-I'm sick. But smiling because the sun's on my shoulders and I'm riding my bike. Should I train when I have a cold? That depends on how I feel.
If I have no energy, no. I stay in bed. If I feel sorta okay, I'll hop on my bike for a easy recovery ride. I just seem to get better quicker if I do something. And there's some scientific validity to this.
As many of us know, the high levels of endorphins released during an intense session or race can weaken immune system. But some endorphins from lower intensity exercise can help our immune system. So keeping the intensity down is key to recovering from a cold. In addition, when your heart is pumping, it helps white blood cells circulate, oxygenate your muscles and raise your temperature slightly - all of which also help you get better. So a little bit of easy to moderate training has lots of benefits.
Perhaps the hardest part is knowing when you shouldn't do anything at all. Coach Phil Mosley who has written for numerous endurance magazines wrote an excellent blog at https://www.myprocoach.net/blog/should-you-train-when-youre-sick/ . While I typically prefer more scientific-based articles, like Coach Mosley's, I did find this Shape magazine article ( https://www.shape.com/lifestyle/mind-and-body/how-get-rid-cold-lighting-fast) interesting because it gave a day-by-day account on how to treat your cold. I do think zinc helps but I haven't tried the other suggestions; let me know if they work for you.
And just like talking to a friend - not a doctor or an expert - about your cold, at the end of the day you need to do what is right for you. But hopefully we can all get back to training faster.