An individual with influenza infection faces severe weakness owing to an increase in the expression of muscle-degrading genes and a decrease in expression of muscle-building genes in skeletal muscles, a study has concluded.

It is well-known that muscle aches and weakness are prominent symptoms of influenza infection. However, the cause of weakness in the body is primarily created by these muscle-degrading genes. Researchers at the University of Connecticut noted that every year, 5 to 20 per cent of the people in the United States are infected with influenza virus. An average of 20,000 of these people require hospitalisation, while up to 50,000 die.

Furthermore, researchers observed that people over the age of 65 are especially susceptible to influenza infection since the immune system weakens with age. In addition, they are more susceptible to long-term disability following influenza infection, especially if they are hospitalised. Interestingly, many of the body's defences that attack the virus also cause many of the symptoms associated with the flu.

While the influenza virus is wholly contained in the lungs under normal circumstances, several symptoms of influenza are systemic, including fever, headache, fatigue and muscle aches. In order to properly combat influenza infection, the cytokines and chemokines produced by the innate immune cells in the lungs become systemic -- that is-- they enter the bloodstream, and contribute to these systemic symptoms. When this happens, a cascade of complicating biological events occur.

Functionally, influenza infection also hinders walking and leg strength. In young individuals, these effects are transient and return to normal once the infection is cleared. However, these effects can linger significantly longer in older individuals. This is important since a decrease in leg stability and strength could result in older folks being more prone to falls and subsequent injuries while recovering from influenza infection. It could also result in long-term disabilities and give rise to the need for a cane or walker to move around.