When your muscle cells no longer have an adequate amount of oxygen, why are you still able to get enough energy to complete a 200 m race?
Many things happen on various levels and timeframes. Immediate effects will be a change in heart rate and breathing patterns. Longer-term effects can include muscle soreness.
Lack of oxygen is called hypoxia. [ hypo means "less, under, low", ox means "oxygen", and -ia means "condition, state, or process". So hypoxia is a condition of low oxygen. Hypoxia causes the heart to beat faster in an
attempt to push more oxygen to the body and its cells.
On a cellular level, cells use oxygen to initiate their cycles. In other words, oxygen is one of the fuels (other than glucose) that drive each tiny cell's activities. Without any oxygen, cells stop functioning and can eventually die. This is called necrosis.
Oxygen is needed by the mitochondria in order to produce energy. When oxygen supplies are low, the mitochondria of the cells make lactic acid instead.
Lactic acid is the chemical most of us know as being associated with muscle soreness after exercise, especially when we've pushed exercise past our limits. What happens here is that your cells run out of oxygen, you run out of energy, and your muscles feel sore due to the lactic acid dumped into the muscle tissues by your cells.
What the body's cells are pretty convincingly trying to tell you here is- stop exercising or we will die. Most of us indeed know when to stop and wait until our cells have recovered before placing high demands on our muscles again. ]
There are no new answers.