Oxygen Uptake and Cardiac Performance in Obese and Normal Subjects during Exercise

Abstract

Work capacity and cardiopulmonary performance were studied in a group of 11 young obese subjects (BMI 39.9 kg/m²) and a group of 10 young normal subjects (BMI 22 kg/m²). First of all they underwent an incremental cycle ergometer test up to exhaustion. Subsequently, every subject of the two groups performed a constant work rate test at different work loads to estimate cardiac output (q̇) below anaerobic threshold (AT) by a 20-second CO₂ rebreathing method. Obese subjects had a significantly lower AT (79 vs. 109 W). The ratio between oxygen uptake and heart rate (v̇O₂/HR) (O₂ pulse) was higher in the obese group; nevertheless, this variable became significantly lower if we took into consideration the ratio between O₂ pulse and kilogram fat-free body mass or kilogram body weight. Both these observations suggest that their reduced work tolerance is linked with a reduced oxygen supply to the muscles in activity. q̇ increased in similar ways in obese and normal subjects at the preset work rates. The ratio q̇/body surface (cardiac index; CI) that we considered in order to try to minimize the differences in body sizes between the two groups, increased less in response to increasing work rates in our obese subjects than in normal subjects. As a whole, these data appear to be in line with a relatively less efficient cardiac performance during progressive work rates in obese subjects.

Influence of Excess Adiposity on Exercise Fitness and Performance in Overweight Children and Adolescents

“…[12][13][14][15][16][17] Increased fat mass is associated with decreased exercise performance in overweight children and adolescents. [12][13][14][15][16][17] However, the cause of this limited exercise tolerance remains in question. Several investigators, primarily those who have studied moderately overweight and obese children and adolescents, have reported similar maximal oxygen uptake (V o 2 max) relative to body weight compared with normal-weight control subjects.…”

“…22 Whether these differences significantly influence fitness and performance is unclear. Obesity-related changes in exercise catecholamine response, 15,16,21 myocardial metabolism, and left ventricular morphology 22 may be associated with these findings.We hypothesized that the primary factor limiting severely overweight adolescents when they undertake sustained exercise would be the increased metabolic cost resulting from having to move a greater mass and that there would also be a smaller but still important effect of diminished cardiorespiratory reserve. We predicted that differences in the energy costs of exercise in overweight and nonoverweight adolescents would be demonstrable most clearly during submaximal exercise tasks: compared with nonoverweight adolescents, overweight adolescents would use a larger percentage of their total cardiorespiratory reserve when performing a submaximal task such as "unloaded" pedaling on a stationary bicycle.…”

“…In addition, the greater metabolic cost of unloaded cycling was shown to predict a poorer performance during the functional performance evaluation walk/run test. Part of the metabolic cost of motion in significantly overweight adolescents likely is attributable to decreased mechanical efficiency.Although several previous studies have found no significant differences in absolute V o 2 max or LTV o 2 in overweight and nonoverweight adolescents and adults, 16,36,37 numerous different methods have been used to scale V o 2 max to account for the larger size of overweight individuals. Weight in kilograms, fat mass, fat-free mass, BMI, and height all have been used as normalization measures.…”

Critical review of the equations predicting 6-minute walking distance in obese subjects

“…Variables used in the existent literature may not thoroughly capture the complexity of disability in obese people. In fact, obese individuals, in association with the increased BMI, show an energetic, cardiac and respiratory, limitation leading to a mobility impairment [45,46], together with the relative reduction of skeletal muscle strength and general deconditioning, also leading to disability [47,48]. Other potential contributors to the disabling status of obese subjects are the friction of the skin through fat depositions on the thighs, the increased plantar foot pressure (first and lesser metatarsal, mid-foot and heel region), as well as the pain and discomfort experienced when performing physical activities [30,[49][50][51].…”

The Association of Body Fat and Leisure Time Physical Activity Called into Question for Asian Indians

“…13,14 The fattest participants would thus have been expected to perform less physical activity during leisure time. However, this hypothesis seems unlikely to explain the differences in LTPA because it has been observed that obese children and adolescents do not have differentiated maximal oxygen consumption capacities but are burdened by the metabolic cost of their excess mass.…”