Background— Obesity is associated with heart failure, but an effect of weight, independent of comorbidities, on cardiac structure and function is not well established. We sought whether body mass index (BMI) and insulin levels were associated with subclinical myocardial disturbances. Methods and Results— Transthoracic echocardiography, myocardial Doppler-derived systolic (sm) and early diastolic velocity (em), strain and strain rate imaging and tissue characterization with cyclic variation (CVIB), and calibrated integrated backscatter (cIB) were obtained in 109 overweight or obese subjects and 33 referents (BMI <25 kg/m ² ). BMI correlated with left ventricular (LV) mass and wall thickness ( P 35) had reduced LV systolic and diastolic function and increased myocardial reflectivity compared with referents, evidenced by lower average long-axis strain, sm, cIB, lower CVIB, and reduced em, whereas LV ejection fraction remained normal. Differences in regional or global strain, sm, and em were identified between the severely obese (BMI >35) and the referent patients ( P <0.001). Similar but lesser degrees of reduced function by sm, em, and basal septal strain and increased reflectivity by cIB were present in overweight (BMI, 25 to 29.9) and mildly obese (BMI, 30 to 35) groups ( P <0.05). Although tissue Doppler measures were not associated with duration of obesity, they did correlate with fasting insulin levels and reduced exercise capacity. BMI was independently related to average LV strain (β=0.40, P =0.02), sm (β=−0.36, P =0.002), and em (β=−0.41, P <0.001). Conclusions— Overweight subjects without overt heart disease have subclinical changes of LV structure and function even after adjustment for mean arterial pressure, age, gender, and LV mass.

Globally, obesity is affecting an increasing proportion of children. Physical activity plays an important role in the prevention of becoming overweight and obese in childhood and adolescence, and reducing the risk of obesity in adulthood. Puberty and the following adolescent period are acknowledged as particularly vulnerable times for the development of obesity due to sexual maturation and, in many individuals, a concomitant reduction in physical activity. In many Western settings, a large proportion of children and adolescents do not meet recommended physical activity guidelines and, typically, those who are more physically active have lower levels of body fat than those who are less active. Active behaviours have been displaced by more sedentary pursuits which have contributed to reductions in physical activity energy expenditure. Without appropriate activity engagement there is an increased likelihood that children will live less healthy lives than their parents. Owing to the high risk of overweight adolescents becoming obese adults, the engagement of children and adolescents in physical activity and sport is a fundamental goal of obesity prevention.

The metabolic equivalent (MET) is a widely used physiological concept that represents a simple procedure for expressing energy cost of physical activities as multiples of resting metabolic rate (RMR). The value equating 1 MET (3.5 ml O₂·kg⁻¹·min⁻¹ or 1 kcal·kg⁻¹·h⁻¹) was first derived from the resting O₂ consumption (V̇o₂) of one person, a 70-kg, 40-yr-old man. Given the extensive use of MET levels to quantify physical activity level or work output, we investigated the adequacy of this scientific convention. Subjects consisted of 642 women and 127 men, 18–74 yr of age, 35–186 kg in weight, who were weight stable and healthy, albeit obese in some cases. RMR was measured by indirect calorimetry using a ventilated hood system, and the energy cost of walking on a treadmill at 5.6 km/h was measured in a subsample of 49 men and 49 women (26–45 kg/m²; 29–47 yr). Average V̇o₂ and energy cost corresponding with rest (2.6 ± 0.4 ml O₂·kg⁻¹·min⁻¹ and 0.84 ± 0.16 kcal·kg⁻¹·h⁻¹, respectively) were significantly lower than the commonly accepted 1-MET values of 3.5 ml O₂·kg⁻¹·min⁻¹ and 1 kcal·kg⁻¹·h⁻¹, respectively. Body composition (fat mass and fat-free mass) accounted for 62% of the variance in resting V̇o₂ compared with age, which accounted for only 14%. For a large heterogeneous sample, the 1-MET value of 3.5 ml O₂·kg⁻¹·min⁻¹ overestimates the actual resting V̇o₂ value on average by 35%, and the 1-MET of 1 kcal/h overestimates resting energy expenditure by 20%. Using measured or predicted RMR (ml O₂·kg⁻¹·min⁻¹ or kcal·kg⁻¹·h⁻¹) as a correction factor can appropriately adjust for individual differences when estimating the energy cost of moderate intensity walking (5.6 km/h).