ACSM Clinical Exercise Physiologist (CEP) Practice Exam

The choice indicating "CO2 produced by cell metabolism/O2 consumed by tissues" accurately describes the respiratory quotient (RQ). RQ is a measure used to assess the ratio of carbon dioxide produced by the body to the oxygen consumed, providing insights into the types of substrates that are being metabolized for energy. When carbohydrates, fats, or proteins are metabolized, they produce different amounts of carbon dioxide and consume varying amounts of oxygen. This ratio is particularly useful in understanding metabolic processes, especially during various intensities of exercise and in conditions of rest.

In contrast, the other options do not correctly define RQ. For instance, while CO2 expired/O2 consumed at the mouth may seem related, it does not consider the cellular level of metabolism necessary for RQ. The reference to heart rate during maximum exercise and lactate threshold focuses on other physiological parameters and performance metrics, further confirming that they are unrelated to the precise definition of respiratory quotient.