Which factor can decrease Time of Useful Consciousness?

Time of Useful Consciousness (TUC) refers to the duration a person can maintain effective consciousness and perform tasks under conditions where there is a reduction in the availability of oxygen, typically occurring at high altitudes. Increased physical activity can decrease TUC because it elevates oxygen demand in the body. When a person is physically active, the body requires more oxygen to sustain muscle function and other physiological processes.

At higher altitudes, where the partial pressure of oxygen is lower, the body struggles to meet its increased oxygen demands during physical activity. This increased requirement can lead to quicker onset of hypoxia, which in turn shortens TUC. Therefore, under conditions of stress such as high altitude combined with physical exertion, a person may experience diminished capabilities and a reduced time they can remain functional and conscious.

Rest, lower altitudes, and increased oxygen supply are more likely to enhance TUC by minimizing oxygen consumption and maximizing oxygen availability to maintain consciousness and function. Thus, the correct choice indicates that increased physical activity can lead to a faster drop in available consciousness time under hypoxic conditions.