Answer to Question 1
VO2max is affected by genetics, training, gender, age, and body composition. Although aerobic training can help people attain good or excellent cardiorespiratory fitness, only those with a strong genetic component are able to reach an elite level of aerobic capacity (60-80 mL/kg/min). Further, VO2max is 15-30 percent higher in men. This is related to a greater hemoglobin content, lower body fat, and larger heart size in men (a larger heart pumps more blood, and thus produces a greater stroke volume). VO2max also decreases by about 1 percent per year starting at age 25. This decrease, however, is only 0.5 percent per year in physically active individuals.
Answer to Question 2
Aerobic exercises increase CR endurance. Examples include walking, jogging, swimming, cycling, cross-country skiing, water aerobics, rope skipping, and aerobics.
By contrast, anaerobic activities do not contribute much to developing the CR system. The intensity of an anaerobic exercise is so high that oxygen cannot be delivered and utilized to produce energy. Because energy production is limited in the absence of oxygen, anaerobic activities can be carried out for only short periods-2-3 minutes. Examples of anaerobic activities include races of 100, 200, and 400 meters in track and field, a 100-meter race in swimming, gymnastics routines, and strength training.
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Genes, hormones, and activity affect weight
Formation of a DNA loop allows factors that bind to an enhancer or silencer