One would think that something as good for the body as working out to gain weight and build lean muscle mass would prevent you from suffering what non-trainers tend to get sick.
Well, depending on the frequency of your workout program and how hard or intense you lift weights, you could possibly be stressing your body’s natural immune system. Short term, maximal exercise, can temporarily weaken the immune system and increase your chances of getting the cold or the flu. According to the British Journal Sports Medicine, a study from the National Yang Ming University School of Medicine in Taiwan showed that an intense “endurance” exercise session, which they classified as 85 percent of your maximum effort for at least 30 minutes, disrupted immune system function, destroyed some white blood cells, and triggered whole body inflammation for up to 72 hours.
Now, my take is that you have to take into consideration that this was caused by endurance type of workouts. For the naturally skinny weight trainer looking to gain weight and build muscle this isn’t the type of workouts you’d be engaging in anyway. Weight training, going for the “pump and burn”, is what will get you there, not riding a bike up a hill.
So, take this study’s finding into account in the sense that if you ever feel yourself like you’ve gotten the cold or flu and can’t seem to shake it no matter what, then and only then should you consider that you may be over training. That’s when it would be wise to take a break from the gym until you recover completely. If not, keep pounding away at the weights and gaining weight and muscle along the way!