As the colder months approach, the number of illnesses rise therefore forcing people to isolate in these times. 

First, it is important to consider whether training at high intensity can contribute to making you sick by suppressing your immune system. Longer-duration and high-intensity events do predispose you to infectious illness for a short window of time immediately afterwards, but regular exercise boosts your immunity over that of sedentary individuals (usually laying or sitting). So training during the winter months probably has a net protective effect against getting sick.

When training while ill, the usual symptoms like: runny nose, puffy/red eyes, headache, in most cases these symptoms may actually improve with exercise. Exercise increases the heart rate and stimulates circulation, which might help the body release fluids. It is important to note that staying hydrated by drinking plenty water is vital, especially if you are sick. It is also necessary to consider that different exercises will cause different reactions in the body. In general, it is best to avoid extremely strenuous workouts (require great effort) while sick. Instead, an individual should focus on lighter movement based exercises that get the blood flowing without pushing the body too hard.

When someone is sick, their body is trying to fight off and recover from an illness. As such, it is crucial to keep exercise light. It may not be the best idea to push the body to its limits, such as doing sprints or heavy weightlifting as energy levels will be lowered while your body is busy fighting the germs. 

While your sick sessions can be adjusted to avoid overworking the body while its recovering. Keep the intensity up, but decrease volume, you can maintain intensity and drop volume in a few different ways. For example weight training can be adjusted by maintaining your usual weight by decreasing the sets/number of reps. When adjusting your sessions, removing the accessories like super setting from your sessions and just focus on one exercise at a time. Any HIIT sessions after training (running, cycling) just elevates your internal body temperature, and that’s not good when you’re feeling sick as your temperature will already be heightened. Just do the main lifts, and get back to eating and sleeping well for recovery.