Measurement of maximum oxygen uptake (V O2 Max.) during exercise. Here, a woman's respiration is monitored by a computer as she pedals an exercise bicycle. Exhaled air is collected for analysis in the plastic bag mounted on the stand. The value of V O2 Max. can be raised through increased fitness, and is used by athletes as an indicator of their state of fitness. The value is lowered in many cases of heart or respiratory diseases.