A new method to study human metabolic rate changes and thermal comfort in physical exercise by CO2 measurement in an airtight chamber

The human metabolic rate is probably the most fundamental but least accurately assessed parameter in thermal comfort research and practice. This study aims to test the dynamic changes of the metabolic rate and its effects on thermal comfort perception. An airtight chamber (2 × 2 × 2 m3) was utilized to measure subjects' accumulated CO2 production, and metabolic values then were calculated based on indirect calorimetry theory. During the test, 31 subjects were first asked to ride a spinning bike for 8 min at different intensities, and then asked to remain sitting for 22 min. The results showed how the human metabolic rate changed during different exercise periods. It took the human body 5-6 min to reach a new exercising metabolic level while the human body needed 7-9 min to recover from exercise to a normal sedentary state. The dramatic changes in metabolic rate markedly influenced subjects' thermal sensation and thermal comfort perception. These findings provide a general principle of metabolic rate changes and could serve as a reference for future thermal comfort research.