Complete the sentence with an appropriate term.

The ratio of minute ventilation and oxygen uptake during exercise is $\frac{Ve}{VO_2}$ for oxygen consumption and $\frac{Ve}{VCO_2}$ when evaluating carbon dioxide output. At the onset of lactate accumulating in the blood more rapidly than it can be effectively buffered, the ventilation rate increases at a rate disproportionate to the rate of oxygen uptake in tissues. The lactate threshold and the _________ are very closely connected because of the necessity of clearing excess lactate and $CO_2$ from the body.

During exercise, the lactate threshold and the respiratory system are closely connected because the body needs to clear excess lactate and CO₂ from the body. The ratio of minute ventilation to oxygen uptake (Ve/VO₂) and minute ventilation to carbon dioxide output (Ve/VCO₂) play a role in this process.

Explanation:

In exercise, the rate of lactate accumulation in the blood increases faster than it can be effectively buffered, leading to the onset of a phenomenon known as the lactate threshold. This is closely connected to the respiratory system because the body needs to clear excess lactate and carbon dioxide (CO₂) from the body. This is achieved by increasing the ventilation rate, which is the rate at which air is exchanged in the lungs.

The ratio of minute ventilation (Ve) to oxygen uptake (VO₂) is denoted as Ve/VO₂ and it represents the amount of air moved by the lungs per unit of oxygen consumed by the body. Similarly, the ratio of minute ventilation to carbon dioxide output (VCO₂) is denoted as Ve/VCO₂, representing the amount of air moved per unit of CO₂ produced.

During exercise, as lactate accumulates and the body needs to remove excess CO₂, the ventilation rate increases disproportionately to the rate of oxygen uptake in tissues.