Age and cardiac output during cycle exercise in thermoneutral and warm environments

15 men (7 trained older men, mean age 65 +/- 2 yr; 8 normally active but untrained young men, mean age 26 +/- 1 yr) matched for VO2peak and anthropometric measures, with no history of pulmonary, cardiac, neuromuscular, or endocrine disease and a normal electrocardiogram.

Intermittent incremental cycle exercise at 35%, 60%, 75%, and 85% peak aerobic capacity (VO2peak) in a warm environment (36 degrees C).

Intermittent incremental cycle exercise at the same intensities in a thermoneutral environment (22 degrees C).

Cardiac output (Qc) measured at rest and during exercise using a CO2 rebreathing method.surrogate