Skiing generally happens on higher altitudes such as mountains. It is known that there is less oxygen is available at higher altitudes. There is low oxygen pressure at such height.
The prolonged increase in heart and breathing rate is due to less oxygen available for the cells. This condition is known as hypoxia caused by insufficient blood hemoglobin to supply oxygen for physical activities at higher altitudes.
Taking a look at viruses under the microscope. Unlike other unicellular organisms like bacteria, viruses are commonly referred to as particles rather than cells.