This chapter discusses the speed and stamina limits on the human body.
Physiology of Exercise
At the start of a race, adrenaline levels are increased which trigger the pulse to quicken and heart beat faster. Respiration is deepened, and blood delivers oxygen to the muscles. Vasodilation sends blood to the skin to cool down the body. Lactic acid builds up as the body runs low in oxygen. Adenosine triphosphate, ATP, breaks down to generate muscle contractions. However, very little ATP is stored in muscle tissue, so it must be constantly replenished via creatine phosphate. The rate of ATP production is limited by the rate of oxygen delivery to the tissues. The rate of oxygen uptake is limited by the rate which the heart can pump blood around the bod. When ATP runs low, carbohydrates and fats are broken down for energy. Further, blood is diverted away from less active organs to provide a larger blood supply to the active muscles, especially the heart. Exercise will also release natural endorphins that decrease pain, increase relaxation, and lift someone’s mood.
Speed versus Stamina
For sprinting, carbohydrate is the better fuel because it supplies energy quicker through anaerobic metabolism, without oxygen. This type of speed exercise uses fast muscles that contract rapidly and fatigue easily. For a marathon, aerobic metabolism is preferred as it produces more ATP which allows the body to exercise for longer. This type of endurance exercise uses slow muscles that contract at less than half the rate of fast muscles and are more resistant to fatigue. Long distance runners are usually lean and light which helps to increase heat loss and reduce overheating.
Common misconceptions
Blood pressure does not actually rise during exercise since resistance falls due to an increase in the blood flow to the muscles. Also, breathing is not limiting on performance since the lungs get enough oxygen, but it is the heart that cannot deliver the oxygen fast enough to the tissues. Breathing only becomes a limiting factor in running at higher altitudes. Some athletes will use a technique called carbohydrate loading to ‘overfill’ the carbohydrate stores before the event. However, this is only useful for endurance athletes since this high carbohydrate diet does not provide benefits for a short exercise of under an hour. Also, ATP levels do not drop to zero as this would cause rigor seen during death only. Instead, there is a gradual reduction in the amount of calcium released when there is a prolonged contraction in order to weaken the contraction.
While training can improve individual performance, ultimately physical capacity is determined by one’s genes.
Getting into Shape
Exercising helps improve muscle coordination as well as skilled movements. Training will delay the onset of fatigue by improving the strength and power of the muscle. There can also be an increase in the cardiac output and of heart size overtime. Exercise will also slow the resting pulse which allows for a greater peak cardiac output during exercise to deliver more oxygen to the muscles. However, the effects of exercise are not permanent and can actually be lost pretty quickly when stopping regular exercise. Strenuous exercise can also lead to overuse injury and increase the risk of trauma to the body.
Gender Differences
With the exception of long-distance swimming, women lag behind men in strength, speed and stamina in almost all sports.
Female athletes have been closing the gap in track and field events. However, women have not reached levels that are as fast as men. This is due to the differences in physical abilities. Women have a lower maximum oxygen uptake, higher body fat percentage, less hemoglobin, smaller hearts, and therefore smaller cardiac output. Women also have less anabolic hormones which can effect more physical traits. Yet, women excel in long-distance swimming since their higher fat content is less dense than water and allows them to float more easily and spend less energy in the water than men.
Drugs Enhancing Performance
There have been many instances of athletes using drugs to enhance their performance during competition. These drugs include growth hormone, amphetamines, adrenaline, erythropoietin, testosterone, anabolic steroids, and many others. This practice is now banned by the International Olympic Committee. This is in part due to the side effects that these drugs produce, such as sterility, liver cancer, kidney damage, or heart failure.
Animal Adaptations for Speed
The wider and more frequent the stride, the faster speed an animal can reach. Many animals have evolved longer legs and a flexible spine which allows a longer stride. Many fast animals will even have lighter limbs and smaller bones. Smaller animals have an advantage since the larger the animal, the harder it is to move their limbs.