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
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).