Respiration in Exercise

Although one's respiratory ability is of relatively little concern in the performance of sprint types of athletics, it is critical for maximal performance in endurance athletics.

Oxygen Consumption and Pulmonary Ventilation in Exercise.

Normal oxygen consumption for a young man at rest is about 250 ml/min. However, under maximal conditions, this can be increased to approximately the following average levels:

ml/min

Untrained average male 3600

Athletically trained average male 4000

Male marathon runner 5100

Figure 84-6 shows the relation between oxygen consumption and total pulmonary ventilation at different levels of exercise. It is clear from this figure, as would be expected, that there is a linear relation. Both oxygen consumption and total pulmonary ventilation increase about 20-fold between the resting state and maximal intensity of exercise in the well-trained athlete.

O2 consumption (L/min)

Figure 84-6

Effect of exercise on oxygen consumption and ventilatory rate. (Redrawn from Gray JS: Pulmonary Ventilation and Its Physiological Regulation. Springfield, IL: Charles C Thomas, 1950.)

Limits of Pulmonary Ventilation. How severely do we stress our respiratory systems during exercise? This can be answered by the following comparison for a normal young man:

L/min

Pulmonary ventilation at maximal exercise 100 to 110

Maximal breathing capacity 150 to 170

Thus, the maximal breathing capacity is about 50 per cent greater than the actual pulmonary ventilation during maximal exercise. This provides an element of safety for athletes, giving them extra ventilation that can be called on in such conditions as (1) exercise at high altitudes, (2) exercise under very hot conditions, and (3) abnormalities in the respiratory system.

The important point is that the respiratory system is not normally the most limiting factor in the delivery of oxygen to the muscles during maximal muscle aerobic metabolism. We shall see shortly that the ability of the heart to pump blood to the muscles is usually a greater limiting factor.

Effect of Training on Vo2 Max. The abbreviation for the rate of oxygen usage under maximal aerobic metabolism is Vo2 Max. Figure 84-7 shows the progressive effect of athletic training on Vo2 Max recorded in a group of subjects beginning at the level of no training and then pursuing the training program for 7 to 13 weeks. In this study, it is surprising that the Vo2 Max increased only about 10 per cent. Furthermore, the frequency of training, whether two times or five times per week, had little effect on the increase in Vo2 Max. Yet, as pointed out earlier, the Vo2 Max of a marathoner is about 45 per cent greater than that of an untrained person. Part of this greater Vo2 Max of the marathoner probably is genetically determined; that is, those people who have greater chest sizes in relation to body size and stronger respiratory muscles select themselves to become o

Training frequency ▲ = 5 days/wk

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Essentials of Human Physiology

Essentials of Human Physiology

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