when PO2 is about 20 mmHg

### Myoglobin loading O2

## Step1: Understanding the Concept of PO2### PO2 refers to the partial pressure of oxygen in the blood. It is a measure of the amount of oxygen dissolved in the blood. The normal range for PO2 in the blood is between 75 and 100 mmHg.## Step2: Understanding the Concept of Myoglobin### Myoglobin is a protein found in the muscle cells of animals. It binds to oxygen and releases it when the muscle cells need it for energy production. Myoglobin has a higher affinity for oxygen than hemoglobin, the oxygen-carrying protein in red blood cells.## Step3: Understanding the Relation between PO2 and Myoglobin### When the PO2 in the blood is low, around 20 mmHg, myoglobin will load up with oxygen. This is because myoglobin has a higher affinity for oxygen than hemoglobin, so it will bind to the oxygen when it is available.