Danny O’Dell’s
Explosivelyfit Training News
Strength and power knowledge
15-November-06
ISSN: 1550-2643: Library Of Congress, Washington D.C.,
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Topic discussed:
The origins of fatigue
The ability to maintain superior outputs of strength and power during a sporting event is determined by the level of fatigue one is able to tolerate and subsequently overcome. A rapid onset of fatigue is a direct result of near to maximal efforts in such sports as powerlifting and weight training. The cyclic sport athletes experience their fatigue barriers when slow fatigue accumulates in the organism. Endurance participants in activities, such as distance runners and bicyclists, know exactly what this means.
Endurance (Siff 2000) is defined as that ability to resist fatigue. Isometric hold, sustaining an isometric contraction, or dynamic endurance relating to the several types of muscle contractions, i.e. auxotonic, (contraction changes in muscle length and tension) isotonic and isokinetic (velocity is constant) should not be confused with endurance activity capabilities performed at high speed.
It is easy to see that fatigue is not just one dimensional in nature. Thus we have individual definitions of speed, static strength, dynamic strength, and speed strength endurance. Fatigue may be further broken down into central fatigue and peripheral fatigue with the former associated with the central nervous system (CNS). Those factors corresponding to the CNS include all of the components outside of the muscular system. Decreased motivation for training, impairment of the spinal nerve impulses and altered recruitment of the spinal motor neurons are directly attributable to central nervous system fatigue.
Power sports or the short duration activities fatigue
An intense activation of the CNS through the use of maximal weight loading or maximal plyometrics exercises will take a minimum of 48 hours recovery and more, if restorative measures are not implemented after the training session is over.
Peripheral fatigue on the other hand relates to the processes of the peripheral nervous and the neuromuscular systems. Once these two become affected the ability to fire the muscles becomes inhibited due to interference at the cellular level of excitation. Alterations in this phase lower the capability of the muscle cells to maximize their full force potential. Peripheral fatigue is even broken down into low and high frequency fatigue depending on the frequency at which it occurs in response to electrical stimulation.
Fatigue does not mean the inability to continue on with a task. There are changes taking place in the afferent feedback loop, motor neuronal discharge rates, motor cortical output and the perceived effort develop far in advance of the organisms physiological limits.
Muscle recruitment is a sequential event. The low threshold, slow twitch fatigue resistant fibers fire first under low load conditions with the fast twitch, high powered but low fatigue resistant fibers filling in as the load becomes more intense. Elite athletes train to bypass the recruitment of the slow twitch and go straight to the fast twitch fibers in order to produce the almost instant power needed to succeed. The greater the load and tension, the sooner the fast twitch fibers are utilized with the attending increased muscle tension.
Muscle contraction tension will inhibits the free flow of blood to the muscle fibers, which in turn affects the local muscular endurance capabilities. Without the blood flow the oxygen to the muscle will progressively decrease as the load increases. This does not seem to be the case in loads below 15% of a one repetition maximum. However once this intensity reaches 50% and above the flow is cut off completely due to the compression on the blood vessels by the contraction of the muscle fibers. At this stage the body is relying upon the anaerobic processes to continue the effort.
Of course most strength training and sporting events consist of alternating patterns of contraction and relaxation cycles. It is during these times the body recuperates and sends the nutrients back into the muscles. But if the activity involves isometric or quasi-isometric contractions, as in many wrestling situations, which last longer than six seconds then fatigue quickly builds up.
Endurance activities
Fatigue: is it in the muscles, the mind, or the heart?
Dr. Timothy Noakes, MD. postulates that fatigue originates within the structural makeup of the heart itself and is thus controlled by a ‘Central Governor’. This model of fatigue “proposes the existence of a governor that monitors the state of oxygenation of the heart and perhaps other organs (such as the brain and diaphragm) as well.” (1)
When the oxygenation levels to the heart approach a critical stage of what is deemed safe by the organism the motor cortex of the brain stops recruiting additional muscles to continue the activity at the present pace or intensity. Without new muscle fibers recruited into the activity, the body experiences fatigue. This sensation “is always sensed exclusively by the brain, even though it appears to be coming from” (2) somewhere else. These signals of fatigue may manifest as muscular exhaustion or various degrees of discomfort in the musculature.
Following the lack of additional muscle fiber recruitment, the work output of both the heart and muscles begins to drop off. This leads to a reduced demand for oxygen at the heart. With this reduced demand for oxygen the heart is automatically protected from damage which would occur if it were to be without enough oxygen to function correctly.
Accordingly, “this model predicts that maximum exercise capacity is a process, coordinated subconsciously by the brain, limited by the maximum capacity of the coronary blood flow to supply oxygen to the heart, and regulated to prevent heart damage during maximal exercise.” (3)
With that out of the way here is a new definition of fatigue:
Recall that fatigue is traditionally defined as “the inability to sustain the desired or required force”. (4) Some authorities hypothesize that fatigue is an emotion or sensation and not a direct physical phenomenon. These interpretations of fatigue seem to indicate that changes in the brain commands to the muscles signals the onset of the fatigue condition in our bodies. Added to this theory is the contribution from Noakes, T who believes that fatigue is the ‘manifestation of a change in pacing strategy’. (5)
Summary
Fatigue may not be what it appears, i.e. a physical deterioration of muscle and oxygen utilization. Instead according to this new theory it may well be controlled by the hearts ability to maintain the critical blood flow within the system, specifically to the actively engaged muscles.
Training to overcome fatigue is a fact of life for the strength coach.
That’s all for this time. I hope your training is going well and wish you happiness in your life.
Stay strong, and remain passionately committed to your hearts chosen path.
By Danny M. O’Dell, MA. CSCS*D
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