Age and oxygen utilization during submaximal treadmill exercise in males.

One thousand and fifty-eight men walked on a motor-driven treadmill at 3 miles/hour with the grade increasing 3% at 3-min intervals. (The 30 oldest men walked at 2 miles/hour.) Ventilation, Vo2, and Vco2 were recorded at each treadmill grade. During exercise Vo2 (in ml/min/kg of body wt) is significantly higher in younger compared with older boys. Vo2 increases slightly from age 20 though 59 years at any given work load. The respiratory exchange ratio (Vco2/Vo2) increases throughout the age range, particularly at the higher work loads. Ventilation (in 1/min/kg of body wt) decreases from age 10 to 20 years and increases thereafter, as does the ventilatory equivalent. The increased ventilation in young boys is characterized by an increase in respiration rate, whereas in older men it is accomplished through an increase in tidal volume.