The muscle-building niche is considered one of affiliate marketing’s evergreen niches. It is right up there with the related weight-loss and wellness niches for popularity. These three big niches are so closely related that I initially overlooked this huge niche as a topic to explore.

With websites like Build-Muscle-101.com, BreakingMuscle.com, and a whole slew of others, all about bulking up and increasing your strength, it's easy to guess the muscle-building niche is still strong as...