Hypoxia is a medical condition where there is a deficiency of oxygen in the tissues and organs of the body. As we climb to higher altitudes the oxygen partial pressure decreases. Above 10 000 ft pressure altitude the oxygen partial pressure might not be enough to cover the body needs and hypoxia symptoms might appear.

Time of Useful Consciousness (TUC) is the duration during which an individual can effectively carry out flying duties in conditions where oxygen levels are insufficient. The time of useful consciousness is different for each individual, and depends on the altitude, individual’s state of health and amount of activity.

• Exercise (workload). Exercise or physical activity increases the amount of oxygen required by the body cells. This worsens the situation since lack of oxygen already exists, and reduces the available time until more severe hypoxia symptoms appear (it reduces the time of useful consciousness).