periodization of training back in '63 to the Romanians) from his book "Serious Strength Training"(1998):
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Neuromuscular Fatigue
While the general assumption is that fatigue originates in the muscles, clearly the CNS plays an important role, since incentive, stress, temperature, and other psychological factors can cause fatigue. Increasing evidence suggests that the CNS might be involved in the limitation of performance to a greater extent than once assumed.
The CNS has two basic processes, which are excitation and inhibition. Excitation is a very favorable, stimulating process for physical activity, while inhibition is a restraining process. Throughout training there is a constant alteration of the two processes. For any stimulation, the CNS sends a nerve impulse to the working muscle causing it to contract and perform work.The speed, power, and frequency of the nerve impulse directly depend on the state of the CNS.
The nerve impluses are most effective when controlled excitation prevails, which is evidenced by a good performance. When the opposite occurs, as a result of fatigue, the nerve cell is in a state of inhibition and muscle contraction is slower and weaker. The force of contraction relates directly to the electrical activation sent by the CNS and the number of motor units recruited. Therefore, as fatigue increases, the recruitment of motor units decreases.
The nerve cell working capacity cannot be maintained for a very long time. Under the strain of training or competition demands, the working capacity decreases. If high intensity is maintained as a result of fatigue, the nerve cell assumes a state of inhibition to protect itself from external stimuli. Fatigue, therefore, should be seen as the body's way of protecting itself against damage to the contractile mechanism of the muscle.
The skeletal muscle produces force by activating its motor units and regulating their firing frequency, which progressively increases in order to enhance force output. Fatigue that inhibits muscular activity can be neutralized to some degree by a modulating strategy: by responding to fatigue through the ability of motor units to alter firing frequency. As a result, the muscle can maintain force more effectively under a certian amount of fatigue. If the duration of sustained maximum contraction increases, the frequencey of the motor units firing decreases, and inhibition will become more prominent.
Marsden et al. (1971) demonstrated that compared to the start of a 30 second maximum voluntary contraction, the end firing frequency decreased by 80%. Similar findings were reported by Grimby et al. (1992) who stated that, as the duration of contraction increased, activation of large motor units decreased, lowering the firing rate below the threshold level. Any combination of contraction beyond that level was possible through short bursts (phasical firing), but not appropriate for a constant performance.
The above findings should caution those who promote the theory (especially in football and bodybuilding) that muscle size and strength can only be achieved by performing each set to exhaustion. The fact that as a contraction progresses, the firing frequency decreases, discredits this highly-acclaimed method.
------------------------------------------------------------
Neuromuscular Fatigue
While the general assumption is that fatigue originates in the muscles, clearly the CNS plays an important role, since incentive, stress, temperature, and other psychological factors can cause fatigue. Increasing evidence suggests that the CNS might be involved in the limitation of performance to a greater extent than once assumed.
The CNS has two basic processes, which are excitation and inhibition. Excitation is a very favorable, stimulating process for physical activity, while inhibition is a restraining process. Throughout training there is a constant alteration of the two processes. For any stimulation, the CNS sends a nerve impulse to the working muscle causing it to contract and perform work.The speed, power, and frequency of the nerve impulse directly depend on the state of the CNS.
The nerve impluses are most effective when controlled excitation prevails, which is evidenced by a good performance. When the opposite occurs, as a result of fatigue, the nerve cell is in a state of inhibition and muscle contraction is slower and weaker. The force of contraction relates directly to the electrical activation sent by the CNS and the number of motor units recruited. Therefore, as fatigue increases, the recruitment of motor units decreases.
The nerve cell working capacity cannot be maintained for a very long time. Under the strain of training or competition demands, the working capacity decreases. If high intensity is maintained as a result of fatigue, the nerve cell assumes a state of inhibition to protect itself from external stimuli. Fatigue, therefore, should be seen as the body's way of protecting itself against damage to the contractile mechanism of the muscle.
The skeletal muscle produces force by activating its motor units and regulating their firing frequency, which progressively increases in order to enhance force output. Fatigue that inhibits muscular activity can be neutralized to some degree by a modulating strategy: by responding to fatigue through the ability of motor units to alter firing frequency. As a result, the muscle can maintain force more effectively under a certian amount of fatigue. If the duration of sustained maximum contraction increases, the frequencey of the motor units firing decreases, and inhibition will become more prominent.
Marsden et al. (1971) demonstrated that compared to the start of a 30 second maximum voluntary contraction, the end firing frequency decreased by 80%. Similar findings were reported by Grimby et al. (1992) who stated that, as the duration of contraction increased, activation of large motor units decreased, lowering the firing rate below the threshold level. Any combination of contraction beyond that level was possible through short bursts (phasical firing), but not appropriate for a constant performance.
The above findings should caution those who promote the theory (especially in football and bodybuilding) that muscle size and strength can only be achieved by performing each set to exhaustion. The fact that as a contraction progresses, the firing frequency decreases, discredits this highly-acclaimed method.
