Obesity is inversely related to anaerobic threshold (14) and aerobic capacity. Obesity can increase the oxygen cost and mechanical work of breathing (15). Obesity is associated with higher than normal levels of pulmonary ventilation, oxygen consumption, and carbon dioxide production. These values are particularly elevated during exercise (16). Pulmonary function is altered with increasing deposit of fat on the thoracic cavity and throughout the abdominal cavity. Lowered functional residual capacity in moderate and gross obesity contributed to the decreased chest wall compliance resulting from the accumulation of fat in and around the abdomen, diaphragm, and ribs (17).
Sakamoto, S. et al. found that during exercise, a fatty group demonstrated a higher respiratory rate and lower tidal volume compared with the normal group. The investigators contributed part of this difference in the fattier group to an insufficient ventilation capacity due to increased respiratory dead space (18).
Obesity has been associated with varying degrees of arterial hypoxemia. For some, hypoventilation and hypercapnia may persist. In the obese, hypoventilation is not fully responsible for most cases of hypoxia. Abnormally elevated venous admixture and physiologic dead space ratios seem to be the greatest contributor toward arterial hypoxemia (19).
The severely obese have reduced work tolerance and extreme variability in their initial physical fitness levels. Foss, Lampman, & Schteingart (1975) noted VO2 max ranged from 12.9 to 22.3 ml/kg/min their sample of extremely obese subjects. Interestingly, only weak correlations were found between initial fitness levels and age, body weight, or sex (20).
Older obese men are better able to aerobically support the transport of their body weight than younger obese men. It seems that the older, obese men may have become better physically conditioned throughout the years transporting their excess body fat (21).
When safety precautions are recognized, obese patients can safely perform exercise testing (22), participate in progressive intensity exercise and should be encouraged to do so by medical personnel (20, 23, 24, 25). Before beginning an exercise program, a thorough medical evaluation of the obese patient is recommended. A comprehensive medical history and a detailed physical examination should disclose medical conditions that may contraindicate an exercise program. Conditions of particular interest include cardiovascular disease, uncontrolled diabetes, respiratory insufficiency, and musculoskeletal disease. Medication prescriptions, such as insulin and a ß-blockers, may need to be reviewed and altered by their physician since physical training has the potential to interact with these and other medications (22).
Miller W. C. et al. examined the relationship between relative oxygen consumption and heart rate in obese (N = 86, body fat > 30%, hydrostatic weighing) compared with normal-weight (N = 51, body fat < or = 30%) adults and developed regression equations for predicting maximal heart rate. In normal weight individuals, the equation "220-Age" can be used for predicting maximal heart rate, but for obese individuals the equation 200-0.5 x Age was reported to be more accurate. Once MHR is determined, either the Karvonen's method or the straight percentage technique was deemed appropriate for prescribing exercise intensity for both populations (26).