The body mass index, or BMI, is a commonly used indicator of weight status. BMI measurements of between 18.5 and 24.9 show normal weight while a BMI over 25 indicates your being overweight. When the BMI value exceeds 30, your weight status is considered clinically obese. High BMI measurements have been correlated with reduced levels of physical fitness, including lowered VO2 max.
VO2 Max as a Fitness Indicator
VO2 max is an indicator of your overall physical fitness and incorporates aspects of your respiratory capacity, cardiovascular health and muscle fitness. A decline in the performance of any of these systems will result in a reduced measurement of VO2 max. VO2 max is a measure of the maximum amount of oxygen that your body can consume during maximum workload. The ability of your respiratory system to take in large volumes of air and the ability of your heart and blood vessels to transport oxygen from your lungs to your muscles both contribute to your VO2 max.
BMI and VO2 Max
According to multiple research studies published in the "Journal of Sports Medicine and Physical Fitness," high BMI measurements are linked to lowered VO2 max values. The role BMI plays in reducing VO2 max is related to changes in respiratory capacity and cardiovascular endurance.
BMI and Respiratory Function
Research published in the journal "Chest" has demonstrated a link between increasing BMI measurements and impairments in lung function. When BMI reaches 30, the minimum classification for obesity, the functional residual capacity of the lungs is reduced by 25 percent, and the expiratory reserve volume is reduced by over 50 percent. While these two lung function measurements are not heavily involved in normal breathing, they do drastically limit the lungs' capacity for achieving maximum work and will result in lowered VO2 max values.
BMI and Cardiovascular Function
Increased BMI levels have also been associated with decreases in cardiovascular system capacity. Writing in the "Journal of Sports Science and Medicine," researchers have linked high BMI measurements with declines in several measurements of cardiovascular function that impair cardiorespiratory endurance. Again, while these declines will not overly impair normal activities, they will reduce performance at maximal levels and, therefore, contribute to lowered VO2 max.