Five categories of physiological responses are associated with the training session. And this include the warm up, the training session itself, the recovery, and the supercompensation effect, and of course that all dreaded decay phase. We've talked quite a bit about the warm up effect. Now remember, the warm up is designed to get the athlete's body ready for a higher level of activity. And there are five important adjustments that are made during the warm up. These include the changes that are made to blood circulation, mainly by adjusting heart rate and the dilation or construction of the blood vessels depending on what organ that they're going to. There is an elevation of cold body and muscle temperature. There is an enhancement of the biochemical reactions by activating relevant enzymes into action. There is improved neuromuscular function. And the warm up possibly, possibly I say, prevents injury by preparing the brain for higher level of activity and coordination. The outcome of these adjustments is an increase in blood flow to the active tissue and an increase in fuel mobilization. And there is an activation of fat used that helps to delay the use of blockage in stores and physiologists refer to this as sparing glycogen. The overall result is an improved endurance. In essence, you can think of the warm up as taking the body into an upper range of homeostasis in preparation for the training session. The brain puts the body on hyper alert and is prepared to react very quickly to the extra physical demands. During the training session itself, the body moves into even higher physiological high gear. For example, the cardiovascular and respiratory system and their functioning accelerates. Skeletal muscles demand up to 40 times more oxygen depending on the exercise intensity. And there's an increase in the breakdown of glucose and fat. So, the active skeletal muscles have the fuel they need to generate more ATP for muscle contraction. The nervous and the endocrine system orchestrate all these physiological enhancements. And as the resources needed to keep those physiological activities going at a higher level as they are tasked beyond their capacity, the sensation of fatigue accumulates. And this sensation of fatigue causes a gradual decline in the athlete’s performance. Now, we don't fully understand fatigue but there are three rather elegant theories that that I quite like. One theory proposes that when homeostasis is severely challenged, an inflammatory reflex is triggered, alerting the brain to the dangerous conditions for cells. The resulting fatigue accompanying this inflammatory reflex makes it difficult for the athlete to continue at that particular exercise intensity. There is an overwhelming desire to stop and rest so that homeostasis can be reestablished. A second theory is the complex systems theory. And this theory proposes that one of the many organ systems being used causes this sensational fatigue when there's potential traumatic damage to the tissues of that organ. The threatened organ system slows the activity of the other organs, so physiological functioning is brought back to a safe level. The sensation of fatigue accompanies the slowing of the physiological functioning. And the third theory and probably the most popular theory explaining fatigue is the glycogen reduction theory. Enhanced nerve activity during exercising increases the brain's energy demands. And the brain prefers to use glucose from the blood and then as these declines, it turns to its own glycogen stores. Animal study suggests that the liver can maintain blood glucose levels during intense exercise for around 16 minutes. However, after 16 minutes, blood glucose gradually declines and can be 46% lower than baseline after two hours of training. When the brain turns to its own glycogen stores, they can decrease these stores by 34% to 60%. And this is thought to cause nervous system fatigue and the desire to keep exercising declines. Now, during recovery, the internal environment of the body returns to normal working conditions. The recovery of homeostasis occurs in two phases. And the first phase is where energy resources are replenished and the damaged structures are repaired and the body's chemistry returns to homeostasis. The time taken to accomplish homeostasis depends on the depth of the accumulated fatigue. The second phase is the training effect or supercompensation phase of the recovery period. During this phase, the stressed internal structures used during the training session are reinforced. Now, as we move through this course, you will appreciate the importance of glycogen to the athlete's performance. And research suggests that an important training effect is to supercompensate glycogen stores in the brain and in the muscle and in the liver. But the problem is that super compensation and decay occurs at different rates in these organs. Now, the black dotted line here on this graph represents the normal store of glycogen in the brain and the skeletal muscle and the liver. That's 100% therefore if they stores were full. Now, here is the replenishment in supercompensation of glycogen in the brain. And here it is for skeletal muscle. And here it is for liver. In the case of the brain and skeletal muscle, training has a positive effect on glycogen stores. Glycogen supercompensation of skeletal muscle occurs around 24 hours after exhaustive exercise. And the blue line here represents the glycogen, remember in skeletal muscle. The red circle is the peak of supercompensation for glycogen in skeletal muscle. It occurs four to seven hours after exercise in the brain. The brain's glycogen is restored and supercompensated first before skeletal muscle. The brain and nervous system remember, needs glucose to remain healthy. So, this preferential restoration of the brain's glycogen may be an attempt to prevent permanent nerve damage. Training appears to increase the baseline store of glycogen in the brain and probably in the peripheral nerves as well. And I think you can appreciate that this is a very, very valuable training effect. Note that they appear to be very minor supercompensation of liver glycogen. Remember however, that this research was done on rat so maybe a bit different in humans. But for now, it is probably safe coaching practice to assume that humans will respond similarly. A small amount of supercompensation that does occur, appears to take 48 hours after exhaust of exercise. And this is one rationale for alternating a high day of training with a slightly lighter day of training for the various organ systems. Now, decay occurs in all cases. Brain glycogen supercompensation was fully lost within 36 hours. Supercompensation of skeletal muscle glycogen is fully lost within 48 hours. Now, we're going to return to the decay effect shortly to explain the timing of the next training session.
