Endurance Exercise Ebook
The lactate threshold, however, is higher in endurance-trained athletes than it is in other people. These athletes, because of their higher cardiac output, have a higher rate of oxygen delivery to their muscles. As mentioned in chapter 12, endurance training also increases the skeletal muscle content of mitochondria and Krebs cycle enzymes, enabling the muscles to utilize Increased oxygen consumption lowers the tissue PO2 and lowers the affinity of hemoglobin for oxygen (due to the effect of increased temperature). More oxygen, as a result, is unloaded so that venous blood contains a lower oxyhemoglobin saturation than at rest. This effect is enhanced by endurance training. more of the oxygen delivered to them by the arterial blood. The effects of exercise and endurance training on respiratory function are summarized in table 16.11.
Ischemia, telemetric monitoring may also be necessary. The focus of this program is on ambulation and regaining ADL independence, so the main exercises include ambulation training, treadmill training, and bicycle ergometry. As soon as a patient has recovered sufficiently to transfer safely, a bedside bicycle ergometer is advised to allow for increased endurance training.
Inferior to most men and thus could not effectively defend themselves. Women are socialized to focus on beauty first, and more recently, on physical fitness (i.e., aerobic endurance), but not on physical strength. Like the women of the early twentieth century, modern women believe in their natural physical weakness and do little to change it. These beliefs persist in spite of evidence that shows women are four times more likely to escape a would-be rapist than they are to be raped by him (Riger & Gordon, 1989).
Why would endurance exercise training likely increase this individual's exercise capacity 5. Endurance exercise training would have little effect on any aspect of lung function. However, training would cause adaptations within exercising muscle that would increase muscle oxidative capacity and reduce lactic acid production. By reducing the ventilatory demands of exercise, these changes would increase exercise capacity in this individual.
Anabolic steroid usage is not limited to weight-lifting-power athletes. Endurance athletes (e.g., distance runners and triathletes) have also used anabolic steroids. However, most studies have failed to demonstrate a substantial, beneficial effect of anabolic steroids on maximal oxygen consumption (i.e., key determinate to aerobic-endurance capacity) (103-105). It has been proposed that endurance athletes who use anabolic steroids choose to do so because they recover from exercise training bouts more rapidly. This idea seems logical, because performing more exercise training is a major stimulus to improve the cardiovascular-respiratory system and, thereby, aerobic performance, and androgen treatment should negate the decline in testosterone that normally follows heavy exercise.
Both bradycardia and tachycardia can occur normally. Endurance-trained athletes, for example, often have heart rates ranging from 40 to 60 beats per minute. This athlete's bradycar-dia occurs as a result of higher levels of parasympathetic inhibition of the SA node and is a beneficial adaptation. Activation of
The forces applied to bone during exercise are related both to the weight borne by the bone during activity and to the strength of the involved muscles. Consequently, bone strength and density appear to be closely related to applied gravitational forces and to muscle strength. This suggests that exercise programs to prevent or treat osteoporosis should emphasize weight-bearing activities and strength as well as endurance training. Adequate dietary calcium is essential for any exercise effect weight-bearing activity enhances spinal bone mineral density in post-
Retrospective comparative studies examining isolated, single blood samples have found lower testosterone levels in chronically endurance-trained males. The subjects in those studies were typically distance runners who had been involved with the physical-training aspects of their sport for 1 to 15 yr. In those studies, total and free-testosterone levels in the endurance-trained men were only 60-85 of the levels of matched sedentary controls (7,35,54,56-58). Many of the early studies reporting this finding suffered from small sample sizes. However, recent work with larger numbers of subjects has substantiated the findings (59,60). These low resting testosterone levels are highly reproducible and are not just an aberration of the athletes' seasonal training regime (60). Prospective studies have also been conducted in which blood samples have been collected for weeks or months during endurance training regimens. Findings thus far from such studies have been inconsistent. Some reports...
The maximal oxygen uptake, obtained during very strenuous exercise, averages 50 ml of O2 per minute per kilogram body weight in males between the ages of 20 and 25 (females average 25 lower). For trained endurance athletes (such as swimmers and long-distance runners), maximal oxygen uptakes can be as high as 86 ml of O2 per minute per kilogram. These considerable differences affect the lactate threshold, and thus the amount of exercise that can be performed before lactic acid production contributes to muscle fatigue. In addition to having a higher aerobic capacity, well-trained athletes also have a lactate threshold that is Table 12.5 Effects of Endurance Training on Skeletal Muscles All fiber types adapt to endurance training by an increase in mitochondria, and thus in aerobic respiratory enzymes. In fact, the maximal oxygen uptake can be increased by as much as 20 through endurance training. There is a decrease in type IIX (fast glycolytic) fibers, which have a low oxidative...
Blood flow to the gut decreases in proportion to exercise intensity, as sympathetic vasoconstrictor tone rises. Water, electrolyte, and glucose absorption may be slowed in parallel, and acute diarrhea is common in endurance athletes during competition. However, these effects are transient, and malabsorption as a consequence of acute or chronic exercise does not occur in healthy people. While exercise may not improve symptoms or disease progression in inflammatory bowel disease, there is some evidence that repetitive dynamic exercise may reduce the risk for this illness.
Chronic nonphysiologic stresses modulate ventricular function by causing pathologic hypertrophy. Chronic alterations in the demands placed on the cardiovascular system within the physiologic range can cause modest changes in cardiac mass.169,170 However, measurable changes require very substantial changes in demand. Thus endurance athletes develop modest, physiologic hypertrophy characterized by increased ventricular chamber volume with little or no increase in wall thickness. This adaptation allows for a greater SV.
Endurance exercise training does have significant effects on the major male reproductive hormone, testosterone, and the hypothalamic-pituitary-axis that regulates testicular function. A growing body of evidence suggests that testosterone is chronically lowered in endurance exercise-trained men, and we have referred to this condition as exercise hypogonadism. Although the mechanism of this testosterone lowering is currently unclear, it may be related to a dysfunction or a readjustment in the hypothala-mic-pituitary-testicular regulatory axis brought about by years of endurance training. Currently, the time course of these changes, including their reversibility, remains unresolved and is in need of further scientific investigation (137). The lowered testosterone levels of the exercise-hypogonadal male could potentially disrupt anabolic or androgenic testosterone-dependent processes. Conversely, the alterations in testosterone levels brought about by endurance training could have...
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