With oxygen. When exercise is not too fast and is steady, the heart can supply all the oxygen that the working muscles need.
Summarised as: glucose + oxygen ? energy + carbon dioxide + water.

Without oxygen. When exercise duration is short and at high intensity, the heart and lungs cannot supply blood and oxygen to muscles as fast as the respiring cells need them.
Summarised as: glucose ? energy + lactic acid.

The enlargement of an organ or tissue from the increase in the size of its cells.

Specific, Measurable, Accepted, Realistic, Timebound.

Training at altitude where there is less oxygen. The body adapts by making more red blood cells to carry oxygen. The additional oxygen carrying red blood cells is an advantage for endurance athletes returning to sea level to compete.